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Unit 3 We Are not Alone!

ChApter 7 evolution Gives Our Biodiversity

ChApter 8 Before plants and Animals: Viruses, Bacteria, protists, and Fungi

ChApter 9 Getting to Land: the incredible plants

ChApter 10 Moving on Land and in the Sea: Animal Diversity

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evolution Gives our Biodiversity

eSSentiALS

Bats evolved echolocation to prey on insects such as moths

Island without moths; Ecosystem low in diversity…today

Father and Son Sailing

The island once had many moths

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the Case of the Quiet island I was a young student studying biology in Wales when I talked with my father into sail- ing with me. I had seen my friend sail a small boat earlier in the season, and it looked fairly easy. So my father and I set off to visit an island that our family once vacationed on when I was a child. The wind was at our backs, so we zipped along toward the island with ease. I thought, “I should buy a sailboat and make this my new hobby; I am really great at sailing.”

We docked the boat within a few minutes and began walking the island. It was just a few miles around On an earlier trip I had noticed that the island had many different creatures – plants, birds, bats, and lots of moths, one of my least favorite insects. My father noticed that it was very quiet – very peaceful and a great place to read – I think he was telling me I should get away to this island and quit bothering him with my studies.

We hiked up its small hills and took leaves and plants for study. We noticed that there were very few insects buzzing around us. “How great,” I thought, “no bugs around to bother us.” I had always disliked the arthropods, all of the insect classes, in fact. I recalled times when deer flies bit through a shirt into my neck when I was gardening. “They are good for nothing,” I reminded myself, happy to be relieved of them for at least this walk. There were only small farms on the island, which consisted of quiet country- side cottages. Oddly though, on our walk there were neither birds nor insects to make noise–well, peace at last.

The island had developed a great deal of farming, and the crops looked very healthy. My father commented, “This is what England needs, productivity. Big farms like this one will make Britain strong again!” I had read in a journal article that two-thirds of Brit- ain’s 337 large moth species are in significant decline. It was evening, and I again appre- ciated that there were no moths buzzing around our heads by the lamplights on the road.

“A nice quiet night but where were the moths that I once watched in the lamps along the road?,” I envisioned, recalling their bulbous bodies. As a biology student, I knew that moths were an insect class, Lepidoptera, with 150,000 known species. Moths were not beautiful like butterflies and were pretty gangly, throwing themselves at lights. I would never be an entomologist, who studies arthropods for a living.

My teacher made us read an article reporting that there had been a 99% decline in common garden moths, Marcaria wauaria, in the past few decades. The total num- ber of large moths was down by almost 50% in southern England. Three species of

CheCk in

From reading this chapter, students will be able to:

• Explain the relationship between evolution, biodiversity, and society’s role. • Use moth population changes as an example of evolution and species changes over time. • Discuss the history of how life’s origins were discovered, using ideas on spontaneous generation. • Describe how natural selection leads to species changes. • Define the types of natural selection. • Examine the role of speciation as a cause of biodiversity. • Describe extinction and its role in biodiversity changes throughout Earth’s history. • Discuss and evaluate the evidence for evolution. • Use sexual selection to explain the development of organisms over time.

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Chapter 7: Evolution Gives our Biodiversity 237

moths had disappeared from southern England in the past decade: Orange upperwing, Jodiacroceago; Bordered gothic, Heliophobus reticulate; and Brighton wainscot, Oria musculosa. “Good riddance, life goes on without them; but I wonder why so many were gone?” I pondered.

When we started back to the coast, I realized the wind was against us. I didn’t really know what to do when the wind did not have our sail. My father and I struggled to keep the sail straight and steered helplessly through the waves that had developed while we were on the island. It had become a nightmare. I frantically tried to steer and pull as the boat went out of control. The boom hit my father’s head in the confusion. He yelled, “You idiot, you’ll kill us yet! Why didn’t you tell me you had never sailed?” He was bleeding and I felt terrible. How was I supposed to know that sailing could get so out of control? It seemed easy when the conditions were just right. It dawned on me that the slight shift in wind direction, much like one fluctuation in moth populations, could usher in significant change leading to disastrous effects.

Moths are an indicator species, meaning that the state of the environment is first indicated by moth population health. Fewer moths mean less food for birds and bats, which eat moths. Those organisms eating birds and bats also are affected. One change in the environment can have profound impacts on the whole ecosystem.

The island was quiet like the sea when we arrived. There were few insects and few birds to make sounds, but the quiet island had spoken – and it was quiet no more.

CheCk Up SeCtiOn

In the story, our character is at first happy about the loss of biodiversity on the island. By the end of the story, it dawns on him or her that there may be more to the quiet island. Changing environmental factors, much like sailing conditions, can be unpredictable and get out of control. Moths in England declined in numbers in part due to habitat loss: large-scale farming destroyed hedges lining smaller farms, an area where moths thrive; pesticides also were shown to kill off many moths.

Study the life history of the Marcaria wauaria, noting its prevalence, habitat use, and the pur- ported reasons for its decline in southern England. Some species of moths saw population increases in southern England. The least carpet moth increased by 75,000%. Research why this occurred: How might changes in moth prevalence impact on our society? Do you think the narrator in the story had a change of heart about moths, about the environment?

What Are the Origins of Life? Life originated about 3.5–4.1 billion years ago, giving rise to the great diversity of organ- isms we see today. The origins of our biodiversity emanate from a small set of species of prokaryotes. Stacks of sediment made by colonies of bacteria, called stromatolites, are evidence of our primitive ancestors. Found in Africa, Australia, and the Bahamas, stromatolite layers contain carbon from bacteria dating back to early Earth. Since Earth was formed 4.6 billion years ago, life began relatively early in Earth’s history.

How did life originate from our molten ball of Earth chemicals? Early scientific thinkers believed that life originated from nonliving matter. The idea that life appeared from nowhere, called spontaneous generation, was held firmly by scientists for many centuries.

Spontaneous generation

The idea that states that life appeared from nowhere.

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The 17th-century scientists hypothesized that organic matter in food automatically generated maggots and all associated life when coming into contact with air. (You can make the same observation if you leave food at room temperature for a long-enough period of time; you will likely see mold and flies at the least.) Then, Francesco Redi (1636–1697), an Italian naturalist, became the first to disprove spontaneous generation.

Redi devised an experiment that involved placing a piece of meat into a glass jar. The jar was covered with gauze, which allowed air flow to the meat but no other agents larger than the holes in the gauze. A second control jar was left uncovered to allow con- tact with any external agent. Redi’s experiment is shown in Figure 7.1.

Redi’s results showed that the gauze-covered jar did not have maggots, but that the uncovered jar did. Realizing that some other agent had caused maggots and not the meat itself, Redi’s experiment was the first to disprove the idea of spontaneous generation. We now understand that flies were the cause of new life on decaying meat, with maggots growing from eggs laid on the organic material.

There were no microscopes in the 1600s to view the developing fly eggs on meat. The mechanism for new species growth on food was therefore unknown. However, Redi was criticized because new growth spoiled foods in both his control and his experi- mental jars – we now know the bacteria of decay cause the food to spoil. Thus, debate continued on whether life could arise spontaneously. Scientists also sparred over what caused milk and beer to sour. French biologist, Felix Pouchet (1800–1873) believed that microorganisms spontaneously arose in some foods, such as milk and beer, which had the right combinations to create life.

Pouchet heated flasks of hay brews to 100° C. He sealed the flasks, but even though they were sterilized, bacteria formed. Pouchet thus concluded that organisms could arise from a good mixture of materials, as found in beer and other fermentation environments. He tried many times to sterilize the flasks, but in every case within a short period of time, he observed a sea of bacteria. Pouchet thus reopened the defense of spontaneous generation.

Louis Pasteur (1833–1895) proposed an alternate hypothesis, arguing that bacte- ria were everywhere. He claimed that Pouchet’s experiment was contaminated when he

JAR 1 JAR 2

Figure 7.1 Redi’s experiment. After covering jars, Redi determined that a covered jar does not lead to maggot formation on meat. It was a first attempt to disprove the spontaneous generation of life.

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Chapter 7: Evolution Gives our Biodiversity 239

placed lids onto the flasks. Pasteur designed special long-necked flasks to keep broth placed inside free from bacterial growth as he sterilized its contents. Air was still able to get through to the broth; this eliminated the criticism that life might not have air to breathe, as in Redi’s sealed jars. The lower part of the neck of the flask trapped the heavier dust particles and microbes. His flask design is shown in Figure 7.2.

With no external agent, Pasteur reasoned correctly that the “trap” in the neck kept out microbes, and no new life formed in his flasks. When Pasteur tipped a flask to allow broth to touch the trap, bacteria appeared in the broth in a few days. His rejection of Pouchet’s results brought Pasteur membership in and an award from the French Acad- emy of Science. Pasteur’s experiment showed how his critical thinking led to a solid disproof of spontaneous generation – and led to the birth of microbiology as a discipline.

Personally, Pasteur was a devout Roman Catholic. He performed the experiment to emphasize the sanctity of life. He reasoned that if spontaneous generation were true, then there would be no need for a creator God to exist. His disproof of spontaneous generation was actually a movement against atheism. It worked toward a resurgence of religious faith in the 1800s. While Pasteur promoted his work as an example of pure science, it may show how one’s personal beliefs, even as a scientist, influences thinking about scientific research.

The Pasteur–Pouchet debate illustrates how scientific arguments continue through the centuries. The germ theory of biology, which places a focus on sterile techniques to prevent microbial disease spread, led to important improvements in medicine. The wide- spread use of sterile techniques decreased deaths, especially during childbirth.

The origin of life is of continual interest to scientists. In 1953, physical chemists Stanley Miller (1930–2007) and Harold Urey (1893–1981) devised an experiment demonstrating that precursors to life could have formed from the right mixture of chem- icals. Conditions on early Earth were simulated in a glass tube containing methane, hydrogen sulfide, hydrogen gas, and water vapor. The experiment in Figure 7.3 shows the design of Miller and Urey’s experiment.

An electrode was placed in the glass tube which simulated X-rays, ultraviolet light, and lightning of the early Earth. The environment in Miller and Urey’s glass tube was an oxygen-free system, just like on early Earth. When an electric charge was applied to this primordial mixture of chemicals, organic molecules formed. Fats, sugars, proteins, and genetic material were produced from the simulation.

Organic molecules make up life, and as discussed in Chapter 2, are able to self- assemble based on their chemistry. It is hypothesized that droplets of organic material

Germ theory

The theory that places a focus on sterile techniques to prevent microbial disease spread, led to important improvements in medicine.

Figure 7.2 Pasteur’s experiment.

Nutrient broth is sterilized

No microorganisms grow

Dust particles, bacteria, and other airborne

materials trapped

Microorganisms thrive

Airborne bacteria can now reach

the broth

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formed from the newly made organic products. As shown in Figure 7.4, the droplets formed a sphere that was separate from its environment. This sphere of organic material is called a prebiont and was the first form of new life. It was capable of replicating, absorbing genetic material, and forming new prebionts. These new “cells” further devel- oped into prokaryotes found as fossils within stromatolites. But how did so much life originate from such a simple prebiont?

natural Selection and Biodiversity Take a moment to ponder the fact that living organisms, in all their magnificent diver- sity, emerged from a simple assortment of chemicals on early Earth. Chapter 1 discussed Darwin’s principles of evolution; we will expand on some of those principles here.

When populations have more individuals than an environment can support there is inevitably a struggle for survival. Individuals have varied characteristics, with some better able to survive than others. These more successful organisms reproduce more and thus have better reproductive success (RS), defined as the number of viable offspring

Prebiont

A sphere of organic material that led to first living cells.

Reproductive success

Is the number of viable offspring an individual produces.

Figure 7.3 Miller and Urey apparatus. Gases in the glass tubes reacted to form organic molecules, precursors to life.

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S Figure 7.4 Prebionts. These tiny spheres share some characteristics of life, including a separate membrane to keep it distinct from its environment.

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Chapter 7: Evolution Gives our Biodiversity 241

an individual produces. The frequency with which genes appear in a population change based upon these different RS rates. Organisms with a successful RS increase their relative proportions of genes in a population.

The change in gene frequencies in a population, over time, is defined as evolution. However, evolution acts only upon phenotypes, or the physical characteristics of one’s genes. Those organisms with traits better adapted for a particular environment will increase in numbers. The driving force behind evolution is thus natural selection, or nature selecting for or against certain attributes. It results from an interaction between organisms and their environments. Consider the polar bear, Ursus maritimus, which has white fur. Over time, those bears with a light color as camouflage were better able to blend in with their snowy surroundings. Contrast the darker colors of the brown bear, Ursus ameri- canus, which blends better within darker forests of North America (Figure 7.5).

Their respective environments influence the phenotypic traits that are selected for and against. To illustrate, the dark color of a brown bear roaming the polar ice caps would stand out like a sore thumb, making it easy prey for its enemies and obvious pred- ators to its prey. Thus, different environmental conditions favor different phenotypes at different times. If the ice caps were to melt, becoming forests, polar bears would no longer have an advantage with respect to fur coloration. In our story, the characters wit- ness changes in moth populations on the island. Moth species thus experience a change in gene frequencies within their populations, with some decreasing and some thriving. With declines in the V-moth, Marcaria wauaria and extinctions of three moth species in England, Orange upperwing, Jodia croceago; Bordered gothic, Heliophobus reticulate; and Brighton wainscot, Oria musculosa, natural selection is at work. Changed environ- mental conditions, such as loss of habitats and harmful pesticides in farming, contrib- uted to moth species changes (Figure 7.6).

Why the changes in moth populations in England? Consider that currants and gooseberries, once very popular and found in many gardens, lost favor across house- holds. Currants and gooseberries are a big part of V-moth diets. Without easy access to these foods, V-moth populations declined substantially. On the other hand, some con- ditions favored certain species of moths. In fact, one-third of moth species experienced increased numbers in the region discussed in our story. The reason was the improve- ments in air pollution and acid rain led to a rise in lichens, which are fungi–algae colo- nies. Moth species that increased in numbers had one common feature – they all fed on lichens. This is an example of natural selection occurring before our eyes – changes in moth species in our opening island story due to a response from environmental factors.

Evolution

The change in gene frequencies in a population, over time.

Natural selection

The natural selection for or against certain attributes.

Figure 7.5 a. Brown bear. b. Polar bear.

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In order for natural selection to occur on a particular trait, three conditions must exist: 1) there needs to be genetic variation in a population; 2) variation in traits must be heritable, that is, able to be inherited from one generation to the next; and 3) individuals with one trait must have better RS than individuals with another trait. In the case of the British moths in the story, their characteristics must be different from those of other spe- cies in some ways, and these differences must be inherited for natural selection to work.

In addition to losing important food sources, the declining species differ in their appearance and in their habitat requirements from other moths. Large farms recently emerged, reducing their shrubby habitats. Without places to deposit eggs and food for their offspring, their numbers dwindled. In contrast, it is widely believed that climate change and increased temperatures allowed many of their competitor moths to colonize the island, thus forcing them out. The three moth species experienced low RS, given the changed environmental conditions, resulting in their extinction from England. Changes in the environment may be temporary, but if the gene frequencies within a population also change, sometimes evolution has irreversible results.

types of natural Selection If a person has a harmful trait such as porphyria seen in the story in chapter 6, it affects that person’s survival. If another person is a carrier for porphyria, then his or her phe- notype is normal, and natural selection does not affect survival. Natural selection acts only on phenotypes because the environment only works on those traits expressed by an organism. While nature acts on one’s phenotype, phenotype emerges from one’s genes. The genes within an organism give rise to its physical appearance. Thus, gene frequen- cies change when a population is evolving due to natural selection.

There are three types of effects by natural selection: directional selection, stabiliz- ing selection, and disruptive selection (Figure 7.7). Directional selection occurs when individuals at one extreme of the range of variation in a population have a higher degree of fitness. If a group of dogs is bred, allowing only those with an aggressive disposition to mate, the offspring are likely to exhibit more aggression. Vicious dog breeds are commonly used as attack dogs by owners. The idea that behavior can be modified by selecting for certain characteristics is a theme of behavioral genetics.

Directional selection

The process that occurs when individuals at one extreme of the range of variation in a population have a higher degree of fitness.

Figure 7.6 There are light and dark moths on both the light and dark trees. Which moths do you think are more likely to be spotted and eaten by predatory birds? Why? From BSCS Biology: An Ecological Approach, 9th Edition by BSCS.

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Chapter 7: Evolution Gives our Biodiversity 243

EvolutioN DoES Not CauSE thE BESt oRGaNiSmS to SuRvivE

Evolution is not the survival of the best organisms, only those best adapted to their particular surroundings at any one time. Evolution is a product of the pressure by nature to select out the weak and keep those organisms best adapted for a particular environment. The strongest do not always survive. Consider dinosaurs, which were very strong, according to fossil prototypes, but were selected out; they were not the best adapted at some point in the past. Dinosaurs are believed to have died as a result of a giant meteor impact that added dust and debris to the atmosphere, causing a cool down.

The extinction of dinosaurs is a hotly examined topic. There is a debate between geologists and biologists as to the cause of their extinction. It has long been held that an asteroid hit the Earth about 65.5 million years ago, causing a major shift in climate. Dust from the impact led to less sunlight, fewer plants, and thus less food for dinosaurs and other species. Fossil evi- dence dating back to that period shows higher than normal amounts of certain materials, including iridium, indicating meteor-like hits. The layer of soil con- taining these particles is known as the K–T boundary (Cretaceous–Paleocene boundary) and correlates with a high extinction rate for many species types. The large crater on the Yucatan peninsula is thought to be evidence for this meteor impact.

There is an alternate hypothesis that microbial infections spread through- out dinosaur populations leading to their extinction. Emerging theories of dis- ease or infection as the cause implicate a viral or other parasitic infection as the reason for the dinosaur extinction. The hyper-disease theory of dinosaur extinction states that a microbe evolved rapidly to kill off other living creatures during the time period. While weather-related or biological causes led to their destruction, dinosaurs disappeared from the Earth due to the forces of natural selection, despite their impressive physical strength.

Death from global infectious diseases has had major impacts on society more recently in human history. For example, over 70% of Native American Indians died due to diseases brought by Europeans and not through battles. They lacked a natural immunity to those infectious pathogens such as influenza, small pox, and bubonic plague. The power of epidemics to destroy human cul- tures and other species has historical grounding.

hyper-disease theory

The theory that states that a microbe evolved rapidly to kill off other living creatures during the time period.

Stabilizing selection occurs when individuals at the mean or average range of varia- tion in a population have a higher fitness. In human birth weight, for example, the aver- age newborn is 7.1 pounds or 3.3 kg. This is also the weight associated with the lowest infant mortality and is thus selected for in nature. At other ends of the spectrum, infants with a low birth rate suffer more health complications without the required body fat; and at the higher end, birthing is difficult due to the large size of the baby. Modern medical treatments are allowing greater variation in birth-weight survival.

In disruptive selection, individuals at extremes of the variation spectrum experi- ence higher fitness than at the middle. In fish, larger males are stronger and able to

Stabilizing selection

Occurs when individuals at mean or average range of variation in a population have higher fitness.

Disruptive selection

The process in which individuals at extremes of the variation spectrum experience higher fitness than at the middle.

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obtain females more readily. Oddly, smaller males, known as sneaker males, also have better chances of survival than those of intermediate size. Sneaker males are able to “sneak” into a nest and impregnate a female without the larger male detecting him. It is a peculiar strategy for survival and works to help smaller sized fish persist in populations.

In our story, certain phenotypes result from a winning combination of genes. To illustrate, a set of genes determines the odd pattern on the eyed hawk-moth, Smerin- thus ocellatus. Its coloration allows it to remain camouflaged along bark when it is at rest, and when disturbed, it displays a set of “eyes” that startle its predators, allow- ing it time to escape. As shown in Figure 7.8, a phenotype enabling greater survival chances for an organism such as the eyed hawk-moth increases those gene frequen- cies, causing the species to evolve that trait. Natural selection pushes changes in gene frequencies in certain directions based on their efficacy in an environment, allowing organisms to adapt.

Figure 7.7 Graphs showing three types of natural selection.

A. Stabilizing selection Normal distribution with both

extremes removed

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C. Disruptive selection Bimodal distribution with average size removed ©

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Figure 7.8 Eyed hawk-moth is hidden by its surroundings.

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Speciation increases Biodiversity In Chapter 1, a species was defined as a population of organisms that are able to inter- breed and produce live, fertile offspring. Speciation is defined as the process by which natural selection drives one species to split into two or more species. It occurs when the new groups of species cannot interbreed with each other. Their inability to mate is called reproductive isolation. Several conditions may lead to reproductive isolation: mating songs may be so different that organisms don’t mate; changes in the genetic composition of two groups of organisms may make their offspring unviable, as in the case of the ster- ile mule, which is the offspring of a female horse and a male donkey; and divergence of groups into new geographic areas may prevent members of the new group from mating.

It is likely that the eyed hawk-moth evolved from an ancestor that lacked “eyes.” This beneficial moth phenotype, its “eyes,” enabled greater survival. Those organisms with the trait lived on to become the eyed hawk-moth, while those without the trait were at a disadvantage. Other moths of the Lepidoptera family do not possess this unique phe- notypic advantage. They survive, with other adaptations to help their success. The result is a number of different species, each with differing characteristics.

How do new species emerge from an ancestral species? There are two types of spe- ciation: allopatric and sympatric speciation (Figure 7.9). Allopatric speciation refers to the development of new species when there is a physical barrier separating members of a group of organisms. You can remember this as “all apart” speciation, because groups of new species form when they are all apart in different environments.

When members of a population undergo different environmental pressures, new species may result because different traits are selected. Speciation arises due to mech- anisms that isolate groups, allowing nature to act. Natural selection works differently when there are different conditions in two distinct environments. The different environ- ments may lead to enough changes to develop separate species.

In the case of the changes in diversity of moths on the island in our story, if V-moths decline as a result of a loss of food, perhaps a set of survivors will persist. Perhaps these survivors inherited genes that enable them to eat lichens on the island or some other

Speciation

The process by which natural selection drives one species to split into two or more species.

Reproductive isolation

The inability to mate.

allopatric speciation

The process of development of new species when there is a physical barrier separating members of a group of organisms.

Figure 7.9 Allopatric speciation is shown above. When populations are geographically separated into differ- ent species it is termed allopatric speciation; when populations occupying different ecological zones develop new species, it is termed sympatric speciation. From Biological Perspectives, 3rd ed, by BSCS.

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food not in decline. This group may survive and thrive, while the non-lichen eaters die off completely.

V-moths in other parts of Europe, away from the island, might undergo selection pressures that are different from those experienced by individuals remaining on the island. Consider two groups of V-moths, one on an island in southern England and one in mainland Europe. When enough changes occur in each group’s genetic make-up, the two groups of the same species of moth might diverge, forming two new species. This phenomenon is called adaptive radiation, in which a population of a species changes as it is dispersed into a series of different habitats. Adaptive radiation often occurs after 1) the extinction of a competitor, which helps increase the size of a population of species; 2) finding a new habitat, also allowing a group of species to thrive; or 3) after new genes give new advantages to a group of organisms. In each case, adaptive radiation results in many species emerging from a common ancestor. Recall from Chapter 1 that adaptive radiation occurred when new species of finches developed on the Galapagos Islands.

Another form of speciation results in new species due to behavior patterns. When new species emerge while living within the same geographical areas, it is known as sympatric speciation. It may result from 1) changes in genetic material among organ- isms, as in polyploidy or extra sets of chromosomes in plants, 2) use of different aspects of the same habitat, preventing organisms from interacting with each other, or 3) inabil- ity to reproduce with each other. At times, reproductive barriers separate species by preventing them from mating with one another. In sympatric speciation, members of the same species no longer reproduce with one another, because of either a change in mating behaviors or use of different habitats for food, for example. Sympatric speciation occurred in the meadow grasshoppers, Chorthippus biguttulus and Chorthippus brun- neus. The two species are similar in body size and shape, but they are reproductively isolated. The calling songs of each to attract a mate of the opposite sex have different vibrations, so potential mates may not recognize each other. As a result, natural gene flow between groups ceases, and each group changes with its environment as a separate entity. In the field, the two species of grasshopper do not mate, but in the laboratory, members of the two groups are capable of mating with each other. These premating bar- riers to gene exchange occur simply due to one minor difference in vibration in mating calls between the two species.

extinction The development of biodiversity in our ecosystem is a result of speciation over a long period of time. However, as stated earlier, 99% of all species that have ever lived are now extinct. Extinction is defined as the loss of a species forever, with no remaining organisms to maintain its population reproductively. There have been five great extinc- tion periods in Earth’s history, each explained by environmental causes (Figure 7.10). The last great extinction period occurred 65 million years ago. The sixth great extinc- tion is occurring today, at 80 times the rate at which species go extinct as in nonex- tinction periods. Only 1–2% of all species became extinct in the past century, but their extinction is permanent. Human impacts are believed to be the primary cause of this new great extinction era. Climate change and habitat loss, seen as responsible for moth declines on the island in our story, are primary drivers of environmental change and spe- cies extinction. The trouble with modern extinction is that speciation processes are not replacing extinct species with new ones. In previous extinction periods, many hundreds of thousands of years passed with species lost and gained, but in the current human- derived extinction period, occurring only in the past few centuries, new species do not have time to emerge. The danger to our fragile ecosystem is human unwillingness to

adaptive radiation

The changes that occur in a group of organisms to fill different ecological niches.

Sympatric speciation

The emergence of new species while living within the same geographical areas.

Extinction

The state in which a species is lost forever, with no remaining organisms to maintain its population reproductively.

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EvolutioN DoES Not CauSE iNCREaSiNG ComPlExity

A misconception that evolution leads to increasing complexity is not supported. The best adapted creatures are often the simplest, and many complex organ- isms – for example, dinosaurs – have become extinct. As discussed at the start of this chapter, prokaryotes have been around for most of Earth’s history, 3.5 of the 4.1 billion years of the planet. Prokaryotes remain very competitive because of their simplicity in design. They contain very few organelles and very simple genetic information, with only a primitive nucleus, a cell membrane, and some cytoplasm. There are no fancy organelles as found in plants and animals. This limits the amount of things that can go wrong with these creatures. Evolution does not lead to perfect organisms, only those best able to adapt to our world.

Consider the old VW beetle, which had no air conditioning, no power locks, windows, or brakes. It ran and ran for decades without problems. The VW is much like a prokaryote. Alternatively, more expensive and complicated automobiles contain many features that can break down. Anyone who has had a check engine light turn on appreciates the aggravation in finding the small prob- lem causing an emissions issue. The complexity of humans and other creatures can be their downfall. Over 99% of all organisms that have lived on this planet are now extinct! Complex life does not necessarily survive better, and certainly, I would predict that prokaryotes will outlive humans by billions of years.

Figure 7.10 a. Record of mass extinction periods in geologic history; five mass extinction events in Earth’s history occurred in relatively short periods of geologic time. The latest and most rapid extinction period is blamed on human society and its effects on the environment. From Biological Perspectives, 3rd ed, by BSCS. b. Dinosaurs, such as this Triceratops became extinct at the end of the Cretaceous Period, roughly 65 million years ago. It is hypothesized that a large meteor hit Mexico, leading to climate changes that did not support the life of dinosaurs. From Biological Perspectives, 3rd ed, by BSCS.

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alter environmental conditions so that species can emerge. Perhaps creating and enforc- ing policies that limit climate change effects or curb habitat loss will slow the sixth great extinction.

In our story, it is easy to see how quickly environmental changes can have unin- tended impacts. Other species besides the moths - namely butterflies, have experienced declines in England as well. Obviously, with a 99% decrease in the number of Black Hairstreak butterflies, the species is on its way to extinction there (Figure 7.11). With over 2,500 moth species reported in England, of which 900 are described as larger moths, it is concerning that the total numbers of larger moths has declined 38%, overall. Many biologists have suggested that species declines could lead to losses in biodiversity and extinctions of other species.

In our story, the main character’s final realization that there is a delicate balance in nature is heartening. The character finally shows an interest in learning about declining biodiversity and its effects on the environment. While difficult to detect upon simple observation, species losses affect human society as well other organisms in unintended ways. For example, while some species of moths increased in numbers, most declined. Moths are pollinators and are a food source for animals such as birds, bats, and small mammals. Along with moth species’ decreases, butterflies, bees, and carabid beetles also are declining in number. Biologists point out that this might be a part of a greater contraction in biodiversity in the insect classes as a whole – that England is only a pro- totypic ecosystem suggesting larger changes.

Figure 7.11 The great decline in butterfly species in England. Many species of insects declined in 2012, with 300, 000 fewer sightings of butterflies in one year. Changing environmental conditions, including weather patterns such as increased rainfall are thought to be contributing factors.

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aRE DiNoSauRS ExtiNCt?

Yes and no . . . While dinosaurs as a set of distinct species have been removed from the community of life, their DNA is very similar to that of birds. In fact, many biologists argue that birds are direct descendants of dinosaurs. Feathers were found on dinosaur fossils as far back as 1860. This link between feathers and dinosaurs was found in over 20 species of dinosaurs. Studies of fossils from dinosaurs, namely the Tyrannosaurus rex, show that birds are more closely related to dinosaurs than to other organisms such as reptiles, amphibians, or humans. Through analysis of collagen fibers, ropes of proteins in the soft tis- sues of animals, genetic relatedness between bird and dinosaur species was shown. Obviously, dinosaurs are no longer roaming the planet (Figure 7.13). However, much of their DNA remains – in birds.

Figure 7.12 Ecosystem of island in story – each of these organisms will be affected by a loss of moth species – which means that many other species are also affected.

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Changes in biodiversity are difficult to predict; the moths in our story are food for many species of birds and bats, which are eaten by wolves, owls, and eagles, to name a few. A delicate balance is maintained in our ecosystem (Figure 7.12). While natural selection is natural, humans impacts are not.

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extinction and Biodiversity The majestic coral reefs of the tropical waters are the largest living creatures in the world.

Moreover, they provide large habitats for many ocean species. They are, however, in decline, and their decline threatens the species who live among them. They have been adversely affected by boating, pollution, acid rain, and change in climate. Much like the moths in our story, they are a marine indicator species showing oceanic health.

Corals are resilient to a degree; for example, even if a small portion (or polyp) of the reef is destroyed, the organism can survive. But given the variety of adverse conditions they face, they are slowly dying, and when they die, so will many of the other species that inhabit them.

Skeletons of coral reefs, made of calcium carbonate, are a major component of the soil of the many archipelagos and islands in the tropics. Because coral reefs are so immense, they are not likely to die off from single isolated attacks. Many features of living systems are adapted for their survival (Figure 7.14). Coral reefs are large, living edifices but their survival is not guaranteed.

Coral reefs are just one example of how people often react to changes when it is too late. Our story showed how declines in moth populations could lead to a rocky sea of change for the environment, as the characters experienced in their journey are back from the island. Will it take a seaside sailing expedition for us to see how fragile our environment is?

evidence for evolution The extinction and emergence of new species are not new in Earth’s history. Organisms have changed throughout their time on Earth, as shown in the evidence for their evolution.

Figure 7.13 Dinosaur extinction: Did a meteor hit the Earth and cause their extinction?

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The evidence for evolution is given by four sources: 1) modern day examples of evolu- tion – recent natural selection in organisms based on environmental pressures; 2) the fossil record, which shows organisms of the past in rock layers; 3) homology, or common ancestry; 4) biogeography, or the way species are distributed; and 5) molecular evidence.

Modern Day evolution Organisms are exposed to environmental factors affecting their survival. We do not, however, evolve as individuals, changing with the times. Instead, evolution is a popula- tion concept. That is, it is change over time in the genetic composition of a population. An individual will not develop gills because the Earth becomes an ocean, as in the film Water World. Instead, one mutant human could be born with some sort of gills that help it survive. While far-fetched, such an adaptation would likely take generations to emerge within a population. Also, it would develop only by random chance. In fact, gills slits in humans are not likely to develop. Usually, species go extinct and do not have the chance to survive with such a random mutation.

Evolution usually occurs slowly over many generations in life’s history. However, there are times when we are able to see it happen before our eyes. For example, bacteria reproduce very rapidly, within minutes in some species. The chance for mutation and adaptation among bacteria species is high within our lifetimes because one human gen- eration (25 years) equals many thousands of generations of a bacterium.

The mutations of H1N1 influenza virus are examples of an organism changing in response to the environment. Each year, its viral strains cause great suffering to the humans: 225,000 people are hospitalized each year due to influenza, and between 5,000 and 50,000 die of flu. In influenza-causing bacteria, recognition proteins on the surface of the membrane surrounding the influenza virus are either H, or hemaglutinnin, or N, neuraminidase. When viruses attach to their host to attack, they use these recognition proteins to dock. As they mutate, some forms of N and H are better able to resist our immunizations. It becomes a continual struggle for modern medicine and pharmaceu- tical research to keep these mutating viruses at bay. During some years, influenza hits harder, and the vaccines are said to be less effective than in other years. This happens because the N and H recognition proteins have mutated enough to withstand the effects of the vaccines. Influenza thus evolves before our eyes, forming new strains with new shapes of recognition proteins. As vaccines knock out strains of influenza, the survivor viruses, with new recognition proteins, become resistant to current vaccines.

Fossil record

One of the four sources of evidence for evolution, which shows organisms of the past in rock layers.

homology

Common ancestry.

Biogeography

The way species are distributed.

Figure 7.14 Colors of the coral reef: The vast and varied structure of coral reefs provide a habitat for a large number of species.

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Many species of bacteria have become resistant to antibiotics in a manner similar to influenza. Indeed, when penicillin was introduced in 1944, over 90% of strains of staphylococcus, a skin bacterium, were susceptible to the drug; by 1950, only half were, and today only 30% of staphylococcus strains are susceptible to penicillin. The infamous MRSA, methicillin-resistant Staphylococcus aureus is increasing in frequency in hospi- tals across the United States and is the cause of a variety of difficult to treat infections. These “superbugs” evolved from earlier strains that mutated to resist the ability of peni- cillin to damage their cell walls.

Biologists have also observed the ongoing evolution of two genuses, the Heliconius genus of long-wing butterfly and the Passiflora genus of passion flower plant, each evolving defenses against the other in a process termed coevolution (Figure 7.15). In coevolution, two organisms evolve traits based on their relationship with one another. The Heliconius butterfly lays its yellow eggs on the plant, and when the eggs hatch, the caterpillars eat the plant. The Passiflora evolved yellow spots on its leaves to mimic eggs. This strategy protects the plants since butterflies will not lay eggs on a plant that already has eggs on it. Over time, the Heliconius developed more acute vision that enabled the sharp-eyed individuals to detect the fraudulent yellow spots, and once again use Passi- flora as a nursery and food source for the larvae. In response, the Passiflora developed mutations that coded for extra-floral nectarines, which attracted ants onto the plant to defend it from developing butterflies. Ants eat the Heliconius eggs. This example of coevolution clearly illustrates a logical battle, using natural selection to develop new phenotypes between two species. However, changes are always based on random muta- tions that may or may not benefit each organism. In this case, plants with yellow spots were better able to survive and reproduce, just as butterflies with more acute vision were able to pass on their genes to offspring that had an ample food source. Because of these features, brought about through random mutations, some were more likely to survive than other individuals of the same species.

the Fossil record As the changes on the island in our story illustrated, characteristics of populations change slowly over time or rapidly. Some changes are slow enough that they are measured in eons – periods of geologic time. Geologists can track these changes by

Figure 7.15 Heliconium butterfly and Passiflora flower, a case in coevolution. This Heliconium caterpillar is feeding on a leaf of the Passiflora plant. Passiflora combats this by “faux” eggs. Heliconium eggs resemble those “faux” on the leaf of the Passiflora plant. These “faux” eggs dissuade the Heliconius from laying more eggs on the plant.

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inspecting the fossil layers of the Earth. The fossil evidence for evolution supports the predictions by Darwin that there were changes in species over time. The fossil record shows that prokaryotes did indeed precede all other life and that animal classes devel- oped in predicted taxonomic ways.

The sequence of development shows that first fish fossils, then amphibians, then reptiles then mammals, then birds, and finally humans emerged on Earth’s scene. This sequential order of appearance contrasted with the sudden creation hypothesis that pre- dated evolutionary thinking. Because fossils appeared over many hundreds of millions of years, the fossil record supports species change over time.

Paleontologists study the fossil record by measuring isotopes in the soil, dating layers back to when they were first deposited (Figure 7.16). In the past, before radioactive dat- ing of isotopes, fossils were dated based on how deep in the Earth they were. The deeper the fossil is, the older the layer of soil. However, earthquakes have disturbed layers, mixing fossils of different time periods. This was a primary criticism of the evidence for evolution, in which chronology in development of organisms was confusing.

homology Darwin hypothesized that all species evolved from a common ancestral species. Thus, he surmised that they would have characteristics similar to those of their common ances- tor. Indeed, scientists have since shown, through analysis of the fossil record, that Dar- win was correct. Among several types of evidence, scientists have studied homologous structures – similar structures found in different species (Figure 7.17). Bones such as the femur or thigh bone have the same general shape and relative size in many different species: humans, whales, bats, and birds, for example. While the fin of a whale is used for swimming and the wing of a bat for flying, the bones supporting these structures appear similar to human arm structure. Very often, evolution does not change design entirely. As discussed in Chapter 1, life is efficient, and when a good design works, it persists in many species.

At times, structures that once had a purpose but no longer appear to be functional, called vestigial organs, are found across different species. Snakes, for example, retain their vestigial walking bones such as a pelvis and leg bone, but no longer are able to

homologous structures

Similar structures found in different species.

vestigial organs

Structures that once had a purpose but no longer appear to be functional.

Figure 7.16 Soil layers and fossils found within them. There are many organism classes (from prokaryotes to modern humans) found in layers of the Earth, connecting their existence to different time periods. Note that the rocks with embedded fossils in this layer are from Whitby, England.

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walk. Our tail bone or coccyx, the final bone along our back, is our vestigial tail. The presence of vestigial organs is one sign of common ancestry.

Embryos also show commonality among related species. Pharyngeal pouches in the throat regions of vertebrates exist in embryos but not in adults (Figure 7.18). These pouches all appear similar upon inspection of the embryos but develop into either gills in fish or Eustachian tubes of the middle ear in humans. These structures show that efficient systems were worked out during our common embryological homology, but that different purposes evolved at some point in the past to direct development in other ways. A saying, “ontology recapitulates phylogeny” means that development of embryos (ontology) reiterates phylogeny (classification based on evolutionary evidence), and

Figure 7.17 Homologous structures in several species. These structures are similar because they are derived from the same ancestor. From Biological Perspectives, 3rd ed, by BSCS.

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Figure 7.18 Embryos of several vertebrates: salamander, chicken, chimpanzee, and human. The embryos are similar, passing through the same anataomical stages. Com- parative embryology is evidence that they arise from a common ancestor. From Biolog- ical Perspectives, 3rd ed, by BSCS.

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emphasizes that the similar embryologic structures show our common ancestry and thus is strong evidence for evolution.

Molecular evidence Molecular evidence is perhaps the strongest evidence of all for evolution. Consider that all organisms have the same genetic structures – DNA and RNA – to carry out life func- tions. The central dogma, DNA ➔ RNA ➔ protein, defines the common characteristic found in all living species. Moreover, all organisms use the same general form of DNA because it is efficient.

Molecular DNA data confirm findings from the fossil record and from analysis of homologous structures. Molecular analysis of DNA across species shows that the more DNA organisms have in common, the more closely related the species. Molecular biolo- gists and other scientists study amino-acid sequences in different proteins to demonstrate the degree of relatedness of species . . . Figure 7.19 shows the commonalty of amino-acid sequences in hemoglobin among several species. Common molecular homology is a strong confirming piece of evidence supporting evolution and relatedness of species.

Biogeography The geographical arrangement of organisms he observed first gave Darwin evidence for his ideas on evolution, as described in his Galapagos Island experiences (see Chapter 1.) Different beak characteristics in finches developed according to different environmental conditions on their respective islands.

When organisms in different environments develop the same characteristics, although unrelated, it shows that environment plays a major role in developing traits. Consider the sugar glider of Australia and the flying squirrel of North America (Figure 7.20a). Both organisms have a gliding lifestyle, with wing-like structures, but they are unrelated. They resemble each other but are only distantly related to one another. The sugar glider is more closely related to kangaroos, for example, while the flying squirrel is more closely related to other mammals. Sugar gliders and kangaroos are both marsu- pials, meaning that they complete their embryological development in a pouch. Flying squirrels are mammals, meaning that they complete their development internally in a uterus (Figure 7.20b). Sometimes similar physical appearance does not always imply closeness in two organisms’ evolutionary histories.

In our story, the island had a different climate and different species than in other parts of Britain. Different environmental conditions affect species differently based on their genotypes and thus they display different traits. Island biogeography often gives indications for evolution, because each island may have its own set of environmental

Figure 7.19 Similar molecular DNA comparisons across species. Genetic similarities in hemoglobin structure show very few base differences between humans and other species. Humans and chimpanzees show a very high degree of genetic relatedness. From Biological Perspectives, 3rd ed, by BSCS.

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Figure 7.20 a. Sugar gliders. b. Flying squirrels.

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conditions and organisms. Islands provide a good setting to study how organisms change over time. Island biogeography in our story gives first indications for how the larger ecosystem may change in the future.

evolutionary Design: there is no One right Answer As stated earlier in this chapter, evolution does not favor the strongest or the smart- est. Instead, it is based on a response by organisms to different environmental con- ditions at different times and in different places. A phenotype that works at any one

DoES EvolutioN ExPlaiN thE oRiGiN oF liFE oR thE oRiGiN oF thE uNivERSE?

Evolution does not explain either of these fascinating beginnings; in fact, evolu- tion only explains life after it evolved. The Big Bang Theory attempts to explain how the universe formed, from an extremely hot ball of gases some 13.75 billion year ago (Figure 7.21). The universe continues to expand in what is termed an inflationary epoch. Evidence for the Big Bang Theory is based on observations by scientists of movement and particle attraction. Matter is thought to be explod- ing and expanding outward, with our local sun a by-product of the Big Bang.

Physicists have indirectly detected that over 95% of the universe is either dark matter or dark energy. Dark matter is matter that is cannot be seen but only detected based on its gravitational pull and other evidence for its exis- tence. Physicists estimate that dark matter makes up 23% of the universe and its affiliated dark energy makes up 72%. Matter that is known to us composes only a very small part of the universe. It is strange to think that most of our universe is unseen and undetected by us.

The origin of life itself is traced to our beginnings – we are made of star- dust from the big bang, but before that time, there is no explanation of the forming of matter as we know it.

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Figure 7.21 a. The Big Bang is an explosion that is theorized to have begun matter and the universe. b. The TV show “Big Bang Theory”.

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time may be ineffective at another time. Evolution does not produce a perfect or even the best organism. Contrary to popular belief, evolution does not continually make species better. In fact, at times organisms can get much worse. Selection for large peacock feather to attract a mate actually hampers their lifestyle, preventing them from being able to outrun predators (Figure 7.22). On many farms, chubby chickens have been bred to be so large and tasty that they can no longer engage in sexual rela- tions. They need to be artificially inseminated to produce live young, so selection in this case is artificial and not natural. These are extreme examples of selection that decreases an organism’s quality of life. It is important to note that evolution acts to change organisms in response to their environmental conditions and not to make them better or worse creatures.

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Figure 7.22 Peacock’s large tails attract mates but often interfere with its ability to walk and carry out everyday functions.

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EvolutioN oF DiaBEtES: BlESSiNG oR CuRSE?

Diabetes is a sugar-sparing chemical system. It is not a new disease – it has been a genetic characteristic of humans since the origin of our species. Diabe- tes is, in fact, a useful and natural sugar-sparing characteristic that in prehistoric times conserved energy in times of starvation. Genes linked to diabetes are termed “thrifty” genes because they keep sugar levels high in the blood.

Diabetes is defined as a disease with higher than normal levels of glucose (sugar) in the blood (80–120 mg of glucose/100 mL blood). Under normal con- ditions, sugar in the form of carbohydrates is consumed by an animal, triggering the pancreas to respond by making more insulin hormone. Insulin stimulates the glucose to be ingested into body cells and causes the liver to store it. When blood sugar levels drop too low, the pancreas secretes the hormone glucagon, which stimulates the liver to release sugar. This negative feedback mechanism maintains homeostasis of sugar to around 90 mg/100 mL blood consistently through a lifetime (Figure 7.23).

Diets high in sugar and simple, refined carbohydrates are linked to the development of Type II diabetes because excess sugars “wear out” insulin receptors. Intakes of food with refined sugars, such as donuts and cakes, elicit a surge in insulin and a docking with cells in the body. This wearing-down pro- cess is known as down regulation. Each cell in the body has proteins on mem- branes to which insulin attaches. After docking, insulin causes the target cell to take up glucose. Diets high in sugars wear out insulin receptors and cause insulin resistance. Diabetes Type II (also known as adult-onset diabetes) works in this way; not to confuse it with Type I diabetes, which is an autoimmune attack on pancreatic cells that produce insulin. Both result in hyperglycemia (high sugar levels) but have very different mechanisms.

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Damage to tissues and organs occurs whenever glucose levels are too high or too low. In Type II diabetes, hyperglycemia results in diabetes, with insulin unable to allow sugars to be used by cells. This keeps blood sugar levels high, and cells do not obtain needed energy; thus they are starving. Clearly, these diabetic bouts damage nerves, blood vessels, heart muscle, and other organs. Alternatively, at low levels, hypoglycemia takes place, with individuals suffer- ing from weakness, disorientation, and even unconsciousness as the brain is deprived of needed sugars. This condition would be an evolutionary disad- vantage for prehistoric individuals who regularly missed meals because of the difficulty of getting food in harsh environments.

A mutation to prevent the conversion of glucose to glycogen was bene- ficial at one point in the past. The diabetes mutation maintained sugar levels during starvation conditions. These “thrifty” genes spare sugars in the blood, keeping it available for use. Consider the Neolithic diet, in which calories may be hard to find at certain times of the year; for example, when there is little game to be found. The individual with “thrifty” genes would benefit because normal circulating levels of sugar would be maintained longer for hunting and gathering to find food.

James V. Neel, a geneticist at the University of Michigan, discovered the “thrifty gene” sequence in some human populations. When faced with star- vation conditions, natural selection would have favored such gene sequences. The Pima Indians of Arizona, he found, were not only resistant to insulin’s effects of taking up sugar from the bloodstream but also retained more fat in storage. This helped the Pima endure longer periods of reduced food availabil- ity and starvation conditions.

The advantage of the “thrifty” genes to store more fat and keep circulating available blood sugar was an important survival strategy for populations during pre-agriculture times. However, in modern society, with availability of food much increased and a change from hunter–gatherer lifestyles that required more energy, people with “thrifty” genes are more prone to obesity and dia- betes. In fact, about one-half of the Pima Indians have diabetes, and about 95% of those diabetic individuals are obese. Are diabetes and obesity on the rise due to the dissonance between evolved metabolism and modern diets? Can lifestyle changes improve these maladies?

Studies indicate that a return to more traditional lifestyles and diets could improve the health of individuals. Pimas practicing traditional lifestyles in iso- lated parts of the Sierra Madre mountains of Mexico have significantly lower rates of diabetes (8%) and obesity (rare) compared to the modern U.S. Pima Indian population (Figure 7.24). This may be a case study to guide changes in our approach to combat obesity and diabetes. A diet rich in variety and whole grains, fresh vegetables and fruit, and low-fat protein sources has abundant support in science as a recommended diet.

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Figure 7.23 Negative feedback controls sugar levels. Insulin and glucagon control glucose levels in the blood to keep blood sugar at optimal levels. From Biological Perspectives, 3rd ed, by BSCS.

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Figure 7.24 a. Pima Indians in Sierra Madre Mountains in the 1800s. b. Pimas in Gallup, New Mexico, U.S., 2013.

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Chapter 7: Evolution Gives our Biodiversity 261

Summary Organisms change over time in response to the environment. Change is a part of life’s history whether it is expressed in the emergence of new species, an increase in numbers, a decrease in numbers, or complete extinction. Life’s origins harken back to early Earth conditions, but changes in species have occurred throughout its history. The moth popu- lations described in this chapter show how environmental factors affect species even in a short period of time. Natural selection leads to species changes with extinction as a final step in species loss and speciation as an outcome of adaptive radiation. There is ample evidence for evolution of species throughout Earth’s history.

Sexual Selection Natural selection not based on a struggle for survival but instead based on a struggle for the opposite sex is called sexual selection. In most animal societies, females choose their mates. They choose a male based on one of two factors: his available resources or his appearance. The more resources in a particular male’s territory, the more appealing the male. More resources indicate that the male will be better able to care for their young. A male’s appearance also plays a role in a female’s decision. If a male is more symmet- rical, then the male generally has a better genetic quality. Consider the quest for physical beauty, discussed in Chapter 3, showing the importance of appearance in finding a mate in human society.

While female choice is a primary determinant in mating, male aggression is also important. There are two forms of male aggression in sexual selection: passive sexual selection and active sexual selection. Passive sexual selection involves the development of charms and appearance to attract a mate. It is passive because it is used to attract rather than actively obtain a mate. The mating songs of grasshoppers (discussed earlier) and the feathers of a male Peacock are examples of passive sexual selection. Active sex- ual selection involves aggression by males to obtain a female (Figure 7.25). Antlers on deer, physical strength to fight, and tusks on elephants are examples of weapons used in active sexual selection. Sexual selection and the development of sex were discussed in Chapter 6 to show how variation helps species’ survival. Sexual selection drives the most fit organisms to be perpetuated in a population.

Sexual selection

Is the natural selection not based on a struggle for survival but instead based on a struggle for the opposite sex.

Figure 7.25 Active sexual selection is an example of Bighorn Rams fighting for dominance over females in the herd.

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CheCk OUt

Summary: key points

• Humans play a role in the evolution of other species within the environment, and are intrinsically linked to them.

• The process of discovering life’s origins point to conditions on Earth that were favorable for sponta- neous development of organic molecules and later, primitive cells.

• Natural selection favors certain traits and increases them in a population and disfavors other traits, decreasing them in a population over time.

• Natural selection may lead to speciation, which increases the number of species and thus biodiversity. • Extinction of species leads to permanent decreases in biodiversity. • Evidence for evolution is based on the current examples of modern-day changes in species, the fossil

record, homology, organisms’ biogeography and molecular evidence. • Sexual selection explains how organisms compete for the opposite sex to obtain the best adapted

offspring.

adaptive radiation allopatric speciation biogeography directional selection disruptive selection evolution extinction fossil record germ theory homologous structures homology

hyper-disease theory natural selection prebiont reproductive isolation reproductive success sexual selection speciation spontaneous generation stabilizing selection sympatric speciation vestigial organs

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Chapter 7: Evolution Gives our Biodiversity 263

Multiple Choice Questions

1. Which caused decreases in V-moth populations in southern England? a. Farming b. Acid rain c. Pollution d. Fishing

2. Which scientist used a long-necked flask to disprove spontaneous generation? a. Redi b. Pasteur c. Oparin d. Urey

3. Which best describes how moth populations changed in southern England in recent years? a. All moths declined in their numbers. b. All moths increased in their numbers. c. Some moths became new types of moths. d. Some moths increased in numbers and other moths decreased in numbers.

4. Disruptive natural selection may lead to: a. extinction b. speciation c. convergence d. directional selection

5. Which type of natural selection is most likely to cause adaptive radiation? a. Disruptive b. Stabilizing c. Unidirectional d. Bidirectional

6. Allopatric speciation: a. causes a new species to form. b. causes extinction. c. has the opposite effect of sympatric speciation. d. is less effective than sympatric speciation.

7. Which term is NOT associated with increases in biodiversity? a. Allopatric speciation b. Homology c. Adaptive radiation d. Sympatric speciation

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8. Two organisms are very closely related, with 98% of genes in common. This evi- dence for evolution is based on a. fossil records. b. biogeography. c. homology. d. molecular data.

9. In question #8 above, which provides the best evidence for showing the organisms’ relatedness? a. Molecular data b. Anatomical data c. Geographical data d. Speciation data

10. If two deer fight over a female using their antlers, this is an example of: a. passive sexual selection. b. active sexual selection. c. natural selection. d. adaptive radiation.

Short Answers

1. Describe how human society affects species diversity in your own neighborhood. Use one example of species that raises your concerns.

2. Define the following terms: adaptive radiation and disruptive natural selection. List one way how each of the terms differ from the other in relation to biodiversity.

3. Describe the experiments of two scientists: Francisco Redi and Louis Pasteur. Use a drawing to make the descriptions clear. Show your art work. How did each discover an aspect of spontaneous generation? How did their knowledge build upon one another’s?

4. Draw the Miller and Urey apparatus. What were the products of their simulation? How did Miller and Urey reignite debate on spontaneous generation?

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Chapter 7: Evolution Gives our Biodiversity 265

5. For question #4 above, how might you argue that life could emerge from nonlife?

6. List three ways evolution can be verified. Which piece of evidence is the most con- vincing to make the case that species today are a result of evolution?

7. Explain the process by which moth species declined in England in the past decades? How did some species of moths increase at the same time?

8. Some organisms base their choice for a mate on physical appearance. In barn swal- lows, an experiment showed that after making a male swallow less symmetrical, fewer females chose him. Explain how evolution favors this result in female choice. How will offspring change over time, given the results?

9. Name the type of speciation that results when a species cannot mate due to a change in their use of a habitat. Explain how it results in speciation.

10. A bacterial cell becomes resistant to a type of antibiotic. Predict the outcome for the population of this species of bacteria.

Biology and Society Corner: Discussion Questions 1. Moth populations in the chapter’s story show rapid changes in frequencies. Describe

two steps that the English government could take to help prevent unwanted biodi- versity loss in England. Are there any drawbacks to your suggested approaches?

2. How did Pasteur’s religious views affect his scientific outlook and methods? Are personal or religious views justified in propelling scientific thought? Why or why not?

3. If a person has a nonheritable form of intelligence that enables her to read peo- ple’s minds; what is this trait’s likelihood for changing the direction of evolution in society. Justify your answer.

4. Acid rain is a danger to some organisms and a benefit to others. In the moth species described in this chapter, explain how this is so.

5. An Internet site claims that people are getting smarter and smarter with each gener- ation due to evolution. Is this claim valid? Why or why not?

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Figure – Concept Map of Chapter 7 Big Ideas

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267

Before Plants and Animals: Viruses, Bacteria, Protists, and Fungi

EssEntiAls

Louis Pasteur Rabies virus

Glycoprotein Matrix protein

Phosphoprotein

RNA

Polymerase

Rhabdovirus (rabies virus)

The Death Cap Mushroom is the world’s deadliest poisonous mushroom

Yogurt is a product made by several types of bacteria through fermentation of sugars in milk

Many biofuels are made by bacteria

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the Case of the First Rabies survivor Andre played with his dog almost every day, but this time it was different. His friendly dog was strange; it seemed almost unaware of what was going on. Andre went to his beloved dog to help him get through the door of the barn. Suddenly, the dog lunged for- ward and bit Andre’s arm. This had never happened before.

In the course of the day, Andre’s mother noticed the bite on his arm. She inquired to find out what had happened. Andre explained, “The dog bit me. He was very odd, not himself, and looked like he had foam coming from his mouth.” “What’s wrong, mother?” Andre asked. His mother was crying, knowing Andre would have a horrible death that would come soon.

“Doctor, we brought the boy in just minutes ago. He was bitten by a rabid dog!” exclaimed the nurse. Dr. Louis Pasteur, a different kind of doctor who tried out-of-the- box techniques, was Andre’s last hope. Pasteur had a reputation, and many were afraid that his procedures were too far from mainstream medicine.

Dr. Pasteur was determined that no person would again die of rabies in the future. He had seen so many succumb to the infection. Pasteur worked in the 19th century, in a hospital that had none of the technology found in hospitals today. Still, Pasteur knew the symptoms of rabies that were awaiting Andre: fever, headache, tiredness, drooling and death. He was angry at organisms that he could not even see. “I cannot let another person die of rabies!” Pasteur protested.

Pasteur consulted with his colleagues, Dr. Vulpain and Dr. Grancher, to ask for their recommendation . . . should he attempt a drastic and experimental procedure, never done before? Both responded, “You should try it. Otherwise, this child will die; there is nothing to lose.” “But is it going to work – Is it even ethical to do?” Pasteur wondered. His research on rabies-infected dogs showed Pasteur that living infected dogs survived when injected with a vaccine made of ground up spinal cords from dead rabid dogs. But humans were not dogs, and Pasteur was nervous – “How macabre,” he thought, “to inject a human with ground up spinal cord from a dog.”

ChECk in

From reading this chapter, you will be able to:

• Explain how the diversity of organisms affects our health and society. • Discuss the discovery of pathogens, how they cause disease, and how this knowledge affected the

medical profession. • Describe the characteristics of viruses, types of viruses, and their related diseases. • Compare the lytic and lysogenic life cycle of viruses. • Describe the characteristics of prokaryotes, types of prokaryotes, their biological roles and relation-

ships with humans. • Describe the characteristics of protists, types of protists, their biological roles and relationships with

humans. • Trace the evolution of protists and fungi from ancient prokaryotes. • Describe the characteristics of fungi, types of fungi, their biological roles and relationships with

humans. • List and describe the diseases caused by viruses, prokaryotes, and protists and fungi, evaluating their

impacts on human society.

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Chapter 8: Before Plants and Animals: Viruses, Bacteria, Protists, and Fungi 269

The only other choice was death. Pasteur proceeded, injecting Andre with a spinal cord mixture. The night was long and emotional; as daybreak passed, Andre was still alive, perhaps a bit stronger than the day before. Each day for the next three months, Pasteur injected Andre with small bits of spinal cord. At the end of the treatment, Andre emerged as the first person in history to ever survive a rabies infection. Upon seeing Andre stand, Pasteur recalled the words of mathematician and scientist Blaise Pascal: “Man is but a reed, the most feeble thing in nature; but he is a thinking reed . . . All our dignity consists, then, in thought . . . by thought, I comprehend the world.” Pasteur reflected, “The frailty of the human condition is overcome by the strength of human thought.” He had succeeded in overcoming rabies with his planning and his thoughts. It was a glorious day for Andre and his family – and for biology.

Louis Pasteur’s 1800s discovery of the rabies vaccine shows the human struggle to use the power of the mind to overcome nature’s adversity. The seeds for medical progress and biological research are born of this quality, as shown by Louis Pasteur’s scientific reasoning used to cure Andre.

ChECk UP sECtion

This story embodies the essence of a way of thinking about the natural world, a movement from the power of physical strength to the power of the mind. This story highlights the struggle to overcome nature through innovation in the history of science.

The future of science lies in its past: the passion of the great scientists, their struggles against nature’s challenges, and their creativity in discovery. All point to the characteristics needed to propel scientific thought into our future.

Study the rabies infection, caused by the rhabdovirus, to determine its causes, symptoms, and treatment by vaccine in more detail. How were rabies and other microbial infections discovered, while being unable to see the organisms that cause it? What are some examples of modern diseases that are being studied to better humanity?

Discovering Pathogens and Ways to treat them The world of living organisms previously unseen by human eyes was discovered by microscopy. Anton van Leeuwenhoek described microbes, organisms that cannot be seen with the naked eye, very clearly and accurately in the 1600s as discussed in other chapters. This chapter focuses on the many organisms revealed by microscopy: viruses, prokaryotes, protists, and fungi (see Figure 8.1). Each of these groups has great variety; some organisms are beneficial to humans and some are harmful. Organisms that are harmful to humans are called pathogens.

Pathogens were not generally recognized as agents of disease until the late 1800s. The work of Louis Pasteur, described in our story, as well as that of other scientists, such as Robert Koch who studied tuberculosis in humans, pointed to microbes as infectious agents in plants and animals. Scientists showed that pathogens have a few ways to attack their host:

1) Some directly attack the host, destroying cells, as is the case for viruses and many bacteria. Viruses, including the rabies virus, invade cells and destroy them from the inside. They grow using their host’s resources as fuel and shelter.

Pathogen

Organisms that are harmful to humans.

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270 Unit 3: We Are Not Alone!

Figure 8.1 a. There is great diversity of life on Earth. Some major groups of organisms and their respective numbers of species are given in the figure. Insects comprise the largest proportion of species diversity. As seen in our story in Chapter 7, insects play an important role in our environment. From Biological Perspectives, 3rd ed. By BSCS. b. Some less appreciated forms of life; a. arachnids; b. fungi.

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2) Some pathogens cause disease indirectly, by producing substances that harm the host. For example, diphtheria is caused by the bacterium Corynebacterium diph- theria, which is inhaled and lodges in the upper respiratory tract. There it makes a toxin, or poison, that prevents human cells from making needed proteins and thereby kills them.

3) Some organisms cause damage by eliciting an immune response by the host. In some forms of pneumonia, the bacterium Streptococcus pneumonia causes such overwhelming release of fluids in response to its presence that the fluids fill the air sacs of human lungs, causing the host to have difficulty breathing. The inflammation caused by the pathogen causes damage instead of the pathogen itself.

4) Many pathogens cause multiple symptoms, as in the familiar cases of strep- throat (see Figure 8.2). The disease-causing agent for strep-throat is often Streptococcus pyogenes, which causes throat pain, a fever, and in 0.5% of cases, damage to heart valves, joints, and other tissues of the body. For this reason, strep-throat is considered more dangerous than a normal sore throat. Jim Henson, creator of the Muppets, died of infected heart valves from a strep- tococcus bout.

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Chapter 8: Before Plants and Animals: Viruses, Bacteria, Protists, and Fungi 271

By recognizing that some microbes caused disease, doctors and scientists began taking measures as far back as the 1800s to prevent their transmission. In medical pro- cedures, sterile techniques began to be used to reduce their numbers. Improvements in hygiene, hospital cleanliness, removal of public waste, and water treatment contrib- uted to cleaner surroundings as a result of recognizing microbial illnesses. In the past, for example, a major killer of women and children was childbed fever. It was spread by visiting doctors who carried streptococci from patient to patient as they examined them. The sterilization of instruments and introduction of hand-washing reduced patient deaths from microbes. Before these procedures became common practice, upward of 50% of children died within their first years of life. Since the advent of sterile techniques and vaccinations, the infant mortality rate has declined dramatically over the past cen- tury (see Figure 8.3).

The discovery of the first vaccination is described in our historical opening story. Bacterial and viral infections are treated and prevented through immunization, which

Immunization

The technique that uses dead pieces of disease-causing agents to strengthen immunity against a disease.

Figure 8.2 Strep-throat is a common infection. It is the inflammation of the tonsils and surrounding tissue at the back of the throat, resulting in redness and soreness.

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Figure 8.3 Infant mortality from 1900 to 2007. Dramatic decreases in infant mortality over the past century were a result of the discovery of antimicrobial techniques such as vaccines and penicillin.

1900 1920 19601940 1980 2000

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272 Unit 3: We Are Not Alone!

uses dead pieces of disease-causing agents to strengthen immunity against a disease. (Immunizations will be discussed in Chapter 15.)

In 1935, sulfanilamide, a new “wonder drug” was discovered in Germany, one of the first to control bacterial infections. Penicillin, which attacks cell walls of bacteria, was discovered by Alexander Fleming in 1940. Penicillin is a type of antibiotic, which is defined as any chemical that stops the growth of microorganisms (see Figure 8.4). Many antibiotics are extracted from bacteria or fungi that produce a natural defense against competitor microbes, harvested in antibiotics. Today, antibiotics and vaccines are also produced in laboratories. Antibiotics changed people’s lives and their life spans, as the most dramatic, large scale health improvement of the century.

Many microorganisms, such as the rabies virus, were undetectable under the micro- scope. They were discovered by indirect means, much as Pasteur detected and treated rabies. Because they cause so many plant diseases, viruses were first discovered in plants. Viruses are composed of combinations of nucleic acid, serving as their genetic material, and a surrounding protein coat. Their life cycle centers on their disease-causing ability, (discussed in the next section). Viruses cause many diseases ranging from the common cold to herpes, influenza, and cancer. There are a variety of types of viruses, each with differing shapes (see Figure 8.5).

The first virus-like organism to be discovered was found in studying PSTV, or potato spindle-tuber disease. PSTV is caused by a viroid, a simple virus that leads potato plants to produce long, gnarly, and deformed potatoes. This viroid also infects tomatoes, stunt- ing their growth and twisting tomato plant leaves. Viroids are also causes of disease in citrus trees, chrysanthemums, and cucumbers. Viroids are very simple, composed of only a strand of RNA – which leads scientists to the question: “Are viruses and viroids actually living organisms?”

Viruses: to live or not to live . . . Features Viruses are intracellular parasites, meaning that they invade host cells and live within them. They are not cells and are not included in the classification schemes of living organisms. They are obligatory parasites, unable to live outside of a host cell. Thus, they

Penicillin

An antibiotic obtained from the molds of Penicillium genus.

Antibiotic

Any chemical that stops the growth of microorganisms.

Intracellular parasite

Living organisms that invade host cells and live within them.

Obligatory parasite

Organisms that are unable to live outside of a host cell.

Figure 8.4 Penicillin is a blue-green mold that grows in a colony. Penicillin is a type of antibiotic produced by Penicillium, a mold. a. A penicillium colony. Penicillium produces round spores at the tips of its reproductive structures. It provides a special chemical, penicillin, that has saved millions of human lives. b. Chains of round tips at the ends of its reproductive structures are shown in this figure.

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Chapter 8: Before Plants and Animals: Viruses, Bacteria, Protists, and Fungi 273

are not considered to be living organisms. Viruses do not have an independent metabo- lism and cannot carry out life functions while outside of host cells.

Neither are viruses nonliving matter: they have genetic material, carry out some life functions, make proteins, mutate, and are able to reproduce. The structure of a typical virus includes a set of genetic material – either DNA or RNA – surrounded by a protein coat or capsid. The genetic material is simple, ranging from 1 to 100 genes along either a double or a single strand. A typical virus is shown in Figure 8.6.

Viruses are usually species-specific, with one type of virus affecting only one species of host. A human virus therefore cannot infect a cat and vice versa. The reason for this is that viruses use docking proteins to attach to surface receptors on host cells. As dis- cussed in Chapter 3, cell membrane proteins attach to docking chemicals. Viruses also use this docking system to attach to host cells. There are obvious exceptions, such as rabies in our story, in which Andre is bitten by a member of another species that trans- mits the virus. The docking and transmission between species is able to occur because rabies proteins match many species.

Some viruses have tail ends, shown in Figure 8.7, which enable them to attach spe- cifically to a host. The exception to the species-specificity rule occurs when mutated forms of viruses change enough to cross over to infect a new species. Scientists believe that this occurred in the spread of AIDS (acquired immunodeficiency syndrome), caused by HIV (human immunodeficiency virus), which mutated from nonhuman primates in sub-Saharan Africa in the late 19th or early 20th century.

Size of viruses

To show perspective, a virus size is very small, about .2 µm, while a bacterium such as Escherichia coli is 3 µm, and a human liver cell is large, at about 20 µm. Viruses often exist outside of their hosts as crystals. They remain able to be activated, so catching a virus from a door handle or a toilet seat is its mode of transmission. It remains dor- mant in the crystalline state and activates upon the first opportunity to enter into a host.

Capsid

The protein coat that surrounds structure of a typical virus.

Species-specific

Limited to or found in one species.

Figure 8.5 a. Morphology (shape) of some common viruses. b. Note that the rhabdovirus is bullet-shaped. It possesses receptor proteins on its coat (yellow buttons on the outside of the Rhabdovirus in image) which dock with host cells. Rhabdoviral DNA is spiral in shape and is protected within a protein coat.

Rabies virus

Glycoprotein Matrix protein

RNA

(b)(a)

Phosphoprotein

Polymerase

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274 Unit 3: We Are Not Alone!

Figure 8.6 A color-enhanced image of a T4 virus. It has a protein capsid head surrounding genetic mate- rial and helical tail with fibers and needle to insert its DNA. The virus uses its tail fibers to attach to a host bacterial cell wall.

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Figure 8.7 a. Microscopic view of a virus docking to host membrane protein. There is a specific-fit between a viral protein and receptors on the surface of host cells makes connections very exact. b. A virus then gains entry in a host cell, allowing it to conduct its strategies. In the figure given, viruses use the host cell’s machin- ery to manufacture new viruses.

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Whether airborne through the respiratory membranes of a human throat or via a cut in the skin, a virus returns to “life” when it enters another organism.

Some nonliving infectious creatures are prions, which are simple strands of pro- teins that ”liven up.” Prions cause brain infections such as mad cow disease and chronic wasting disease in deer. People who ingest meats infected with prions may exhibit no symptoms for decades, and suddenly prions reemerge, eating through tissues of the brain. No person has ever lived beyond one year after symptoms emerged from a prion illness. Prion diseases cannot be treated, and the best way to avoid their transmission is to eliminate brain or spinal cord meats from one’s diets. At times, such meats are ground up in hamburgers and in other processed food, with customers unaware of the true contents.

Viruses: the internal terrorist There is no magic bullet to kill a virus because most drugs do not work on a virus- induced illness. There are natural immune defenses, which will be discussed in Chapter 15, but viruses have unique actions that make them a difficult enemy. In addition, while antibiotics directly attack bacteria, viruses lodge themselves within our cells. This pre- vents their targeted destruction because host immune systems must then also destroy their own body cells. There are ways to attack a virus, discussed in the next section, but defenses against viruses are problematic.

Viruses are internal terrorists because they invade host cells, undetected by the body’s defenses, and incorporate themselves into its host’s genetic material. Viruses are successful much in the way that a spy infiltrates its enemy – by remaining unseen and unnoticed. If a host’s immune system detects a virus, it is destroyed and the virus is easily defeated. As long as a virus remains incognito, it can be successful at taking over its host cells.

There are two types of life cycles for viruses: the lytic life cycle, which results in a virus’s immediate destruction of a host cell, and the lysogenic life cycle, during which a virus inserts its genes into a host and waits for a time in the future to destroy the host. During the lytic life cycle, viruses attach to their host cells by grabbing onto their mem- brane proteins (see Figure 8.8). In the example of a bacteriophage, which is a virus that invades a bacterium – for example, an Escherichia coli bacterium, tail fibers on the virus specifically match the shape of host membrane proteins. Often the base of the virus con- tains special enzymes that bore holes to the inside of invaded cells. Some viruses contain a coil that acts as an injection needle to thrust the virus’s DNA or RNA into a host cell. Once inserted into a host, viral genes take over the nucleus of the cell, directing the pro- duction of hundreds and thousands of new viruses. Viruses are terrorists because they use the cell machinery of their hosts to destroy them. Viruses are then released, breaking their host cells – this is the “lytic,” or breaking, part of the cycle. The rabies virus seen in our story uses a lytic life cycle to rapidly kill its host. Andre would have suffered great pain and death from this process because damage occurs instantly when a virus breaks apart cells in the lytic life cycle.

During the lysogenic life cycle, a virus injects its genes into a host cell (see Figure 8.9). Viral genes are incorporated into a host’s DNA or RNA, and every time an infected host cell divides, viral genes divide along with it. It is an unstable relationship because at any one point in time, a set of viral DNA may activate and begin all of the steps of the lytic life cycle. The lytic life cycle is the same as the lysogenic life cycle, with one exception: the lytic process begins after a virus activates its genes within a host genome, while the lysogenic life cycle includes the period of dormancy of viral genes.

Prions

A small infectious particle believed to be the smallest disease- causing agent.

Lytic life cycle

A reproduction cycle which results in a virus’s immediate destruction of a host cell.

Lysogenic life cycle

A reproduction cycle during which a virus inserts its genes into a host and waits for a time in the future to destroy the host.

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Figure 8.8 Lytic life cycle of a bacteriophage invading an E. coli cell. During this part of a virus’s existence, it takes over the cell’s nuclear machinery. The virus in the picture uses a host’s DNA to produce more of its own genetic material and proteins coats, making many new viruses.

A. Attachment

Bacteriophage

Bacterium (host cell)

Host DNA

Viral DNA

B. Injection of DNA

Lysogenic cycle

C. Integration

Bacteria continue to replicate

switch to a lytic cycle, and phages kill the host cell

D. Multiplication

B. Injection of DNA

C. Replication of viral components

D. Assembly of new phages E. Lysis of bacterium host

A. Attachment

Lytic cycle

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Many factors can bring on the start of a lytic life cycle: sunlight, chemicals, or stress are three such factors. In the case of Herpes Simplex I, which causes fever blisters around the lips, anxiety or sunlight stresses may bring a virus out of dormancy of the lysogenic life cycle. This results in cell destruction and, of course, fever blisters. The focus of our story in Chapter 15 is on our immune system’s defenses against the herpes virus’s biology. Because the virus is lodged around nerve cells, fever blisters on lips are very painful, affecting nerve sensations.

You may remember these different life cycles as the one with “lytic” means to lyse or break open, and the one with lysogenic, refers to “genic” or genes that are dormant but may lyse or break a host cell at a later point.

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Chapter 8: Before Plants and Animals: Viruses, Bacteria, Protists, and Fungi 277

Figure 8.9 Lysogenic life cycle of Herpes Simplex I.

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some interesting Viruses Herpes Virus

Herpes viruses come in two types: Herpes Simplex I and Herpes Simplex II. Discussed above, Herpes Simplex I is not sexually transmitted, is localized around the lips of humans. and remains dormant in cells in a lysogenic life cycle (see Figures 8.9 and 8.10). Its viruses recognize skin and nerve cells because they come from the same embryo layer – the ectoderm – which will be discussed in Chapter 16. Stress brings out herpes because the immune system usually keeps it in check.

Herpes simplex II

A sexually transmitted and is characterized by genital sores.

Herpes simplex I

An inflammatory skin disease characterized by the formation sores around the lips.

Figure 8.10 a. Cold sores are symptoms of a Herpes Simples I infection. Eighty percent of adults are infected with the virus causing oral herpes. b. Genital herpes is sexually transmitted and is painful, which frequently recur in some individuals.

(a) (b)

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When a stress is placed upon the body, herpes reemerges from its lysogenic life cycle, entering the lytic phase. Herpes is transmitted by direct contact between two peo- ple. The sores it causes are composed of giant cells that are filled with white blood cells that ingest invaders and damaged materials. Herpes Simplex II is sexually transmitted and is characterized by genital sores (see Figure 8.10). They are recurrent and reemerge during stress on the body in the same way as Herpes Simplex I. Both forms of herpes viruses are delicate and cannot travel through the air.

Rhabdovirus

Rabies is 100% fatal and is an exception to host specificity; it is able to be transferred from one species to another, as described in our opening story. As mentioned earlier, the rhab- dovirus causes rabies, its structure is bullet shaped, and its DNA is helical. When a bite occurs, saliva containing the rhabdovirus transmits it into a new organism. The rhabdo- virus moves along the nerves of the body, up the spinal cord toward the brain.

In the brain, the rhabdovirus multiplies, causing symptoms and irreversible damage. Symptoms include fever, headache, hallucinations, intense muscular activity such as an arched back, and difficulty swallowing. Owing to the last symptom mentioned, a person with rabies shies away from water with a fear of swallowing. Foaming at the mouth, paralysis, and heart and lung failure leading to death are certain without treatment. In our story, before Pasteur’s discovery, society lived in fear of a bite from a rabid animal. It was a certain and horrible death. Rabies vaccination directly acts on the rhabdovirus, with special proteins or antibodies that attack viruses, stopping their action. Rabies vaccine is a form of immunization that acts directly on pathogens and without the help of a host’s immune system.

Rhinovirus

Less serious but nonetheless annoying is the common cold, caused by the rhinovirus. The rhinovirus kills ciliated cells of the upper respiratory tract in humans. The destroyed cilia are replaced with other cells along the throat. Once cilia are damaged, sufferers cannot adequately filter air. The mucous that forms in the common cold is a result of damage to these cells. The body attempts to cover up cell losses with mucous, leading to nasal congestion and respiratory upset. The common cold rarely kills, unlike the rabies virus in our story, but almost everyone is a victim of the rhinovirus because of its frequent occurrences and uncomfortable symptoms (see Figure 8.11).

Myxovirus

One of the illnesses caused by the myxovirus is influenza, which affects three to five million people worldwide each year and causes upward of 500,000 deaths. Its symp- toms include fever, muscle aches, pains, coughing, weakness, and fatigue. Sometimes a secondary infection with bacterial pneumonia occurs, the result of an immune sys- tem weakened by myxovirus. The myxovirus contains eight single strands of RNA, each able to mutate. This is a large amount of genetic material for a virus and explains in part how the influenza virus changes each year, with mutations in RNA sequences making new strains harder to vaccinate against. Myxovirus contains two types of pro- teins: neuraminidase (N), which digests through mucous membranes, and hemagglutinin (H), which enables the virus to bind with its host. Whenever genetic material of the myxovirus mutates, it changes its N and H proteins. Influenza infections have

Rhabdovirus

A bullet- or rod- shaped RNA virus found in plants and animals.

Rhinovirus

The most common viral infectious agent that causes common cold in humans.

Myxovirus

Any group of RNA- containing viruses.

Neuraminidase

A protein found in Myxovirus that digests through mucous membranes.

Hemagglutinin

A type of protein that enables Myxovirus to bind with its host.

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spurred pandemics, killing people worldwide. In the United States, more people died in the 20th century from influenza than from all of the major wars combined, as show in Table 8.1.

Papillomavirus

Human warts are benign tumors of the skin caused by viruses. Papillomavirus, the cause of human warts, contains double-stranded DNA surrounded by an icosahedral or 20-sided protein coat. Human papillomavirus (HPV) is associated with cervical cancer and is the basis of the relatively new vaccine against cervical cancer. It is spread by human contact, and in the case of cervical cancer through sexual transmission. There is debate as to whether or not to vaccinate all girls at age 11–12 to prevent most forms of cervical cancer. The debate occurs because it is a sexually transmitted infection, and people view teen-age sex through a variety of lenses. There was no debate when Pasteur saved victims from rabies, as described in our story – only celebration.

Papillomavirus

A group of virus that cause papillomas or warts.

Table 8.1 Influenza outbreaks occur due to mutated strains of the myxovirus. In the 20th century, there were more U.S. deaths from the 1918 flu outbreak than due to all of the major wars combined. Worldwide it is estimated that 30–50 million people died in the pandemic. Each year in the 20th century, the flu killed an average of about 36,000 people.

US Deaths 20th Century - Flu and War

WWI

WWII

Korean

Vietnam

Total

1918 Flu

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Figure 8.11 The common cold, caused by rhinovirus, is a nuisance but rarely kills its sufferers.

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THe WAR ON VACCINeS

Long forgotten are the benefits of vaccination to human society: fatalities from small pox fell from 2 million per year in 1967 to 0% by 1980; the Salk and Sabin vaccines prevented more than 5 million cases of paralytic polio; and vaccina- tions against infectious childhood diseases prevent more than 3 million deaths in young people each year.

Yet if you do a web search on the harmful effects of vaccines or the autism-vaccine link, thousands of sites are listed, all convincing their readers that vaccines are bad news. Hollywood stars such as Jenny McCarthy advocate for ending vaccines in the face of rising autism cases.

The risks and side effects of vaccines are unproven or extremely low. Many people do not recognize the benefits of vaccinations because they did not live through the many fears of life without them – polio, influenza, mumps, measles, hepatitis, small pox, to name a few. Our life span increased enormously from 38 years of age in 1850 to roughly 75–85 years today, in part because of vaccines. In the time before vaccines, people died early or during childhood or child birth without the benefits of vaccines to keep harmful microbes at bay.

The movement against vaccines is resulting in the reemergence of some diseases. For example, when an outbreak of measles swept across Europe in 2010–2011, 48,000 people were hospitalized and 28 people died unnecessarily. When less than 90% of the population is unvaccinated, dangerous spreading of disease becomes more likely. Over 80% of those infected in this outbreak were not vaccinated. In fact, being unvaccinated endangers the most suscepti- ble among us – children under 5 years of age.

The press reported two studies in the late 1990s that linked vaccines with autism: One was a false link between mercury-containing preservatives in vaccines and autism and a second was a discredited claim based on a study of only 12 children claiming that the measles-mumps-rubella (MMR) vaccine was linked to autism. The dangerous outcome of such reports is not in questioning the side effects of vaccines but the panicked decision by the public to avoid vaccination. It engenders a long-term danger that diseases may reemerge or harmful microbes may thrive and even mutate, and become stronger, making their prevention and treatment more difficult. There is little debate on the value of the rabies vaccine. Its direct link to surviving rabies, as seen in our story, is undisputable. We have come a long way, but perhaps we’ve come a bit too far for public health.

(source: Wall Street Journal, “Rolling Back the War on Vaccines,” February, 2013)

Oncovirus

Any virus that carries a gene associated with cancer is known as an oncovirus. It is able to insert its genes, called oncogenes, into a host genome, potentially causing cancer in the host and in the host’s offspring. Its genes are inherited, and this is a basis for evidence for the genetic cause of cancer. Oncogenes from an oncovirus become activated due to an event. The event might include an environmental stimulus like smoking or drinking, which causes oncogenes to turn on, resulting in cancer. Oncogenes could take decades to emerge or not show up at all in one’s phenotype, unlike the guaranteed death that rabies affords. Prevention of cancer at the genetic level of research holds the most promise in tackling the root cause of the disease.

Oncovirus

Any virus that carries a gene associated with cancer.

Oncogene

A normal gene that under certain circumstances can cause cancer.

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Chapter 8: Before Plants and Animals: Viruses, Bacteria, Protists, and Fungi 281

Figure 8.12 The oncogene theory. Oncogenes are mutations from normal genes which then cause cancer. For example, in human bladder cancer, small changes in the position of base pairs on a gene create oncogenes. As a result of a Chromosome #17 base pair change in the p53 shown in the figure, cancer develops. From Biology: An Inquiry Approach, 3rd ed by Anton E. Lawson.

Guardian of the Cell The p53 gene keeps tumors from forming. It either stops a damaged cell from growing into a tumor—or kills it outright.

The p53 protein locks onto genes, activating the cellular- defense system.

p53 PROTEINCHROMOSOME 17

3 If the p53 gene is healthy, it instructs the cell's protein factory to make p53 protein.

2 The p53 gene is located on the short arm of chro- mosome 17.

CELL

1 Every human cell (except sperm, eggs and red blood) contains 23 pairs of chromosomes.

P53 GENES

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The characteristics of cancer cells were discussed in previous chapters, but oncogenes point to their genetic origin. In a study by Weinberg, who isolated genes from bladder cancer cells, he found that only one base differed between normal cells and cancer cells: base #35 in normal bladder cells contained a guanine nucleotide and in an oncogene, base #35 contained a thymine nucleotide. Such a small difference genetically can lead to large changes in an organism’s health and survival. See Figure 8.12 for a visual descrip- tion of oncogene theory and the p53 oncogene.

Retrovirus

AIDS is caused by HIV, which destroys a human immune system’s fighting capabil- ities. HIV is a retrovirus, which is a virus containing RNA and the enzyme reverse transcriptase. Reverse transcriptase retroactively makes RNA into DNA, the opposite of the central dogma described in Chapter 5. The invasion of a host cell by HIV begins with its attachment to T-helper cells, which are key immune cells in humans. T-helper cells have a CD4 receptor on the cell membrane that matches with HIV-docking proteins. When the two attach, their membranes fuse, and RNA from HIV comes out of the virus and into the host’s cytoplasm. HIV is unique in its ability to convert its single-stranded RNA into single-stranded DNA, able to carry out life processes. Once viral DNA migrates to the nucleus, it uses host enzymes to make double-stranded DNA. In this form, it is integrated into the host’s genome, now “invisible” to the human immune system in a lysogenic life cycle. All progeny of T-helper cells are now infected with this dormant viral DNA. At a point in time, it reemerges and shunts into the lytic life cycle, causing the symptoms of AIDS. The course of the disease and its symptoms are shown in Figure 8.13 and Table 8.2. In the graph, you can see that at first the number of T-helper cells increases due to the host’s immune system fighting the infection. However, the numbers decline substantially as T-helper cells become more and more infected. With the immune system compro- mised, AIDS patients become susceptible to numerous illnesses, including pneumonia and rare cancers such as Kaposi’s sarcoma. Eventual death often results along with men- tal deterioration as the brain finally becomes infected. Its life cycle is slower than the rapid rabies advance on the brain that would have happened to Andre in our story.

Multiple drug treatments have result in marked improvement in the treatment of HIV and AIDS. A drug cocktail containing AZT, azidodeoxythymidine, inhibits reverse

Retrovirus

A virus containing RNA and the enzyme reverse transcriptase.

Reverse transcriptase

An enzyme that generates complementary DNA from a RNA template.

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transcriptase in HIV and has been shown to be effective in halting the disease course and extending life for HIV patients for many years.

Prokaryotes: the little things in life Features From an evolutionary perspective, the most successful kingdom is the prokaryotes, commonly known as bacteria. They have survived over 3.5 billion years, are adapted to almost every environment on Earth, and reproduce rapidly, allowing their colonies to change to adapt to new conditions in a short period of time. They are found in hot

Table 8.2 Symptoms of HIV infection.

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Figure 8.13 The decline in T-cells (immune defense cells, seen to the right) in AIDS patients over the course of the disease. After infection with HIV, T-cells are invaded by the virus. At some point, HIV enters a lytic life cycle and destroys T-cells. T-cells usually defend humans against infections. When T-cell numbers decline, susceptibility in AIDS patients becomes dangerous, almost always leading to death if left untreated. Infections occur later on in the disease’s course. From Biological Perspectives, 3rd ed by BSCS.

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springs, in deep-sea vents beneath the ocean, under arctic ice, in our guts, and on our teeth. As discussed in Chapter 7, their simple, efficient ways of dividing and mutating help them to change with the times and inhabit just about any environment.

Classification of the 4,000 different species of bacteria is based on appearance or upon metabolic, chemical reactions rather than evolutionary relationships, as opposed to naming systems in other organisms. There are testing methods, such as the API testing strips, used to determine which organic molecules are metabolized by bacteria. Micro- biologists classify bacteria into two different groups: archaebacteria, or ancient forms of bacteria, with only a few surviving branches; and bacteria, which were once called eubacteria, and are the modern prokaryotes. Continual developments in molecular tech- niques make the field of classifying bacteria changing. At this point, the two domains of prokaryotes are most commonly accepted.

Bacteria have small sizes compared to eukaryotes, with diameters less than 5 µm. A typical bacterial cell is many million times smaller than a human being, but it is much larger than the nanometer size of viruses such as the rhabdovirus of our story.

While tiny in size, prokaryotes outnumber all other life, making up more than 99% of all living creatures by sheer mass. Their circular genes are simple and, unlike those of eukaryotes, are not surrounded by a nucleus. They contain no organelles except for ribo- somes. Eukaryotes, which comprise all other life, are more complex. Eukaryotes contain all of the organelles discussed in Chapter 3 (see the comparison of cells in Figure 8.14). Their cells have genetic material surrounded by a nuclear membrane, heavier ribosomes, more complex DNA, and larger diameters ranging from 10 to 100 µm.

Archaebacteria

Ancient forms of bacteria, with only a few surviving branches.

Bacteria

Single-celled microorganisms that are found everywhere.

Figure 8.14 Comparison of prokaryotes and eukaryotes. The simple prokaryote has few parts but is able to outcompete eukaryotes because of its simplicity. The many organelles of eukaryotes (see Chapter 3) are shown in this figure with few in prokary- otes besides genetic material and ribosomes. From Biological Perspectives, 3rd ed by BSCS.

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Figure 8.15 Decomposition and recycling of nutrients by bacteria. Bacteria, along with other organisms, recycle organic matter, such as dead animals and plants, into reusable products. Several organisms described in this chapter work together to break down organic matter and return to useable materials in the environ- ment. From BSCS Biology: An Ecological Approach, 9th Edition by BSCS.

Decomposer food chain

1. mustard-yellow polypore (shelf fungus)

2. oyster mushroom

3. amanita 4. yellow morel 5. snail 6. sow bug 7. centipede 8. wood roach 9. springtails

10. mite 11. ant 12. carrion beetle 13. soil fungi 14. soil

protozoans 15. earthworm 16. inorganic

compounds 17. soil bacteria

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Only a few prokaryotes cause diseases in humans; most are beneficial to us and to the environment. Life on Earth would not exist without the activities of bacteria. Bacteria return nutrients to the Earth through decomposition (see Figure 8.15). Prokaryotes are used in the production of many chemicals, such as acetone and butanol, in fingernail polish, and cleaning agents. They make vitamins and antibiotics, milk, and cheese. As described in Chapter 6, they are used in gene technology to manufacture insulin for diabetics and human growth hormone (HGH) to treat dwarfism. In Chapter 4, we saw how the bacteria Lactobacillus acidophilus is used in yogurts through the process known as fermentation In fact, L. acidophilus bacteria are used to treat gastrointestinal illness because they are normal inhabitants of the human digestive tract. As they grow, L. acidophilus bacteria outcompete potentially troublesome bacteria in our bowels and produce lactic acid, which keeps other bacteria from growing. The roles of bacteria in human society are diverse, and many things in our environment require the workings of prokaryotes. While viruses like rabies create mostly human harm, we require bacteria for our existence.

shapes, sizes, and types The morphology (shape) of bacteria allows a general identification of its many strains. There are roughly 10,000 types of bacteria. They may be classified based on their metab- olism and their shape and arrangements. They may be round cells called coccus, rod- shaped, called bacillus, or spiral, spirillum. Bacteria may be arranged either singly or in groups. When bacteria are found in chains, they are classified with the prefix strep-; when they are found in clusters, they are classified as staph-. Figure 8.16 shows the shapes and arrangements of bacteria.

Morphology

The form of an organism that allows a general identification of its many parts.

Coccus

Round-shaped bacteria.

Bacillus

Rod-shaped bacteria.

Spirillum

Spiral-shaped bacteria.

Strep

The prefix given to bacteria that are found in chains.

Staph

The prefix given to bacteria that are found in clusters.

Figure 8.16 Common shapes of prokaryotes: Spiriulum (spiral), Baccilli (rod), and Cocci (round). The arrangement of chains (staph) and clusters (staph) of bacteria is also shown.

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MR. TOOTHdeCAy ANd MR. PIMPLeS ARe HARMFuL TO OuR HeALTH

Strains of Streptococcus are leading causes of tooth decay, such as Streptococ- cus mutans, which deposit acids on the enamel of teeth. Staphylococcus strains cause pimples on skin surfaces, as well as boils and other serious skin infec- tions. Some strains of Staphylococcus aureus, for example, cause necrotizing fasciitis or flesh-eating bacteria syndrome. While skin is not actually “eaten” by bacteria, it is destroyed rapidly by a spreading infection that, if left untreated by surgery and antibiotics, is fatal.

Figure 8.17 Gram-negative (pink) and Gram-positive (purple) bacteria cell walls. Each type of bacteria stains differently due to the thickness of their layers of peptido- glycans. Gram-positive bacteria have thick peptidoglycan layers while Gram-negative bacteria have thin peptidoglycan layers.

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Almost all prokaryotes have cell walls, like plants, but the structure of the cell wall is different from that of plants. Bacterial cell walls contain peptidoglycans, which are a type of protein known as glycoproteins. Sugars cross-link with each other to hold pep- tidoglycans together. There are two types of bacterial cell walls that identify bacteria as being one of two categories, based on using a dying technique called the Gram stain: Gram-positive bacteria are colored purple by the staining technique, and Gram- negative bacteria are colored pink. Gram-positive bacteria have simpler cell walls, with a thick layer of glycoproteins. This layer retains the dye from a Gram stain and appears pur- ple. Gram-negative bacteria have more complex cell walls, with less peptidoglycan, and gram stain washes away, making cells appear pink (see Figure 8.17). Gram-negative bacteria also have an outer membrane with lipopolysaccharides that protect their cells. Even though they are simple, bacteria are much more complex in structure than the rabies virus infecting Andre.

Peptidoglycan

Are a type of protein found in bacterial cell walls.

Gram stain

A dying technique that identifies bacteria as being one of two categories.

Gram-positive bacteria

A group of bacteria that retains the dye in Gram staining method of bacterial differentiation.

Gram-negative bacteria

A group bacteria that lose the crystal violet dye in Gram staining method of bacterial differentiation.

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Figure 8.18 Flagella arrangements around bacteria. Flagella may be arranged as single tails as shown in the image of the bacterium that causes cholera in humans, Vibrio chol- era. Bacteria cells also contain flagella grouped in tufts or as strewn throughout their surfaces.

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Penicillin works well in treating Gram-positive bacteria because it prevents cross-linking of peptidoglycans in the cell layers. Gram-positive bacteria walls thus fall apart due to penicillin. However, in Gram-negative bacteria, penicillin cannot move through the outer layer, preventing it from working to kill bacteria.

Many strains of bacteria have a capsule surrounding them, allowing them to prevent water loss and live in dry areas, such as in deserts and on our skin surface. Capsules are sticky and help bacteria to adhere to surfaces and to other bacteria.

Bacterial surfaces often have pili, surface hairs that allow bacteria to bind with each other. Through pili, bacteria exchange substances, including genetic material. This is bacterial sex; while not very elaborate, it serves to give bacteria greater genetic vari- ation. This exchange of genetic material through pili is known as conjugation. Pili are also used to help bacteria bind to surfaces. Neisseria gonorrhoeae, for example, fastens itself onto mucosal genital regions in humans. It is the cause of the sexually transmitted disease, gonorrhea. In fact, bacteria and microbes cause a number of sexually transmit- ted diseases.

Prokaryote nutrition More than half of all prokaryotes have motility. They move by means of flagella, fila- ments around their outer cell walls (see Figure 8.18). They also move by gliding, secret- ing chemicals on surfaces to move quickly. Flagella may be arranged as either scattered units, in tufts, or as a single length. Salmonella typhimurium, which causes the food- borne illness Salmonella, has scattered flagella leading to uncoordinated movement. Motile bacteria are characterized by taxis, which is movement toward or away from a stimulus. In chemotaxis, for example, bacteria move toward or away from food or oxy- gen sources. In phototaxis, bacteria move toward light.

Bacteria are also metabolically diverse. In phototaxis, some bacteria move toward light in order to obtain food via photosynthesis. These bacteria use a process of photo- synthesis that is quite different from plants. MIT Technology Review recently announced the bioengineering of photosynthetic bacteria to produce up to 30 times more sugar per

Pili

Surface hairs that allow bacteria to bind with each other.

Conjugation

The process of exchange of genetic material through pili in bacteria.

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acre than sugarcane plants for biofuel. When grown in transparent containers, these organisms use sunlight to produce ethanol from sugars to be used in cars as fuel (see Figure 8.19).

When bacteria use inorganic chemicals as energy, they are known as chemoautotrophs. These bacteria use inorganic molecules such as hydrogen sulfide and ammonia rather than food or sunlight to produce energy. They are independent, able to make their own food, and use carbon dioxide as their source for organic molecules. Chemoautotrophs do not require sunlight or oxygen. As shown in Chapter 7, the environment of early Earth provided an environment in which chemoautotrophs could have survived.

It is thus believed that these were the first organisms on Earth. Organisms in our intestines, which produce sulfur odors and methane gases, fall under this category. Nitro- gen-fixing bacteria, living in root nodules of bean, pea, and clover plants, use gaseous atmospheric nitrogen to produce ammonia (NH3) in their reactions to obtain energy. In the process, ammonia is made available as soil nitrogen, which is vital for plants. Most bacteria are heterotrophs, such as decomposers, which use dead organic matter for energy. They use dead matter to release carbon dioxide into the atmosphere as a product to be fixed later by plants in the Calvin cycle (described in Chapter 4).

Bacterial Reproduction Prokaryotes reproduce by splitting in half through the process of binary fission. A circular bacterial chromosome divides, attaches to its cell wall, and as the bacterial cell grows, the replicated chromosomes separate into opposite ends of the cell. Plasmids, small circular strands of DNA, also replicate, moving into two new cells. Daughter cells form after parent cell cytoplasm pinches inward.

Most of a prokaryote’s DNA codes for proteins, unlike in eukaryotes, in which 90% of the genes are not used in protein synthesis. Thus, binary fission is efficient and productive once a new cell forms. Fission can occur very quickly, within 20 minutes, resulting in over 20 billion cells in only 12 hours! It is able to maintain genetic variation through mutations, with so many chances for changes because of the many times a pro- karyote divides. As discussed in the previous section, conjugation also affords unique combinations of genetic material to recombine in prokaryotes.

Two other processes contribute to their genetic diversity. Transduction occurs when a virus, known as a bacteriophage, invades a prokaryote, inserting its genes into

Chemoautotroph

Bacteria that use inorganic chemicals as energy.

Binary fission

The process of reproduction by splitting in half.

Transduction

The process that occurs when a virus invades a prokaryote, inserting its genes into the host.

Figure 8.19 Biofuels made by crops of photosynthetic bacteria. A possible solution to the energy crisis? Shown, is a pond filled with photosynthetic bacteria in Hawaii.

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the host. Genetic recombination, as discussed in Chapter 6, is accomplished using a bacteriophage in the procedure. Insulin and HGH are manufactured in this man- ner. Transduction results in a transgenic prokaryote, with new genes added from the virus. Imagine a rhabdovirus transduced within a new bacteria. While fictitious, this would form a transgenic new organism, capable of causing rabies through bacteria transmission!

In addition, when prokaryotes absorb DNA from their environment, either through eating dead or dying bacteria or scattered matter, the genetic material is added to their own genome. This process is called transformation because the newly inserted DNA from the environment changes or transforms a bacterial cell into a new genotype (see Figure 8.20). Recall that Griffith's discovery of DNA in chapter 5 studied transformation in pneumonia-causing bacteria.

Prokaryote Diversity Archaebacteria

Archaebacteria are a type of prokaryote that is now classified as a separate domain from other bacteria are surrounded by cell walls that lack peptidoglycans, have unique cell membranes, contain RNA polymerase that resembles eukaryotes rather than other

Transformation

The process in which a newly inserted DNA from the environment changes or transforms a bacterial cell into a new genotype.

Figure 8.20 Transformation in bacteria. Foreign DNA from a dead bacterium enters its host bacterium. Once DNA is exchanged, this results in a new cell with dead DNA incorporated. This adds to genetic diversity in prokaryotes. New DNA is a new com- bination for organisms to use and their offspring to inherit.

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bacteria, and live in extreme environments, resembling early Earth conditions – in short, they appear different than other bacteria.

There are three groups of archaebacteria. The first group is the methanogens, which react to oxygen as a poisonous substance. Methanogens use hydrogen to reduce carbon dioxide into methane, CH4. They must therefore live in areas that have no oxygen such as marshes and guts of animals. Sewage treatment plants and landfills use underground methanogens to convert garbage to methane. This causes the typical sulfur odor of a landfill.

The second group of archaebacteria is the halophiles. Halophiles are “salt lovers,” which means that they are able to live in very salty conditions that few other organisms can withstand. Halophiles living in very salty lakes, such as Mono Lake in California (see Figure 8.21), use “pumps” to flush out the salt. Few other organisms can compete with halophiles in hypersaline areas such as Mono Lake in California, the Dead Sea in Israel, and the Aral Sea between Kazakhstan and Uzbekistan.

The third group of archaebacteria is thermacidophiles, which “love it hot and acidy.” They exist in temperatures from 60 to 80°C and in pH levels of 2–4. Sulfobus, found in sulfur springs in California, is one such organism that thrives in the extreme conditions of the hot springs. The extreme lifestyle of the archaebacteria leads scientists to believe that they were our most distant ancestors and the precursors to all life.

Bacteria

Most prokaryotes are bacteria, with varied morphology and functions. Some interesting bacteria follow, which show the variety of forms of bacteria that play a role in human health and the environment. One type of bacteria is the actinomycetes which have fil- ament strands and resemble fungi. Actinomycetes are decomposers recycling dead organic matter. As heterotrophs, actinomycetes rely on dead material to obtain food and therefore return organic materials back to the soil (see FIgure 8.15 for the decomposition process).

Cyanobacteria, such as Anabena and Nostoc, are photosynthetic and contain bacteriochlorophyll (chlorophyll pigment found only in bacteria). These bacteria pro- duce much oxygen in our atmosphere. Upon closer inspection, cyanobacteria contain large cells, called heterocysts, which contain nitrogen-fixing complexes that return nitrogen to the soil for plant use. Cyanobacteria reproduce by splitting at their hetero- cysts, breaking them open to produce new chains (see Figure 8.22).

Methanogens

Organisms that react to oxygen as a poisonous substance.

Halophiles

Are organisms that grow or live in very salty conditions.

Thermacidophiles

Organisms that thrive in strongly acidic environments at high temperatures.

Actinomycetes

A type of bacteria having filament strands and resemble fungi. They are decomposers recycling dead organic matter.

Cyanobacteria

Are photosynthetic bacteria and contain bacteriochlorophyll.

Figure 8.21 Mono Lake, California.

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Figure 8.22 a. Cyanobacteria microscope photo (Anabaena). b. Kingdom Monera: The evolutionary tree of Monera shows its vast diversity from a common ancestor. Cyanobacteria are only one example of the many species within the domains Archae and Bacteria. From Biological Perspectives, 3rd ed by BSCS.

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A GeRMOPHOBe’S NeW PeN

Metals high in copper content, such as brass, have been certified by the Envi- ronmental Protection Agency to be antimicrobial. Brass pens, doorknobs, and light switches have been used throughout the past centuries (Figure 8.23). These metals have long been known to work against diseases. Copper is an ancient disinfectant, killing bacteria, viruses, and other disease-causing agents, including six of the most common strains of bacteria such as S. aureus and E. coli. The more copper in a substance, the more it is antimicrobial in nature. Copper causes chemical reactions in microbes leading to oxidative damage: copper harms bacterial cell membranes and proteins, preventing microbe functioning.

In studies conducted by the University of Southampton, copper alloys were shown to eradicate influenza A, H1N1, and various stomach bugs within 10 minutes of dry contact on copper surfaces. This finding has motivated a switch to copper and brass products in some hospitals, to keep microbes at bay among the sick. Should we all purchase a brass pen?

Endospore-forming bacteria are Gram-positive, flagellated rods. They form endo- spores to endure harsh, dry conditions such as those found in deserts or dried-up marshes. In this form, spores as old as 250 million years, from Bacillus permeans, were found in the ancient salt sea underneath Carlsbad, New Mexico, and successfully revived. This ability to survive unfavorable conditions and revive in optimal ones marks a similarity between viruses and spore-bearing bacteria, but viruses like the rhabdovirus must find a host in order to reproduce.

Bacteria range in sizes, with the smallest known bacterium, the mycoplasma. They are between 100 and 250 nm in size, approaching some viruses in size. They lack a cell wall and are thus unaffected by most antibiotics, such as penicillin. Mycoplasmal pneu- monia is a serious illness caused by this bacterium.

Phototrophic anaerobic bacteria reduce NADP+ with electrons from H2S rather than H20, as seen in the process of photosynthesis described in Chapter 4. These bacteria do

endospore-forming bacteria

Are Gram-positive, flagellated rods that form endospores to endure harsh, dry conditions.

Mycoplasma

The smallest known bacterium.

Phototrophic anaerobic bacteria

A group of bacteria that do not release oxygen in their photosynthetic-like processes because the photolysis of water does not occur.

Figure 8.23 Brass acts as an antimicrobial agent. It has been used throughout history as pens, door knobs and handles, and as plates on light switches. Studies show that the chemistry of brass keeps microbes at bay.

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not release oxygen in their photosynthetic-like processes because the photolysis of water does not occur. Instead, they break-up H2S, which releases sulfur gas. This gas gives areas with these bacteria, for example, southern U.S. marshes, the characteristic smell of sulfur.

Enteric bacteria are found in animal digestive tracts. They are Gram-negative and include E. coli, for example. They thrive in conditions free of oxygen, without compe- tition from aerobic bacteria in other areas. Enteric bacteria are beneficial, providing vitamin K for humans, among other things.

Our interactions with bacteria should be studied in part to understand the human role in their life cycles. As seen in our story of Andre, our place in the ecosystem and possibilities for disease prevention are better implemented through researching life cycles of other organisms.

the Misfit kingdom: Protista Protists are eukaryotes, are mostly unicellular, have asexual and sexual reproduction, and move via cilia or flagella. Other than these common features, protists share few similarities, and may be viewed as a group of misfits because of their dissimilarities. Protista is the most diverse kingdom: its members have very different structures, metab- olisms, and ecological roles. They range in types of organisms, from the strange trum- pet-like Stentor to the giant kelp, which grows 150 feet “long at a rate of 2” per day. With 60,000 species of brown algae alone (of which the giant kelp is one), protista comprise a very diverse kingdom (see Figure 8.24).

Molecular evidence shows that Protista were the first eukaryotes, emerging roughly 1.5 billion years ago. About 1 billion years prior to their appearance on Earth, the oxy- gen revolution resulted from the photosynthetic activity of cyanobacteria. Prokaryotes evolved as some of the life forms able to use oxygen in energy processing. As dis- cussed in Chapter 3, the endosymbiotic model explains that eukaryotes then developed as prokaryotes absorbed oxygen-using creatures and evolved larger, more complex cells. Mitochondria and chloroplasts helped these new eukaryotes to obtain energy.

Figure 8.24 Images of Protista. They are the most varied of all the kingdoms. Some are motile and some sessile; some are plant-like and others animal-like. Depicted in this image is the sessile. Stentor, far left and the very active Paramecium, far right.

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According to the autogenous model of protist formation, primitive protists also evolved by invaginations of their membranes to form some of the membranous organ- elles such as the endoplasmic reticulum. The nucleus probably formed by invaginations around existing genetic material in primitive cells. This added benefit helped protists protect their DNA from environmental conditions. The complexity of protists helped them to survive and reproduce, competing with the simpler prokaryotes.

The first of these cells to develop were the Protista, which developed over 1 billion years after the oxygen revolution began. However, the protists of 1.5 billion years ago would not resemble those found today. Evolution and speciation have led, over these past 3 billion years, to speciation and the vast diversity in Protista. Biologists agree, however, that all other kingdoms – fungi, plants, and animals – originated from early protists.

Classification New techniques in electron microscopy, molecular analysis of DNA and new biochem- ical techniques make classification of Protista a changing field. The number of phyla, divisions of Protista and relationships within the kingdom are being debated. Biologists generally agree that there are three broad categories: 1) those that resemble plants – algae such as the giant kelp; 2) those that resemble animals – protozoans such as the stentor; and 3) those that resemble fungi – slime molds such as Physarum cinereum that creep across turf grass on lawns.

Algae Algae comprise a wide variety of what is commonly known as seaweeds. Algae are mul- ticellular organisms that are photosynthetic, and they contain a variety of pigments such as chlorophyll a and b (green), carotenoids (yellow-orange), phycobillins (red and blue), and xanthophyll (brown). These pigments increase the photosynthetic output of algae, making them responsible for over 50% of all oxygen production by the process on Earth. Pigments also give algae their definitive colors, which are used in their classification.

The giant kelp, mentioned earlier, is a member of the brown algae or phaeophyta, which has roughly 2,000 species. They are vast organisms, growing rapidly to form large regions of seaweed in temperate areas of the ocean in North America, South Africa, and the South Pacific. Giant kelp resemble sea forests with their dense mats of plant-like leaves, which provide a home to many hundreds of marine species – from other protists, fish and snails, to larger marine mammals such as the sea otter and gray whales.

Diatoms, or bacillariophyta, are a major producer of oxygen via photosynthesis. Diatoms live in oceans, as well as freshwater rivers, lakes, and streams. Their unique arrangements, due to complex silicon dioxide shells, make them a beautiful, ornate organ- ism (see Figure 8.25). Diatoms are part of the many protists that make up phytoplankton, which are all of the aquatic organisms that absorb carbon dioxide and release oxygen into the atmosphere. Phytoplankton form large and dense layers of organisms in water systems. Alone, they comprise about 25% of all oxygen production on Earth. Their eco- logical role in climate change and pollution is one of the most important dynamics of ecological study because of their contribution of oxygen in our atmosphere.

Other colors and forms of algae are found in bodies of water (see Figure 8.27): 1) Red algae, or rhodophyta, are red due to their phycoerythrin (red pigment), found along tropical coasts; 2) chlorophyta, or green algae, comprise about 7,000 species and are similar in cell structure and pigments to modern plants. Thus, they are believed to be ancestors to the first plants, discussed in Chapter 9. Chlorophyta are also a component of lichens, which are green algae or cyanobacteria living in association with fungi found

Autogenous model

The model that states that eukaryotes developed directly from a prokaryote by compartmentalization of functions of the prokaryote plasma membrane.

Algae

Are multicellular organisms that are photosynthetic, and they contain a variety of pigments such as chlorophyll a and b (green), carotenoids (yellow-orange), phycobillins (red and blue), and xanthophyll (brown)(algae is in bold).

Protozoan

A group of single- celled protists that resemble animals.

Slime molds

Organisms that live freely as single cells but form multicellular reproductive structures upon reaching a certain size.

diatoms

A single-celled algae that are a major producer of oxygen via photosynthesis

Phytoplankton

All the aquatic organisms that absorb carbon dioxide and release oxygen into the atmosphere.

Lichens

Green algae or cyanobacteria living in association with fungi.

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throughout most ecosystems (see Figure 8.26). Lichens are partnerships of organisms, with algae providing food from photosynthesis and fungi providing a physical place for algae to live. They are widespread – there are over 24,000 species of lichens, named by their type of fungal species, which is usually an acomycete fungus variety – and they can survive dry, harsh conditions, requiring only light, air, and a few minerals. 3) Chryso- phyta or golden-brown algae contain carotenoids and xanthophylls to give them their rich color. They form cysts that can survive very harsh conditions. They are colonial organisms and are biflagellated, with two flagella to propel them around; 4) Euglena or euglenophyta are unique in that they are both plant and animal-like. They contain an eye spot, which helps them to detect light and move toward it to carry out photosynthesis. Euglena, while able to make their own food, are also somewhat heterotrophic, requiring vitamin B-12, which they obtain through eating particles via phagocytosis.

euglena

A green single-celled, motile freshwater organism.

Figure 8.25 Phytoplankton, a type of diatom shown in this image. Diatoms serve an important role in aquatic habitats, from producing large amounts of oxygen to providing a food source for many organisms.

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Figure 8.26 There are over 24,000 species of lichens. Their algal layer produces food from sunlight and their fungal mycelium protects algae and anchors it to underlying substrates. Two species of lichens are shown on this branch.

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Protozoans Protists that have motility and are heterotrophic are characterized as protozoans. They include single-celled organisms such as the Amoeba, in the phylum Sarcodina. Amoebas are able to extend their cytoplasm, in the form of pseudopods (false feet), to move or obtain food. Sarcodina are the simplest protozoans, but their simple appearance does not mean that they are simple. They are able to behave in complex ways to obtain food, for example. When an amoeba senses its prey, through chemical detection, it extends its pseudopods toward and around its victim. It will also pursue its prey as long as it is close enough; amoebas judge the size of their prey, sending out just the right amount of pseudopod to ensure a meal (see Figure 8.28a).

Paramecia, in phylum Ciliophora, move using their fully ciliated bodies, by creat- ing waves in the liquid of their surroundings. They obtain food by beating their cilia to make currents to bring organisms into their oral grooves along the side of their cells (see Figure 8.28b). Paramecia are capable of both sexual and asexual reproduction.

Figure 8.27 A sample of Protista diversity: types of colored algae. A brown and red algae bed is shown beneath the ocean.

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Figure 8.28 a. An amoeba uses its pseudopods to move and also to engulf prey. b. Paramecium consumes food, usually entering through their oral groove.

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Those organisms in the phylum Mastigophora, such as trypanosoma gambiense, are parasites, causing sicknesses in the organisms they inhabit. Trypanosoma, which causes African sleeping sickness, is transmitted in the bite of a Tse tse fly. This illness may lead to kidney dysfunction, nerve problems, and eventual death. Trypanosoma is a reminder, as in our story, that microbes may cause serious disease among humans, with scientific research required to continually search for cures.

Another mastigophore is Trichonympha, which lives in the guts of termites, allow- ing cellulose, a plant substance, to be broken down for energy. This organism provides its host the ability to digest wood. However, most mastigophores are parasites, causing sickness in humans.

slime Molds Slime molds are often referred to as lower fungi because they resemble fungi.

However, they are different from Fungi in terms of their structure and biological processes. They are slimy because they release an oozing substance that flows along surfaces to engulf prey, such as other protists, bacteria, and fungi (see Figure 8.29). They are similar to fungi in that they both live in cool, dark, and moist places, such as forest floors and shower drains. All slime molds are heterotrophic and use spores to reproduce by forming fruiting bodies that release those spores.

Figure 8.29 Slime molds form fruiting bodies used in reproduction. The red-colored spheres in the image contain spores that are used to spread new mold.

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THe AGGReSSIVe AMOeBA

In a terrible twist of events, a young boy, 12 years old, was admitted to the hospital in central Texas. He attended a summer camp but went home “not feeling well.” He had been participating in water sports in a nearby lake to the camp, along with the other children. His mother took him to the hospital after days went by and he continued to have fever, loss of smell, and flu-like symp- toms. After admittance, several diagnoses were tentatively made: meningitis, pneumonia, and bacteremia. Then the horrible discovery in his cerebrospinal fluid: amoebas. The boy died only 5 days after being admitted to the hospital.

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A Favorite Fungus What is your favorite fungus? . . . Mushrooms for making soup? Yeast for bread? Penicil- lin for your illness? or perhaps Athlete’s foot, found in over 25% of the U.K. population? Each of these is an example of a fungus; they are found everywhere from feet to forest floors, usually in moist, dark places.

Features and types Many people think of mushrooms when they imagine a fungus. However, fungi are diverse, as shown in our examples. Fungi were once classified as plants, but structur- ally and chemically, they are more closely related to animals than plants. They do not contain chlorophyll, and their cell walls contain substances found primarily in animals. Their classification is not fully agreed upon among biologists, but most of their species fall into two phyla: Ascomycota, or decomposers, and Basidiomycota, commonly seen as mushrooms and puffballs. While most species of fungi are multicellular eukaryotes, some, such as yeasts are unicellular. Molds, which are difficult to remove from homes and cause poor air quality due to their spores, can also be beneficial, for example, as a source of the antibiotic penicillin. There are approximately 100,000 species of fungi

The temperature of the lake in Texas in which the boy was swimming in the summer of 2007 was 84.4°F (29.1°C). This was warm enough to support the life cycle of amoeba parasites. The story is based on a real report by Texas health authorities chronicling the events surrounding the death of a Texas boy. The infection was a result of Naegleria fowleri, a species of freshwater amoeba, which enters the brain and aggressively destroys it. While it is a rare illness known as amoebic meningoencephalitis, there are regular cases in which pond water enters into a patient’s nasal passages. Amoebas pass through the very small opening between the nasal passage and the frontal region of the brain, which houses the olfactory bulbs, used for smell. The parasite lodges itself there, right above the nasal passages, dividing and causing large lesions. Symp- toms first include a loss of smell or a sense that something is burning or rotting. Amoebas rapidly advance through the brain, dividing and damaging all areas until the victim’s death.

The course of the disease takes only between 3 and 12 days. Its survival rate, with aggressive medical treatment, is very low at only 3%. Other symptoms of amoebic meningoencephalitis include headache, fever, nausea, vomiting, and a stiff neck but later result a loss of balance, seizures, hallucinations, and death.

There have been only 160 cases since 1960, including two from using tap water through a neti pot irrigation system. The CDC (Centers for Disease Control and Prevention) report that warm pond water as well as some well water and municipal drinking water, may become infected with amoebas. While drinking infected water is harmless, when it travels through a person’s nose, then the potential exists for amoebic meningioencephalitis.

The disease remains a protist mystery, with unanswered questions: Why are some susceptible while others go unharmed, swimming in the same waters? How does the amoeba work to move across nasal membranes and into the brain? With such a small number of cases, is the public outcry about the illness an overreaction? Should people stop swimming in warm pond water?

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with many more expected to be discovered. Fungi emerged relatively recently in Earth’s history, about 500,000 years ago. An aquatic protist was most likely its ancestor.

The body of a fungus is generally composed of a mass of filaments called myce- lium. Each individual fungal filament is called a hypha, and the hyphae together create a mycelium mat (see Figure 8.30). These mats anchor deep into material that it is decom- posing in order to absorb its matter. Hyphae are one cell-layer thick, making it easy for fungi to absorb substances from their surroundings. A septum divides hyphae filaments into compartments, each septum having openings for communication. The cell walls of hyphae are composed of chitin, a polysaccharide found primarily in insect exoskeletons, their hard outer covering. Chitin is a strong substance, giving support to fungal cell walls. Chitin is rarely found in plants, an example of their distant relationship with fungi.

Fungi are not motile, but instead move rapidly through growth of their hyphae. Some fungi produce more than a kilometer of new hyphae in a single day. They have high rates of growth. For example, the yellow honey mushroom fungus, in Oregon grows so quickly that it covers an area of over 4 square miles. Their growth allows them to exert a great deal of pressure (1,200 psi) against other organisms, enabling them to penetrate deeply into plants, for example. Tips of fungal hyphae have the ability to penetrate hard surfaces, such as plant cell walls, insect coats, and even human skin. When given the chance, studies show that fungal hypha grow directly through human skin.

Fungi play a critical role in nature. As heterotrophs, fungi obtain nutrients through absorption of dead matter. Fungi eventually consume all living things. Thus, fungi act as decomposers, along with bacteria, to recycle organic matter through our ecosystem (see Figure 8.15).

Fungi also occur in relationship with other organisms, sometimes living on other organisms as in Athlete’s foot, ringworm, jock itch, and beard itch. Fungal diseases are very contagious because their spores survive for long periods on surfaces.

At times, fungi exist in a positive relationship with other organisms, as seen in our lichen example earlier in this chapter. In another symbiotic arrangement, root fungi or mycorrhizae live in root nodules of plants. Fungi benefit by obtaining sugar from the plant, and plants benefit by obtaining nitrogen and phosphorous from fungi, extracted from the soils around them. Many plant diseases are also fungal in origin, such as the

Mycelium

The mass of filaments that form the vegetative part of a fungus.

Hypha

Each of individual threads that make up the fungal mycelium.

Septum

A partition that separates two chambers of tissue in an organism.

Figure 8.30 The entire strand of fungal cells is knows as its mycelium. Mycelium is composed of hyphae that are divided into separate cells. The fungal cell’s components are shown in this figure.

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Figure 8.31 In the reproductive cycle of a fungus, spores form under the gills of mushrooms, forming new hyphae, able to mate and produce new fruiting bodies. Mush- rooms are fruiting bodies, producing spores for a fungus. Meiosis within gill cells of a mushroom produce haploid spores, which combine to form a new organism through the mating of compatible hyphae.

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fungus Cryphonectria parasitica, causing a blight that led to the destruction of the American chestnut tree.

Fungi reproduce both asexually and sexually. In asexual reproduction, a piece of mycelium breaks off, creating a new organism, in a process called fragmentation. In sexual reproduction, spores form in a tightly packed set of hyphae. A mushroom is actu- ally a reproductive structure produced by a fungus to develop and release spores (see Figure 8.31). Mushrooms occur as dikaryotic structures, meaning that their cells have two haploid nuclei that do not fuse. Some parts of a mushroom become diploid, with their haploid nuclei fusing. These diploid portions produce haploid spores through mei- osis, which are released into nature. These combine with other spores to result in a new diploid organism. Sexual reproduction gives more variation to fungal species, unlike mutations, the sole source of variation in the rabies virus discussed in our story.

Fragmentation

The stage in asexual reproduction in which a piece of mycelium breaks off, creating a new organism.

ROOT BeeR

When yeast ferments sugars, as discussed in Chapter 4, ethanol is made as a by-product. It is ethanol that gives alcoholic beverages their kick. When fermentation is stopped before alcohol fermentation really takes off, large

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Chapter 8: Before Plants and Animals: Viruses, Bacteria, Protists, and Fungi 301

summary The variety of organisms that are not plants or animals have many important functions in our ecosystem, but certain forms can also be harmful. Viruses have unique characteris- tics that classify them as an in-between living and nonliving state. They are intracellular parasites that seize a host cell’s machinery. Prokaryotes, much larger cells, carry out all life functions and play key roles in human health and in the ecosystem. They are our ear- liest ancestors evolutionarily. Their simplicity contributes to their success. Protists, the most diverse of life’s kingdoms, and quite a bit more complex than prokaryotes, emerged as our closest eukaryotic ancestors. They were the first eukaryotes, containing organ- elles and contributing to the evolution of higher plants and animals and fungi. Protista emerged about 1.5 billion years ago after the oxygen revolution made adaptations to use oxygen beneficial. Fungi emerged recently, only about 500,000 years ago, from protists. Fungi play a key role in the ecosystem, recycling dead matter. Fungi have many human uses ranging from medicines, wine, and breads to beer and delicate foods.

amounts of sugar are left and only small amounts of alcohol. The result is the popular drink root beer. It was originally produced from the root of a sassa- fras plant or bark. Roots are used as a source of many soft drinks. In the 19th century, farmers used yeast to ferment sugars in the sassafras root to make root beer that contained a small amount of alcohol. It was popular during their gatherings and a light-alcohol beer alternative.

The first commercially produced root beer was sold at the Philadelphia Centennial Exhibit in 1876, by pharmacist Charles Hires. It became quite pop- ular during the Prohibition era of the 1920s and early 1930s, as a substitute for beer. In 1960, the main ingredient of the sassafras root, was found to be carcinogenic and was banned by the FDA. Since then, artificial sassafras acts as a key ingredient, giving root beer its unique taste. Using and understanding natural products, as Pasteur did to discover a rabies vaccination, is a key to advances in health science.

ChECk oUt

summary: key Points

• Viruses, prokaryotes, protists, and fungi affect our environment and human health in many ways, from recycling chemicals and providing food and medicine to a variety of diseases.

• The discovery of the many non-animal/plant organisms showed their many characteristics, shared evolutionary history and role in the environment.

• Viruses are intracellular parasites, with two major types of life cycles: the lytic and the lysogenic. • Prokaryotes are simple and evolutionarily successful ancestors to eukaryotes. • Protista have three general groups: algae, protozoans, and slime molds, each of which contains a

variety of organisms with varied characteristics. • Fungi are decomposers; molds, yeasts, mushrooms, mycorrhizae, and lichens are types of fungi,

which are heterotrophic, and absorb nutrients from their environment.

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actinomycetes algae, red, green, brown, golden-brown antibiotic archaebacteria autogenous model bacillus bacteria binary fission capsid chemoautotroph coccus conjugation cyanobacteria diatoms endospore-forming bacteria euglena fragmentation Gram-negative bacteria Gram-positive bacteria Gram stain halophiles hemagglutinin herpes simplex I and II hypha immunization intracellular parasite lichens lysogenic life cycle lytic life cycle methanogens morphology

mycelium mycoplasma myxovirus neuraminidase obligatory parasite oncogene oncovirus papillomavirus pathogen penicillin peptidoglycan phototrophic anaerobic bacteria phytoplankton pili prions protozoan retrovirus reverse transcriptase rhabdovirus rhinovirus septum slime molds species-specific spirillum strep- staph- symbiosis thermacidophiles transduction transformation

Key TeRMS

• Fungi and Protista evolved from prokaryotes after developing membranous organelles, such as mitochondria.

• Diseases caused by organisms in this chapter include viral: rabies, herpes, influenza, cancer, the common cold; bacterial: necrotizing fasciitis, food poisoning, pneumonia; protist: amoebic meningio- encephalitis, African sleeping sickness; fungal: Athlete’s foot, ringworm, and jock itch.

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Chapter 8: Before Plants and Animals: Viruses, Bacteria, Protists, and Fungi 303

Multiple Choice Questions

1. Which organism is LEAST useful to human society and the environment? a. Virus b. Protista c. Bacteria d. Fungi

2. Which is a process by which pathogens work to harm host cells? a. They cause inflammation. b. They directly attack host cells. c. They produce toxins. d. All of the above.

3. Species specificity states that a virus has this many host species: a. 1 b. 2 c. 3 d. 4

4. The lysogenic life cycle holds viral _____ dormant within host cells: a. proteins b. genes c. carbohydrates d. fats

5. A cluster of spiral bacterial cells would be classified as: a. staphylococcus b. staphylospirillum c. steptobacillus d. coccus

6. Which represents a logical order, from early to later, in the evolution of organisms? a. protista ➔ fungi ➔ archaebacteria ➔ bacteria b. archaebacteria ➔ bacteria ➔ protista ➔ fungi c. fungi ➔ archaebacteria ➔ bacteria ➔ photosystem II d. protista ➔ fungi ➔ bacteria ➔ archaebacteria

7. A motile, eukaryotic, and heterotrophic organism is discovered on a distant island, with cilia surrounding its unicellular structure. Which is its best classification?

a. Slime mold b. Bacteria c. Algae d. Protozoa

8. Which term includes all of the others? a. Hypha b. Mycelium c. Chitin d. Septum

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9. In question #8 above, with which kingdom are the terms most associated? a. Protista b. Fungi c. Prokaryote d. Virus

10. In question #8, which process helps these organisms to obtain needed ATP energy a. Photosynthesis b. Absorption c. Exocytosis d. Species specificity

short Answers

1. Describe three ways in which prokaryotes benefit humans. List three ways in which prokaryotes harm humans. Be sure to list and describe each.

2. Define the following terms: transduction and conjugation. List one way each of the terms differ from the other in relation to genetic variation and biodiversity.

3. Describe the rabies experiment of Louis Pasteur discussed in the story. Research how Pasteur’s injections cured Andre. How do rabies immunizations work today?

4. Name three characteristics of viruses. Are viruses living or nonliving? Defend your answer.

5. For question number 4 above, list two types of viruses and describe their life cycles.

6. List the three groups of archaebacteria. How are they different from bacteria? Which would most likely be found in a hot liquid with a pH of 3? Why?

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Chapter 8: Before Plants and Animals: Viruses, Bacteria, Protists, and Fungi 305

7. Explain the structure and function of a mushroom. Use the following terms in your answer: spores, haploid, dizygotic, diploid.

8. A disease destroying mycorrhizae in forests concerns a group of biologists. Why are they worried about the effects of the disease on the ecosystem? On humans?

9. Explain the role of phytoplankton in our environment and in human society.

10. Diseases due to viruses are plentiful. Name three diseases caused by viruses in humans. Which are not species specific? Why?

Biology and society Corner: Discussion Questions 1. In order to prevent amoebic meningioencephalitis, measures should be taken to

reduce risks by government agencies. Research amoebic meningioencephalitis and list three recommendations you might make to improve public health with respect to the disease. Are your recommendations justified? Why or why not?

2. Louis Pasteur took a great risk with another person’s life. Give an example of an experimental procedure that you have heard about which is controversial. Are such risks in medicine justified? Why or why not?

3. The overuse of penicillin and antibiotics is well documented in medical research articles. Based on your research of these articles, why is it bad practice to prescribe antibiotics such as penicillin to patients with a common respiratory illness? Should you or your loved ones request these drugs during a patient-doctor visit? Why or why not?

4. Bioengineering of photosynthetic bacteria increases ethanol production greatly. Describe one way that this procedure might have unintended negative effects on human society and the environment.

5. A lumber company claims that dead trees need to be removed from forest floors to keep the forest clean and healthy. Defend their statement, and then also refute their statement. Use your knowledge of bacteria and fungi to formulate your answer.

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Figure – Concept Map of Chapter 8 Big Ideas

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307

Getting to Land: The Incredible Plants

EssEnTIaLs

A group of bryophytes live in a village

A population of mosses live on a forest floor

Mosses form little villages

A conifer towers over the mossesA large maple towers over the conifer and mosses

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The Case of the Wet Village We are all short and physically weak; our neighbors are all tall and strong. Perhaps we are a bit jealous of those who dominate among us. Before the neighbors came to our area, our shortness did not matter – I once heard this axiom from a friend: “In the absence of what you are not, what you are isn’t.” In other words, if there is no one tall around us (what we are not), then what we are (short) isn’t. Our height never mattered until ‘the others’ came along. We were the most efficient group of settlers before them and our methods worked the best. Now things are different.

When our ancestors first settled the village, they knew that water was the most important resource that would help the settlement to survive. Water is still the resource that is most scarce – while some say it is oil or gold – we all need water to survive and many towns and nations die off without access to clean water. We are environmentalists, in that sense; we are also against the pollution of our air and water. Villagers are also energy conscious – each settler has their own solar power plants, producing energy from sunlight. When the others are not overshadowing us, we are efficient at obtaining energy from the sun.

There have been many floods, wiping out entire villages of our neighbors. But floods never harm our villages. We are a hardy group – we love the rains – it gives us new life. In fact, our lifestyle helps to prevent flooding for everyone. We use water so quickly that the neighbors benefit from our flood-control practices. Indeed, during rainstorms our community celebrates and procreates, in a local “fertility festival.” The watery streets bring the village together, and there are always new births after the rainstorms.

Along “shady lane,” a northern district of the neighborhood, there is a densely pop- ulated group of villagers. Our population is growing in that direction, perfectly content to live in wet and shady conditions, where fewer of our larger neighbors overshadow us. At times, a larger animal, feline in character, lays its reign over the town. We are all scared, especially when it digs around in our village, but we survive. It likes our village because we are so comfortable, providing a soft area of rest visitors.

ChECk In

From reading this chapter, you will be able to:

• Explain how plants play their role in the ecosystem and in relations with human society. • Trace and explain how plants evolved onto land. • Describe the characteristics of plants. • Classify plants according to its several divisions, using examples. • Describe sexual and asexual reproduction in plants. • Describe the three types of plant tissues: dermal, vascular, and ground. • Connect plant growth with its transport and hormonal systems. • Explain how plants respond to their environment, using hormones and chemical and mechanical

defenses.

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Chapter 9: Getting to Land: The Incredible Plants 309

We all hear about and see climate change occurring before us – it has led to some villages drying out and dying off. We cannot live, or produce the new generation, with- out lots of water. We are scared of what the climate changes could do to us; and without us, the larger community will suffer.

We comprise 12,000 species found throughout the world, from forests to deserts and peat bogs. Our villages grow best in shady, moist areas, or bogs but we reach from Antarctica and the arctic to the tropics. Villagers are never more than 15 centimeters in height and absorb minerals and water from soils via diffusion. Diffusion, as you recall, is a slow process that moves materials only so high, requiring that we have such small heights. We do not have structures to allow water and minerals to be transported far up our bodies.

Humans use our villages to enhance other soils, in the form of peat moss. We col- onize areas, controlling floods and make the soil ready for larger plants. We do fear humans as well, because we are first indicators of their pollution, and we are so sensitive to changes in the environment.

This is the story of “our town.” A bryophyte’s perspective . . .

ChECk UP sECTIon

This story shows the biology of a group of plants called bryophytes, which comprises modern mosses, liverworts, and hornworts. Their place within our ecosystem is vital and their role should be protected.

Study the life cycle and contributions of bryophytes to our ecosystem and to human society. A number of species of bryophytes are considered endangered. Which are they? What factors are leading to this problem? What suggestions would you make to help protect their communities?

The Village’s Move to Land: a history Imagine a primordial sea of one-celled algae crowded together, exhausting minerals found in the sea such as nitrogen, sulfur, and phosphorous. This is how algae existed before their evolutionary move to land. The sea was a place of intense competition, and the quest for limited resources is always expensive, taking energy from other life functions.

Thus began the transition of plants, including bryophytes, from the sea to the land. It occurred about 400 million years ago. All plants appear to have emerged from a single group of green algae, chlorophyta, (discussed in Chapter 8). The transition to land prob- ably occurred at the coasts, where green algae were swept ashore. Tidal seaweeds were exposed to land at low tides and gradually became permanently land-based.

Along coastal land areas there were likely rich deposits of minerals that were washed up from ocean and river bottoms. Mutations enabling green algae to persist on coastal land were very valuable to exploit these mineral reserves (see Figure 9.1). Perhaps an extension helping a cell to anchor to the coastal land or a protective layer to help it from drying out enabled algal cells to make the transition to land areas possible. Biologists also surmise that a symbiotic fungus might have aided algal cells to colonize coastal lands. While the bryophyte village in our story had challenges, namely from their larger neighbors, the land afforded them many advantages.

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The land had a number of benefits for algae and the succeeding primitive plants:

1) Most importantly, there were no competitors for the algal cells. No other organ- ism had emerged on land to overshadow or out-produce them. The land was an open ecological space.

2) There was ample carbon dioxide in the air to allow plenty of carbon fixation. 3) There was continual light on land, unlike the filtered light obtained through

multiple layers of water in aquatic environments.

In the story, the emergence of the “others” who were taller eclipsed some of these advantages. Today, taller trees and pollution by humans stunt bryophyte growth (see Figure 9.2), making conditions less favorable than they were 400 million years ago. But the move back to the sea would be ill advised – the pros of being land-based outweigh the cons, as we will see.

What were the major drawbacks to the move onto land? There was less water than in the sea, so drying out of plant cells on land limited survival and reproduction. Bryophytes in the story could grow only so high, limited by the pull of gravity in getting water to all of their cells. Bryophytes rely on diffusion for movement of materials, such as water and

Figure 9.1 Plants emerged from the sea. Primitive algae, as show in this image, aggregated along coasts to attach to dry land.

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Figure 9.2 Mosses in a forest live side-by-side with other plant life.

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Chapter 9: Getting to Land: The Incredible Plants 311

minerals, through their bodies. Later, larger plants evolved a vascular system, which consists of vessels that transport water and minerals up plants more efficiently than via simple diffusion.

Standing upright also presented challenges to land plants. Before, in water, they could remain horizontal, absorbing light. On land, plants needed to grow taller, in part to compete as more plants evolved to reach sunlight for photosynthesis.

A lack of water on land led to other adaptations. To cope with it, all plants exhibit an alternation of generations, in which there are haploid and diploid phases of their life cycle function in reproduction. This life cycle allows gametes to move through watery surroundings, mating with other organisms. (We will discuss alternation of generations in more detail later in this chapter.) Plants developed a number of strategies for prevent- ing water loss. For example, a thick layer such as a cuticle surrounding a leaf prevents water loss (see Figure 9.3). Stomata that open to exchange gas then close to prevent evaporation also helped plants to transition to land (see chapter 4).

Evidence for Green-algae ancestry Several pieces of evidence lead biologists to believe that green algae are the ancestors of plants. First, both green algae and plants contain chlorophyll a and b and beta-carotene, both of which are used for photosynthesis. Second, both plants and green algae contain cell walls made of cellulose, a strong structural carbohydrate that allows plants to grow to great heights. Third, both plants and green algae carry out cytokinesis using a cell plate instead of cytoplasmic pinching, which is seen in other organisms.

The first plants appeared in the fossil record about 475 million years ago. They were likely mere patches of low-growing green plants, without more complex roots, stems, or leaves seen in modern plants. These primitive plants were colonies of cells that could survive on land but had no upright structure.

After the transition to land, plants diverged into two lineages roughly 75 million years later: bryophytes and tracheophytes, or vascular plants. The difference between the two groups is that tracheophytes have a developed vessel system and bryophytes do not. Bryophytes first appeared in the fossil record during the start of the Devonian period, 350 million years ago, but they were probably present on Earth millions of years before. Bryophyte fossils appear very similar to modern-day bryophytes, indicating that there was little change over this long period. Vascular plant fossils were very different

Alternation of generations

The life cycle of plants in which haploid and diploid phases of their exist for survival and reproduction.

Tracheophyte

Vascular plant; plants having a well developed vessel system.

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Figure 9.3 Prickly pear cactus; note the thick cuticle on a leaf of this desert cactus. It prevents water loss and allows cacti to lie in very dry conditions.

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from those seen today, and experienced a tremendous divergence. These changes led to many branches of tracheophytes that will be discussed later in this chapter.

What are Plants? All plants are eukaryotes and multicellular organisms that do not move once their seeds take hold. Most species of plants produce their own food through photosynthesis using chlorophyll and sunlight to convert carbon dioxide and water into sugar. There are over 280,000 species of plants ranging in size from 1 mm (0.04 inches) to 117 m (380 feet). Plants provide many resources for human society ranging from food, building materials, and medicines. They trap energy to build the carbon-based mass of which their bodies are composed. Through photosynthesis, they recycle the air, adding oxygen, and remov- ing carbon dioxide. Plants structures also provide a home for other organisms, such as birds and insects. When plants die, their organic matter is recycled by decomposers to enrich their soils with nutrients and layers of new soil.

Most plants adhere to the described definition, but there are a few exceptions. The Dodder plant, for example, lacks chlorophyll and derives its nutrients by living parasiti- cally on other plants. The Ghost Orchid (Epipogium aphyllum), is another plant without chlorophyll. Because it cannot make its own food from photosynthesis, it uses nutrients from a network of fungi (mycorrhizae) beneath its roots. It grows underground for most of its life cycle but emerges from the soil only to flower. Both are examples of how some plants adapt to their living conditions.

Plants are most closely related to algae evolutionarily, which are also photosynthetic. The difference is that plants have the ability to live on dry land and algae must remain in watery environments. First to evolve were the bryophytes. Plant evolutionary history traces how they emerged from watery environments onto land. After bryophytes, the first of the tracheophytes to evolve was Rhynia major, now extinct but found in the fossil records esti- mated to be 400 million years old. While adapted to land just like the bryophytes, Rhynia major differed in that it had a central tube of vascular tissue. This may be seen in the fossils recreation of Rhynia shown in Figure 9.4, containing a central vessel that allowed it to transport materials up its structure. While primitive, this structure provided a major advan- tage over bryophytes, which were limited in size due to their need to rely on diffusion for transport. Rhynia major could grow taller and be the biggest among the plants of that time, obtaining the most sunlight and thus food. Rhynia major plants were “in the absence of what it was not. . .” – other taller plants. They overshadowed the bryophytes of our story.

Plant structure Refinements to help Them Live on Land The centralized vessel allowed plants to grow larger and larger. Over time, plants devel- oped more and more elaborate conducting vessels to transport water and nutrients. The conducting system of modern tracheophytes consists of two types of tissues: the phloem, which is a series of tubes that carry sugars and dissolved organic materials down a plant, and xylem, which is a series of tubes conducting water and dissolved minerals up a plant (see Figure 9.5). These tissues carry needed materials to every cell in a plant. Their ves- sels are always within diffusion’s distance from any plant cell. In aquatic worlds, there is no need for these structures because watery nutrients bathe every cell.

Second, root systems, the parts of plants below the surface, formed to absorb water and minerals from soils (see Figure 9.5). Sugars are not the only source of food for a plant. Many required nutrients are also absorbed through the soil. Recall in Chapter 2 that proteins require nitrogen to build amino acids, and ATP requires phosphorous for

Phloem

A series of tubes that carry sugars and dissolved organic materials down a plant.

Xylem

A series of tubes conducting water and dissolved minerals up a plant.

Root system

The parts of plants below the surface.

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high-energy bonding. At times, roots reach far beneath the surface, tapping needed water supplies. The wild fig tree at Echo Caves, Ohrigstad, Mpumalanga, South Africa, has a root system 400-feet deep.

Third, plants have a shoot system, stems that support the leaves that carry out photo- synthesis (see Figure 9.5). The shoot also gives height to a plant, enabling it to maximize sunlight. Shoots are strengthened by lignin, a stiffening substance that supports plant cell walls as they grow recall from Chapter 3.

Fourth, plants have mechanisms to prevent water loss. A thick cuticle, for example, surrounds desert cactus leaves for protection from evaporation. Stomata on the under- side of its leaves limit a plant’s loss of water through evaporation.

Fourth, protection from predators is vital because plants cannot move to escape con- flicts. Their methods of response to the environment will be elaborated upon later in the chapter. Prickly thorns found on a rose bush or a rash caused by poison ivy is no accident – these defenses function evolutionarily to prevent predators from killing plants.

Shoot system

The system that consists of stem, leaves, lateral buds, flowering stems, and flowering bud.

Figure 9.4 a. Rhynia major From BSCS Biology: An Ecological Approach, 9th Edition by BSCS. vs. b. Mosses Rhynia major was one of the earliest known vascular plants with primitive stems containing vessels (vascular tissue). Its stems were photosynthetic. Rhynia major lacked leaves and roots but had sporan- gia that produced spores. It had an advantage over the mosses – it could grow taller because its vessel system transported water to higher heights.

spore cell from vascular tissue

epidermis cortex

vascular tissue

cross section of branch

stomate

epidermis with stomate

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Finally, the fifth adaptation of plants to land is their life cycle with its alternation of generations. To elaborate, on dry land gametes (sex cells) cannot easily travel from one organism to another, as they can in an aquatic environment. So, plants evolved a system of travel adapted for land in their alternation of generations. Plants never meet to have sex by walking around and socializing, and instead rely upon a separate structure – a gametophyte generation, which we will discuss in the next section, that allows plants to bring their sex cells to one another. In some plants, they use animals to carry their gametes; in others, wind or water does the task.

Divisions of Plants Bryophytes As discussed earlier, when plants first arrived on land, they quickly separated into two divisions: bryophytes (nonvascular plants) and tracheophytes (vascular plants). In the opening story, vascular plants had a big advantage over nonvascular plants: they could carry water higher and thus grow taller to obtain sunlight. Bryophytes include mosses,

Figure 9.5 The plant body. Roots absorb water from the soil shoots have leaves for photosynthesis; and the vascular layers, xylem (on the inside) and phloem (on the out- side) transport water and nutrients. From Biological Perspectives, 3rd ed by BSCS.

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liverworts, and hornworts, comprising about 12,000 species of plants. Bryophytes grow only in a moist environment, and they tend to be smaller in size. Their need for water to reproduce requires that there is enough moisture for sperm to swim from one organism to another through the environment.

The bryophyte life cycle shows an alternation of generations, which is specifically defined as a life cycle that contains a period of time in which there is a multicellular haploid phase and another multicellular diploid phase. The mossy village seen in the story or in nature is composed of adult mosses that are haploid organisms, also known as gametophytes because they produce the gametes (see Figure 9.6).

Gametophytes are adult moss plants that are either male or female, with respective parts. Gametes, sperm and egg, are produced by these reproductive structures. When water is sufficient in their surroundings, mosses release their male gametes, the sperm swimming through the community in the “fertility festival” described in our story. When a sperm reaches a female moss plant, it fertilizes an egg, dividing to form an embryo. The embryo develops from a female forming a new structure, called a sporophyte. This structure elon- gates from a female body and produces haploid spores. Spores land in moist areas, again leading to another gametophyte generation and the production of new adult mosses.

Adult mosses, gametophytes, contain only cells with half the number of chromosomes or N. The haploid condition, with its genetic components, was discussed in Chapters 5 and 6. They do not have a complete set of DNA. The sporophyte generation is diploid or 2N, and represents a complete genetic organism. It is strange to think that the adult mosses in the village in our story consisted of organisms with only half of their full set of DNA. In bryo- phytes, the gametophyte generation is thus said to be dominant because most of their life cycle is spent in this haploid period. This trend is common among plants, all exhibiting a haploid state at some point in their life cycle, to cope with their move to land and potentially dry conditions (see Figure 9.6). Spores are able to tolerate a dry or hostile environment.

Gametophytes

Haploid organisms that produce the gametes.

Sporophyte

The diploid organism, producing spores.

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Figure 9.6 Moss life cycle: haploid and diploid phases alternate in the life of a moss. Spores comprise the haploid phase while spore-forming structures (sporophytes) comprise the diploid phase.

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Tracheophytes Vascular plants, or tracheophytes, are those plants containing a vessel system for trans- port of materials. They differ from the more primitive nonvascular bryophytes in this way. However, the evolution of the seed, an embryonic plant with its own internal and protected supply of water and nutrients, also led to another division of plants: seedless and seeded. Seedless plants, of which bryophytes are one type, are described in our story. Bryophytes use spores for longer distance movement away from their parents. Spores are haploid and contain only DNA, RNA, and some proteins. Spores grow up to become a gametophyte. While bryophytes and some tracheophytes have spores that transmit their haploid genotypes, most tracheophytes have seeds. Seeds offer an advantage to longer distance travel because they contain all of the required materials to help an encapsulated diploid organism grow where the seed lands.

seedless Plants Seedless tracheophytes evolved as an advantage over bryophytes. Seedless plants include Pteridophyta (ferns), Sphenophyta (horsetails), and Lycophyta (club mosses). While spores instead of seeds are used for reproduction in each of these phyla, they are better adapted to land than the mosses in our story. Each seedless plant also has a primitive vessel system, while bryophytes have none. However, the seedless plant vessel system is the most primitive of all the tracheophytes. Nonetheless, this enables seedless plants to grow to greater heights than bryophytes, less limited by water uptake. However, ferns also have a branching vessel system from their central canal that brings water and nutrients within diffusion distance of all its cells. This system is more elaborate than that of other seedless plants, enabling ferns to grow even taller and be more efficient at transport of water and minerals.

Seedless plants require water for reproduction, in a similar way to the bryophytes. Ferns have sporangia on the underside of their leaves in which spores are produced. Adult fern plants are composed of the sporophyte generation, containing diploid cells. When water is available, ferns transport their gametes via a watery environment. However, the sporophyte generation is said to be dominant because this phase is the form of the adult fern.

Because of their vascular system, seedless tracheophytes grow taller than bryo- phytes, allowing wind to carry their spores farther from parents. When a spore lands in a moist surface, it grows into a prothallus, which is the free living haploid generation of ferns. The prothallus produces both eggs and sperm; sperm travel during wet peri- ods, much as in the moss village in the opening story, to fertilize eggs within another prothallus. The prothallus is short, heart-shaped, and is much like a moss plant in that it allows its sperm to move through water to obtain an egg within another prothallus. Fertilization within a prothallus produces another embryo which grows into an adult fern, the sporophyte (see Figure 9.7).

seed Plants Seeds were the great adaptation to land–enabling plants to traverse the globe. Seeds have food and protection to make a long journey away from their parent. In the film, Failure to Launch, a 35-year old man, played by Matthew McConaughey, does not leave his par- ent’s home to make an independent life for himself. A seed, with its comfortable set-up containing nutrients and protection, does not experience a “failure to launch.”

Thus, the gametophyte generation is greatly reduced in seed plants. There is no need for spores because seeds contain a whole diploid organism within its protective covering.

Seed

An embryonic plant with its own internal and protected supply of water and nutrients, also led to another division of plants: seedless and seeded.

Prothallus

The gametophyte generation of ferns.

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This allows offspring of seeded plants to be transported as fully formed organisms to their next home in one swift move. There are several approaches plants use to transport seeds, as will be discussed later in this chapter. Seeds are diploid, containing genetic material from both parents, and grown in the right conditions of a new environment, develop into a new organism. Moving longer distances from parents lessens competition and inbreeding between parent and offspring.

There are two groups of seed-bearing plants: gymnosperms, plants with seeds that do not develop in an ovary, usually cone producing; and angiosperms, which are flower- ing plants with seeds developed in an ovary. Seed plants have a life cycle of alternating generations as well, but their sporophyte generation is dominant. Adult seed plants are sporophytes, but they possess gametophyte male and female reproductive structures that produce sperm and egg, respectively. Animals, as will be discussed in the next chapter, also have a reduced gametophyte generation consisting of sperm and egg cells.

Gymnosperms Pine trees like the one in Chapter 4’s story, can inspire awe in their admirers. Gymno- sperms are the tallest, oldest, and thickest of all plants. They comprise the imaginary forests of Snow White and of medieval eras in our minds – images evoked are a dark forest with soft pine needle ground. Gymnosperms consist of roughly 1000 species of four major groups: conifers, cycads, gnetophytes, and ginko plants (see Figure 9.8).

Conifers, cone-bearing plants such as pines and firs, were the first plants to com- pletely evolve away from reliance on water. Their use of seeds about 160 million years ago helped them to populate land first, before the angiosperms invaded. Because they did not need water for reproduction, their sperm encapsulated in pollen, they could grow in many more areas than bryophytes. No longer relegated to low-lying and wet con- ditions, gymnosperms took advantage of new environments. The dinosaurs probably roamed in solely coniferous forests, with flowering plants evolving only much later, about 35 million years ago.

Gymnosperm

Plants with seeds that do not develop in an ovary, usually cone producing.

Ovary

A female reproductive organ containing ovules in which eggs develop.

Angiosperm

Are flowering plants with seeds developed in an ovary.

Figure 9.7 An alternation of generations is still evident in the fern life cycle but its gametophyte generation is smaller than in mosses. The gametophyte is a heart-shaped structure which produces egg and sperm cells.

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Gymnosperms have familiar appearances, as conifers or evergreens – pines, spruces, firs and redwoods, commonly found in temperate regions – all have needles forming their leaves. But gingko, also a gymnosperm plant, looks very different, with large leaves, very unlike a pine tree. There is only one species of gingko plant, but there are 9,000 conifers.

Needles on conifers, with their thick cuticles, are adapted to protect cells beneath from cold and water loss. This allows most conifers to retain their needles throughout the winter in temperate areas, enabling photosynthesis to occur all year. Tamaracks are one of the few species of conifers that lose their leaves in response to winter.

Sap in conifers contains chemicals that act as antifreeze and enables flow in freezing temperatures. This benefit enables gymnosperms to grow in cold as well as warm areas. Sap allows transport in vessels even at sub-zero temperatures. Conifers are found in every non-frozen region on Earth. They may grow for many decades. Conifers contain woody bark that is resistant to diseases caused by the many organisms described in the last chapter. Many woody plants are also resistant to herbivore attacks, growing too tall for other organisms to reach their leaves.

So valued by the lady in our story in Chapter 4, the largest and oldest trees are often gymnosperms. The tallest tree in the world is the coast redwood at 380 feet and the oldest tree, a Great Basin bristlecone pine, is the Methuselah tree, at 4,800 years (see Figure 9.9). Some root systems are said to be over 8,000 years old, regrown after shoot death occurs. The greatest predator of trees is human society, which harvests wood for many uses; wood is the third largest globally traded commodity, with only oil and gas ranking higher.

angiosperms The vast botanical beauty of our surroundings is composed of angiosperms, or flower- ing plants. Most of the flowering plants on Earth resemble their early forms according to the fossil record, changing little since they first evolved. There are 250,000 plant species of angiosperms, each with flowers with unique shapes, sizes, and colors (see Figure 9.10). Flowering plants include trees, bushes, and grasses of many types and occupy over 90% of the Earth’s vegetative surface. Almost all crops that provide us

Figure 9.8 What kinds of gymnosperms live today? a. A cycad called Encephalartos woodii, b. A gnetophyte called Welswitschia mirabilis, From BSCS Biology: An Ecological Approach, 9th edition by BSCS. c. The giant sequoia tree is a conifer. There are two people in this photo. Can you find them? From Biology: An Inquiry Approach, 3rd ed by Anton E. Lawson.

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Figure 9.9 a. Methuselah tree (oldest known tree) and b. Coast Redwood (tallest tree); Conifers have reached the oldest ages and the greatest heights of all plants.

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food are angiosperms, as well as large trees and all flowering plants. It is the angio- sperms that make mosses in our story most jealous – they have so many characteristics that outshine bryophytes.

Flowers, Fruit, and Plant Reproduction What makes angiosperms so special? Angiosperms have flowers to attract insects and birds. All flowers have certain common features. First, flower structures are generally the same. All flowers are supported by a stem with modified leaves, called petals. Pet- als may be colorful or flashy to attract other organisms. Angiosperms have male and/ or female structures, most often on the same plant. The male reproductive structure is called the stamen, which is composed of an anther, or capsule which hold pollen grains supported by a stalk or filament. The female reproductive structure is called the carpel, which is composed of a stigma, or sticky flat surface on which pollen grains land, a style, which extends downward to an ovary, which contains ovules in which eggs develop. Mosses seen in our story do not have flowers, with only a feathery end that produces gametes. Angiosperms possess male and female reproductive structures, much more complex and often very beautiful.

Some flowers have both male and female parts, called monoecious; and some have only a male or a female part, called dioecious flowers, with stamen and carpals on separate plants. Corn plants are monoecious, with “ears” as clusters of carpals and tassels as stamen. Date palms are dioecious, with a few males able to provide hundreds of females with pollen.

Movement of pollen from one plant to another is called pollination. In pollination, pollen is placed on the stigma of a carpal. Often, many pollen grains are released during pollination, with very few obtaining a place on the stigma. While many pollen are wasted in the effort, pollination has persisted among plant species through their evolutionary history. As indicated in Figure 9.11, the stamens in a flower are shorter than the carpel of a female. This limits the chances of pollen landing on the stigma and self-pollinating.

For both gymnosperms and angiosperms, plant gametophytes consist of pollen grains, the male gametophyte, and ovules, the female gametophyte. When pollen grains land on a female reproductive structure, the pollen grows a tube down into the ovule.

Stamen

Male reproductive structure.

Anther

A reproductive structure that holds pollen grains.

Filament

Thread-like structure supports the anther.

Carpel

An organ found at the center of a flower and bears one or more ovules.

Stigma

A sticky flat surface on which pollen grains land.

Style

The part of carpel that extends to ovules in which eggs develop.

Monoecious

Flowers that have both male and female parts.

Dioecious

Flowers that have only a male or a female part, with stamen and carpals on separate plants.

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This tube is directed chemically (usually with calcium) into the ovary. Two sperms then enter the ovary containing an egg. This enables one male sperm to fertilize a female egg in the ovule. The fertilized egg develops into an embryo forming a new plant. The sec- ond sperm fertilizes another structure, the central cell (2N) of the embryonic sac, which forms the nutritious endosperm. The endosperm provides food for the embryo as it germinates. The endosperm is triploid because it contains a 3N arrangement of nuclear material. The ovule develops into the hard external layer of a seed. This process is called double fertilization because two sperms fertilize two separate structures to form a seed.

Flowers function to attract other organisms, such as birds and insects to spread pol- len or fruit seeds, carrying them farther from parent plants. Nectar, which is the sugary attractant to insects and birds, bring them to flowers. Sticky pollen grains attach to birds and insects, getting a ride to farther distances. Sometimes wind carries pollen across distances.

When flowers are fertilized, they develop into fruits. Fruits are defined as a matured or ripened ovary-containing seeds. The ovule of a carpel develops into the seeds of a fruit and the ovary develops into the fleshy part of the fruit. Fruits attract animals to eat them. Fruits are colorful, tasty, and good sources of energy for animals. Animals spread

Pollen grains

The male gametophyte.

Ovule

The female gametophyte.

Endosperm

The nutritive tissue found inside the seeds of flowering plants.

Pollination

Movement of pollen from one plant to another.

Figure 9.10 Sample of angiosperms. Angiosperrms are flowering plants, which reproduce by forming fruits which are often dispersed. From BSCS Biology: An Ecological Approach, 9th Edition by BSCS.

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Figure 9.11 a. Flower structure: male and female reproductive structures. The anther and filament make up the stamen of the male, which produces pollen. The sigma, style, and ovary together comprise the female structure called the carpel. The ovary of a female produces eggs. Pollination is facilitated via wind, insects, and birds. b. Pollination: Pollen lands on the stigma of the female and grows downward through the style. The pollen tube’s growth is a different, more complex, process as compared with the moss gametophyte’s simplicity. In mosses egg and sperm diffuse travel through water and land on female structures. Reproduction in flowering plants is a competition between pollen grains forming tunnels and reaching eggs within the ovary. c. Pollination is facilitated via wind, insects, and birds.

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Single microspore

3 antipodal cells

Embryo sac (female gametophyte)

2 polar nuclei

2 synergids and central egg

Viable megaspore Mitosis

4 microspores

Mitosis

Pollen tube

Haploid (1n) 2 sperm cells

Meiosis Diploid (2n)

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Flower (sporophyte)

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Fruit

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Figure 9.11 (Continued)

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seeds by excreting them as they travel. This process, along with pollination, increases a plant’s ability to grow at farther distances from its parent. Thus, bryophytes may have a reason to be jealous of angiosperms, if they could think about it.

Insect, animal, and wind pollination prevent inbreeding in several ways. First, wind and insect pollination transfer pollen to places at some distance from the parent plants. Once a tree roots, it is there for life. Its only chance to get away from family members is at the pollination or seed dispersal times. Outbreeding increases the biodiversity of plants by adding to the chances of getting as many genetic combinations as possible through mating with less related organisms.

For this reason, many plants with both male and female reproductive structures have mechanisms to prevent self-breeding. In fact, while some monoecious flowers self-pol- linate, it occurs very infrequently. Stigmas may mature after pollen grains fall onto their surface or a stigma may not allow pollen grains of the same genotype to develop on its surface. Outbreeding is genetically desirable in plants, preventing the genetic defects found in inbreeding.

Asexual reproduction is common among plants, during which all offspring have the same genotype as the parents. Clearly, the drawback is genetic uniformity in new populations. In the event of an environmental change for which a particular genotype is susceptible, the results more likely destroy a population. Genetic diversity among plant populations is vital in maintaining their survival in nature.

However, there is efficiency in simply cutting off a branch of a willow tree and growing a new one. If you place a cut willow stem in a jug of water, it sprouts new roots easily. Asexual reproduction also occurs in strawberries, which form runners along the ground to sprout new plants. In dandelions, unfertilized seeds form new plants, which is very effective in colonizing new areas. Mosses in our story also have asexual reproduc- tion by regenerating certain parts, called gemmae, of broken off pieces of moss.

However, danger remains for any plant population that is solely asexually repro- duced. When a disease wipes out their singular genotype, as occurred for the American elm tree, they experience a widespread destruction from infection – the elm by the fun- gus Ophiostoma ulmi.

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Monocots and Dicots In their initial development embryos in a seed produce their first leaf, called a cotyledon. Angiosperms produce seeds with two varieties: some contain an embryo with one seed leaf, called a monocot, and some contain an embryo with two seed leaves, called a dicot. Monocots include corn, rice, and lily plants, and dicot examples include maple trees, oaks, and peanut plants.

Monocots and dicots differ in some important structures . Dicots have a large ver- tical root called a taproot that burrows downward, anchoring the plant, while mono- cots have fibrous root system, which give increased exposure to water in soils. Some desert plants have fibrous root systems over 100 feet in diameter to obtain scarce water. Taproots are stronger and more secure for dicots, allowing them to grow much larger. Dandelions have a nasty taproot, preventing them from being pulled easily from garden

Cotyledon

The first leaf developed during the initial development of embryos in a seed.

Monocot

Angiosperms- produced seeds that contain embryo with one seed leaf.

Dicot

Angiosperms- produced seeds that contain an embryo with two seed leaves.

Taproot

Large vertical root that burrows downward, anchoring the plant.

Fibrous root

A root system made up of numerous branching roots and give increased exposure to water in soils.

COCOnuT Oil – FRiEnD OR FOE?

Coconuts are an example of a fruit that helps to spread offspring to new areas. Coconuts contain high amounts of fats attractive to animals, which consume them and spread their contents throughout the land. This spreads plant populations across larger surfaces, diminishing competition.

Whether coconut oil is good or bad for human health has been debated in recent studies. There is a clear answer – coconut oil has a very high amount of saturated fat. As described in Chapter 2, these oils are bad for the heart. The good fats – monounsaturated fat – are found only in small proportions, unfortunately. Coconut oil contains more than 92% saturated fat, and about 6% monounsaturated fat and 2% polyunsaturated fat.

Recall from Chapter 2 that saturated fats contribute to increased levels of “bad” cholesterol (LDLs, or low density lipoproteins) in the body. In contrast to coconut oil is olive oil, which contains only 14% saturated fat and 74% monounsaturated fat with 11% polyunsaturated fat. Olive oil is much better for the heart because of its high amount of monounsaturated fat, which is linked to “good” HDL cholesterol.

Recent research shows that coconut oil’s saturated fats are medium-chain triglycerides (MCTs), which are linked to improving weight loss. However, these studies are only found in animal models and do not stand up at this point to rec- ommendations for improving human health. Human studies do not support the benefit of MCTs over other saturated fat in risks for heart disease and obesity.

Often pointed out are the high rates of good heart health in Pacific Island and Asian populations. They have diets naturally high in coconut oil. Thus the relationship is drawn that their health is due to the coconut oil. However, consider that these populations have a more active lifestyle, eat primarily vegetarian foods and have little access to fatty meats.

Making a comparison to island diets is not scientific because of the many intervening variables affecting health. Island populations are so unlike those found in the developed nations because of their very different lifestyles. Why is there a movement afoot to show coconuts as healthy? Is it to bolster trade with nations or companies with products containing coconuts? Evidence clearly indicates that coconuts are bad for our heart health.

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and lawns. Stems of dicots are also different, ordered in vessels systems around a ring; but monocots have scattered vascular tissue. Monocot leaves have parallel vessels while dicots have branching vessels.

Plant Tissues Plant tissues of three types carry out their life functions. Dermal tissue, the epidermis, covers plants in a single layer of cells surrounding the entire organism, especially young plants. It functions in the same way that skin does, to cover and protect the human body. Dermal tissue specializes depending on the area in which it is located. In roots, dermal tissue develops into root hairs to increase surface area and thus absorption. Most absorp- tion occurs in the root tips due to these hairs. In leaves, dermal tissue forms a waxy layer called a cuticle that helps the plant retain water.

On the underside of leaves, stomata or openings allow gas exchange (also discussed in Chapter 4). Stomata are surrounded by guard cells, which control their opening and closing (Figure 9.12). Based on water pressure within guard cells, stomata open when guard cells fill with water and close when they have less pressure. When guard cells take in water, they become turgid, and their cellulose fibers radiate outward. This causes guard cells to buckle, creating an opening space between them. When guard cells lose water, they become flaccid again, closing the hole. Closing minimizes water loss via evaporation from water contained within xylem of plants. However, stomata must remain open to obtain needed carbon dioxide for carbon fixation and oxygen for cell respiration. Water loss is a constant threat to a plant’s survival, with a mature, temperate tree losing upward of 100 gallons of water each day. Moss gametophytes in our story do not have stomata; instead they obtain needed gases through diffusion in their thin “leaves.”

Vascular tissue, or xylem and phloem, transports water, minerals, and food through- out a plant. Plants have no heart, unlike animals which use it to pump blood for trans- port. Instead, plants use physics principles to transport materials (not circulate them around) from one spot to another. Xylem conducts sap, which moves water and minerals

Vascular tissue

Tissues that transports water, minerals and food throughout a plant.

Figure 9.12 a. A general structure of a leaf. The mesophyll layer of a leaf contains the vascular bundle, which transports food (phloem) and water and minerals (xylem) through vessels. b. Stomata are pores on the underside of plant leaves. They are surrounded by guard cells which regulate their opening and closing.

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upward, from roots to shoots of plants. These vessels contain cells that are dead at matu- rity, called tracheids and vessel elements (see Figure 9.15). Their cell walls make up the vessel walls of xylem. Tracheids are long, thin cells with tapered ends and thick lignin partitions. Vessel elements are wider and shorter, with thinner walls. Both contribute to the vessel tubes of xylem. Gymnosperms contain only tracheids, which make their vascular systems less efficient. Angiosperms have both tracheids and vessel elements, enabling faster delivery of materials.

Phloem conducts sap downward from leaves, where food is produced through pho- tosynthesis, to all parts of a plant. (see Xylem and Phloem in Figure 9.12a) Phloem sap contains sugars and dissolved organic materials, which are needed for a plant’s life functions. Sieve-tube members (Figure 9.15), which are cells that transport sap through phloem vessels, are alive at maturity, unlike xylem cells. They do, however, lack a nucleus, ribosomes, and vacuoles. In angiosperms, walls between sieve-tube members, called sieve plates, have pores to allow the flow of fluids. Phloem is also composed of companion cells (Figure 9.15), which lie next to sieve-tube cells. They are connected to sieve-tube cells through plasmodesmata, or gap-like cell junctions, allowing organelles to serve sieve-tubes. Together, these types of cells conduct sap through phloem in angio- sperms and gymnosperms. Mosses in our story lack these vital vessels.

Plants use several types of cells composed of ground tissue that support their structure and store and produce food. Ground tissue includes parenchyma cells, also called the typical plant cell, which carries out most of the metabolism in plants (Figure 9.13a). For example, in leaves parenchymal cells produce sugars via photo- synthesis; in stems and roots they have plastids which store starch; and in fruits, they make up the fleshy part. These cells photosynthesize, produce ATP, repair damaged cells, and make hormones. They carry out most of a plant’s activities. Parenchymal cells are also precursors to other more specialized cells, changing into them at cer- tain points in a plant’s development. Whenever you see a live plant cell, it is likely a parenchyma cell. In fact, most of a plant is actually dead material; roughly 98% of most very old trees are dead cells.

Sclerenchyma cells are stringy and elongated, with thick cell walls (Figure 9.13b). Plant cell walls have embedded lignin, which provides support. Their irregular arrange- ment allows plants flexibility so that they can twist and bend. The stringy appearance of asparagus stalks after cooking them is exemplary of this cell type. Sclerenchyma is not alive at maturity, unlike other ground tissue. Sclerenchymal cells have lignin cell walls. Lignin comprises the woody parts of a plant and cannot be digested directly by animals.

Tracheids

Elongated cells found in the xylem of vascular plants that conduct the transport of water and mineral salts.

Vessel element

A cell type found in xylem.

Sieve-tube members

Cells that transport sap through phloem vessels, are alive at maturity, unlike xylem cells.

Companion cells

Are specialized parenchyma cells found in the phloem of flowering.

Ground tissue

Tissues that are neither vascular nor dermal and support a plant’s structure and store and produce food.

Parenchyma cells

The typical plant cell that carry out most of the metabolism in plants.

Sclerenchyma

Stringy and elongated cells with thick cell walls.

Figure 9.13 Selected cells of the vascular system. a. Parenchyma. b. Sclerenchyma.

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Plant Growth Plant growth occurs in all regions, emanating from the meristems, which are undiffer- entiated or unspecialized cells. Seeds remain dormant until a stimulus – usually wearing away of the seed coat through digestion, fire or water – causes a seed to germinate or grow. Germination starts with the massive influx of water into the seed. This process, called imbibition, expands the seed so that it ruptures. In the process, metabolic changes take place within the developing embryo to cause its rapid growth and resulting in a new sporophyte’s root and shoot system. Enzymes digest endosperm nutrients, mostly starch, for an embryo to use. Primary growth thus starts right away, within meristems, elongat- ing roots and stems. At the end of primary growth, cells differentiate into the three plant tissues, forming leaves and branches.

Meristems have the potential to divide into any type of plant cell. Mitosis occurs in meristems at very high rates. Apical meristems are found at the tips of roots and in shoot buds to begin primary growth (Figure 9.14). Primary growth is growth in length and gives rise to the three types of plant tissues. Lateral meristems are found along the sides of stems and roots which gives rise to secondary growth. Secondary growth is growth in width, thickening plants when they divide.

Primary growth in plants pushes roots through their soils. A root cap protects root meristems as they grow, secreting a polysaccharide that also lubricates the soil. In roots, there are three zones of development: a zone of cell division, in which mitosis occurs ema- nating from a quiescent center in the apical meristem, which contains cells that divide in a slow but protected manner; a zone of elongation, in which cells elongate over 10 times to push root tips through the soil; and a zone of differentiation, in which cells become one of the three types of plant tissues. Here, a protoderm gives rise to the epidermis; a procam- bium layer becomes xylem and phloem; and ground meristem emerges as ground tissue.

Primary shoot growth is very similar to root growth: first there is mitotic growth, then cell elongation and finally differentiation. Shoots contain vascular bundles that

Why DO VEGGiES CAuSE GAS?

Does eating vegetables cause gas? Most vegetables, including beans and legumes, contain lignin components, such as sclerenchyma, that cannot be digested by intestinal enzymes in humans and most animals. Thus, it takes bacteria in the large intestines in humans, for example, to break down these materials, forming gases: Hydrogen (H2), carbon dioxide (CO2), and methane (CH4). Flatulence develops from the buildup of these gases. The telltale sign of gas pains is a shooting sensation alleviated by movement, as abdominal muscle contractions move gas bubbles.

Many bean varieties contain raffinose oligosaccharides, a substance that is broken down by bacteria, causing significant amounts of flatulence. The pres- ence of raffinose oligosaccharides leads to increased bacterial action and thus more gas. Oddly, the environment in animal large intestines is very similar to early Earth conditions, discussed in Chapter 7. It is anaerobic with the same gases permeating the region. Sulfur gas gives flatulence its odorous qual- ity, probably quite similar to early Earth’s atmosphere. Our first ancestral bacteria, the archaebacteria, resembled microbial life in our intestines today, and developed from similar conditions.

Meristem

A formative plant tissue responsible for growth whose cells divide to form plant tissues and organs.

Germinate

To begin to grow.

imbibition

The process in which germination starts with the massive influx of water into the seed.

Apical meristem

Meristems that are found at the tips of roots and in shoot buds to begin primary growth.

lateral meristem

A type of meristem that is found along the sides of stems and roots which gives rise to secondary growth.

Root cap

A section of tissue at the tip of a plant root.

Zone of cell division

One of the zones of development in which mitosis occurs in a slow but protected manner.

Zone of elongation

One of the zones of development in which cells elongate.

Zone of differentiation

One of the zones of development in which cells become one of the three types of plant tissues.

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also grow along with them. Stems hold leaves and grow to maximize their sunlight intake. Plant hormones, discussed in the next section, lead these plant growth direc- tions. Stems grow to develop into wood, our most valued nonedible plant product. Stem growth occurs in various plant areas, sometimes underground, as in potatoes and some- times across the ground, as runners in strawberries. Stem and leaf growth alongside root development is seen in radishes in Figure 9.14b.

Secondary growth is also known as plant thickening. It occurs in all living plant tis- sues, emanating from two lateral meristems: the vascular cambium produces xylem and phloem, and the cork cambium produces thickened outer coverings of stems and roots. Vascular cambium occurs between xylem and phloem, growing new xylem cells continu- ally toward the inside of the vascular cambium and new phloem cells toward the outside of the vascular cambium. Multiple layers of xylem form sapwood, which is poor at conduct- ing water. However, layers closer to the vascular cambium are good transporters of water.

Cork cambium contributes to the girth of a stem and the external hard layer of bark. It is found outside of the phloem, adding new but dead tissue to the exterior of a stem. This new material is called cork (phellam) which is dead upon production and serves to protect inner layers of stems. Beneath the sapwood layer, at the very center of a tree, the heartwood is composed of dead parenchyma cells, vessel elements, and tracheids. Heart- wood provides a support column for a plant but it is not active in a plant’s life functions, such as transport of materials (Figure 9.15).

The age of a tree may be calculated by counting the number of rings of xylem pro- duced each year: the thicker the ring, the better the growth in a given year. Cambium lay- ers are cylinders of cells that remain young forever, making new plant tissues for growth. Plants have such longevity because meristems remain able to differentiate perpetually. This is the fountain of youth for trees.

Transport of Water and nutrients in Plants The shock and awe that water and nutrients can move over one hundred feet up an oak tree sparks the simple question: How? Roots absorb water and minerals from the soil, as discussed earlier in this chapter. Roots also exchange gases with the soil, putting out carbon dioxide and taking in oxygen (to enable root cells to carry out cell respiration). Water and minerals are transported upward through xylem from roots because of an upward force or pull. This is called transpirational pull. Loss of water from leaves by evaporation through stomata as discussed earlier, is called transpiration and creates an

Secondary growth

Growth in vascular plants emanating from two lateral meristems resulting in wider branches and stems.

Vascular cambium

One of the lateral meristems that produces xylem and phloem.

Cork cambium

A tissue found in a plant’s stem and is responsible for thickening stems and roots.

Transpirational pull

The process in which water and minerals are transported upwards through xylem from roots because of an upward force or pull.

Transpiration

Loss of water from leaves by evaporation through stomata.

Figure 9.14 Root tip structure.

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Zone of elongation

Zone of cell division

Root capRoot tip

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upward force. Water leaving through stomata must be replaced as it evaporates, creating a suction-pull from roots to shoots (Figure 9.16a).

The tendency of water to leave an area is called its water potential. Water moves from an area with a higher water potential to an area with a lower water potential. It is measured in megapascals, MPa. The more water that leaves via stomata, the greater the water poten- tial pulls driving water up a plant (Figure 9.16b). Water leaving stomata will lead to regions in xylem that are unoccupied. Adhesive (water–xylem wall attraction) and cohesive forces (water–water attraction) create a line of water from roots to shoots, with pressure from water potential and adhesion/cohesion resisting the force of gravity. Each time a water molecule leaves via transpiration, it must be replaced by a molecule beneath it in the line. This creates a pull from the top down in a plant, suctioning water and minerals into roots.

Figure 9.15 The cross section of a stem. a. Xylem and phloem occur together in vascular bundles circling the outer part of the stem. From Biological Perspectives, 3rd ed by BSCS. b. This is a pumpkin stem section.

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(a)

Figure 9.16 a. Transpirational pull in a tree. Water moves through the xylem of a plant driven by concen- tration differences between soil and stomata. b. Plant nutrients move from source (high pressure) to sink (low pressure), bringing food down the plant. From Biological Perspectives, 3rd ed by BSCS.

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In xylem, negative water potential exists in leaves as transpiration proceeds, causing a bulk transport of water and minerals up a plant. Transpiration may lose up to 200 liters of water per hour. Each hour, all of this water needs to be replaced. Xylem sap may rise up to 300 feet against the force of gravity. At night, transpiration is low, but roots keep taking in water causing water to continue to flow up xylem. Water droplets (dew) on leaves in the morning are formed from this excess water in plants overnight, causing guttation or droplet formation on leaves. Mosses in our story, which depend on diffusion, avoid this entire process.

In phloem, sucrose moves from source (leaves) to sink (nonphotosynthetic parts of plants) down a concentration and gravity gradient. Transpiration is a necessary evil: plants lose 90% of their water through stomata transpiration. However, it is required to allow gas exchange for photosynthesis and cell respiration. Transpiration also drives the movement of water and minerals up a plant and serves in evaporative cooling of plants; since the hottest molecules of water evaporate in transpiration, leaving a plant. Plant tem- peratures are lowered between 15 and 20°C in evaporative cooling, preventing high tem- peratures from denaturing enzymes in plants. In desert plants, the rate of transpiration is less because their enzymes can tolerate heat better, and water loss is the greater threat.

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Plant Responses to the Environment hormones and Tropisms While plants do not have motility, they do respond in many ways to environmental stim- uli. To accomplish this, plants have hormones. Plant hormones are chemicals produced by a one tissue and carried to other tissues to cause a response in them. There are five types of plant hormones: auxins, abscisic acid, gibberellins, ethylene, and cytokinins. Each hormone performs functions to help a plant respond to cues in its environment.

The most important cue from the environment is sunlight. Phototropism is defined as the growth of a plant toward sunlight (see Figure 9.17). It occurs when auxins, a type of plant hormone, migrate from the light side to the darker side of a shoot tip. Auxin hor- mones cause elongation of cells on the darker surface, bending the shoot in the direction of sunlight (Figure 9.19). In general, auxins stimulate plant growth by cell division and elongation in root and vessel formation. Plants also use their hormones to carry out inter- nal cycles throughout a single day or even through a century. Sunflowers turn toward the sun every day they are in bloom, like clockwork. They have an internal clock directing this activity, through the work of hormones. Yearly, the century plant, Agave Americana which lives 10–30 years, blooms only once at the end of its life and then dies. It is called a century plant by mistake, but probably due to its long period of time to bloom. Hormones guide these rhythmic workings, often referred to as an organism’s biological clock.

Geotropism, or the growth of shoots upward and roots downward in response to grav- ity, results also from plant chemicals. Regardless of the orientation of a plant, whether upside down or not, roots grow downward and shoots grow upward in response to grav- itational pull. Abscisic acid, another plant hormone, directs movement of roots down- ward, for example. Abscisic acid also serves plants by inhibiting their activity during stressful periods. During harsh conditions of dryness or the onset of winter, abscisic acid inhibits seed germination and stomata opening. Conservation of energy during these conditions is often critical to a plant’s survival. Wasting energy on flower production during a spring ice storm might kill a plant.

Most plants lose leaves in response to cold weather and freezing water. Plants do not detect the cold or freezing water, however. It would be bad if a cold spell could trick a plant into dormancy. Instead, each year, plants detect decreased sunlight during the chang- ing seasons, causing them to lose their leaves. A loss of leaves is called leaf abscission. It enables plants to conserve water that would otherwise be lost through transpiration. While it is wasteful to make and lose leaves, plants are thus able to survive harsh conditions.

Any response to touch, called thigmotropism results in growth changes in plants. For example, climbing plants such as beans or ivy adhere to surfaces in response to their

Phototropism

A tropism in which the growth of a plant is toward sunlight.

Geotropism

The growth of shoots upward and roots downward in response to gravity, results also from plant chemicals.

leaf abscission

Loss of leaves.

Thigmotropism

Any plant growth response to touch.

Figure 9.17 Phototropism: A bean plant bends toward the sun. It is a way that plants “move” to obtain the necessary resources in the environment.

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physical contact. Gibberellins are hormones that stimulate growth of plants in many ways, including their response to touch. Gibberillins work in several capacities: elon- gation of cells in roots and shoots, stimulation of mitosis in apical meristems, inducing seed germination, blooming of flowers, and enlargement of fruit size. These hormones are analogous to human growth hormone, and can cause enormous sizes in plants. Note the healthy, growing red cabbage, fed gibberillins by farmers, in Figure 9.18.

When fruits ripen together, as seen in a set of bananas, ethylene is at play. Ethylene is a gas that causes fruit and vegetable ripening in almost every part of a plant. Ethylene gas permeates through a pile of fruit leading to rapid ripening in all of them. Some fruits – strawberries, for example – are resistant to ethylene gas.

Cell division and growth are also initiated by cytokinins in almost every tissue in plants. Cytokinins are plant hormones that work in concert with auxins to stimulate and sustain growth in plants throughout their lifetimes (Figure 9.19). Cytokinins also stimu- late new branches from lateral buds and seed germination.

Figure 9.18 A field of red cabbage, Brassica oleracea. Red cabbage contains the red pigment anthocyanin, which acts as a pH indicator. It turns red in acids and blue-green to yellow in alkaline solutions.

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Plant Defenses In a plant’s defense, it cannot move and cannot directly attack it stalker. It does, however, have a host of strategies, depending upon the plant, to combat herbivores. Some plants are carnivorous, such as the Venus fly trap, described earlier in the text. It works by trapping insects, a frequent friend (pollinator, as you recall) and enemy (herbivore) of plants, in a chamber, secreting enzymes to digest the fly’s body. However, this example is not only a defense, but satisfies the fly trap’s nitrogen requirement for the synthesis of proteins, a component of amino groups.

Other defenses manifest as chemicals in over 3,000 plant species. Consider can- nabis sativa, the plant from which marijuana is derived. It contains a hallucinogen, THC or delta-9-tetrahydrocannabinol, which deters animals from continued eating the plant by causing them to be disoriented. Obviously, this chemical gives the charac- teristics of marijuana’s effects. However, they occur due to plant defenses instead of human needs.

Many mechanical defenses also help plants to keep herbivores at bay. Raspber- ries and blackberries have thorny branches to deter animals from casually eating them. Waxy leaves and saps on stems have been shown in studies to cause insects to glide right off. For example, thick cuticles on the prickly pear cactus prevent water from forming droplets, within which fungi spores develop. Mimicry such as that of the Passiflora plants (see Chapter 7) is a mechanical defense mechanism as well. The yellow spots on their leaves resemble the eggs of the Heliconius butterfly, causing butterflies to lay their eggs elsewhere. While not always fail-safe, plant deterrents help them to survive herbivores.

summary Plants play an integral role in our ecosystem and in human society. They emerged from oceans roughly 475 million years ago as adaptations of green algae. While on land, plants diversified into bryophytes and tracheophytes, with unique characteristics in each division. Bryophytes, including mosses, have simple structures and small sizes, produc- ing spores but lacking a vascular system. Tracheophytes are diverse, usually tall, and always more complex than bryophytes, with seedless and seed varieties. Some trache- ophytes, including gymnosperms and angiosperms, use seeds to reproduce. Gymno- sperms include conifers that comprise many of our evergreen forests. There are many species of angiosperms, all of which use flowers and fruits in reproduction. Plants, unable to move as adults, respond to their environmental changes through the use of hormones. Plants protect themselves by chemical and mechanical style defenses, using trickery at times and toxic substances at other times. Plants remain a vital part of our ecosystem.

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ChECk oUT

summary: key Points

• Plants photosynthesize using sunlight to produce food for themselves and for the animals eating them. • Plants evolved from green algae by developing roots, shoots, and methods such as seed formation to

prevent them from drying out. • Lower plants without a vessel system are bryophytes, such as mosses. • Higher plants or tracheophytes developed transport vessels to help them to grow taller, which aides

them in obtaining sunlight and dispersing their seeds. • Plants are able to asexually reproduce, but attain genetic diversity through sexual methods. • Dermal plant tissue covers plants, vascular tissue forms vessels for transport, and ground tissue

is used for daily life functions of plants. • Plants use hormones such as auxins to grow in response to light as well as develop new tissue.

alternation of generations angiosperm anther apical meristem carpal companion cells cork cambium cotyledon dicot dioecious endosperm fibrous root filament gametophytes geotropism germinate ground tissue gymnosperm imbibition lateral meristem leaf abscission meristem monocot monoecious ovary ovule parenchyma cells phloem

phototropism pollen grains pollination prothallus root cap root system sclerenchyma secondary growth seed shoot system sieve-tube members sporophyte stamen stigma style tap root thigmotropism tracheids tracheophyte transpiration transpirational pull xylem vascular cambium vascular tissue vessel element zone of cell division zone of elongation zone of differentiation

KEy TERMS

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Multiple Choice Questions

1. Which division of plants is LEAST likely to provide wood for human societal use? a. angiosperm b. bryophyte c. gymnosperm d. conifer

2. Which group of organisms most likely aided in the first transition of primitive plants from aquatic to land environments? a. animalia b. sarcodina c. fungi d. monera

3. The shoot of a plant is composed of all of the following EXCEPT: a. a cotyledon b. an endosperm c. a leaf d. a quiescent center

4. The ferns belong to the _____ division of plants: a. bryophyte b. seed tracheophyte c. seedless tracheophyte d. gymnosperm

5. In a cluster of mosses growing stalks that produce diploid grains, a stalk is called: a. a gametophyte b. a prothallus c. a sporophyte d. a quiescent center

6. Which represents a logical order, from early to later, in the evolution of plants? a. green algae ➔ bryophytes ➔ gymnosperm ➔ angiosperm b. angiosperm ➔ gymnosperm ➔ green algae ➔ bryophyte c. gymnosperm ➔ angiosperm ➔ bryophyte ➔ green algae d. bryophyte ➔ gymnosperm ➔ angiosperm ➔ green algae

7. The anther within an angiosperm is analogous to: a. testes in humans b. ovaries in humans c. buds in yeast d. daughters in prokaryotes

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8. Which term includes all of the others? a. tracheophytes b. ferns c. gymnosperms d. conifers

9. In question #8, which process helps these organisms to obtain genetic dispersal and variation in their populations? a. photosynthesis b. pollination c. asexual reproduction d. species specificity

10. Which plant hormone is most responsible for growth of a group of geranium plants toward light on a window sill? a. auxins b. ethylene c. gibberillins d. abscisic acid

short answers

1. Describe two ways in which plants benefit humans. List two ways in which plants are harmed by humans. Be sure to list and describe each.

2. Define the following terms: gymnosperm and angiosperm. List one way each of the terms differ from the other in relation to their 1) morphology; 2) diversity; and 3) reproduction methods.

3. A plant bears cones, contains pollen, and grows to over 50 feet. Make use of the characteristics of plants in this chapter to classify this organism. Why did you place it in its group?

4. A plant becomes wilted, loses its leaves, and enters a dormant state. Which plant hormone is likely involved in this process? What factors might determine whether a plant enters dormancy? In nature, what is the most important factor causing leaf abscission? Why?

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Chapter 9: Getting to Land: The Incredible Plants 337

5. During sexual reproduction in angiosperms, seeds have unique properties that help plants survive on land. List three characteristics of seeds that make them more efficient than spores. How are these characteristics helpful for seed plants in their survival on land?

6. List and draw the male and female reproductive structures in flowers. How are they different from each other? How is their arrangement important in limiting inbreeding?

7. Explain the process of transporting water within a vascular system. Use the fol- lowing terms in your answer: xylem, water potential, transpirational pull, adhesion, stomata.

8. Transpiration is considered a necessary evil in plants. Explain why this is so.

9. What type of plant tissue is a parenchyma cell? How is it important in a plant’s functioning?

10. Draw a diagram showing the underside of a leaf, with stomata open. Be sure to label guard cells and stomata in the diagram. Indicate the direction of water flow when stomata are open.

Biology and society Corner: Discussion Questions 1. Plants play an important role in our society, comprising a large portion of our trade,

both import and exports, for our economy. Research the importance of heartwood in developing products for human use. Name one region where timber production led to negative ecological consequences. Could it have been prevented?

2. The movement to limit bad fats and increase good fats in our diets has led to many nutritional claims. Choose a type of plant oil that you consume, either through cooking with it or as a component of your dietary intake. Research the nutritional chemistry of the oil and make a recommendation on its benefits or drawbacks for your own health.

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3. Ethylene gas naturally ripens fruits. Industrial calcium carbide is used to ripen fruits but contains arsenic and phosphorous, potential human health hazards. Research the use of calcium carbide to determine the consequences of its use. Should you or your loved ones avoid food ripened with calcium carbide? What are the current laws in the United States regarding its use?

4. Colony Collapse Disorder (CCD) is a disease affecting insects that live in commu- nal colonies, most in the hymenoptera order. Many honey bees have died off as a result of CCD. Explain how this disease may affect genetic diversity and reproduc- tion in plants. How may CCD have eventual impacts on human society?

5. Our opening story in this chapter showed the importance of bryophytes in flood con- trol. Wetlands are areas designated with certain flora and animal life that make them unique. Research the geographical areas in your local neighborhood to determine where wetlands are designated. What plants and animals are found in wetlands? Research those wetlands and make recommendations to preserve those regions. Are there any societal forces endangering those wetlands?

Figure – Concept Map of Chapter 9 Big Ideas

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339

Moving on Land and in the Sea: Animal Diversity 10

A beaver family of four

Beaver(s) are usually working hard, here shown is a Beaver family lodge built by hard workLittle John shares the work of

the beaver

Beavers hard work changes the environment–this dam is impressive

This beaver prepares wood material for the dam

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the Case of the Homey Homeotherm The stone patio had taken months to build. The farmer worked each day, meticulously placing each flat rock into the soil. He obtained the rocks from the river bed right next to the area on which he was building the patio. The stone patio had to be solid, so that the river would not wash it away in a storm. The rocks were heavy and required two people to lift them.

His only help was his sister’s 11-year-old son, little John visiting from the city. Lit- tle John was not ambitious, seemed to argue about helping out, and was listless as his uncle worked. Little John had gotten into some real trouble with the law, hanging out back in the city with the neighboring kids. They sent Little John to get away from a bad neighborhood element. His sister thought that Little John would benefit by staying the summer in the countryside and helping with chores; but little John hated being there.

Digging was difficult, but the farmer laid each piece with care, solidly into the dirt. It was a beautiful patio which would be his grandest accomplishment. “Stones last for- ever, Little John,” explained the farmer. But Little John did not care – he wanted to go home, back to his friends. The farmer was very unhappy with his nephew and gave up on him.“He’ll wind up in trouble before he even grows up,” he told his sister – “little John is a hopeless case.”

A new neighbor moved in next door and made the situation all the more difficult. “There goes the neighborhood,” remarked Little John, “beavers make terrible neigh- bors.”After the beaver arrived, in less than a month’s time the beaver family, a couple with six beaver babies, was creating a swamp around the stone patio. Quickly, the bea- vers used their front teeth to gnaw and fell trees from the farmer’s surrounding forest. Beaver teeth grow continuously through their lives, sharpening as they chew and strong enough to build a three-foot dam across the river. “If this keeps up, the beaver dam will be 10 feet high and my stone patio will be underwater,” thought the farmer, “I am going to have to kill the beavers.”

Soon the beavers built a two-room lodge using sticks and mud. The beaver couple shared all of the work, from gathering plants and berries for food to felling trees and using their tails to pack their lodge with mud.

Little John became intrigued with the beaver lifestyle, reading about their ways. He found out that beavers are herbivores, monogamous (one spouse) through their lives, and have excellent hearing and smell to compensate for poor eyesight. They are the largest in the order Rodentia, with two major species: one in North America, Castor Canadensis, and the other in Eurasia, Castor fiber. They maintain their properties well, putting a

CHECk in

From reading this chapter, you will be able to:

• Explain how animals play their roles in the Earth’s ecosystem and in relation with human society. • Trace the evolution of animals, from simpler to more complex organisms, explaining the four ways

to classify animals • Describe and Define vertebrate, invertebrate, Cambrian explosion, endoskeleton, exoskeleton, exo-

therm, endotherm, and chordate and use them appropriately to explain the four ways to classify animal phyla.

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great deal of effort into their territory. They use scent glands to mark their borders and an alarm call by flapping their tails against the water to let other family members know an invader is present. Beavers are family oriented and live in their lodge together with kin. They recognize kin by anal gland scents, helping them to get along as a family unit. They are homeotherms, meaning they maintain a stable internal body temperature, making their lodges important in keeping them warm.

European exploration of North America was in part based on trapping beavers for their skin to make clothing and their glands, which had perfume and medicinal purposes. So successful were the hunters that they were hunted to near extinction by the early 1800s. Before European settlement, the North American beaver population was at up to 150 million. There are now between 6 and 12 million beavers left in North America, a 90% decline from their peak. In Europe, their numbers also dwindled to the point of extinction at some points in history. Beavers are being reintroduced into many areas of Europe to repopulate them. After 200 years, beavers returned to New York City, making dams in the Bronx River.

The beaver children watched and learned from their parents all summer long. Sur- prisingly, Little John watched too, as the beavers worked and worked, building up a home for themselves. Little John began to help his Uncle around the farm a good bit more.

“I think I want a home of my own one day, like the beavers,” said Little John, “don’t kill them.” At that moment, the farmer realized that Little John was not hopeless. The beavers set a good example for making a respectable life. “The beavers can stay as long as they like,” responded the farmer to Little John.

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This story indicates the complexity of behavior that may be seen in the animal kingdom. A beaver’s place within our ecosystem is interesting – second only to humans, beavers modify their environment more than any other organism, building dams and creating wetlands and aquatic systems.

Study the biology of the Castor genus to determine its relationship with the ecosystem and human society. Research the island of Tierra del Fuego, in southern Chile, which experienced beavers as an invasive species in the past century. Explain how they are coping with the beaver population explo- sion. What factors are leading to this problem? What suggestions would you make to help protect their communities?

Unity and Diversity of Animals When most of us think about animals, we imagine mammals such as the beaver of our story. In reality, over 90% of animals are invertebrates – meaning that they do not have a backbone – and 75% of all animals are arthropods, of which most are insects (see Figure 10.1). In fact, 25% of all known species are beetles, the most diverse group of animals. Animals having a backbone, called vertebrates, include the more complex organisms such as humans, whales, beavers, and frogs. More than 1 million species of animals have so far been discovered. The branch of biology that is dedicated to the study of animals and their characteristics is zoology.

Invertebrates

Animals that lack a backbone.

Vertebrates

Animals having a backbone.

Zoology

The branch of biology that is dedicated to the study of animals and their characteristics.

Homeotherm

Organisms that maintain a stable internal body temperature.

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Animal fossils emerged over 600 million years ago, probably from a single protist, with rapid diversification following in a short time frame – so short that it represents only 1% of life’s history on Earth. These rapid increases in animal species occurred during a period in geologic time called the Cambrian period, and the burst of diversi- fication is known as the Cambrian explosion. Since this time period, through roughly 530 million years, many species of animals developed and changed. The result today is roughly 30 different animal phyla.

While there are many differences in structures and lifestyles among the animals, they have amazing similarity. All animals have common methods of development, with similar structures and functions of organs and organ systems.

This chapter tours only nine of these phyla, which include almost all of the known animal species. Their adaptations in each animal phylum represent a branch taken in evolution to adjust to environmental changes. A sea urchin developed its structures to be a successful sea urchin and a beaver developed its ways of life to be successful in rivers.

Features unique to each phylum show how animals changed to suit their unique needs. No one phylum is better than another, and humans are not the “highest” species in development. An organism’s evolutionary success is determined by its survival on Earth, which remains to be seen. Extant organisms are those that exist today and extinct organisms are those that have died off. Any species still existing in today’s environment are thus far successful, because they is still here despite a competitive and harsh world.

Animals’ sheer numbers and omnipresence on Earth attest to their ecological impor- tance. The beaver in our story modifies its environment greatly, showing how even one family of animals may have significant ecological impacts. An excellent example of biodiversity and the importance of each species can be found simply by scooping a spade of dirt from one’s garden: if you examine that sample carefully you might find earthworms, beetles, nematodes, spiders – all living within a small cube of land. Even a tiny area of the ocean might have lobsters, crayfish, eels, and sharks living around a sponge population.

Animals trump all other species in terms of their visible, unique differences, from beavers and parrots to monkeys, rams and the butterfly (see Figure 10.2). This vast diversity is attributed to their complex needs to live on land. All animals need to obtain food from other organisms, as they cannot carry out photosynthesis. They must therefore adapt ways to obtain food from their respective environments.

Thus, all animals are multicellular, heterotrophic organisms that have motility. They need to be able to move to obtain a mate, find food, and defend themselves. To meet these needs requires a complex body organization: obtaining food, a mate, and a proper environment suitable for living is no easy task. Animals often have specialized cells and

Cambrian explosion

A evolutionary event during which rapid diversification of multicellular animal life occurred.

Extant

Are organisms that exist today.

Extinct

Are organisms that have died off.

Figure 10.1 This chart shows the diversity of animal species

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tissues that enable them to carry out their unique life functions. In most phyla, cells are coordinated, often in the form of muscle and nerve tissue, to allow motility and respond to stimuli. Animal cells lack a cell wall because structure and height given by walls is less important in animals than in plants. Instead, it is more important that animals are able to move about on land and in the water, without the encumbrances of a rigid cell wall. Their body plan differs among the animal phyla, but the same goals apply – eating, mating, and defense against predators.

Figure 10.2 Animal diversity: Each of these animals share common characteristics of life, but carry out different ways of performing those life functions. Birds and butterflies are aquatic while camels and rams live on land.

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Four Ways to Classify Animals While all animals evolved from a common ancestor – a single-celled, protist – each spe- cies has certain features. These may be classified according to a simple system. There are four key ways to divide animals into their groups (refer to Figure 10.5).

Specialized Cells First, animals may be either composed of specialized cells forming tissues or contain no spe- cialized cells. The simplest body plan is found in the phylum Porifera or sponges, which are merely colonies of cells living in association with each other. Sponges do not have specialized cells; sponge cells do not coordinate activities but remain together, operating as solitary units of life. They are aggregates of cells which work well as a colony but they do not comprise a whole, unified organism. Sponges will be discussed as our first phylum. All other animal phyla are characterized by complex tissues, operating together in a coordinated way. Humans, for example, discussed in the next unit of this text, have a specialized, complex set of tissues – muscles, nerves, and bones – to enable movement and other life functions (see Figure 10.3).

Symmetry Second, animals develop a shape that has either radial symmetry or bilateral symmetry (see Figure 10.4). Radial symmetry describes any organism that is structured so that when a line is drawn down the middle of it, at any orientation both sides are identical. Animals with radial symmetry include mostly slow moving or floating organisms such as sponges and sea anemones. Animals with bilateral symmetry, meaning that they are roughly identical upon surface observation when a line is drawn down their middle, include faster moving organisms. These include most of the more complex species, such as frogs, fish, and humans. They respond better to stimuli than less complex organisms, giving them improved means of hunting, mating, or escaping from predators.

Molting Third, some animals molt, or shed their external exoskeleton or outer covering as they grow, forming a new one to fit their new size. Molting organisms include spiders, lob- sters, crayfish, and insects. While it appears a waste of energy to molt off an exoskeleton, this process enables growth while at the same time protecting organisms from predators.

Specialized cells

Cells that carry out a particular function.

Radial symmetry

Symmetry that describes any organism that is structured so that when a line is drawn down the middle of it, at any orientation, both sides are identical.

Bilateral symmetry

The property of being roughly identical upon surface observation when a line is drawn down their middle.

Molt

To shed the outer covering.

Exoskeleton

A rigid outer covering of an animal.

Figure 10.3 Humans, like other animals, have specialized structures and exhibit great complexity.

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All other animals grow continuously as they add mass to their bodies. Earthworms, grasshoppers, squids, humans, and dogs are all animals that grow continuously. They some- times have an endoskeleton or internal skeleton as a support system to give them structure.

Body Cavity Formation Fourth, animals are divided by the manner in which their body cavities form. Bilateral animals mature either by first forming a mouth or by first forming an anus during their embryo development. Organisms forming their mouth first are called protostomes, which include animals with simpler body plans such as flatworms, roundworm, and insects. Those animals forming their body cavity from the back, or anus region, are called deu- terostomes. These include starfish, monkeys, and humans, which have the more com- plex body plans among animals. The developmental stages of these two groups are best observed as embryos; it is more difficult to see this development as adults. Body cavity development separates animals based on their evolutionary lineages. Deuterostomes are much more closely related with each other than with protostomes and vice versa.

the Major phyla Animals consist of nine major, separate evolutionary lineages, as shown in Figure 10.5. The rest of this chapter examines each phylum in greater detail, showing the changed characteristics for each group in relation to their respective environments.

To start, beavers in our story are classified as mammals, the final phylum to be dis- cussed. Beavers have specialized cells and bilateral symmetry; they do not molt but grow continuously, and form their anus first during development, making them deuterostomes.

porifera: the Scattered Sponges Unlike the clever and hard-working beaver, which is clearly an animal, sponges may appear almost nonliving or plant-like to the casual eye. Sponges were once placed in the subkingdom Parazoa, which means “besides the animals,” due to their evolutionary and physical differences from the other animal groups. They are sessile as adults and appear to sit in one spot for most of their life cycle. They do move as juvenilesto colonize new areas and are heterotrophic. However, while they are the least animal-like of any mem- bers of the animal phyla, they are indeed animals.

Protostomes

Organisms that form their mouth first.

Deuterostomes

Animals belonging to the group Deuterostomia, in which the body cavity first forms from the back, or anus region.

Sessile

Immobile.

Figure 10.4 All animals (except sponges) have either radial or bilateral symmetry. a. This butterfly exhibits bilateral symmetry. b. The sea urchins exhibit radial symmetry.

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Internal skeleton that acts as a support system to vertebrates.

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Sponges, in the phylum Porifera, represent a large group of organisms that exist as colonies, aggregates of unspecialized cells. These cells lack coordination, are sessile for most of their life cycle, and have no symmetry of body plan, as described earlier in the chapter. Sponge cells are hollow tubes that contain pores that filter out food from the water passing through their bodies.

Sponge cells are not, however, haphazardly arranged. Sponges organize into sets of colonies, based on their particular species type. While sponges have no specialized tis- sues, they contain three types of cells to carry out life functions: epidermal cells cover and protect sponges; choanocytes or collar cells, which have beating flagella that move water through the internal cavity of the sponge; and amoebocytes, which transport food through the sponge body (see Figure 10.6). As microscopic food such as algae and bacteria travels through the sponge cavity, it becomes trapped by a sticky, gelatinous mucous on the surface of collar cells. Digestion occurs separately in each sponge cell. Sponges lack a transport system, so movement of digested food via amoebocytes is their only circulation method.

Porifera

A phylum of aquatic invertebrates that comprise of sponges.

Epidermal cells

A type of sponge cell that covers and protects sponges.

Collar cells

A type of sponge cell that has beating flagella move water through the internal cavity of the sponge.

Amoebocytes

A type of sponge cell that transports food through the sponge body.

Figure 10.5 Phylogeny of animals: classification scheme based on the four character- istics of animals showing all nine phyla branched.

Single-celled protist ancestors

Multicelled ancestors

Bilateral symmetry

Sponges

Cnidarians (radial symmetry, no coelom)

Flatworms

(no coelom)

Roundworms (pseudocoelom)

True coelom

Protostomes (mouth is 1st embryonic opening)

Mollusks

Annelids

Arthropods

Chordates

Echinoderms

Deuterostomes (mouth is 2nd embryonic opening)

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Reproduction in sponges occurs either asexually or sexually. Fragmentation, a sim- ple breaking off of a piece of the sponge, is usually the asexual route for reproduc- tion. Alternatively, sponges are hermaphrodites, meaning that they have both male and female reproductive parts. However, only one sex is active at any one time, preventing self-fertilization. When a male-acting sponge produces sperm, it swims to the female part of a female-acting sponge. In the next phase, sponge larvae are free-swimming, the only stage at which they are motile. During this period, larvae float to find a new home to grow into future colonies.

Sponges, comprising 5,000 different species, were used in a number of ways by humans in the past. The hollow interiors of many sponges are absorbent and soft, so they were used as shock absorbers in army helmets during medieval times, and as cleaning and painting products in more recent memory. In the past, the absorbent qual- ity of sponges made them useful in house cleaning activities. Our modern household sponges do not derive from living organisms, however, because sponges are scarce due to overfishing. Instead, kitchen and bathroom sponges are now made of manufactured materials.

Cnidarians: Creatures with an open Cavity Cnidarians include jellyfish, sea anemones, hydras, and corals, which all contain an open body cavity. This cavity is called a coelenteron, or hollow cavity open to the outside environment, in which digestion occurs. Those containing such a cavity are called coel- enterates. When we think of Cnidarians, we think of jellyfish, which are really not fish. Instead they belong to the phylum Cnidarian.

Cnidarians are among the most poisonous of all animals. If you have been stung by a jellyfish on the beach, you are familiar with its venom. Their gastrovascular cavity or “hollow gut,” also known as a coelenteron, has only one opening. Within this cavity poisons and enzymes are secreted to carry out external digestion.

Hermaphrodite

A person or animal having both male and female reproductive parts.

Coelenterons

The open body cavity present in Cnidarians and opens to the outside environment, in which digestion occurs.

Cnidarian

An aquatic invertebrate that comprises coelenterates.

Amebocyte

Incurrent pore (ostium)

Pore cell

Collar cell

Gelatinous material (mesenchyme)

Outcurrent pore (osculum)

Spicule

Internal cavity (spongocoel)

Barrel sponge

Figure 10.6 Sponge body cells.

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How do Cnidarians obtain food from their environment? In their sting, they also have poison to help in their attack on other organisms. Cnidarians, all possess tentacles at the ends of a gastrovascular cavity that paralyze their prey. Cnidarians have stinging cells called cnidocysts, each containing a set of nematocysts, barbed threads that thrust outward when another organism touches them. Usually a poison accompanies the barbed thread, engulfing its prey. Figure 10.7 shows the overall body plan of Cnidarians and varied examples of Cnidarians.

Nematocysts

Barbed threads found in tentacles of Cnidarians.

Figure 10.7 What do cnidarians look like? a. Radial symmetry of the cnidarian body plan; b. Cnidarian use stinging cells with nematocysts to attack prey. When cnidarian stinging cells are stimulated, they discharge toxic substances and nematocysts which paralyze prey; c. A jellyfish from the Red Sea; d. Burrowing sea anemone, Pachycerianthus; e. Hydra. a. From BSCS: An Ecological Approach, 9th Edition by BSCS.

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Stinging cells present in Cnidarians.

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Cnidarians are more coordinated than sponges. They contain a nerve network, which is a set of nerve cells to help them respond to stimuli. Cnidarians sense the outside world using their nerve networks. The nerve network does not have a centralized area (or brain) to process information, however. It acts only to respond to external stimuli. This system benefits Cnidarians evolutionarily, to enable them to be effective heterotrophs, moving and responding to stimuli to obtain food and defend themselves.

Cnidarians all have radial symmetry, digestion in their open body cavity, and con- sist of two layers, an ectoderm or outer layer and an endoderm, an inner layer. In between the two layers is a gelatinous filling called a mesoglea or “middle jelly” layer. These layers surround their gastrovascular cavity.

Cnidarians have both sexual and asexual reproduction, like the sponges. The life cycle of Cnidarians has two stages: the polyp and the medusa stage. During the polyp stage, cnidarians are sessile, and in the medusa stage they have movement. Polyp or medusa stages may last almost throughout a Cnidarian’s life cycle or may comprise only a short period. Jellyfish are able to move through most of their lives in a medusa form, but sea anemones move very little and remain in a polyp form for most of their lives (Figure 10.8).

Jellyfish The “cup animals” which have a central cavity making them appear as cup-like, com- prise mostly jellyfish. They have the characteristic stingers on their end tentacles. They are ominous in movies and after we get stung. They range in size from 2 cm in diameter to over 15 m, including tentacles, in the case of the Lion’s Mane Jellyfish.

Their nerve networks respond to organisms surrounding them, often leading to their discharge of poison from their cnidocysts. A jellyfish sting may lead to serious harm and even death in humans. Often, multiple bites from the same jellyfish occur because of the many tentacles that it possesses.

Nerve network

Set of nerve cells that help Cnidarians respond to stimuli.

Ectoderm

The outermost layer of a Cnidarian.

Endoderm

The innermost layer of a Cnidarian.

Mesoglea

The gelatinous filling found in between the two cell layers in the bodies of Cnidarians and sponges.

Polyp stage

The stage in which Cnidarians are sessile.

Medusa stage

Cnidarians in their free swimming stage.

Jellyfish

Free-swimming marine creatures that have a central cavity making them appear as cup-like.

Figure 10.8 Cnidarian life cycle: Obelia, a marine colonial organism.

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Sea anemones Sea anemones appear as flower-like tubes, with their colors depending upon the pigments contained within them. They are not pretty flowers, however; they are carnivorous animals that sting their prey. Their tentacles move other organisms into their open body cavity, where they digest the prey. A sea anemone body cavity is divided into vertical chambers, each allowing digestion to occur separately. Sea anemones are often used in studies of fertilization because it is relatively easy to stimulate their production of gametes.

Hydras One of the most studied classes of cnidarians contains the hydra. Hydras are medusa-like, with a set of tentacles on the outside of their coelenterate opening. Hydras have a gland cell that secretes digestive enzymes into their body opening. Another digestive cell, the nutritive cell, uses a flagellum to mix food. Their pseudopods (false feet) extend outward from the hydra to absorb the digested nutrients. Hydras reproduce in part through an asexual process called budding. In budding, a new smaller hydra grows from the parent and falls off to start a new life. Hydras also have complex movement, such as gliding or somersaulting, coordinated by a nerve network guiding simple muscular movement.

Corals Corals live mostly in the polyp phase within large colonies composed of limestone skeletons. Their appearance is pretty, but they have tentacles, like other cnidarians, that sting and capture prey. Corals are cnidarians that secrete calcium carbonate (limestone) as their outer covering. This hard exterior gives corals their characteristic appearance. As they die, limestone layers build up, forming a complex structure. As discussed in another chapter some of the largest, most diverse ecosystems are composed of coral reefs. Beneath the sea, the 2,000-km long Great Barrier Reef, off the coast of Australia, is a complex of corals. It is so large that it may be seen from outer space.

Algae live within the cavities of corals in a symbiotic relationship. Algae provide oxygen and food for the coral, while corals afford algae a protected home and carbon dioxide to carry out photosynthesis. As temperatures increase in the changing climate, algae are expelled by corals, causing many of them to die. Algae give corals their colors and when they are expelled, corals appear white and are called bleached. Coral bleaching is a telltale sign that environmental conditions are problematic (see Figure 10.9).

Sea anemone

Water-dwelling animals that are brightly colored and fix themselves onto rocks.

Hydra

Freshwater organisms with a set of tentacles on the outside of their coelenterate opening.

Budding

A form of asexual reproduction in which new organisms develop from a bud as a result of cell division at one specific site.

Calcium carbonate

A naturally occurring chemical compound, making up by coral skeletons.

Coral bleaching

The loss of algae from corals, and resulting coral death.

Figure 10.9 a. Bleached elkhorn coral in the great barrier reef off the coast of Australia. Pollution causes harm to coral reefs throughout the world. b. Bleaching at the Great Barrier Reef, Queensland, Australia.

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Corals

Marine invertebrates that live in large colonies composed of limestone skeletons.

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Compared with mammals, such as the beaver in our story, cnidarians are quite sim- ple. However, their simple design is adequate for their life functions. While sponges are collections of organisms, each cnidarian independently works to survive and respond to its environmental conditions.

Worms There are three phyla of worms: flatworms in phylum Platyhelminthes, segmented worms in phylum Annelida, and round worms in phylum Nematodes. All of these worm groups have bilateral symmetry, along with an ability to move forward. As a group, worms did not develop together from one branch of the evolutionary chain. Instead, they are less related to each other than to organisms in other animal phyla. Nematodes, for example, are more closely related to arthropods such as insects than to other worm classes. Anne- lids are closer to mollusks (clams and oysters) than to Nematodes. Annelids have a body cavity or coelom, surrounded by specialized tissues, and the other worms do not. All worm phyla have parasitic species, making them interesting in terms of human disease.

Flatworms Flatworms do not have a body cavity, but have a compact body plan, giving them their name. Flatworms lack a space or coelom between their organs and instead have a central gastrovascular cavity to propel fluids. They are the first animal phyla to develop a distinct head and tail end. Flatworms range in size from 1 mm to 20 m (65 feet). They are found in abundance, reaching over 20,000 species. They feed through a single mouth that also serves as the anus, where digested food is also expelled. Flatworms also contain clusters of photosensitive cells that detect light and movement. These appear in some species as eyespots (see Figure 10.10a).

When reproducing, they are either asexual or sexual in their processes. During asex- ual phases, they simply split in half through binary fission, leading to two new organisms. In a simple experiment, if a flatworm, the Planaria for example, is cut in half, it will regrow its lost parts, forming into two new organisms. Planaria are also hermaphroditic,

Flatworms

Any worm belonging to the phylum Platyhelminthes.

Segmented worms

Worms characterized by cylindrical bodies segmented both externally and internally.

Round worms

A nematode worm infesting the intestine of mammals.

Gastrovascular cavity

The primary organ of digestion found in Cnidaria and Platyhelminthes.

Figure 10.10 a. Flatworms are a species in the phylum Platyhelminthes have well-developed organ systems. The Planaria’s body plan exemplifies this. Note its well-developed nervous system in the figure. Its many different systems interact to allow planarians to carry out their life functions. b. Tapeworms have long bodies and are able to produce thousands of eggs in animal intestines.

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containing both male and female gametes, used in their sexual phases of reproduction. Planaria contain flame cells that serve to remove their wastes. They also have a set of eyespots connected with nerve cords that enable them to respond to stimuli such as light.

There are over 5,000 species of parasitic flatworms called tapeworms, most causing disease in their host species. Blood flukes, also called schistosomes, cause intestinal pain and anemia in over 200 million people worldwide each year. Tapeworm larvae are found in uncooked meats, especially pork and fish. Larvae grow in size up to 2 m in human intestines, causing blockages and preventing nutrient absorption (see Figure 10.10b). This is why cooking meats is so important, preventing the spread of a number of worm-related diseases.

Roundworms There are 25,000 known roundworm species, the most abundant worms on Earth. They are found mostly in aquatic environments or wet soils. Nematodes or roundworms have a sepa- rate mouth and anus, as compared with flatworms, meaning that they do not eat and excrete through the same opening. Nematodes are almost always parasitic, living on the energy of their hosts, with 15,000 species responsible for human diseases. For example, Trichinella is a roundworm which infects human intestines, after which it burrows into muscle tissue (see Figure 10.11). Its related disease, called trichinosis, is potentially fatal and is caused by eating uncooked pork. Roundworms are spread by fecal contamination of food or soil.

Flame cells

Specialized excretory cells found in certain invertebrates.

Tape worms

Parasitic flatworms that live in the intestines of people and animals.

Figure 10.11 Roundworms (Trichinella).

Mouth

Pharynx

Nerve ring (brain)

Excretory tube

Intestine

Genital pore

Vagina

Ovary and oviduct (wrapped around uterus)

Penial spicules

Ovary

Oviduct

Uterus

(unwrapped)

Testis

Seminal vesicle

Vas deferens

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Segmented Worms Earthworms are the most common example used to describe segmented worms. They are rarely parasitic to humans. Annelids or segmented worm all have repeating chambers or units, which are called segments. Each segment has a digestive cavity, including a mouth and anus, which directs digestion through the worm. Each segment is identical to the others. The segments contain specialized organs that digest nutrients as they pass through and excrete wastes.

Segmented worms comprise 16,000 species and range in size from 1 mm to 3 m, in the case of the giant Australian earthworm. Earthworms are bulk-feeders, meaning that they pass food through their digestive systems as they burrow through the soil. They therefore recycle matter, passing digested material back into the soil. Earthworms mix and aerate the soil, helping other plants and animals to grow.

There are three groups of Annelids: marine, terrestrial, and leeches. Marine anne- lids or polychaetes combine bristles with their segments. They live on the seafloor and burrow through the soil to obtain food. Polychaetes use their tentacles to bring food into their mouths. Earthworms or oligochaetes are soil dwellers, for example, the common earthworm seen in your backyard. Earthworms also have a circulatory system, with aor- tic arches operating as simple hearts to pump blood. They contain nephridia, which are specialized tubes to excrete their wastes. A coelom or open body cavity also separates the organs of the annelid (see Figure 10.12). They are also hermaphroditic, able to repro- duce sexually and asexually. In asexual reproduction, earthworms spilt at a special spot called their clitellum, which results in two new, identical offspring.

Leeches live in aquatic environments and have segmented bodies. About half of the leeches are blood suckers, using an anticoagulant chemical to keep blood flowing once they grab hold of a host. The other half of leeches act as predators, which feed on other animals.

Mollusks Mollusks include snails, clams, oysters, and squids, which are all soft-bodied animals most of which are protected by a hard outer shell. Some mollusks – for example, slugs and octopuses – have reduced shells or have lost their shells through evolution. However, all mollusks have the same three-point body plan: a muscular foot used for movement; a visceral mass containing the internal organs of the mollusk; and a mantle which secretes the outer shell (see Figure 10.13).

Gastropods. Slugs and snails are gastropods, mollusks with an enlarged foot to help them move. The slime of gastropods is used to defend against predators. For example, when a bird attacks a slug, its slime sticks to the bird’s beak along with debris such as leaves and twigs. Some slime is toxic, harming predators that eat or touch them.

Bivalves. Clams, oysters, and mussels are bivalves: they have two shells hinged together. Bivalves are marine and freshwater organisms living in the mud underneath the water. When water passes through their gills, bivalves capture food particles making them filter feeders.

Cephalopods. Squids and octopuses comprise the majority of the third group of mollusks called cephalopods. Cephalopods are more mobile than other mollusks, with reduced or missing shells enabling greater flexibility. They have enlarged brains, giving their name “cephalo” which refers to their brain development; and cephalopod translates into head-foot. They also have well-developed sensory organs, enabling cephalopods to stalk and capture prey efficiently. Cephalopods are not, however, brilliant or even smart, as sometimes depicted by the media. An octopus, for example, is able to manipulate

Segments

The repeating chambers or units found in annelids.

Polychaetes

A marine annelid worm.

Oligochaetes

Aquatic and terrestrial worms.

Aortic arches

The simple hearts of segmented worms.

Nephridia

Excretory organs found in many invertebrates.

Coelom

An open body cavity that separates the organs of the annelid.

Mollusk

Invertebrates, chiefly marine, characterized by a soft unsegmented body and an external hard shell.

Muscular foot

One of the three-point body plans of mollusks, used for movement.

Visceral mass

One of three-point body plans of mollusks that contain the internal organs.

Mantle

One of the three- point body plans of mollusks that secretes the outer shell.

Gastropods

Mollusks with an enlarged foot.

Bivalves

The property of having two shells hinged together.

Cephalopods

The third group of mollusks characterised by a large head, eyes, and a ring for sucker- bearing tentacles.

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things very well – they are capable of untwisting lids of jars or prying to open clam shells – but intelligence is a difficult concept to demarcate. A cephalopod’s brain activity is only thus far demonstrated in terms of its use of techniques to obtain prey and sur- vive – not to plan and strategize in an abstract way. Its intelligence is overestimated by many news reports. While cephalopods have a distinct brain, it is difficult to measure their intelligence. Unlike the beaver in our story, which monitors and performs complex building and feeding activities, cephalopods do not exhibit planning behavior.

Figure 10.12 Earthworm anatomy. The digestive system of the earthworm is com- plex, using several specialized chambers for the breakdown of foods. Its clitellum houses the earthworm’s reproductive structures.

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Anus

Setae (bristles)

Prostomium

Clitellum

Mouth

Pharynx

Esophagus C rop Gizzar

Intestine

Hearts (five) Dorsal vessel

Ventral vessel Segmental vessels

Brain

Nerve cord Segmental nerves

Anterior seminal vesicle

Middle and posterior seminal vesicles

Seminal receptacles Ovary Egg funnel and oviduct

A. Surface anatomy

B. Alimentary canal

C. Circulatory system

D. Nervous system

E. Reproductive system

Segments

Longitudinal muscle

Circular muscle

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Arthropods Once segments specialized, each with differing roles, such as mouth parts and antennae, arthropods emerged on life’s scene. Arthropods are invertebrates with a specialized seg- mented body and a protective external skeleton, or exoskeleton, and joint appendages. Their body segments consist of a head, thorax (midsection), and abdomen.

Arthropods comprise the most numerous and diverse of all animal phyla, with over 950,000 known species. There are three major groups of arthropods including insects (flies and moths), arachnids (spiders and marine arthropods), and the crustaceans (lob- sters and crayfish). There are over 90,000 species of flies alone, and arthropods total a population of billions (1018) of organisms on Earth. Thus, they outnumber humans 150,000:1. If you sit in a forest or in a city subway, you are probably aware that arthro- pods are omnipresent – they are everywhere (see Figure 10.14).

All arthropod exoskeletons are composed of chitin, a protective polysaccharide that is the most abundant living protein on Earth. The hard exoskeleton protects arthropods.

Arthropods

Invertebrates with a specialized segmented body and a protective external skeleton, or exoskeleton, and jointed appendages.

Insects

Small invertebrates with a head, thorax, abdomen, six legs, and one or two pairs of wings.

Arachnids

An arthropod characterized by having eight legs.

Crustaceans

An arthropod characterized by having five sets of appendages.

Stomach

Esophagus

Cilia

Mouth

Intestine

Anus

Nephridium

Mesodermal cells (give rise to many tissues and organs)

Stomach Intestine

Heart

Anus

Posterior adductor muscle

Developing gills

Foot

Mouth

Esophagus

Anterior adductor muscle

Digestive gland

Muscles

(a)

(b)

Figure 10.13 Mollusk three-point body plan. Mollusks have bilateral symmetry and possess a muscular foot, a visceral mass containing its internal organs, and a mantle that secretes its protective shell.

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When their body grows, an arthropod must shed its exoskeleton through molting. Until another exoskeleton grows back, the organism remains vulnerable to predators. While an exoskeleton helps them to defend against attack, it also preserves their internal water supply, especially important to those species that live in very dry areas.

All insects have wings so they are able to fly, avoiding their predators. Other arthro- pods, such as arachnids, have poison glands that produce toxins to paralyze their enemy. They then use their appendages to dismember their prey and eat the liquid contents. An arthropod’s many specialized structures make them very resourceful in multiple situa- tions. This is the reason they are able to live in so many areas.

Arachnids Arachnids are arthropods that have eight walking legs and live on land. They include spiders, the most numerous group, as well as ticks, mites, and scorpions. In addition to walking limbs, arachnids have a pair of feeding appendages to capture and kill prey.

Spiders construct often complex webs composed of silk to trap prey, including insects. Most spiders are harmless to humans. Pholcus phalangioides or cellar spider,

Figure 10.14 What kinds of present-day arthropods exist? a. Spiders are arachnids. b. Lobsters are crus- taceans. c. a millipede. d. dragonflies. a and b Corel. c. From BSCS Biology: An Ecological Approach, 9th Edition by BSCS.

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commonly known as the daddy long-legs, is a gangly arachnid, but harmless to humans because its bite is unable to penetrate our protective skin layers (see Figure 10.15). How- ever, some spiders, such as the black widow spider, cause a bite to humans that can be deadly (see Figure 10.16).

Crustaceans Almost all of the crustaceans are aquatic arthropods. Crustaceans, all have one feature in common: five sets of appendages with three sets used for feeding on prey and two sets to sense their environment.

Crustaceans are very different from each other in other ways, ranging from the small and sessile barnacle to the large, complex, and mobile lobster (see Figure 10.17b). Each species of crustacean possesses specialized appendages that serve unique functions. Lobsters and crabs have modified limbs that hold their eggs or new offspring.

Some crustaceans have value as a delicacy to humans: shrimp, crab, and lobster are expensive dishes in restaurants.

Figure 10.15 Daddy long-legs are harmless to humans. It looks gangly and leggy.

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Figure 10.16 A female black Widow Spider (Lactrodectus mactans) sits in wait for prey on its web. Its venom is a neurotoxin, paralyzing its prey.

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The only terrestrial crustacean is the pillbug, shown in Figure 10.17a, which is not at all tasty, with little meat for food appeal. Pillbugs are some of the oldest species of arthropods.

insects Insects always have three pairs of appendages and one or two pairs of wings in addition to the other characteristics of arthropods. Insects comprise the most numerous group of arthropods, representing 60% of all animal species. Examples include beetles, flies, butterflies, and moths (see Figure 10.18).

Figure 10.17 Pillbugs and lobsters are examples of crustaceans. a. Pillbugs have little flesh to serve in human meals, but the lobster b. is a delicacy.

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Figure 10.18 There are many examples of insects.

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Many insects grow through a process known as metamorphosis, in which they undergo a series of molts, changing to look more and more like their adult form in each stage. First, insects hatch as an egg to become larvae, which appear as caterpillars or maggots, for example. In this stage, larvae consume food to develop, molting into a pupa form, which is cocooned. In the cocoon, the pupa organs break down and adult organs develop rapidly. The adult emerges from the pupa cocoon, entering the world (see Figure 10.19). Caterpillars emerge as butterflies, and maggots become flies, while grubs develop into beetles.

The common housefly, Musca domestica, represents about 90% of all fly species (see Figure 10.20). Like many insects, houseflies carry pathogens, causing almost 100 different diseases in humans. Cholera, diphtheria, tuberculosis, and typhus are diseases carried by the common housefly. Insects spread diseases affecting about 250 million people a year and cause 2 million of their deaths. They also carry diseases that harm other animals. An outbreak of tula- remia in Urbana’s Meadowbrook Park in Illinois in 2013 killed a beaver population through fly and tick bites. Tularemia is caused by a bacterium spread by insect bites between animals.

Metamorphosis

A complete change of physical form.

Egg

The female reproductive cell in plants and animals.

Larvae

The active immature form of an insect.

Pupa

The stage between the larval and adult stage, in a cocoon.

Adult

Fully grown or developed.

Figure 10.19 Metamorphosis of a moth.

Egg

Larvae

Pupa

Adult

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Figure 10.20 A common housefly. Flies carry many microbes, some of which cause disease. Beaver fever and malaria are spread through the bite of mosquitoes.

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Echinoderms Echinoderms are a group of marine animals with a spiny skin and an endoskeleton. Their hard endoskeleton is found beneath the skin, giving echinoderms their structure. The endoskeleton is made of calcium carbonate. The prefix “echin-” is Greek for spiny, which refers to the prickly plates covering their surfaces. The phylum includes sand dollars, sea cucumbers, sea urchins, and starfish, which are probably the most familiar to people. Echinoderms comprise 7,000 animal species, all characterized by adults with radial symmetry. They do not have body segments and instead have specialized struc- tures within one larger unit.

Echinoderms have a water-vascular system, a set of internal channels that circulate water through their bodies, enabling gas exchange and waste removal. The water vas- cular system ends in small suction cup-shaped feet, called tube feet, which are used for holding prey. Echinoderms carry out complex movements but have no brain; instead, they have a nervous system composed of a central ring which branches into the append- ages to sense their environment.

Echinoderms move using their water-vascular system, in which water fills the canals and pushes out through tube feet. Water enters starfish, shown in Figure 10.21, through a central canal and fills its arms. As water enters the arms, they move outward, and to contract them back into position, starfish use their muscular system. The system oper- ates based on a hydraulic set up, with high-pressured water pushing outward to propel an echinoderm forward.

Food sources for echinoderms include algae, shrimp, sea urchins, sand dollars and mollusks, which starfish pry open to obtain their luscious interiors. The water-vascular system transports foods and wastes throughout an echinoderm body.

Echinoderms

A group of marine animals with a spiny skin and an endoskeleton.

Water-vascular system

A set of internal channels that circulate water through echinoderm bodies, enabling gas exchange and waste removal.

Tube feet

A small suction cup- shaped feet that are used for holding prey.

Central canal

A central tube through which water enters the arms of a starfish.

Figure 10.21 Starfish anatomy.

Sieve plate

Cardiac stomach

Pyloric stomach Anus

Gonads

Arm

Digestive glands

Spine

Eye spot

Central canal Ampulla Radial canal Tube feet

Water vascular system

Digestive gland

Gonad

Ampulla

Radial canal

Tube feet

Coelomic cavity

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Chordates and echinoderms are the most closely related animal phyla. They are the only other animal phylum to contain an internal endoskeleton. While both phyla appear very different from each other, molecular and embryo evidence show their similarity. An echinoderm’s embryo stage of development most closely resembles those found in chordates.

Chordates Fish, salamanders, reptiles, birds, mammals, and other common images of animals such as the beaver in our story are classified as chordates. Chordates are animals with a spi- nal cord or spinal cord-like structure (see Figure 10.22).

First, all chordates have a rod of tissue, called a notochord, extending from head to tail. In complex chordates, this tissue develops into a backbone, which is a set of nervous tissue surrounded by bones for protection. In simple chordates, the notochord is unpro- tected. Organisms with a backbone are classified into the subphylum vertebrates. Verte- brates have a backbone and an endoskeleton, shared in common only with echinoderms. Second, all chordates contain a nerve cord extending across their backside. Third, chor- dates have pharyngeal slits at some point in their development, which act as gills. Gills enable chordates to feed and breathe as water passes through them. Very often gills are only found in the embryonic stages of a chordates life, as in beavers and humans. A post- anal tail extends beyond their normal digestive tract at some point in development, as the fourth characteristic of chordates. Humans lose their tails after the embryo phase, with their tailbone or coccyx exhibited after birth as a vestige of this common phase.

Subphyla: Lancelets and tunicates While vertebrates comprise one subphylum of chordates, two others exist. 1) Lancelets comprise about 20 species of small eel-like organisms. They resemble other chordates at both larval and adult stages; and 2) Tunicates comprise about 2,000 species, which appear as sessile organisms, with holes that pull in food and water. They most resemble chordates in their larval stages. As adults, tunicates are the size of our thumbs and appear as blobs of gelatinous masses. Both subphyla are filter feeders; they draw water through

Notochord

A tissue rod found in chordates that extends from head to tail.

Backbone

Set of nervous tissue surrounded by bones for protection.

Nerve cord

A dorsal tubular cord of nervous tissue present in chordates.

Pharyngeal slits

Openings in the pharynx that develop into gills in some chordates.

Post-anal tail

An extension of the spinal cord that extends beyond an animal’s normal digestive tract at some point in development.

Figure 10.22 Remains of early human ancestors show a distinct backbone, character- izing humans as vertebrates. From BSCS Biology: An Ecological Approach, 9th Edition by BSCS.

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Are animals with a spinal cord or spinal cord-like structure.

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a system that filters out small, microscopic food particles in their feeding process. They do not contain a backbone and do not have a cranium; but they all have the other chor- date characteristics.

Vertebrates Fish

The first vertebrates were aquatic, evolving early in the Cambrian explosion, about 540 million years ago. They were jawless and lacked fins but obtained food through scav- enging dead animals or sucking on prey. Without jaws, it was difficult for these early vertebrates to defend themselves or to obtain prey.

About 470 million years ago the fossil record indicates that the first jawed fish evolved in the sea. They had fins, which helped them to move quickly through water to obtain food. A typical fish has seven fins, which enable movement in almost any direction. Their mobility, coupled with the development of jaws and teeth, made fish excellent predators. This evolutionary advantage still serves fish well.

The evolution of fins and jaws was a major change in vertebrates. It resulted in rapid speciation into the many classes of vertebrates that we see in our environment. There are three major categories of fish. Cartilaginous fishes are those that have a skeleton composed of the flexible but solid connective tissue, cartilage. Cartilage is the same tissue found in our nose and in the discs between our backbones – it allows multiple movements due to its structure. There are about 880 species of cartilaginous fish includ- ing sharks and rays, as commonly known examples (see Figure 10.23). Their flexibility allows cartilaginous fish species to maneuver quickly in the water. Sharks have a keen sense of smell but poor eyesight. They are also able to sense small vibrations in the water, which help them to easily detect prey.

The second category of fish is the bony fishes that have skeletons composed of bone. Calcium phosphates strengthen bones, making them rigid much like those found in our human skeletons. Over 97% of fishes are a ray-finned type of bony fish, including 27,000 species. These have skeletal rays emanating from their central backbones. Examples of ray-finned fish include those we commonly see: guppies, bass, goldfish, and trout.

Bony-fish groups contain an internal swim bladder, which acts as a precursor to lungs. The swim bladder fills with air to keep bony fish buoyant. This buoyancy allows bony fish to remain afloat without constant movement, unlike cartilaginous fish, which

Cartilaginous fishes

Are fishes that have a skeleton composed of the flexible but solid connective tissue, cartilage.

Bony fishes

Type of fishes that have skeletons composed of bone.

Ray-finned fishes

Fishes characterized by skeletal rays emanating from their central backbones.

Swim bladder

Organ that is present in many bony fishes and helps them maintain buoyancy.

Figure 10.23 Cartilaginous fish: a Shark. Their skeletons are made mostly of cartilage, which is softer than bone.

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must keep moving to avoid sinking. Their buoyancy also helps them to conserve a great deal of energy. Bony fish have both an excellent sense of smell and eyesight to enable them to capture prey and avoid predators (Figure 10.24).

Almost all fish species reproduce by laying eggs that are fertilized externally as well as male and female gametes that are released into surrounding waters. There are a few exceptions, with many shark species having internal fertilization. Some fish, including guppies, carry their eggs within their mothers until a live birth.

The third, smaller group of fishes is the lobe-finned fishes. Lobe-finned fish spe- cies have a sturdy pelvis and two solid, muscular fins on the underside of their bodies. These resemble appendages, which later developed into limbs in terrestrial vertebrates, described in the next section. They have two primitive lungs developed from gills. Their lungs are developed, with a complex series of air sacs that facilitate gas exchange, much more efficient than that occurring in the gills of other groups. Lobe-finned fishes con- tain only eight species, including six species of lungfish (see Figure 10.25) and two

Lobe-finned fishes

A smaller group of fishes having a developed pelvis, primitive lungs and muscular fins — precursors to life on land.

Figure 10.24 Bony fish body anatomy.

Spinal column and cord Spiny dorsal fin

Esophagus

Head kidney

Gills

Brain

Optic nerve

Olfactory tracts and bulbs

Conus arteriosus (to gills)

Atrium Ventricle

Pectoral fin

Liver

Intestine

Anus Urogenital opening

Caudal fin

Anal fin

Soft dorsal fin

Urinary bladder

Kidney

Air bladder StomachG

onad

(a) Generalized fish anatomy

EsophagusStomach

Spleen

Pyloric cecaDuodenum

Intestine

Rectum

Anus

Posterior cardiac vein

Anterior cardiac vein

Dorsal aorta

HeadBody

Common cardiac vein Sinus venosus

Atrium

Ventricle Heart

Conus arteriosis Ventral aorta

Gills

(b) Alimentary canal (c) Diagrammatic circulation © K

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species of coelacanth, once thought to be extinct. Lungfishes live in coastal wetlands, gulping air when they emerge from the water.

Amphibians, the First on Dry Land

The Greek “-amphibios” translates into “living a double life.” It is apropos because amphibians, including frogs, toads, and salamanders, live a portion of their lives in water and another portion on land. Amphibians were the first vertebrates to develop features that enabled life on land. There are approximately 6,000 species of amphibians, com- prising about 12% of all vertebrate species. All terrestrial vertebrates – amphibians, reptiles, and mammals – evolved from a common ancestor, the lobe-finned fishes.

Amphibians undergo a metamorphosis, in which their eggs develop into a larval stage called a tadpole, resembling a fish, with gills and no limbs. Then tadpoles develop limbs, air-breathing lungs (losing their gills), and external eardrums. Their movement to land is complete in this adult stage, except that their reproduction is linked to the sea because frog eggs lack a shell and would dry out on land (see Figure 10.26).

There were four vital adaptations for moving onto land:

• First, lungs developed in the lobe-finned fish to enable them to breathe air when oxygen concentrations were too low in warm coastal waters.

• Second, a sturdy backbone to support the weight of an organism moving on land was developed. Interlocking vertebral bones, which not only support but also cushion and flexibly move a terrestrial creature, were a major advance. The struc- tured backbone resisted the pull of gravity and attached to four moveable legs.

• Third, limbs evolved from the sturdy underside fins of the lobe-finned fish as the third important development for moving on land. Lungfish fins are homologous to our limbs, resembling them in terms of both their internal form and their functions. Lobe-finned fishes used them to walk on the sea surfaces and in shallow waters.

• Fourth, the ability to produce an egg that resisted drying out when exposed to air. Before the move to land, animals required a liquid environment for their embryos to develop. This is still the case – an embryo needs water and a watery surround- ing during its development

Amphibians

Vertebrates that live a portion of their lives in water and another portion on land.

Lungs

Pair of organs that people and animals use for breathing air.

Limbs

An arm or a leg of a person or animal.

Figure 10.25 African Lungfish have a pairs of lungs on either side of their throat. They can survive long periods if their habitat dries up. This is one of only six living lungfish species.

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The female reproductive cell in plants and animals.

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Amphibians still fertilize and lay their eggs in a watery ecosystem, called external fertilization because it occurs outside of their bodies. Other terrestrial animals, such as reptiles and mammals developed an amniotic sac to surround developing embryos. In these cases, embryos may exist within a mother or a waterproof eggshell, which both enable development to occur in a wet world.

Thus, terrestrial animals are divided into two groups, amphibians, which are non-amniotes and develop their eggs in the absence of an amniotic sac, and amniotes, such as reptiles, birds, and mammals, which develop their eggs encapsulated within an amniotic sac.

Vertebrates: Reptiles, More Efficient on Land

Once the development of amniotes took hold on land, reptiles, which include snakes, lizards, turtles, crocodiles, and alligators, as well as birds (often called the feathered reptiles) and dinosaurs emerged on land. Reptiles are a group of amniotes that share certain common features.

These features are specially adapted to living on dry land. First, they developed waterproof skin in the form of scales, which prevent water loss. Second, they have inter- nal fertilization, with egg and sperm combining inside their bodies. This prevents the need, as seen in amphibians, for a watery ecosystem to have sexual reproduction. Third, the reptile egg is the most important feature distinguishing them from other terrestrial animal groups. It is a self-contained pond, with an amniotic sac that surrounds a devel- oping embryo with its own water and food supply. Requiring no water from an external source, reptile eggs form within a hard shell made of calcium salts (see Figure 10.27). Reptile lungs, the fourth feature helping their adaptation to land, are more efficient and better adapted lungs than amphibian lungs. Reptile lungs have a greater surface area and better exchanges of gases than amphibian lungs. Amphibians use lungs to breathe only

External fertilization

The fertilization process that occurs outside the bodies of animals. Non-amniotes

Terrestrial animals that develop their eggs in the absence of an amniotic sac. Amniotes

Terrestrial animals that develop their eggs encapsulated within an amniotic sac.

Scales

Dermal or epidermal structures that form the external covering of reptiles, fishes, and certain mammals. Internal fertilization

The fertilization process that occurs inside the bodies of animals.

Reptiles

Cold-blooded vertebrates that crawl or creep.

Figure 10.26 Life cycle of an amphibian (Rana arborea). Amphibians undergo growth and developmental changes at certain points in their lives.

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as adults, and even then gas exchange mostly occurs through their skin. Reptiles use their lungs to breathe at all stages of their life cycles.

All reptile species except for birds are ectotherms, meaning that they rely on their environment to set their internal temperature. Many people are surprised that birds are reptiles and not part of mammals because they are endotherms, meaning that they gen- erate heat produced internally by cell respiration to maintain a stable internal body tem- perature. Endotherms are also called homeotherms, as the title of our story describes the beaver. Birds have all of the characteristics of reptiles, except that they are homeotherms and have feathers for insulation.

Dinosaurs are a branch of reptiles that died off 65 million years ago as discussed in another chapter. They were the most dominant terrestrial animal roaming Earth during the Mesozoic era, from 250 million years ago to their extinction. The fossil record shows transitional species linking modern day reptiles to dinosaurs.

Ectotherm

Organisms that rely on their environment to set their internal temperature.

Figure 10.27 Adaptations of reptiles to inhabit land: note the eggs and scales in the examples. a. The Horned Adder snake is protected by its scales. b. This baby crocodile, hatching, has been protected by its egg.

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ARE DINOSAuRS REALLy RELATED TO BIRDS?

Dinosaurs are extinct because they are no longer roaming the Earth in the forms that once existed. However, molecular evidence shows that dinosaur DNA is very similar to that of birds. Scientists agree that the birds are the direct descendants of dinosaurs. Feathers evolved in birds and in reptiles, with some species of dinosaurs exhibiting feathers well before the evolution of birds. Back in the 1860s, paleontologists found feathers on dinosaur species linking over twenty species with bird-like feathers.

Fossils of dinosaurs and birds, along with molecular DNA evidence of both groups indicate that they share a close relationship. Birds are a type of dino- saur, and both are classified as reptiles. Birds branched off at a point in evolu- tionary history, with dinosaurs more like birds than any other reptile, fish, or amphibian species. Birds probably evolved from a group of two-legged dino- saurs known as theropods.

Endotherm

Organisms that generate heat produced internally by cell respiration to maintain a stable internal body temperature.

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Vertebrates: Birds, the Other Reptile

Birds were previously classified as mammals, in the class Aves, but are now recognized as reptile homeotherms. There are about 10,000 species of birds, almost all of which have flight. Those that are flightless – ostriches and penguins – probably evolved from birds that did fly. The evolution of flight was a dramatic shift in life’s history. Being able to escape predators, find and out maneuver prey from the air, and soar high to reach new regions to colonize, make flight a great development.

All of the anatomical features of birds contribute to their ability to fly (see Figure 10.28). Birds have no teeth, which would otherwise add weight to their skulls and drag them down head first during flight. Instead, they chew or grind their food in a com- partment next to the stomach called a gizzard. Their bones are honeycomb in struc- ture, which gives their skeletons strength but is very light. Large spans of bones form wide wingspans without the weight of a heavy skeleton beneath them. A frigate bird has a wingspan of more than 2 m (6.6 feet) but only a weight of 113 g (4 ounces). Females contain only one ovary instead of the two found in other mammals, to reduce their weight. Birds have strong breast muscles, which we commonly called white meat, which expend a great deal of energy to create wing motions for flight. Feathers are light but serve to insulate birds all around their bodies. They are made of the same chemicals as reptile scales, showing their relatedness. The shape and size of the wings of birds are aerodynamic – they enable a “lift” based on wind currents in some bird species, such as eagles and hawks, soaring to great heights. These movements ended the story in Chapter 4, as the old lady watched the great tree’s eagles soar, showing the beauty of such flight ability. Other birds, such as the hummingbird, require constant flapping of

Birds

Warm-blooded vertebrates characterised by feathers, wings, beak with no teeth, scaly legs, and typically by being able to fly.

Studies of the Tyrannosaurus rex also show a close genetic relationship with birds. Collagen fibers, that are strands of proteins found in the soft tissues of animals, were studied to compare their make-up between the species. While it is obvious that dinosaurs no longer roam the planet, their related genes remain – mostly in the birds.

Figure 10.28 The bird skeleton is lightweight, highly adapted for flight. Note the inside of its bones on the left, with many open spaces giving it a light weight.

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wings to keep them afloat. All of these adaptations make birds a unique branch of rep- tiles. Figure 10.29 gives a sample of birds and their features.

Unlike other reptiles, birds are endotherms, able to use cell respiration to gen- erate heat and maintain a stable internal body temperature. Flight requires a great deal of energy and its movement provides ample heat for maintenance of its body temperature.

Vertebrates: Mammals, Homeotherms That Thrive on Land and in the Sea

Before birds appeared, mammals evolved from reptiles as small, nocturnal creatures. Mammals are homeotherms that produce milk to feed their young; they have hair for insu- lation and protection. The first mammals branched from reptiles about 200 million years ago. Mammals lived side-by-side with dinosaurs for 130 million years. After the dinosaur extinction, mammals lost a major predator and thrived. This resulted in rapid speciation and development of the numerous species of mammals we know of today. There are 5,300 species of mammals and most of them are terrestrial. There are 80 species of aquatic mam- mals, such as whales and dolphins, and 1,000 species of winged mammals, such as bats.

Mammals

Are homeotherms that produce milk to feed their young.

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Figure 10.29 All these modern birds have similar characteristics such as feathers and light bones, but each differs from the other markedly in its appearance. a. The Atlantic puffin is a protected species in Maine. b. The Southern Cassowary male is brightly colored to attract females. C. The male Peacock has a majestic tail to attract females.

DO OSTRICHES REALLy HIDE THEIR HEADS IN THE SAND?

Ostriches do not hide their heads in the sand or anywhere. Instead, what appears to be hiding in the ground is actually their moving their heads closer to their bodies to appear as a ball to predators.

Pliny the Elder (AD 23-79), a Roman historian and naturalist wrote of the ostrich: “[they must] imagine, when they have thrust their head and neck into a bush, that the whole of their body is concealed.” giving rise to this myth. Ostriches are not cowards; they have very strong legs that they readily use to defend themselves and their young. They avoid predators to prevent unneces- sary conflicts by maintaining a ball-shaped posture.

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There are three groups of mammals: eutherians, monotremes, and marsupials. Over 95% of mammals are eutherians, which are those developing their embryos inter- nally and nourishing them using a placenta. A placenta is an organ inside the mother’s body that provides food and removes the waste of a developing organism. Eutherians include most of our known mammals: cows, horses, dogs, cats, apes, and humans.

Marsupials have a short pregnancy, giving birth to small and not completely devel- oped offspring. They are still embryonic and require further development within a protected region in its mother, most often a pouch. These offspring complete their devel- opment attached to their mother, nursing on their nipples, obtaining milk. Marsupials include kangaroos and koalas; they live in regions in Australia, New Zealand, and North and South America. Australia is the habitat for most species of marsupials, with little competition from eutherians. Thus, in Australia marsupials occupy ecological areas that are usually reserved for eutherians.

The only mammals to lay eggs are the monotremes, which include only two species: the duck-billed platypus and the spiny anteater. Both organisms nourish their young with milk after they are born. They live primarily in Australia and New Zealand, along rivers and streams. They use leaves and warm nests to incubate their eggs.

Human Evolution

During the rapid speciation of mammals after the dinosaur extinction, some mammals evolved into primates. Primates evolved about 55 million years ago, with new features to make them more competitive. Primates are adapted to living in trees, with binocular vision to allow three-dimensional vision for jumping, shoulder and arm joints to rotate, and digits – fingers and toes – to grasp. These features of primates enabled them to move about more efficiently in an arboreal environment.

The primates include prosomials, including lemurs and tarsiers; anthropoids or monkeys; and hominids, which include the apes and humans. Apes such as orangutans, gorillas, and chimpanzees are most closely related to humans. Chimpanzees and humans share 99% of our genetic material in common (see Figure 10.30). The 1% of gene differ- ences between us accounts for many of the features that make us human.

Primate evolution may be traced as a wide bush, with many evolutionary branches emerging from their common ancestors. Newly evolved features included the develop- ment of wider dental arches and stronger teeth for powerful chewing; and bipedalism (ability to walk on two legs), which allowed for faster movement on land. Bipedalism evolved first, about 4 million years ago, enabling our ancestors to leave trees and walk on land, opening up a new set of habitats including the grasslands (see Figure 10.31). Walking on two legs uses less energy than on four legs.

Several groups of bipedal hominids existed between 4 million and 1 million years ago, known as the genus Australopithecus. There were at least two species including

Eutherians

Mammals that develop their embryos internally and nourish them using a placenta.

Placenta

An organ inside the mother’s body that provides food and removes the waste of a developing organism.

Marsupials

A type of mammal in which young ones are born immature and continue to develop in a pouch.

Monotremes

Primitive mammals that lay eggs.

Anthropoids

A higher primate, including monkeys.

Hiding one’s head in the sand is akin to being unaware of one’s surroundings or happenings. However, ostriches have acute hearing and vision and are able to detect predators from long distances. They are also able to move at speeds up to 31 mph, two advantages that compensate for their being flightless.

Ostriches emerged on the evolutionary tree over 120 million years ago. Their unique strategies enabled them to survive for those many years. They are actually the fastest runner of all two-legged animals. They have adapted strong wings to hit back predators and defend themselves and their young.

Hominids

A primate belonging to the family Hominidae.

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Australopithecus africanus and Australopithecus robustus. They had a small brain size, their bodies were the size of chimpanzees, roughly 1 m in height (about 3 feet tall), and they weighed about 30 kg (60 pounds).

Up until about 1.5 million years ago, Australopithicus lived in Africa. With the devel- opment of smaller teeth, larger brains, and the ability to use tools, our modern genus Homo emerged. “Homo means human” in Latin, referring to the similarities between those early species and modern humans. Several groups of Homo evolved from Australopithecus including the group Homo erectus and Homo ergaster. H. erectus left Africa, migrating to regions in Asia and Europe, while H. ergaster remained in Africa. H. erectus were

Figure 10.30 a. Chimpanzee (Pan troglodytes) have opposable thumbs and big toes. They are 99% geneti- cally similar to humans. b. Primate characteristics. From Biological Perspectives, 3rd ed by BSCS. c. Comparing genetic similarities across selected primates. From Biological Perspectives, 3rd ed by BSCS.

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Figure 10.31 Adaptations for bipedal motion

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successful hunters who shared food and worked cooperatively together forming com- munities. They had fire and lived in caves, protecting them from a host of environmental dangers. H. erectus lived from between 1.5 million years ago until 300,00 years ago.

Modern Homo sapiens or humans probably evolved from H. ergaster. H. ergaster evolved into Homo heidelbergensis and branched into either Homo neanderthaensis or Homo sapiens. Brain size and height and weight doubled as compared with earlier Homo forms. H. erectus evolved into another group that lived alongside them called Homo floresiensis about 200,000 years ago (see Figure 10.32).

Human evolution begins roughly 100,000 years ago based on fossil and molecular genetic evidence. Homo sapiens left Africa after their evolution, as a small group of only 100 people, diverging into Europe, Asia, and Australia, according to mitochondrial DNA evidence. They had an advanced sized brain capacity and this helped them to compete with the other groups of Homos that they encountered. About 15,000 years ago they crossed over into North America via Alaska, colonizing the New World.

Humans encountered three major groups of Homos in their journeys around the Earth. 1) Homo neanderthalensis or Neanderthals, our closest ancestor, lived from 150,000 to 35,000 years ago at the same time as modern humans. Neanderthals used fires, lived in caves, buried their dead, and lived in social groups. It is possible that we interbred with Neanderthals, but their lineage dies off, with ours emerging successfully into humans today. Homo floresiensis lived as small “hobbit-like” creatures, only about the size of their ancestors. They were more advanced in their social activity, using tools and living in groups. Their ancestors, members of H. erectus, lived alongside them for almost 200,000 years.

Once humans invaded regions of the Earth, all of its Homo relatives eventually became extinct. Neanderthals died off 30,000 years ago, H. erectus about 27,000 years ago, and H. floresiensis went extinct 12,000 years ago. Most anthropologists concur that humans exterminated all of the other Homo species, leaving us as the only surviving group in the continued evolution of our genus.

Figure 10.32 Hominid timeline.

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Summary Animals emerged from a single protist roughly 600 million years ago. After the Cambrian explosion, divergence into 30 different phyla of animals reflects the many adaptations to changing environments encountered since that time period. Animals are broadly divided into invertebrates and vertebrates, depending on whether they contain a backbone. There are four characteristics which are used to classify animals: cell specialization, symmetry, molting, and direction of development. Porifera are the simplest animals, as sponges with aggregates of unspecialized cells; cnidarians are more complex, including the jelly- fish and corals; worms have segments with specialized structures, often causing diseases such as the intestinal tapeworm; mollusks are soft-bodied animals usually protected by a shell, such as oysters and clams; arthropods have segments, nonrepeating, and each with their own specialization, including insects and spiders; echinoderms, including starfish and sand dollars, have an endoskeleton; chordates developed a more complex nervous system, enabling more effective responses to stimuli. Chordates include the most com- plex animals, such as fish, frogs, reptiles, birds, beavers, and humans. Chordate’s move to land included a number of adaptations such as lungs, scales, and shelled eggs to com- plete their move to land. Human evolution occurred relatively recently in earth’s history: during the past 100,000 years. Our triumph over other Homo genus’s has resulted in our lone existence among this group.

CHECk oUt

Summary: key points

• Animals interact with one another and with the environment to effect changes, as seen in the par- asitic nature of the roundworms, the aerating effects of earthworms in soils and the vast ecological changes produced by the activity of the beaver.

• Animals increased in complexity as evolution progressed, adding special adaptations to exploit more environments and new environmental conditions.

• Animals are classified based upon their cell specialization, body symmetry, ability to molt, and direc- tion of gut formation.

• Porifera are sponges with asymmetry and no specialization. • Cnidarians have radial symmetry but all other animals have bilateral symmetry. • Roundworms and arthropods are the only animal phyla that molt. • Flatworms, segmented worms, mollusks, echinoderms, and chordates grow continuously. • Echinoderms and chordates are the only animal phyla that develop from the back to the front. • Human evolution of the Homo genus occurred only in the past 100,000 years, emerging from the

Australopithecus genus.

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adult amniotes, nonamniotes amoebocytes amphibians aortic arches anthropoids arachnids arthropods backbone bilateral symmetry birds bivalves bony fishes budding Cambrian explosion calcium carbonate cartilaginous fishes cephalopods chordates cnidarian cnidocysts collar cells coelenterons coelom coral bleaching corals crustaceans deuterostomes echinoderms ectoderm ectotherm egg endoderm endoskeleton endotherm epidermal cells eutherians exoskeleton extant extinct external fertilization eye spots flame cells flatworms gastropods

gastrovascular cavity hermaphrodite homeotherm hominids hydra internal fertilization invertebrates insects jellyfish larvae limbs lobe-finned fishes lungs mammals mantle marsupials medusa stage mesoglea metamorphosis mollusk molt monotremes muscular foot nematocysts nephridia nerve cord nerve network notochord oligochaetes pharyngeal slits placenta polychaetes polyp stage porifera post-anal tail protostomes prosomials pupa radial symmetry ray-finned fishes reptiles round worms scales sea anemone segments

KEy TERMS

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segmented worms sessile specialized cells central canal swim bladder tape worms

tube feet vertebrates visceral mass water-vascular system zoology

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Multiple Choice Questions

1. Which animal is among the first to exhibit the environmental effects of pollution? a. Insects b. Corals c. Segmented worms d. Clams

2. The Cambrian explosion resulted in: a. rapid animal speciation b. rapid animal extinction c. decreased parasitic diseases d. decreased protist–animal relationships

3. Which animal phylum has a distinct endoskeleton? a. Cnidarian b. Polychaete c. Arthropod d. Echinoderm

4. 75% of animal species belong to the _____ grouping of animals: a. invertebrate b. arthropod c. chordate d. vertebrate

5. In a cluster of sea anemones growing together, a line may be drawn in any direction and both sides of it are the same. This refers to its a. radial symmetry b. bilateral symmetry c. protostome development d. deuterostome development

6. Which represents a logical order, from early to later, in the evolution of chordates? a. fish➔reptiles➔frogs➔mammals b. reptiles➔mammals➔fish➔bryophyte c. fish➔frogs➔reptiles➔mammals d. frogs➔fish➔reptiles➔mammals

7. Which phylum contains organisms with asymmetry: a. Cnidarian b. Mollusk c. Porifera d. Echinoderm

8. Which serves as a heart for earthworms? a. Segment b. Nephridia

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c. Aortic arch d. Coelom

9. Which group of organisms BEST represents the most important link between land and sea adaptations? a. Cartilaginous fishes b. Bony fishes c. Ray-finned fishes d. Lobe-finned fishes

10. Which anatomical adaptation BEST facilitated the Homo move from trees to grasslands? a. Bipedalism b. Use of fire c. Increased size d. Larger teeth

Short Answers

1. Describe two ways in which animals, such as the beaver in our story, are benefi- cial to humans. List two ways in which animals harm humans. Be sure to list and describe each.

2. Define the following terms: vertebrate and invertebrate. List one way the terms dif- fer from each other in relation to their: 1) anatomy; 2) diversity among the animal phyla; and 3) behavior.

3. An animal is discovered by a group of zoologists on the coast of Antarctica. It has radial symmetry, is heterotrophic, contains repeating segments, does not molt and develops mouth first. Use the characteristics of animals in this chapter to classify this organism. Why did you place it in its group?

4. A mollusk contains three basic parts to its body plan. List these three parts and describe their functions. Which is most important in a mollusk’s survival? Are there any parts missing in some species?

5. Is a cephalopod, such as an octopus, really smart? Why or why not?

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6. List and draw the body structure of a Porifera. Use the following terms in your drawing: epidermal cell, amoebocyte, collar cell?

7. Explain the “double-life” of an amphibian. Be sure to draw and label the steps of its life cycle. How is the double-life of amphibians an adaptation to living on land?

8. For question #7, how does the size of a pond affect an amphibian’s reproductive process? If a pond is too large, what are its advantages and disadvantages? If a pond is too small, what are its advantages and disadvantages?

9. List four adaptations reptiles developed to make their transition to life on land? How is each important in a reptile’s functioning in a terrestrial world?

10. Describe the two theories explaining how Neanderthals became extinct. Which is most plausible? Why?

Biology and Society Corner: Discussion Questions 1. The Cambrian explosion resulted in a diversification of animal species. Each spe-

cies developed into a more complex set of organisms as compared with those that came earlier. Does this make humans, last to evolve, the “highest” organisms in the evolutionary chain? Why or why not?

2. Some cnidarians, including jellyfish species, are notorious for their sting, inhabit- ing beach waters and washing onto the sand. Choose a pollution threat to cnidarians which has emerged in the past 25 years. Research the effects of the pollutant and make a recommendation on its benefits or drawbacks for your own health.

3. Almost all of the 15,000 species of nematodes cause animal diseases. If a pharma- ceutical company could eradicate all of these organisms, should we proceed to do it? Should you or your loved ones be concerned about the destruction of nematodes? Why or why not?

4. Amphibians are an indicator species, much like the moths in Chapter 7, first showing the effects of environmental changes due to their delicate nature. Many amphibian species are in decline in the United States and in Puerto Rico. The island of Puerto Rico provides a study unit to view amphibian dynamics. Research amphibian pop- ulation decline in Puerto Rico, and list three reasons for it. How may amphibian deaths have eventual impacts on human society?

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5. Our opening story in this chapter showed the importance of beavers in flood control and their effects on humans. Beavers are second only to humans in their effects on the environment around them. How did humans affect other Homo species as Homo sapiens emerged in Africa and as they explored other parts of the world?

Figure – Concept Map of Chapter 10 Big Ideas

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379

Unit 4 the Dynamic Animal Body

ChApter 11 Animal Organization

ChApter 12 Metabolism: Digestion and nutrition

ChApter 13 the heart–Lung Machine: Circulation and respiration

ChApter 14 regulation: nervous, Musculoskeletal, and endocrine Systems

ChApter 15 A War against the enemy – Skin’s Defenses and the immune Attack

ChApter 16 Urogenital Functions in Maintaining Continuity

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381

Animal Organization 11

Starfish

Many starfish wash up along the beach

A Starfish, parts of its cell

Micrographs of the four tissue types of a Starfish

Sabrina helps a starfish

She throws her starfish back into the ocean

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382 Unit 4: The Dynamic Animal Body

the Case of a Saved Star A college freshman, Sabrina walked along the beach in South Texas, at Padre Island. There were parties and excitement with college students abounding, running into the water and celebrating a coveted Spring Break. Everyone was having a good time, except Sabrina. She walked alone along the beach, much as she did in most of her life. She wondered why nobody noticed the thousands of starfish washed up on the shore from the last night’s storm surge. All of the starfish were dying on the shore, without seawater to nourish them.

Sabrina recalled the water chemistry lectures in class, which explained the need for a strict balance of ions in all living tissues. Her heart broke as she spied the drying out parts of each starfish, as they lay lifeless on the beach.

She saw their skin or epidermis, consisting of a thin cuticle made of epithelial or covering tissue cracking and dry. Bumps on the starfish, made mostly of calcium car- bonate, jutted out in the form of spines. This was the starfish endoskeleton, made of connective tissue resembling bone, which maintains its structure and connects different parts of the animal. Sabrina looked more closely at the mouth of the starfish, trying to help it back into the water. When she touched its tube feet, they retracted backward. She recalled from biology class that each of the tube feet is sensitive to touch, connected to a set of nervous tissue forming a nerve net beneath the epidermis of the starfish. Nerves fire and cause motion in the arms of the starfish and in its muscles to close its mouth. The movements of their tube feet stimulate muscles within starfish arms to contract and grasp onto objects. Sabrina noted the weakness of the starfish muscles as they dried. Its central mouth could not close and its arms were unable to respond normally. She felt compelled to change this wretched situation.

A panic came over Sabrina as she realized that the animals needed to be returned, as quickly as possible, back into the sea. So, she started throwing the dying creatures back, one by one, into the ocean. It was an arduous task in the hot sun and she knew that she could not save all of the starfish.

A few college classmates ran by and called out to her, inquiring – “What are you doing?” Sabrina responded that she was returning the starfish to their homes. She said, “They’ll die in the sand. Why don’t you come here and help me bring them back?” Many laughs came thereafter from her crowd of “friends,” with one of her worst critics

CheCk in

From reading this chapter, you will be able to:

• Explain how knowledge about proper functioning of body tissues plays an important role in human health.

• Describe methods of studying human structures, and define anatomy, physiology, gross anatomy, histology, cytology, and developmental anatomy.

• Explain complementarity by giving an example connecting a structure’s anatomy with its physiology. • Explain how homeostasis is maintained using negative and positive feedback mechanisms of control,

and define those terms. • List, describe, and compare the four types of human body tissues. • Locate different regions of the human torso using the language of anatomy, and organize and place

different body structures within their appropriate organ systems.

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Chapter 11: Animal Organization 383

exclaiming, “Why don’t you come swim with us or would you rather be with the star- fish? You know you can’t save them all . . . it’s hopeless.”

Sabrina saddened for just a moment. Then, she picked up a single starfish and held it up to her peers and said, as she threw it back into the ocean, “At least I made a difference for this one!” Sabrina’s classmates listened to her words and experienced a change of heart. One by one they joined her in returning the starfish to the ocean.

Adapted from The Starfish Story: http://www.ordinary people change the world.com/ articles/the-starfish-story.aspx

CheCk Up SeCtiOn

However, all animals including humans are composed of the same four types of tissues – epithelial, connective, nervous, and muscle – in its organization.

In the last chapter, the overview of animal diversity showed many different types of organisms. Like all human systems, the starfish body is organized to perform at its best within the right con-

ditions, with its four tissues working together. For example, the Starfish is structured to function with the right amount of water and temperature in its surroundings to prevent it from drying out.

Sabrina was inspirational in her attempts to save the life of the dying starfish. What societal checks do we have in place to maintain the proper balance and health of our tissues? Choose one lifestyle choice that disrupts this balance in society. Do you live your life to maintain the health of all of your tissues?

Orientation to the human Body This story describes the four tissue types that compose our internal structures. The com- plexity of our systems and their capacity to work together to enable life functions is the focus of this chapter. The desiccation or drying out of Starfish tissues creates an imbalance in life functions of the animal, the basis of disease. Disease occurs when an organism’s systems do not maintain balance while working together. Celiac disease, for example, impedes proper absorption of food for energy from foods consumed. In addition to describing the workings of the human organism, in the next chapters of this unit we will also consider some of the diseases associated within each organ system of the body.

So far, the text described many forms of living systems, from the elegant Stentor and fruiting bodies of slime molds to the giant redwoods and other ancient trees. However, it is a focus on human systems in this next unit that explains the many happenings within our bodies. A major goal of this text is to show how human biology and human society interact with other living systems.

In this unit, we will discuss the body systems separately, but in fact they interact with each other constantly to perform body functions efficiently and maintain a steady state. The relationship between different systems is shown in Figure 11.1. When one sys- tem fails to function properly, this affects the workings of other systems. For example, when a weak heart is unable to carry sufficient blood through the body, it also fails to push enough excess water out of the kidneys. As a result, swelling in the legs and abdo- men are common signs of a weakening heart. Water balance is vital for the survival of all organisms, as shown in Sabrina’s starfish’s plight with dehydration in the story. All of the body systems in humans work in concert to carry out multiple, simultaneous functions to keep organisms alive. Figure 11.1 shows the relationship of the urinary system (which maintains water balance) with other interdependent systems.

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The drying out of the starfish in our story is a great introduction to the study of the tissue types that make up the organ systems that carry out the life functions of the human body. Outside of the seawater, starfish tissues quickly experience breakdown and a loss of structure. Environmental conditions need to be just right for those tissues to maintain their structure. The study of the structure of body parts is known as anatomy. Anatomy describes what a structure, such as an organ or tissue, looks like. There are several sub- divisions of anatomy, depending upon the focus of study. Figure 11.2 illustrates that the branches of anatomy study life at different levels of its organization.

First, many medical techniques and surgeries work on structures visible to the naked eye, in what is termed gross anatomy. Gross anatomy refers to the study of body parts that can be seen without the use of microscopy. Some of these medical procedures include setting broken bones, treating skin wounds, or massaging muscles. Starfish tis- sues viewed by Sabrina in our story are also examples of gross anatomy.

Second, all study of structures too small to be seen with the naked eye is called microscopic anatomy.The use of a dissecting microscope or electron microscope includes study of cells and cell structures. The study of cell parts is called cytology, which researches cells and their organelles such as mitochondria and the nucleus. The study of tissues, or groups of cells performing the same overall functions is called histol- ogy. Histology studies groups of cells that are also too small to be seen casually without a microscope. Both cytology and histology are branches of microscopic anatomy.

Anatomy

The study of the structure of body parts.

Gross anatomy

The study of body parts that can be seen without use of microscopy.

Microscopic anatomy

The study of structures too small to be seen with the naked eye

Cytology

The study of cell parts.

Histology

The study of tissues.

Figure 11.1 The body’s systems are interdependent upon each other. Human diges- tion is accomplished only with the help of other organ systems. For example, without the heart, food from digestion would not be brought to needed parts of the body. Without the kidneys, wastes from food would build up, and be fatal. From Biological Perspectives, 3rd ed by BSCS.

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Figure 11.2 a. Hierarchy of body structure. Chemicals form cells, which form tissues that combine to form organs. Related organs form organ systems comprising a whole organism. b. Studying life’s changes. The different branches of anatomy studying life at different levels of its organization. Gross anatomy is the study of those parts able to be seen with the naked eye. In this figure, the orientation of the upper limb muscles is studied by gross anatomy.

Cellular level

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Organ system level

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The study of changes in structures of an organism since its birth is called develop- mental anatomy. All organisms grow and change throughout their lifetimes. Humans experience periods of growth and spurts in their development. These lead to their matu- rity into adulthood. Embryology, or the study of anatomy before birth, looks at structures of developing embryos and fetuses.

How an organism’s parts function and malfunction, as seen in the dehydration of tissues in the starfish case, is a focus of medical and other types of scientific study. The study of the function of body parts is called physiology, which looks at how an anatomi- cal structure works. The orientation of an elbow joint enables it to work in a certain way to bend and allow movement of the arm. A kidney cell’s unique structure enables it to conserve water. The long strands of nerve cells shown in Chapter 1 transmit electrical messages to allow thought; we also saw, how plaques interfere with such transmissions to cause Alzheimer’s disease. The starfish tissues began ceasing to function properly and weakened the organism in the dry, hot sand. All of these examples show how the anat- omy of a body part helps to determine its proper working or physiology.

An imbalance in the proper working of a tissue, organ, or organ system is known as disease. All of our bones are joined together at certain regions called joints. Joints allow bones to move and at the same time protect the structures within them. Many joints are moveable because they have other structures, such as ligaments, connecting them together. When a joint malfunctions, pain and swelling usually limit motion and sometimes result in immobility. An overstretching of one’s joints may result in damage to ligaments or other tissues surrounding the joint, requiring physical therapy and/or sur- gery as treatment. Damage to knees constitutes over 60% of joint injuries, particularly in young women active in sports. A healthy knee joint is shown in Figure 11.3. Note the multiple ligaments holding the bones in place.

Anatomy and physiology both study life at different stages. At the end of life, senes- cence, or the process of aging, accompanies the extension of adulthood into old age. Senescence is characterized by the loss of cell functions. Many age-related illnesses limit functionality in older people. In Chapter 1, aging of the brain led to our character Hans’ development of Alzheimer’s disease.

Complementarity The function (physiology) of any body part always depends upon its structure (anatomy). In other words, function always follows form. This is called complementarity because the anatomy of a structure complements the way that structure works. When complementar- ity fails to work properly, the result is disease or dysfunction. In our story, the Starfish’s tissues normally function to process nutrients and respond to stimuli. Its tissues are held intact by an endoskeleton and muscles. The dehydration of the support structure led to weakened muscle and a nonfunctioning mouth, both an imbalance in its processes.

If you consider almost any anatomical part, you will be able to see complementarity. For example, bones in humans and in Starfish endoskeletons are impregnated with min- eral deposits and strands of fibers that make them hard. Thus, in humans bones are able to function as protectors, with ribs surrounding delicate and thin lungs, and the flat ster- num (breast bone) covering the vital beating heart. In each case, a living, hardened bone supports the structures that it surrounds. In particular, bones meet within joints in animals to enable protection but also movement. Consider the knee joint in Figure 11.3, which consists of two bones joined together with ligaments and tendons acting as straps. Mus- cles strengthen the joint and movement is possible with this unique arrangement. Without this unique structure, both the goals of movement and protection would not be possible.

The anatomy of a structure also fits its physiology to meet chemical needs in the body. Consider fish gills, which are composed of very thin tissues, with filaments only

Developmental anatomy

The study of changes in structures of an organism since its birth.

Embryology

The study of anatomy before birth; looks at structures of developing embryos and fetuses

Physiology

The study of the function of body parts.

Disease

An imbalance in the proper working of a tissue, organ, or organ system.

Senescence

The process of aging.

Complementarity

The state in which the function of any body part always depends upon its structure.

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a few cell layers thick. The surface area of fish gills is large, reaching many square feet when dissected and spread out evenly. The thin construction of gills allows gas exchange across the moist membranes. In addition, blood moving through the gills flows in the opposite direction as the water current. This countercurrent exchange, as it is called, maximizes the rate of exchange between fish gills and the gases in the water.

Diffusion of gases, as discussed in Chapter 3, occurs only across short distances and through thin tissues. Oxygen gas is needed for proper cell functions, and carbon dioxide gas is a waste product. Both are transported into and out of the human body through the lungs. Gases must be continually exchanged in the lungs to enable cell respiration and energy uptake by cells, as described in Chapter 4. After all, a cell can only live a maximum of 4 minutes without oxygen before it dies! An imbalance in lung physiology occurs in the presence of pulmonary diseases such as asthma, emphysema, and lung cancer. In these diseases, the membranes for gas exchange no longer operate efficiently, preventing sufficient gas exchange. Breathing diseases will be discussed in greater detail in other chapters.

Studying how body parts work and their related diseases requires clinical analysis. Generally, medical practitioners first use observation and descriptions of symptoms to diagnose illness. They might observe a wound that does not heal and take pictures, mea- suring its progression. Physical manipulation is also used to either help treat symptoms or to diagnose the cause of a disease or injury. For example, when a joint is dislocated, often the best treatment is to place the bones back into their proper position.

Observation

The act of obtaining information from a primary source.

Manipulation

Manual movement of anatomical parts to either help treat symptoms or diagnose the cause of a disease or injury.

Figure 11.3 The human knee is the body’s largest and most complex joint. It is easy to damage and resembles two matchsticks stuck together with many ligaments and tendons. The muscle around it helps to add strength.

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Palpation, or feeling structures with one’s hands, is important in determining diag- nosis. In Sabrina’s case, it was clear upon palpation that the muscle tissues of the Star- fish were weakening. However, palpation in humans and animals requires experience to detect abnormalities. For example, when a lump or swelling in the testicles is found, it is indicative of testicular cancer, a disease affecting mostly young men between ages 17 and 34 years. Palpation of the lump requires professional analysis for a clear diagnosis. Auscultation, listening using a stethoscope, gives indications about heart health. Mur- murs or turbulent blood flow sounds are detected using this procedure, often indicating a valve leak in the heart.

Some tests, such as blood tests and medical images, indirectly give data on a per- son’s health. There are several types of medical imaging (see Figure 11.4). X-rays visu- alize dense structures within the body. The X-rays that are absorbed appear lighter and show a thicker structures such as a tumor. Bones are imaged well using X-ray imaging. In order to visualize softer tissues, other techniques were developed in the past half century. CT (or computerized axial tomography) scans use multiple sections of X-rays to image body regions. This method eliminated the need for many exploratory surger- ies and led to a three-dimensional view of internal structures. However, CT scans have been recently associated with increased risks for developing cancer due to their use of a large amount of radiation. Even one CT scan increases the risk of getting cancer by 400 times. MRI (or magnetic resonance imaging) maps the body part’s hydrogen atoms within water of soft tissues. The magnetic spin of hydrogen within water creates waves and an image to study. This is a generally harmless test that studies soft tissues and provides a three-dimensional image. Ultrasound technology, developed during World War II, emits high-frequency sound waves and creates images based on the echo received back from the body part. Ultrasound technology explores surface anatomy of parts within the body. It may look at the surface of internal abdominal organs or the structure of a developing fetus. Ultrasound has a low penetration of its sound waves into body structures, prevent- ing it from showing deeper images.

homeostasis is Vital for Carrying Out Life Functions As discussed in Chapter 1, maintaining a steady set of environmental conditions is known as homeostasis. Body temperature, acid–base levels, and chemical concentrations in living systems must be in balance to keep organisms functioning properly. Internal con- ditions often vary within narrow limits; they do not exist in a fixed state but fluctuate

Palpation

The act of feeling with one’s hand.

Auscultation

Listening to sounds produced within the body.

X-rays

A form of EM radiation that visualizes dense structures within the body

CT scan

Computerized axial tomography that produces detailed images of internal organs.

MRI

A technique that uses radio waves and magnetic field to generate detailed images of tissues and organs.

Ultrasound

A technique that emits high frequency sound waves and creates images based on the echo received back from the body part.

Figure 11.4 Images enable doctors to see inside regions without using exploratory surgery. a. MRI. b. Ultrasound. c. X-ray.

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Maintaining a steady set of environmental conditions.

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within a range of values. Body temperature is generally considered normal in humans at 98.6°F, but this value represents an average. Many people exhibit temperatures that are normally above or below this value. Some people run “hot,” at 99.1°F and there is no disease pattern associated with their higher than normal temperature. Of course, when temperatures rise too high within an organism, chemicals such as enzymes do not work optimally or fail to function. Homeostatic processes keep conditions within a range that is acceptable for proper functioning.

As seen in our story, sometimes the ordered structure experiences failure, creating an imbalance in proper functioning. A failure to maintain homeostasis is commonly called disease. In our Starfish example in the opening story, homeostasis was disrupted by a change of environment from seawater to dry land. This led to drying out of tissues and changes in the water chemistry of the muscle tissue, weakening it. Usually homeo- stasis is maintained, in part by regulating the water chemistry of tissues in organisms.

The general components of a system that maintains homeostasis are shown in Figure 11.5. The system first receives information either from internal cues or from the external world. These cues are the stimulus, which is detected by a receptor, a special protein that monitors the environment. Receptors send messages, based on their stimulation, to a control center (in humans this is usually the brain) to cause or affect a response accord- ing to some set point value at which the organism should be maintained. The response is carried out by an effector, which is often a muscle that moves or a gland that sends out chemicals to carry out the response.

negative Feedback Homeostasis is most often maintained in living systems by negative feedback mechanisms. During negative feedback, the response counters the effects of the original stimulus. For example, if body temperature rises above 98.6°F, receptors detect and send messages to the skin to sweat and lose heat and to blood vessels in the skin to expand or vasodilate to bring blood closer to skin surfaces and lose further heat. The opposite effect occurs when body temperature decreases, with messages directing the skin to sweat less and shiver to create heat and the capillaries to vasoconstrict (or narrow) to lessen blood flow (and thus lose heat) from the skin’s surface. Negative feedback elicits an effect opposite that of the original stimulus. In the case of body temperature, the set point is maintained when tem- perature changes are detected. The mechanisms of controlling body temperature through negative feedback are important for every day health (Figure 11.6).

Stimulus

Something that causes an organ or cell to react.

Receptor

A special protein that monitors or received information from the environment.

Control center

An operational center for a group of related activities.

Set point

The normal value at which a variable physiological state stabilizes.

Effector

A muscle that moves or a gland that sends out chemicals to carry out the response.

Negative feedback

A key mechanism that regulates the physiological functions in living organisms.

Vasodilate

Widening of blood vessels.

Vasoconstrict

Narrowing of blood vessels.

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Receptor

Effector

Figure 11.5 General components of a homeostasis system. This diagram represents a negative feedback system.

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Another example of negative feedback is the regulation of chemical levels within living organisms. In humans, blood sugar (or glucose) must be maintained around a set point of 90 mg/mL of blood (see Figure 11.7). When blood sugar levels increase, after eating a sugary food such as a donut, the hormone insulin is released from the pancreas. Insulin causes body cells to uptake glucose from the blood to be used by cells. This action decreases glucose levels in the blood. When sugar levels decline, as occurs in between meals, the pancreas produces the hormone glucagon, which causes the liver to convert stored glycogen into glucose, sent into the blood and thus available for cells to use. This prevents the damaging effects of low sugar levels in blood.

The set point of 90 mg/mL of blood glucose varies within a range of roughly 30 units. Many homeostasis mechanisms allow some flexibility around their set points, but often there is a point at which damage occurs. Movement beyond the sugar range in humans may lead to damage of body structures. Diabetes results from an inability to control blood sugar levels.

Negative feedback returns organisms to their optimal points of functioning. Sabri- na’s Starfish would not properly function within land conditions for very long. Thus, it is expected that it would eventually reset its water chemistry balance once returned to the ocean environment.

Disruptions in negative feedback, preventing returns to normal set points in the body, lead to disease. Disease and its treatments will be a focus of each chapter within this unit. For example, during senescence, a loss of functioning and of proper negative feedback mechanisms is common. One in eight seniors reports mental deterioration at some point in their life due to an improperly functioning feedback mechanism. In the aging process, physiological declines are expected, but the goal of biology and medical science is to find treatments to help people.

positive Feedback In order to maintain proper functioning of an organism, at times an original stimu- lus must be exaggerated. When a response enhances the original stimulus, it is called positive feedback. These events are uncommon in everyday functioning, but examples include unusual events such as blood clotting and childbirth.

Insulin

A hormone released from the pancreas, which causes body cells to uptake glucose from the blood to be used by cells.

Glucagon

A hormone produced by pancreas, which causes the liver to convert stored glycogen into glucose, sent into the blood and thus available for cells to use.

Positive feedback

A key regulatory mechanism that enhances the original stimulus.

Figure 11.6 A negative feedback system. Body temperature is one of the internal systems that is maintained within a narrow range via a negative feedback system.

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During blood clotting, special fragments of cells, called platelets, recognize a break in a blood-vessel wall. When platelets attach to the broken region, they release clotting proteins within them. This causes a clot to start forming to prevent blood loss. Platelets release chemicals that attract more platelets to the site of blood vessel breakage. The original stimulus (the start of the clot by platelets) is enhanced by chemicals released from platelets. The exaggeration of the original stimulus is necessary to get the job done – to form a clot big enough to patch the hole in the blood vessel – before ending the positive feedback mechanism. This process is depicted in Figure 11.8.

Another example of positive feedback occurs during labor contractions. During labor contractions, an odd stimulus for the body – a newly formed baby – elicits a drive to return the body back to normal. Normalcy in this case is a body without a baby inside its uterus. Thus, the goal of positive feedback during labor contractions is to give birth to the baby.

When the baby’s head hits receptors on the cervix, which detect pressure, nerve messages are sent to the mother’s brain to cause the release of the hormone oxytocin. Oxytocin enhances the stimulation of muscle contraction in the uterus, which further pushes on the baby. Oxytocin therefore causes more pressure on cervical receptors, stimulating more messages sent to the brain to release more oxytocin. It is a self-feeding system, in which more and more contractions stimulate more and more production of

Platelets

Special fragments of cells that recognize a break in a blood vessel wall during clotting of blood.

Oxytocin

A hormone released by the pituitary gland that enhances the stimulation of muscle contraction in the uterus.

Figure 11.7 Blood sugar regulation. Insulin and glucagon restore sugar levels in the blood via a negative feedback system. From Biological Perspectives, 3rd ed by BSCS.

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Figure 11.8 Positive feedback: blood clotting within vessels is initiated and enhanced by platelets via a positive feedback system. David Phillips/ Visuals Unlimited; Basics about the Body’s Organization.

PROSTAGlANDINS AND PAIN RElIEF: “YOU lEFT ME, jUST wHEN I NEEDED YOU MOST…”

Prostaglandins have long been recognized as the hormones that increase pain perception. They have several functions, ranging from causing increased pain and enhancing uterine contractions during childbirth to causing menstrual cramps; they also play an important role in immunity and inflammation. During pregnancy, prostaglandins decrease, inhibiting pain and uterine contractions in the expecting mother. This is necessary because contractions would end a pregnancy. However, just at a time when an expecting mother could use pain relief, her prostaglandin levels shoot up during labor. These increase the force and frequency of labor contractions. However, pain is felt ever more acutely during this time because prostaglandins enhance sensations of pain. The concomitant benefit to increased prostaglandins during childbirth is that a mother, who feels great pain, is more likely to push her baby out than if there were little pain. Of course, this is cold comfort for the expecting mother who has enjoyed diminished pain throughout her pregnancy, with reduced levels of prostaglandins. The pain relief left her, just when she needed it most; but it is evolutionarily beneficial because the end result is a more likely successful child- birth. The processes of childbirth are shown in Figure 11.9.

Prostaglandins and pain have a continual association in our bodies at all times. Aspirin is used because it inhibits the effects of prostaglandins in the body, decreasing perceptions of pain. The Nobel Prize in Physiology or Med- icine for 1982 was awarded to Bengt Samuelsson and Sune Bergstroem of Sweden and John Vane of England for their efforts in clarifying the role of pros- taglandins in the human body.

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the hormone oxytocin that causes the contractions. As shown in Figure 11.9, oxytocin, alongside other factors, brings child birth to fruition. This feedback loop continues until child birth, which is the end result of the positive feedback mechanism. Giving birth returns the female’s body to its normal state, one without a developing fetus.

Systems of homeostasis: interplay between endocrine and nervous Controls In each of the examples given in this section, homeostasis is maintained by two systems: 1) the endocrine system, which produces internal chemicals called hormones that cause a response in another organ or tissue; and 2) the nervous system, which transmits mes- sages from one part of the body to another. Hormones such as insulin, glucagon, and oxytocin are made by glands and are only a small subset of chemicals that regulate an organism’s life processes. Nerves form a network of cells throughout the bodies of most animals to rapidly communicate between different parts. While nerve messaging is rapid and almost instant, as can be observed when we touch a hot iron, endocrine responses require slower mechanisms of transport. Figure 11.10 shows the glands of the endocrine system and the branches and cells of the nervous system.

Hormones require diffusion to move in between cells of the body. They may take minutes or hours to work, unlike the milliseconds taken by ionic signals of the nervous system. Together, however, the endocrine and nervous systems work efficiently to main- tain homeostasis in organisms. These two systems will be discussed in greater detail in other chapters.

Discovery of homeostasis In Chapter 1, Charles Darwin was shown to be influenced by capitalism, which led to the development of his ideas about evolution. As a close parallel, Sir Walter Bradford Cannon (1871–1945), the first discoverer of homeostasis, developed his views in part based on his attraction to communist economic theory. Communism is defined as the economic model in which there is no individual ownership and land, property, and so

Endocrine system

Glands and parts of glands that produce internal chemicals called hormones that cause a response in another organ or tissue.

Nervous system

Network of nerve cells that transmits messages from one part of the body to another.

Figure 11.9 Child birth process: during labor, uterine contractions are stimulated by prostaglandins and oxytocin, both hormones that enhance contractions. It is an example of positive feedback. From Biological Perspectives, 3rd ed by BSCS.

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Figure 11.10 Hormonal and nerve systems interacting. Both systems communicate with the body’s organs, tissues, and cells to integrate different systems. Hormones diffuse through the bloodstream to effect changes in body cells. Nerves send messages to all parts of the organisms. From Biological Perspectives, 3rd ed by BSCS.

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on are held collectively. The government controls the means of production in a state or nation that is purely communist. In short, there is a central controller in communism as well as in homeostasis.

Communism is the opposite of capitalism, which led to the development of evolu- tionary thought. In capitalism, as you recall, individuals own the means of production and the fittest businesses survive. In communism, governmental control of the econ- omy maintains a steady state in economic happenings. For instance, during the great depression, communist Russia was effectually immune from the economic downturn. While the communist government controlled which jobs people had, how they would be educated, their access to goods and services, capitalist countries allowed individuals the freedom to fail when the economy languished.

Cannon saw the benefits of communism while he watched his friends and family fail in business. He saw a benefit in communism as a way to stabilize the economy, through redistributing wealth and giving all citizens a small but stable portion.

Cannon was a Harvard physiologist and World War I medical doctor. While work- ing on soldiers with injuries incurred during World War I, Cannon noticed that damage to nervous tissue in the brain or hormonal organs such as the pancreas could create major disruptions and death in his patients. Similarly, he noticed that removal of certain organs, such as the hypothalamus of the brain or the pancreas, resulted in an imbalance in homeostasis or disease. He determined that certain regions of the body of his patients were under a centralized control system. Making an analogy with the centralization of banks and centralized control of jobs and trade in communist economic theory, he hypothesized that the brain served much like the central government in communism, regulating many processes in the human body. He also determined that the nervous and endocrine systems were the two major conduits through which human homeostasis occur. The link between his social and economic leanings in developing Cannon’s ideas on homeostasis is clear. Our purpose in relating the development of Cannon’s hypothesis about the existence of a control system like homeostasis to his affinity for a particular economic view is not to debate the efficacy of true capitalism, true communism, or its hybrids, but it is to denote the importance of one’s upbringing and one’s society in influencing scientific thinking. Evolution and homeostasis are just a couple of examples of how society influences the direction of biological thought and of much scientific advancement.

the Major types of tissues As discussed in Chapter 1, groups of cells performing similar functions and with similar structures are called tissues. There are four types of tissues in animal systems: muscle, epithelial, nervous, and connective. (This can be remembered by an acronym using the first letter of each tissue: MENC). Each tissue has a general function:

1) Muscle tissue is composed of cells that are able to contract. Muscles either move materials (as in digestion) or bones and body parts (as in walking or breathing) in a variety of directions via their contractions. Heart, skeletal muscles, and organ muscle such as the stomach contain muscle tissue.

2) Epithelial tissue is made of cells that either covers other tissues or cells that pro- duce hormones or other materials for export. The most obvious epithelial tissue is skin, a surface tissue, but epithelial tissue is found in many regions of the body to cover and support areas. In addition to skin, glands such as sweat glands and salivary glands, and linings of the throat, lungs, blood vessels, and digestive tract are composed of epithelial tissue.

Muscle tissue

A type of tissue that is composed of cells that are able to contract.

Epithelial tissue

Tissue made of cells that either covers other tissues or cells that produce hormones or other materials for export.

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3) Nervous tissue is an excitable tissue, specialized to send, store, and receive ionic impulses much in a way that electricity moves along copper wires. The brain and spinal cord are composed primarily of nervous tissue.

4) Connective tissue binds and supports different parts of the animal body. It is sometimes referred to as the misfit group of tissue because so many varied types of tissues belong to it. Blood, bone, ligaments, tendons, fat, and cartilage all belong to the connective tissue grouping.

Histology studies each of the four types of tissues as well as a large number of different, specialized subgroups. Subgroups of tissues are structured in unique ways to help them to carry out their specified functions. The form of cells within each tissue type directs its functions, as expected in complementarity. For example, a group of fat cells have large storage vacuoles specialized to store fat. This enables the primary function of fat storage and insulation. The anatomy of a tissue always fits with its physiology.

There are blood vessels (connective tissue) permeating all of the Starfish tissue, enabling nutrients to arrive at cells. The digestive muscle bands (muscle tissue) through their arms propel Starfish. Along their entire digestive canal, absorption cell layers line the tract (epithelial tissue), which bring nutrients into the body. Nerves (nervous tissue) transect all of the other tissues to direct their activities, in part controlling the rate of processing of waste materials. Sabrina’s Starfish case uniquely illustrates how internal tissues can be exposed for observation as they die away. Luckily, the return of the Star- fish’s four tissues into the ocean water usually results in continued, normal functioning. The four tissue types are shown in the Starfish anatomy in Figure 11.11.

epithelial Sweating, absorbing nutrients, walking on a hot floor, or making oils are all, in part, due to the functions of epithelial tissue. Epithelial tissue looks like sheets of cells arranged in different patterns. All epithelial tissues have a free side called the apical surface. Cells are anchored on their other side onto a basement membrane. Connective tissue, which nourishes epithelial cells, is always found on the other side of the basement membrane. The structure of epithelial cells is shown in Figure 11.12.

Note that epithelial cells are avascular, meaning that they do not contain blood vessels of their own to nourish them. Blood vessels within connective tissue provide nutrients and remove wastes for epithelial cells.

The system for naming epithelial tissue is based on two factors: number of layers of cells and the shape of the cell. When epithelial tissue is only one cell layer in thickness, it is called simple. When epithelial tissue is two or more layers thick, it is called stratified. Epithelial tissue has two names: its first name gives the number of layers the tissue has, simple or stratified; its second name indicates the shape of the epithelial cells, usually the shape of those cells nearest to the apical layer. The three shapes of cells are squa- mous, or flattened and squashed in appearance; cuboidal, or square, cube-like in shape; and columnar, or shaped like a brick, column-like. The epithelial cell shapes are shown in Figure 11.13. Epithelial cells found along the surface of Sabrina’s starfish’s skin, sim- ple columnar in classification, protected the animal.

Each of these cell shapes is tightly held together and serves three functions: 1) to cover other tissues, organs, and systems, 2) to transport materials, and 3) to secrete products.

1) Protection: In their role of covering other structures, epithelial tissue serves as an important first line of defense in protection. Tight junctions and desmosomes hold epithelial cells closely, preventing leakage and penetration by enemies such

Nervous tissue

An excitable tissue specialized to send, store, and receive ionic impulses

Connective tissue

Tissue that binds and supports different parts of the body.

Apical surface

The free side of all epithelial tissues.

Basement membrane

A thin extracellular membrane underlying the epithelium of many organs.

Stratified

An epithelial tissue that is two or more layers thick.

Simple

An epithelial tissue that is only one cell layer in thickness.

Squamous

Flat-shaped cells.

Cuboidal

Composed of cubical elements.

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Suction cup-like structures (Tube foot)

Ring canal

Radial canal

Lateral canal Bulb-like structure (Ampulla)

Water in (Madreporite)

(a)

(b)

Figure 11.11 a. The body plan of a starfish. The four tissue types found within all animals including mus- cles and nerves in the arms of the starfish, the epidermal covering the skin and its underlying exoskeleton functioning as the support structures, made of connective tissue. b. The four type of tissues (micrographs).

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as viruses and bacteria. In the skin, for example, multiple layers of cells prevent entrance by many microbes that inhabit our skin’s surface. Internally, the stom- ach compartment has a very low pH, with acidic contents that would destroy stomach cells. Epithelial cells line the stomach to prevent such a breach from causing damage, such as ulcers.

2) Transport: Transport within the body works through epithelial cells acting as a gatekeeper to allow certain materials through its layers and not others. For exam- ple, in the kidneys, epithelial cells regulate in which molecules are eliminated

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Figure 11.12 General structure of epithelial tissue: apical surface, basement mem- brane, stratified layers, connective tissue is on the other side of the basement mem- brane of epithelial tissue. Adapted from Anatomy I and Physiology Lecture Manual by John Erickson and c. Michael French.

Figure 11.13 Examples of a. transport (air sac of lung) through the squamous shape; b. secretion (tubules of glands) from the cuboidal shape, and c. absorption (digestive tract) by the columnar shape.

Apical Layer

Basement Membrane

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as urine and which are reabsorbed into the bloodstream for use. Often based on size and shape of the molecule, epithelial cells filter out materials flowing through the blood.

3) Secretion: Glands are specialized groups of epithelial cells that secrete sub- stances either out of the body or into body compartments. Materials that are secreted include hormones, saliva and sweat, milk, mucus, and earwax.

Simple Epithelial Tissues

A number of simple epithelial types of tissues are found throughout the body. All of the simple forms are used for transport because the single layer of cells is useful as a screen to filter and absorb materials selectively. Multiple layers of stratified tissues would pre- vent the ease of transport afforded by a simple design. Would a thick tissue with many layers make sense surrounding an air sac? No. Simple squamous epithelial tissue, for example, is found in areas in which exchange of materials occurs. In air sacs of the lungs, where oxygen and carbon dioxide are rapidly moved through a thin membrane, a simple layer of epithelial cells facilitates gas exchange. Nutrients and wastes are moved between blood and the atmosphere via capillaries. When thickened, as in emphysema cases, transfer of gases is impeded and diseased lungs have poor oxygen exchange. Sim- ple squamous epithelial tissue is also found in capillary walls, as it is thin enough to allow exchange of nutrients and wastes.

In another example, within the digestive system simple columnar epithelial tissue also acts as a filter to absorb smaller, digested products. Simple columnar cells are larger than squamous cells and thus involved in larger scale absorption processes. Large amounts of nutrients are needed for larger animals to survive and columnar cells are able to accomplish this.

Stratified Epithelial Tissue

Owing to multiple layers of stratified cells, some tissues are best suited for protection. With many layers, damage to one or even several cell layers does not compromise the integrity of the tissue. Tissues and organs beneath stratified epithelial cells are well pro- tected. To illustrate, skin is composed of stratified squamous epithelial tissue, number- ing more than 100 layers in thickness in some areas, such as the soles of feet. Multiple layers of flattened cells protect the blood vessels, nerves, and bones that lie beneath and within the skin. Their layers form from a deeper, lower layer, called the basal layer. The basal layer of cells lies on a basement membrane that anchors it. The basal cell layer is usually cuboidal or columnar in shape and is mitotic. Stratified squamous epithelial tissues are also found in linings of the esophagus, mouth, and vagina.

Some stratified epithelial tissue forms glands. Glands are collections of epithelial cells that secrete a product such as hormones. When glands are active, their products are made in greater amounts. There are two types of glands: endocrine glands, such as the adrenal glands atop the kidneys and the pineal gland in the brain, which have no ducts into the bloodstream and produce hormones; and exocrine glands, which have ducts emptying their contents into the bloodstream, such as saliva, milk, mucus, and sweat. Exocrine glands serve in many parts of the body, such as the salivary glands to lubricate and provide nourishment.

Some stratified tissues form specialized structures. Transitional epithelium, for example, is used in areas of the body that require stretching such as the bladder, which holds urine. Its form fits its function. Transitional epithelial tissue looks at times cuboi- dal and at other times squamous in shape. When the bladder fills with urine, its cells

Basal layer

The lowest layer of epithelial layers.

Glands

Collections of epithelial cells that secrete a product such as hormones.

Transitional epithelium

A type of tissue that consists of multiple layers of epithelial cells, which looks at times cuboidal and at other times squamous in shape.

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flatten and become squamous in shape. This shape change allows the bladder to be flexible and distend when urine enters it. Cells that accommodate fluid changes, such as transitional epithelial, are well suited for the urinary system in humans.

Connective tissue: An Overview Connective tissue is the most abundant type of tissue in most animals. There are many types of connective tissue; these different types hold together and support many parts of the body. Connective tissue supports many functions of movement, such as walking; oxygen is transported by blood and used by muscles during walking; cartilage covers the ends of long bones to cushion them as the leg muscles move them; ligaments and tendons, also connective tissues connect bones and muscles together to allow the joint to move during running.

Construction of connective tissues uses the same general plan used for all connec- tive tissue types, with its general structure given in Figure 11.14. An extracellular matrix made of noncell substances (polysaccharides and proteins) is found in every connective tissue type. The extracellular matrix may be solid (bone), semi-solid (cartilage), or liquid (blood plasma). Within the extracellular matrix, cells are found suspended such as: mature cells of the tissue, defense cells, or macrophages, and fibroblasts, which build new tissue. Connective tissue cells produce the extracellular matrix. Holding the cells together within its matrix, fibers (collagen, reticular, elastic) are embedded in connective tissue, giving

Extracellular matrix

Is a collection of proteins and carbohydrates found in every connective tissue type.

Fibers

Threadlike structure embedded in connective tissue, giving strength and support.

Figure 11.14 Connective tissue structure. The fibers and ground substance of the extracellular matrix are infused with cells of many types.

Blood vesselAdipocyte (fat cell)

Mesenchymal cell

Elastic fibers Collagen fibers

Fibroblast

Reticular fibers Collagen fibers

Macrophage

Protein fibers (collagen)

Extracellular matrix

Ground substance

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strength and support. Fibers are nonliving and provide a site onto which cells may anchor. The fiber types each have a unique function: collagen or white fibers add strength, elastic fibers allow pulling on the tissues and reticular fibers join tissues together, also adding strength. As you may deduce, elastic fibers are found in tissues that need to withstand a great deal of tension or pull, such as in the ear or along some blood vessels. Collagen fibers are found in tissues that need added strength, such as bones and tendons. The construction of connective tissues in terms of cells and fibers determines their unique functions.

Types of Connective Tissue

We will look first at Connective tissue proper (CTP), a set of tissue types that act as package materials in the body. CTP may be loosely or densely packed, with varying types shown in Figure 11.15. All connective tissues emerge from embryonic connective tissues, called mesenchyme.

The first type of loosely held connective tissue is areolar connective tissue, which cushions organs and other tissues. Areolar tissue mirrors the function of packaging pea- nuts in shipped boxes. When humans move in one direction, organs often slide past each other in the other directions and are cushioned by areolar tissue to prevent damage. The second loose CTP type is reticular connective tissue, which traps foreign invaders such

CTP (connective tissue proper)

A set of tissue types that act as package materials in the body.

Areolar

packaging type tissue.

Mesenchyme

Embryonic connective tissue that gives rise to all the connective tissues.

Reticular

A connective tissue that traps foreign invaders such as bacteria.

Figure 11.15 Types of connective tissues: each connects, supports, and anchors materials within the body.

Bone Cells in Lacunae

(a) Diagram: Bone

Cartilage Cell

Lacunae

(b) Diagram: Hyaline Cartilage

Chondro- cytes in lacunae

Collagen fibers

Nuclei of fibroblasts

Collagen fibers

(d) Diagram: Dense Regular

Areolar tissue

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as bacteria. Reticular connective tissue appears as a spider’s web, with large amounts of reticular fibers strewn about. Reticular tissue is found in the lymphatic system, such as lymph nodes and the spleen, which function in immunity. Adipose tissue is also able to store energy in the form of fat, stored in adipose tissue. Adipose tissue cells contain very large fat vacuoles, sometimes comprising over 90% of the space in adipose tissue cells.

Dense CTP often contains fibers that give strength and flexibility to its tissues. Dense regular connective tissue is tightly packed CTP that is composed mostly of col- lagen fibers. These tissues include tendons, which anchor muscles to bones, and liga- ments, which anchor bones to bones. Dense regular connective tissue has a high amount of tensile (pulling) strength. Alternatively, dense irregular connective tissues are com- posed of irregularly arranged fibers; because they crisscross in varied directions, these tissues are also able to withstand pulling forces from many directions. Dense irregular tissues are found in the dermis (lower part) of skin or in capsules of joints to allow pull- ing and movement along several planes. The skin, for example, is able to be pulled from several directions.

The second type of connective tissue, called special connective tissue, is unique because it can have either a rigid or a liquid extracellular matrix. Blood and bone are the most familiar type of connective tissue. Blood connects different parts of the body by providing nourishment and removing wastes in all parts of the body. However, the matrices of blood and bone are very different from each other. Blood is formed within

Adipose

A body tissue used for fat storage.

Dense regular

Connective tissue composed mostly of collagen fibers.

ligament

Band of tissue that anchor bones to bones.

Tendon

Strong fibrous tissue that anchors muscles to bones.

Dense irregular

Connective tissue composed of irregularly arranged fibers.

Special connective tissue

A unique connective tissue that has either a rigid or a liquid extracellular matrix.

Blood

A red fluid that connects different parts of the body by providing nourishment and removing wastes.

(g) Diagram: Reticular

Red blood cell

Spleen

Wandering cells

Reticular fibers

Fibers of matric

(e) Diagram: Areolar Tissue

Nuclei of fibroblasts

Mucosa epithelium

(f) Diagram: Adipose

Vacuole containing fat droplet

Nuclei of fat cells

(h) Diagram: Blood

Red Blood Cells

White Blood Cells

Blood Cells in Capillary

Figure 11.15 (continued)

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the bones in marrow cavities, but has a liquid matrix. Its cells, such as red blood cells, travel in vessels and along with dissolved proteins within a watery matrix.

Bone has a solid form, with calcium salts embedded within fibers of its extracellular matrix. Bones connect together and form our skeletal system. The cellular arrangement of bone serves as support and protection for other body parts, with concentric rings or pillars of calcium salts. Bone forms a hard substance and is able to withstand tremen- dous compressive (pushing) and even tensile pressures. In fact, bone has the same tensile strength as steel of the same size and shape.

Cartilage is a dense connective tissue that provides cushioning support in verte- brates. It is a flexible, hard gel that is less hard than bone (a solid) but harder than tendon (a softer strap-like tissue). Cartilage is strong but has enough softness to act as a cushion between bones and joints; it also provides support in ears, noses, and fetal skeletons. In some organisms, such as the shark, it forms the entire skeletal structure.

While there are three types of cartilage, all forms have the same general structure. Cartilage is made of large amounts of collagen and elastin fibers along with proteins embedded in between the fibers. Each cell within cartilage is called a chondrocyte and is found inside a lacuna “lagoon” in which the chondrocyte sits.

Hyaline cartilage is composed of large amounts of collagen fibers, giving it strength. Hyaline cartilage is found in the nose, embryonic skeleton, trachea, and larynx (voice box), and forms the ends of long bones. It serves to cushion the ends of bones and enable joints to move without damaging associated bones.

Elastic cartilage is composed of large amounts of elastic fibers, which is able to withstand pulling forces. If you ever pull your ear, it works well to resist the force placed upon it. Elastic cartilage is found in the external ear and the epiglottis, which covers our windpipes. Elastic cartilage is poor in resisting compression. Place your ear in between your thumb and a finger and push it together. It folds quickly, without much resistance. Elastic fibers are very weak in maintaining shape against compressive forces. It has an extracellular matrix that contains randomly scattered elastic fibers surrounding its lacuna.

Fibrocartilage contains elastic and collagen fibers in its extracellular matrix. It is found in between the vertebrae of the backbones and in the pubic symphysis, which is a tuft of material that connects the hip bones. Fibrocartilage is able to resist both ten- sile and compressive forces effectively. For example, while our backbone cushions the forces placed upon it while walking or running, it is flexible enough to allow bending and stretching. It has an extracellular matrix with relatively parallel fibers surrounding its lacuna.

Muscle Muscles function to move things – bones, ligaments, tendons, internal materials within the intestines. Muscles contract when nerves stimulate them. Muscles have long, strap- like fibers, which work together to hold onto the body parts, particularly bones, that they move.

There are three types of muscle tissues (see Figure 11.16):

1) Skeletal muscle, which is long, and contains alternating patterns of proteins called striations, or stripes. Skeletal muscles are under voluntary control; thought is required to move them. They are found attached to bones of the skeleton and move the bones. Some skeletal muscles move no bones, such as the tongue. However, their purpose is to provide movement of the skeleton. Sabrina’s star- fish’s arms and mouth are composed of skeletal muscle. It is therefore under voluntary control, allowing conscious regulation of the rate of movement.

Bone

Is the substance that has a solid form, with calcium salts embedded within fibers of its extracellular matrix.

Cartilage

A dense connective tissue that provides cushioning support in vertebrates.

lacuna

An open space containing a chondrocyte in cartilage.

Chondrocyte

A cell within cartilage.

Elastic cartilage

A type of cartilage that is composed of large amounts of elastin fiber, which is able withstand pulling forces.

Hyaline cartilage

A type of cartilage that is composed of large amounts of collagen fibers, giving it strength.

Skeletal muscle

Long muscles that are found attached to bones of the skeleton and move the bones.

Striations

Alternating patterns of proteins in the skeletal muscle.

Fibrocartilage

Cartilage that contains elastic and collagen fibers in its extracellular matrix.

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2) Cardiac muscle is found only in the heart and beats spontaneously to pump blood throughout the body. Cardiac muscle is striated and involuntary, meaning that one does not need to think about this muscle to contract it. Cardiac mus- cles’ cells are long and contain many branches. To add strength to withstand the pumping pressures placed upon them during heart beats, cardiac muscles have intercalated discs. Intercalated discs are specialized desmosomes that bind car- diac cells together.

3) Smooth muscle is not striated and is involuntary. Its cells are spindly in shape and are found on or within organs, such as the stomach or small intestines. They provide support and propel movement of food through the organs in which they are found. Smooth muscles are weaker than cardiac and skeletal muscles, lacking striations and support, but they function well in organs. Muscles along the diges- tive tract of Sabrina’s Starfish are composed of smooth muscle. It is thus not con- trolled consciously and involuntarily holds in wastes as well as digestive tissues.

nervous Nerve cells, or neurons, are special cells that store and transmit information in animals. They are found in the brain and spinal cord of vertebrates. Neurons are composed of a cell body that contains the machinery of the cell, with organelles and a nucleus that

Cardiac muscle

The muscle found only in the heart and beats spontaneously to pump blood throughout the body.

Smooth muscle

Muscle tissue that provides support and propels movement of food through the organs in which it is found Neuron

Are special cells that store and transmit information in animals.

Cell body

The central part of the neuron that contains the machinery of the cell, with organelles and a nucleus that directs nerve functions.

Striations

Nuclei

(a) (b)

(c)

Figure 11.16 Three types of muscle tissue. a. Skeletal muscle is found on the bones. b. Cardiac muscle is found in the heart. c. Smooth muscle is found in the organs.

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directs nerve functions. Two types of projections emanate from the cell body: dendrites, which receive signals, and an axon, which transmits information to other cells away from the cell body. The parts of the neuron are shown in the example in Figure 11.17.

Almost 90% of nervous tissue is composed of helper nerve cells called glial cells, also called neuroglia. Neuroglia cells do not carry or store information but instead assist in nourishing or supporting neurons. These are vital for nervous system functioning. Albert Einstein had more neuroglia than the average person, perhaps contributing to his higher level of intelligence.

In vertebrates, all of the neurons within the brain and spinal cord comprise the cen- tral nervous system, or CNS. Brain and spinal nerves process information as they enter and travel within the CNS. Those nerves found outside of the CNS are classified as the peripheral nervous system, or PNS. PNS nerves detect stimuli, and send messages to and from the CNS using peripheral nerves. Peripheral nerves send messages to muscles or glands to elicit a response. In Sabrina’s Starfish, nerves within the nerve network connect beneath its epidermis along its radial nerve in each arm. Starfish nerves do not connect to have a brain, but are joined to a central ring to allow some degree of central control. PNS and CNS subdivisions in humans are shown in Figure 11.18.

Neurons communicate with one another but also with muscle cells to produce their movements. Nerve transmission may be compared with electricity, in that both transmit a current of ionic charges. In the case of nerve impulses, sodium and potassium ions move along neurons instead of electrons as found in electricity. Thus, transmissions excite cells that they move along.

the Language of Anatomy Animal Organization Animals are ordered systems, composed of groups of cells in many arrangements, including tissues. These systems are organized and work together to maintain life func- tions. The goal of all life is to separate itself from its environment. This separation allows organisms to keep conditions, such as pH and temperature, appropriate through using homeostasis for maintaining life functions.

As discussed in Chapter 1, life is ordered into a hierarchy of organized struc- tures. Tissues and organs work together in the form of organ systems to carry out vital functions such as breathing and obtaining nutrition.

Dendrite

A long thread-like structure of the nerve cell that receives signals from other cells

Axon

A long thread-like structure of the nerve cell that transmits information to other cells away from the cell body.

Neuroglia

Helper nerve cells present in the nerve tissue.

CNS (central nervous system)

The part of the nervous system that consists of the brain and spinal cord.

PNS (peripheral nervous system)

The portion of the nervous system situated outside the brain and spinal cord.

Figure 11.17 Giant multipolar neuron. A neuron conducts signals along its long anatomy. There are many dendrites that receive information from other neurons, send- ing messages to the cell body.

Motor Neuron

Dendrites

Neuron Cell Body

Axon Terminal End

Neurilemma (Myelin Sheath)

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Figure 11.18 Divisions of the PNS (peripheral nervous system and CNS (central nervous sys- tem). The CNS consists of the brain and spinal cord nerves while all other nerves are considered part of the PNS. Illustration by Jamey Garbett.

Spinal Nerves

Spinal Cord

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When studying the anatomy and physiology of the human body, a specific language of anatomy is used. Medical terminology and references are described in the next sec- tion to demonstrate how to effectively communicate with in the medical community. One cannot merely state that there is a spot on one’s liver; it is too general a statement. Instead, to be specific, in medicine, it is more specifically described as a lesion in the left quadrant of the liver, 1 cm in diameter. The metric system is used to quantify the size of the lesion. There is always a term for the specific location of the lesion on the human body to give detail to its description.

Surface regions In medicine, there are numerous body landmarks or surface regions with specific names to describe the locales. These body landmarks are used regularly in medical communi- cation. Many of the regions in Figure 11.19 reappear in this unit on human biology.

Body landmarks (surface regions)

Terms for the specific location of the lesions on the human body to give detail to their descriptions.

Brain

Spinal Cord

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Orbital Nasal Oral

Axillary Thoracic

Abdominal

Digital

Pubic Pelvic

Umbilical

Brachial

Cervical

Buccal

Carpal

Femoral

Tarsal

(a)

Cephalic

Cervical

Thoracic Axillary

Brachial

Carpal

Digital

Pelvic

Vertebral

Femoral

Tarsal

(b)

Anterior or Ventral View

(c)

Figure 11.19 a. Surface regions of the human body. Each area of the body has a name, which often corresponds to structures found within that region. For example, the femoral region contains the femur (bone), the femoral nerve, the femoral artery, and the femoral vein. b. Table of anatomical landmarks. c. Anatomical position.

Abdominal: Anterior trunk between ribs and pelvis

Axillary: armpit Brachial: arm Buccal: area of the cheek Carpal: wrist Cephalic: head Cervical: region of the neck Digital: fingers and toes Femoral: thigh

Nasal: area of the nose Oral: mouth Orbital: area of the eye Pelvic: area of the pelvis Pubic: area of the genitalia Tarsal: ankle Thoracic: chest Umbilical: navel Vertebral: area of the spine

Anatomical landmarks

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The bones, muscles, nerves, and other structures will often have the same name when they appear within one of the surface regions. For instance, the femur is the primary bone in the upper leg area or femoral region, which contains a femoral nerve, a femo- ral vein, and a femoral artery. Each of these structures includes the term “femoral” to indicate the region of the body where it is found. Anatomy is made much easier when terminology is remembered and ordered.

When studying the surface regions in Figure 11.19, find the anterior and posterior body landmarks on yourself and on a human torso, palpating the structures in those

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areas. Becoming familiar with the terms associated with one’s own anatomy helps to organize medical study of the human body. In our example earlier, pain in the upper leg is located in the femoral region. This descriptor clearly denotes the exact area of symptoms.

Anatomical position The regions of the human body are usually referred to using the anatomical position, which describes a specific way of positioning for a human body. The anatomical posi- tion is also shown in Figure 11.19(c). As you can see, in this positioning a person is faced forward, feet together, thumbs pointed to the outside. The palms face forward and the arms are to the side.

When considering a patient in anatomical position, it is important to note that the right side of the body is the right side of the patient and not the observer’s right side. The left side of the patient is his or her left side and not the observer’s left side. In other words, the right acromial (shoulder) region of a patient is the right side of the patient even though it is on your (the observer’s) left side.

An observer must imagine himself or herself from the patient body’s perspective, not one’s own. The observer’s side is always the opposite of the patient’s. Perspective is important to keep in mind when considering directions to avoid medical errors. Over 2,700 surgeries are performed each year on the wrong body part, often due to confusion about the correct side in anatomical position.

Directional terms Anatomical position is a starting point in describing directions and regions on the human body. However, direction is always a relative term. Directional terms are words that describe a location on the human body. Two locations should be given when using direc- tional terms to show position. Consider the statement, “The United States is south…” “South of what?” should be the next question. A second location would show how the United States is positioned in relation to other areas. The United States is south of Can- ada but north of Mexico.

In anatomy, and all medical communication, this rule also applies. For example, the statement that the pollex (thumb) is distal makes no sense, except in relation to another anatomical structure. Using the terms found in Figure 11.20, complete the sentence: the pollex is distal _________. If you wrote in “distal to the arm (brachial region) or to the forearm (antebrachial region),” you were correct.

Directional terms are used to describe one location on the body in relation to its position with another location. The terms proximal and distal, used in our example, describe structures on limbs (arms and legs) only. Whenever a structure is farther from the point of attachment of a limb, it is considered distal or more distant from the point of attachment of the limb. When a structure is closer to the point of origin, it is a proximal location. The brachial (arm) region is thus proximal to the antebrachial (forearm) region. And the vice versa approach is also true: the antebrachial (forearm) region is thus distal to the brachial (arm) region.

Figure 11.20 depicts the general directions of the terms on a human body. The follow- ing directional terms are opposites: anterior (ventral) and posterior (dorsal); superior (cephalic) and inferior (caudal); lateral and medial; and superficial and deep. Anterior refers to the belly side of a human, and posterior refers to its back side. A four-legged animal’s anal direction is called its posterior and its head is referred to as its anterior, but in humans the classification is different. In humans, any body part toward its head

Anatomical position

The position that describes a specific way of positioning for a human body.

Directional terms

Are words that describe a location on the human body.

Distal

Situated away from the point of attachment.

Proximal

Situated close to a point of attachment.

Medial

Situated in the middle.

Superficial

A surface marking.

lateral

Of or relating to the side.

Posterior

Backside.

Deep

A surface marking that is considered superficial and away from a surface.

At the front of or situated before.

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Midline

Anterior or Ventral View

MedialLateral Lateral

Superior

Inferior Lateral View

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(d) (e)

(b) (c)

Anterior (Ventral)

Posterior (Dorsal)

Deep

Superficial

Rostral

Inferior S

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Distal

Proximal

Deep

Superficial

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Figure 11.20 a–e. Direction terms are used in medicine and to indicate location in animals.

is said to be superior and anything away is said to be inferior. Any body part away from the midline along the middle of a human is termed lateral and toward this line is con- sidered medial. A surface marking is considered superficial and away from a surface is called deep. For example, Sabrina’s starfish’s endoskeleton is deep to its epidermis but its epidermis is superficial to its endoskeleton.

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Body planes: imaginary Lines on the human Body While a plane conjures up the image of a flying aircraft, in mathematics and anatomy, it refers to an imaginary line dividing up different regions. In anatomy, a plane shows the cut and the perspective with which to view a structure. When observing different regions in the body, there are four different planes anatomists use that can move through the body to divide it into parts: 1). Sagittal; 2). Frontal; 3). Transverse; and 4). Oblique. These planes are shown in Figure 11.21. A sagittal plane divides the left and right side of an organism. When the sagittal plane runs along the middle of the organism, it is called a midsagittal plane. When the sagittal plane runs along the side of the middle of the organism, it is called a parasagittal plane. The plane that divides the front (anterior) and back (posterior) regions of the body is known as the frontal plane. The plane that divides the top (superior) from the bottom (inferior) part of the body is called the trans- verse plane. When a plane runs at an angle to the organ or organisms considered, it is called an oblique plane (not shown in Figure 11.21).

Planes divide different parts of the body in order to give perspective in surgery and in study. For example, a surgeon should know along which plane an incision should be made during a medical procedure. During imaging of body structures, it is vital to know the correct perspective with which a part is being viewed.

If you recall the movie “Ghost Ship,” at the start of the movie, a metal rope breaks and cuts the passengers into two pieces, tops falling down to the ground. Which plane was sliced? A transverse plane made the whole movie quite a horror! Figure 11.21 shows three of the four planes along a human specimen. Select an organ from the human torso and practice using the body planes to visualize sections.

the Abdominopelvic regions The human body is further divided by anatomists into nine sections, appearing as a tic- tac-toe grid along the body. These nine regions delineating specific parts of the abdomi- nal and pelvic area (abdominopelvic for short) are shown in Figure 11.22: Right and left hypochondriac, epigastric, right and left lumbar, umbilical, right and left iliac (ingui- nal), and hypogastric. Figure 11.22 also shows the nine regions with the organs of the human body found within those regions. As practice, use Figure 11.22 to organize a list of the organs found within each region. For example, the rectum is located within the hypogastric region of the body. It is at the end of the digestive canal and beneath most of the digestive organs.

Sagittal plane

A vertical plane that divides the left and right side of an organism.

Frontal plane

The plane that divides the front (anterior) and back (posterior) regions of the body.

Oblique plane

A plane running at an angle to the organ or organisms.

DIRECTIONAl TERMS PRACTICE

Complete the following exercise to help you with the directional terms: 1) The knee is _________ to the toes. 2) The breastbone is __________ to the collar bone. 3) The elbow is __________ to the wrist. 4) The stomach is __________ to the spleen. 5) The kidneys are __________to the spine.

* Note that there may be more than one answer to the above fill-in-the blanks.

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Figure 11.21 The four body planes: 1) Sagittal; 2) Frontal; 3)Transverse; 4) Oblique (not shown and rarely used, but divides at an angle). Each divides body parts in two different sections to study. Adapted from Anatomy I and Physiology Lecture Manual by John Erickson and C. Michael French.

Figure 11.22 Abdominopelvic regions: The abdomen and pelvis is together divided into nine specific areas.

Frontal (Coronal) Plane

Horizontal (Transverse) Plane

Sagittal Plane

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Organ Systems This unit will treat the major organ systems of the body. It is important to note that, while we look at them individually here, they do not operate in isolation. As mentioned previously, they act as an integrated whole, to keep an organism alive and functioning. This is no easy task and requires a careful interplay between the organs of each system with one another to maintain homeostasis.

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You might think of the body as a machine, with many moving parts. If just one has a malfunction or imbalance, the whole body can suffer from disease.

As you study the organ systems in the coming chapters, their relationships with one another will become clear. The optimal pH and ion conditions, regulated by the kidneys (renal system) enable proper nerve transmissions, which use ions. Healthy nerves allow for clear brain functioning and control of our skeleton’s movements. Moving one's skel- eton helps the heart’s health by relieving it from some work in pumping blood because muscles also push blood along the body. A healthy heart pumps blood through the kid- neys efficiently, and does not do damage by exerting excess pressure.

Inspect the organ systems in Figure 11.23 and identify the organs in the list below. Assign each organ to the proper organ system(s) to which it belongs above. In which organ system are the kidneys, which fail first when humans are dehydrated, like the Star- fish in the story, classified? Yes, in the urinary organ system; but all organ systems work together to the extent that, when one fails, others compensate. The heart races faster when kidney failure occurs to compensate for the buildup of wastes. Intravenous fluids can quickly help to return a dehydrating person’s water chemistry back into balance. As discussed at the start of this chapter, organ systems are interdependent, working together closely for proper body functioning.

Figure 11.23 An overview of the twelve organ systems of the human body. Organ systems of the human body

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Integumentary System – Isolates internal contents of the body from external access. It senses the environment, releases heat, and produces vitamin D.

Skin

Hair

Nails

Skeletal system – Provides support and protection. It results in movement when muscles attached to bone contract. It is also the site for blood cell production and mineral storage.

Cartilages

Joint

Bones

Muscular System – Due to its attachments between bones or bone and skin, the muscles contract to cause movement.

Skeletal Muscles

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Figure 11.23 (continued)

Nervous System – Provides rapid communication, sensing of the environment, analysis and decision making, and stiumulation of muscle.

Brain

Sensory receptor

Spinal cord

Nerves

Endocrine system – Provides slow sustained communication between cells through chemical messages (hormones)

Testis (male)

Pancreas

Pituitary gland

Ovary (female)

Adrenal gland

Thyroid gland (parathyroid glands on posterior aspect)

Cardiovascular system – Consists of a pump (the heart) and vessels through which substances can be transported in the blood

Heart

Blood Vessels

Lymphatic System – Collects and cleans excess tissue fluid and returns it to the bloodstream. It is responsible for immunity.

Thoracic duct

Lymph nodes

Lymphatic vessels

Spleen

Thymus

Tonsils

Respiratory System – The location where atmospheric gases can exchange with blood. It also assists with controlling blood pH.

Nasal cavity

Pharynx

Larynx

Trachea Bronchus

Lung

Digestive System – Breaks down nutrients to their simplest components then absorbs those nutrients into the bloodstream.

Oral cavity

Esophagus

Stomach

Small intestine

Large intestine

Rectum

Anus

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Urinary System – Removes excess or unwanted substances.

Kidney

Ureter

Urinary Bladder

Urethra

Male Reproductive System – Provides sperm containing

Seminal Vesicles

Vas Deferens

Testis

Prostate Gland

Scrotum

Penis

Female Reproductive System – Produces ovaries

Mammary Glands (in Breasts)

Uterine Tube Ovary

Uterus

Vagina

Figure 11.23 (continued)

a) Identify the following structures using the human torso in Figure 11.23:

Ovaries Brain Pancreas Cartilages Rectum Small intestines Esophagus Skin Spinal cord Heart Spleen Stomach Kidneys Testes Large intestines Ureters Urinary bladder

b) Assign each of the above organs to the following systems:

Digestive: Urinary: Cardiovascular: Endocrine: Reproductive: Respiratory: Lymphatic: Nervous: Integumentary:

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CheCk OUt

Summary: key points

• Understanding the role of tissues, organs, and organ systems helps individuals make better, more informed decisions about their health.

• Complementarity of structures leads to their unique roles in living systems. • A variety of methods are used to study animal body structures, with different strategies to help

identify and treat diseases. • Homeostasis, the maintenance of stable internal environments, adds stability to living systems. • The economic theory advocating communism parallels homeostasis, both using a central control

center. This relationship helped scientists to discover the role and processes of homeostasis in organisms.

• The four types of tissues are structured to carry out unique roles within the body. • The four types of tissues work together to carry out life’s processes. • Body structures are placed in humans in expected and specific locations. • Body structures are identified, described, and measured using the specific language of anatomy.

Summary Anatomy, the study of structure, and physiology, the study of function of body parts, together describe the shape, size, orientation, and workings of structures, and processes in the human body. The anatomy of a body part always fits its physiology – in other words, its form fits its function. The structures work together to maintain balance, or homeosta- sis. Most body systems maintain homeostasis through negative-feedback mechanisms, which return the system—body temperature or sugar availability, for example – back to normal conditions. The four tissue types of which organs are composed work together in concert to add diversity and specialization to life’s processes. A language of anatomy is used in medicine to precisely communicate about these body structures and living processes.

adipose anatomical position anatomy anterior apical surface areolar auscultation axon basement membrane blood body landmarks (surface regions) bone cardiac muscle

cartilage cell body complementarity connective tissue CTP (connective tissue proper) CT scan cuboidal cytology deep dendrite dense irregular dense regular developmental anatomy

KEY TERMS

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directional terms disease distal elastic cartilage embryology endocrine system epithelial tissue extracellular matrix fibers fibrocartilage frontal plane glands glucagon gross anatomy histology homeostasis hyaline cartilage insulin lateral ligament medial mesenchyme microscopic anatomy muscle tissue MRI negative feedback nervous system nervous tissue neuroglia (glial cells)

neuron oblique plane observation oxytocin palpation physiology platelets positive feedback posterior proximal receptor reticular sagittal plane set point simple skeletal muscle smooth muscle squamous stratified striations superficial tendon transitional epithelium ultrasound vasoconstrict vasodilate ventral x-rays

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Multiple Choice Questions

1. Which played a role in causing problems for the Starfish, in the opening story? a. Water chemistry balance b. Homeostasis disruption c. Changed environmental conditions d. All of the above are true

2. This study of tissues within the gums of teeth is classified as: a. physiology b. senescence c. embryology d. histology

3. The anatomy of a tooth fits its physiology, enabling it to tear food into small parts. Which term best describes the relationship between chewing and tooth anatomy? a. Histology b. Complementarity c. Cytology d. Dentarity

4. “Listening” is most closely associated with: a. auscultation b. observation c. palpation d. CT scan

5. A set of cells comes together and send signals out to add more cells to an area. This refers to: a. positive feedback b. bilateral feedback c. negative feedback d. organ feedback

6. Which represents a logical order, from low sugar levels to normal sugar levels, in the process of negative feedback in glucose regulation? a. insulin release ➔ uptake by cells ➔ kidney ➔ increased glucose b. insulin release ➔ liver activated ➔ glucose ➔ increased glycogen c. glucagon release ➔ insulin release ➔ liver ➔ increased glucose d. glucagon release ➔ liver activated ➔ glycogen ➔ increased glucose

7. Which social or economic development is most closely associated with the discov- ery of homeostasis? a. Alliance systems b. Communism c. Capitalism d. Democracy

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8. Which tissue both carries and stores messages? a. Muscle b. Epithelial c. Nervous d. Connective

9. Which group of tissues is BEST described by the terms “apical,” “basement mem- brane,” and “stratified?” a. Muscle b. Epithelial c. Nervous d. Connective

10. Which anatomical structure is found in the digestive system and in the right iliac region of the body? a. Appendix b. Brain c. Kidney d. Stomach

Short Answers

1. List the four types of tissues found in humans, as described in this chapter. Research the condition of dehydration to explain how a failure of some of the tissues or organs may lead to disease.

2. Explain how the return of Starfish to freshwater might not help to Sabrina’s starfish in the story. Use the terms “osmosis” and “diffusion” in your explanation. Why?

3. Define the following terms: smooth muscle and striated muscle. List one way the two terms differ from each other in relation to their a. anatomy; b. location in the human body; and c. role in controlling digestion.

4. Homeostasis is a process that uses different mechanisms within the body. Describe one way positive feedback maintains homeostasis. Give an example. Describe one way negative feedback maintains homeostasis. Give an example.

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Chapter 11: Animal Organization 419

5. Any epithelial tissue contains three basic parts to its tissue plan. List and draw the basic structure of a stratified cuboidal epithelial tissue. Be sure to include the labels: apical surface, connective tissue and basement membrane. Which of these terms is most important to its nourishment and survival?

6. Is a cardiac muscle under voluntary or involuntary control? Why? Which two organ systems are most responsible for maintaining homeostasis within the body? Which acts more quickly? Which works more slowly? Give an example and name another system that works with these two to maintain homeostasis.

7. A patient’s axillary lymph node is enlarged. Which areas of the body would you check to determine this diagnosis?

8. A poison is given a drug to destroy fat vacuoles. Which type of connective tissue would be most affected? Why?

9. An old man was fond of saying, “A fool and his cartilage is soon parted…” Describe the problems associated with overworking an area of the body. Choose one of the three types of cartilage and explain how its loss leads to illness.

10. Describe the anatomical position. How is it important in medical treatments and procedures?

Biology and Society Corner: Discussion Questions 1. In the opening story of the chapter, Sabrina’s starfish could not properly function

because it did not have the proper nutrients on dry land? Our human bodies are also uniquely structured and its environment should be protected, especially those of children. To what extent should parents be held accountable for their children’s (a) use of helmets during cycling; or ( b) use of life jackets during swimming; and (c) the diets parents provide for their children?

2. The human body is not structured to resist all the forces placed upon it during athletic competitions. High school and college football are both notorious for player inju- ries, especially head (nervous) and cartilage (connective tissue). What precautions

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should be taken to prevent such injuries? Should there be limits to participation in these sports? To what extent are players participating “at their own risk”? Should they be compensated or even insured when placing themselves at anatomical risk during these sporting events?

3. How is the study of the organization and functions of living systems important to our society? How did a knowledge of water chemistry help Sabrina realize the need to return dying Starfish back into the ocean in the story? Should you or your loved ones be concerned about the role of water in their diets to support different tissues? Would such a knowledge have helped Sabrina’s friends better appreciate the plight of the Starfish?

4. Cartilage deterioration and damage is responsible for many types of replacement surgeries in the United States. However, a statistic showing that knee replacements and hip surgery, performed on 775,000 Americans last year (both treating carti- lage problems) offer no more pain relief after surgery than experienced by patients before surgery. Construct an argument in favor of and one against, the use of such surgeries.

5. In the above question #4, medical decisions are based on science and data from a patient. Explain how a parasagittal CT scan of the knee, to determine a need for surgery, might have drawbacks. Are treatments sometimes worse than cures for patients? Give an example of a case in which this might be true.

6. Which two organ systems are most responsible for maintaining homeostasis within the body? Which acts more quickly? Which works more slowly? Give an example and name another system that works with these two to maintain homeostasis.

Figure – Concept Map of Chapter 11 Big Ideas

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421

Nutrition and Digestion 12

Paulo is very chatty at parties

A person suffering from anorexia

Is this a healthy food choice?

Obesity is an international epidemicEnergy is all around us

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the Case of the sweet Breath Date “I know that I talk too much and should keep my mouth shut, but I am a social creature – how is that bad?” asked Paulo, as he described the latest events at the dorm party last night. “I think the two new members of our floor are going to get romantic.” Paulo said. But Tommy did not want to hear what amounts to a whole lot of gossip from his friend. Tommy said to Paulo, “Just stop talking about people – you are getting yourself in trouble.”

Paulo was a nice person; always willing to help you study or greet you with a smile whenever a bad day came along. But he had one major flaw – he was a gossip. He told everyone everything, and it caused many bad feelings among their friends. The sad part was that Paulo was totally unaware that he was doing anything wrong. He said whatever came to his mind – but you at least knew where you stood with Paulo. He always said the truth, at least as he saw it. Paulo particularly liked to diagnose people using his pre- medial knowledge, and at times offended them.

“Paulo, you are going to be a physician’s assistant. You will have to keep confidenti- ality when it comes to your patients. Sometimes you can be very insensitive.” explained Tommy. “I want you to be on your best behavior when I introduce you to my new girl- friend, Jenny, tomorrow night.” Paulo was hurt; of course he knew how to be discreet. He was a pre-health student and knew a great deal about medicine and talking to patients. “I don’t need you to tell me that – I know how to impress the ladies. Trust me.” bragged Paulo, allaying Tommy’s concerns.

It was time for the big night out, at a college party in the pub downtown for the spring semi-formal. Everyone was going to be dressed to the hilt and it would be a blast. Paulo was actually a lot of fun at parties – always had something to say or a funny story – and kept things lively. Paulo was his best friend, and Tommy planned to introduce Paulo to his new girlfriend, Jenny. They all planned to meet before the party at the First Street Café, where Paulo could get more closely acquainted with Jenny.

Jenny was the person Tommy most wanted – and needed – to impress. Tommy was sure that the pub party would be a great chance at showing Jenny that he and his friends were fun and that she could relax around him. Tommy was, however, a bit worried about his relationship with Jenny. When they went out to dinner, she never ate more than a few bites of food. It was a difficult situation. Tommy was concerned that Jenny was nervous around him and that she might even have an eating disorder. Tommy pondered, “Maybe she will feel a little support speaking with his close friend and getting to know him better this way; it might really help to relax Jenny if his friends hit it off with her.”

Jenny came into the cafe looking terrific in a new black dress, and Tommy wanted to show that he had class too. He brought her around the cafe, introduced her to his

ChECk iN

From reading this chapter, you will be able to:

• Explain how nutrition and digestion disorders interface with societal factors. • Define and describe the eating disorders anorexia nervosa and bulimia, and explore characteristics

of and factors contributing to eating disorders and the obesity epidemic. • List and describe the six types of nutrients, both micronutrients and macronutrients. • Explain the prevailing theories about how weight is gained and lost. • Describe mechanical and chemical digestion, listing the structures in the alimentary canal and describ-

ing their functions in the digestive process. • Locate and describe the diseases associated with the alimentary canal.

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Chapter 12: Nutrition and Digestion 423

many friends and then came Paulo sitting at a table. “Paulo, this is Jenny, my new friend who I was telling you about.” “It is a pleasure to meet you, Jenny,” said Paulo in a very gentlemanly manner. But as Paulo approached Jenny, he noticed her breath smelled and inappropriately asked her, “Do you have ketone breath?”

Paulo had just left his student physician’s assistant clinicals, and smelled the breath of a patient who had anorexia nervosa. He noticed that Jenny had the same breath. Paulo explained to the group, “In this condition, a person does not intake enough calories. The body breaks down oxaloacetic acid in the Krebs cycle to get the needed energy. It changes it into glucose, and then into the needed calories.” Tommy looked perplexed at Paulo but he went on, “You see, the Krebs cycle shuts down and acetyl-CoA cannot get into it. So, it changes into ketones, which are organic acids”.

“Don’t you see, Jenny…” explained Paulo, “your breath is sweet just like ketones.” Tommy was obviously horrified at Paulo for being so rude.

ChECk Up sECtioN

This story describes the process of ketosis, which arises from a lack of calories. The way food is pro- cessed and stored is associated with a number of diseases, including anorexia as well as obesity. Many Americans suffer from these illnesses.

List the symptoms of anorexia nervosa. Research its biological and psychological symptoms and develop a plan for treating a person with this illness.

Why are cases of anorexia so prevalent in the United States society today? How do aspects of our culture contribute to the development of anorexia nervosa and related illnesses?

Eating Disorders This chapter first discusses the social issues facing people in relation to the digestive system. It explores the causes and possible resolutions to anorexia, bulimia, and obesity, disorders found emanating from both psychological and physiological processes of nutri- tion practices and the digestive system. In the next part of the chapter, the role of nutri- ents in food processing in the body is connected with weight gain and loss. Finally, an overview of the parts of the digestive system is given, alongside its associated disorders.

anorexia and Bulimia Eating disorders, as depicted in our story of Jenny, are omnipresent. It is estimated that about 8 million Americans – almost 3% of the U.S. population – have an eating disorder. Of those, 7 million are women and one million are men. Anorexia nervosa is an eating disorder characterized by a loss of appetite for food and a fear or refusal to maintain normal body weight. One in 200 women suffers from anorexia nervosa. About 3% of females have another eating disorder, related to anorexia called bulimia. Bulimia is char- acterized by purging food to maintain lower body weight. Roughly 10–15% of those suffering with an eating disorder are male. Anorexia nervosa and bulimia are the two most common eating disorders in the U.S. population.

Weight is a sensitive issue for people to discuss. It is laden with psychological issues based on how a person views herself or himself. In the story, Paulo’s insensitivity to others shows lack of awareness and knowledge about how to address the disease. While Paulo seems to understand the biology of ketosis, he does not appreciate the psycholog- ical complexity of eating disorders in society.

Anorexia nervosa

An eating disorder characterized by a loss of appetite for food and a fear or refusal to maintain normal body weight.

Bulimia

An eating disorder characterized by abnormal and constant craving for food alongside purging.

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424 Unit 4: The Dynamic Animal Body

In a study by the National Association of Anorexia Nervosa and Associated Disor- ders, upward of 10% of anorexics die within 10 years of onset of the disease, and 20% are dead after 20 years. Often, the person with an eating disorder feels shame, guilt, and denial. Sadly, as a result, only 1 in 10 people with eating disorders ever receive treat- ment. This contributes to low recovery rates of between 30 and 40%. Actresses Justine Bateman, Tracy Gold, Jane Fonda, and actor Sam Attwater each suffered publicly with eating disorders (see Figure 12.1).

Anorexia nervosa and bulimia are often derived from an individual’s desire to main- tain control over his or her life through food. However, the origins of the diseases are complex and in part stem from society’s focus on body image. We are not sure if Jenny in our story really had anorexia or bulimia, but eating disorders constitute a rising threat to young adults – especially females, aged 15–24 years for whom the death rate from anorexia nervosa is 12 times higher than for all other causes of death combined.

the obesity Epidemic While Jenny showed a few signs of anorexia nervosa, many Americans exhibit symptoms of a disease at the other end of the spectrum that is growing at an alarming rate – they are overweight or obese. The obesity epidemic occurring in developed nations contributes to a host of illnesses and premature death. Heart disease, stroke, cancers, and diabetes are only a few diseases with strong associations with obesity.

The headlines are not lying when they report obesity as an epidemic in the United States: “A chubbier America!”; “Obesity nation…”; and “More donuts, less carrots.” In 2010, the Centers for Dis- ease Control reported that 69.2% of Americans are either obese or overweight. There are many reasons for the change in society, but it is a relatively recent phenomenon, accelerating in the past few decades. In 1914, this statistic was very different: only 5% of Americans were overweight or obese. In 2014, over 70% of Americans fall into an overweight or obese category.

How is obesity determined? Obesity is defined by a body mass index (BMI), which gives a num- ber value to a person’s body mass based on his or her height and weight. The National Heart, Lung and Blood Institute (NHLBI), a division of the National Institutes for Health (NIH) uses the BMI as a baseline for measuring the health of both males and females. A BMI from 25 to 29.9 is considered overweight, and a value of 30 or more is considered

Figure 12.1 Actor Sam Attwater suffered with buli- mia at an earlier time in his life.

e a

tu re

fla sh

/S h

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to c

k. c

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Obesity

The state of being overweight with a BMI greater than 30.

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Chapter 12: Nutrition and Digestion 425

obese. A BMI below 18.5 is considered underweight. While only a small portion of the population are underweight, a century ago, more than 40% of military recruits were rejected based on low weight. Being underweight is associated with poor nutrition and development. Use the chart in the accompanying Figure 12.2 to determine your BMI

category, based on your height (with shoes) and weight.

Obesity is associated with a number of diseases, increas- ing the risk for high blood pressure, heart disease, type II diabetes, stroke, sleep dis- orders such as sleep apnea, certain cancers, and arthritis. These illnesses are based on known physiology about how the body works. For example, chronic high blood pressure, which can worsen with weight gain is based on physical laws. Each pound of fat a person gains requires 1,000 feet of extra blood vessels to support it (see Figure 12.3a). As a result,

Figure 12.2 Body mass index (BMI). This chart uses weight and height to calculate a number to evaluate one’s overall body mass health.

e rb

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tt e

rs to

c k.

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Figure 12.3 a.“A Pound of Fat” – 1000 feet of blood vessels are built, required to support a pound of fat gained in a person.

ik u

l N o

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ch12.indd 425 11/12/15 6:32 pm

C R O O M , D O N A V A N 4 6 4 5 T S

426 Unit 4: The Dynamic Animal Body

the heart has to work harder to overcome the added resistance of more blood vessels. The more pounds gained, the higher the blood pressure from the heart required to push blood through body vessels. Thus, one’s blood pressure increases as one gains weight.

Gaining weight is not an automatic indicator of higher blood pressure. Some people may be healthy at higher weights, and some may have high blood pressure and be within normal weight ranges. There are many unexplained factors affecting how diseases are developed and who responds to treatments. Of course, obesity does not need to be a permanent condition – if a pound of fat is lost, most blood vessels are reabsorbed, and blood pressure generally decreases.

While obesity is an increasing problem for adults, a particular worry is the rising obesity rate among children and adolescents. The Centers for Disease Control and Pre- vention also reported that 12.4% of younger children aged 2 to 5 are obese, 17% of those aged 6 to 11. Among adolescents, 17.6% who are aged 12 to 19 are classified as obese, and many will remain obese as adults. It is estimated that 30% of children who are obese will become obese adults. Increasing obesity rates are reported throughout the industrialized world.

Why is obesity Rising? Increasing obesity may be a result of a variety of factors. First, as mentioned in Chapter 6, obesity genes have an effect on people’s weights, with 50–70% of the trait due to the effects of genes. While genetics plays a role, changes in lifestyles and in the types and quantities of foods that we eat compared to diets in the past may influence obesity prevalence. Although shuffled, the same genes are in our population as existed 100 years ago when the obesity rate was only 5%. What are the primary factors contributing to the modern increases in average weight?

First, in industrialized nations, such as the United States and western Europe, trends in types of work have changed. Society transformed into a service and white collar labor force. Whereas a century ago more than half of the population was involved in farm work, today most people have white collar jobs. Over 90% of the labor force in the United States has a sedentary office job. Many of the once active jobs, for example, construction and factory jobs, are now assisted with or replaced by machinery. All of this resulted in diminished physical requirements at the job.

Second, nutritional choices have changed since 100 years ago. In the past, food was not processed, and diets were dependent on whole foods such as grains, fruits, and vegetables, with small quantities of meats and cheeses (both high in calories). Today, more than 70% of people eat some form of fast foods every week. Fast foods – French fries and burgers being popular choices – are high in sugar and energy, adding calories without the same nutritional value as whole foods. Check the nutritional values of each of these foods. Note that preparation of foods matters – a plain baked potato is healthy in comparison with its French fried version – with unprocessed foods containing less fat, salt, and calories. One plain potato contains only 68 calories; it has a low saturated fat level, is low in cholesterol and salt, and has ample vitamin B6, potassium, and vitamin C. French fries contain concentrated amounts of simple sugar and are high in saturated fat and salt, with few of the nutrients of a plain potato.

There are also many ingredients in foods, for example, high fructose corn syrup, that were not present a century ago. The role of HFCS (high fructose corn syrup) in

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Chapter 12: Nutrition and Digestion 427

foods was discussed in Chapter 2. The average American consumes about 62 pounds of HFCS per year and is another example of changed diets over the past century. Food is also more readily available, in particular meats, cheese, and processed products, often served in large portions, adding calories, fat, and sugar. Even one-third of homeless people in the United States are obese. Obesity is now ranked as the second preventable cause of death in the United States, second only to smoking. Causes of the obesity epidemic are complex. While greater access to food products for the public is a valued change in society, knowledge about nutrition (and digestion) will help people to make better decisions about the foods they choose.

Nutrients The goal of eating is to obtain nutrients for the healthy functioning of our bodies. Nutrients are the substances that the body uses to obtain energy and to maintain the body’s activities, such as growth, repair, and reproduction. Figure 12.4 shows foods containing the six classes of nutrients: water, vitamins, minerals, carbohydrates, lipids (fats), and proteins.

Macromolecules (carbohydrates, lipids, and proteins) are the nutrients that pos- sess energy within their bonds, and are referred to as macronutrients because our bodies require them in relatively large quantities. An overview of the macromole- cules was given in Chapter 2. Vitamins and minerals are known as micronutrients, because they are needed in small quantities. Micronutrients include vitamins, min- erals, and water. Micronutrients do not have long bonds from which the body can derive energy. However, micronutrients are vital for processes that unleash energy from bonds in macronutrients. Vitamins and minerals are associated with processes that break food down into useable energy. Water is also an essential micronutrient in which all cell reactions occur. All of the micronutrients are needed in living systems.

the Micronutrients Vitamins. There are 13 vitamins that are essential to human life processes. While vita- mins and minerals are required only in very small amounts, they are needed to facilitate chemical reactions in almost every living process. The 13 vitamins are classified into two categories. Fat-soluble vitamins include D, A, E, and K, which accumulate in fatty tissues in the body. Fat-soluble vitamins may become toxic in large doses. Water-soluble vitamins include all of the other vitamins such as the B vitamins and vitamins C and K. Water-soluble vitamins can be taken in large doses and do not become toxic because they are eliminated through the urine.

Vitamins A, C, and E (you can remember these as “ACE”) are antioxidants, which eliminate molecules with extra electrons, called free radicals, thus preventing damage to body structures. Free radicals cause cancer and heart disease, so vitamins A, C, and E are associated with better health and fitness. A lack of essential micronutrients, as occurs in cases of malnutrition and eating disorders, as described in our story, can be dangerous. Nerve and heart-muscle impairment occur with disruptions in mineral bal- ances. The major vitamins and minerals and their primary function in the body are given in Figure 12.5.

Macronutrients

Macromolecules that possess energy within their bonds.

Micronutrients

Chemical substance required in small quantities, namely vitamins and minerals.

Antioxidants

The substances that eliminate molecules with extra electrons, thus preventing damage to body structures.

Free radicals

Molecules with extra electrons that cause damage to body structures.

Fat-soluble vitamins

Includes D, A, E, and K, which accumulate in fatty tissues in the body.

Nutrients

The substances that the body uses to obtain energy and to maintain the body’s activities, such as growth, repair, and reproduction

Water-soluble vitamins

Includes B vitamins and vitamins C and K, can be taken in large doses and do not become toxic because they are eliminated through the urine.

ch12.indd 427 11/12/15 6:32 pm

C R O O M , D O N A V A N 4 6 4 5 T S

428 Unit 4: The Dynamic Animal Body

M aj

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ch12.indd 428 11/12/15 6:32 pm

C R O O M , D O N A V A N 4 6 4 5 T S

Chapter 12: Nutrition and Digestion 429

F ig

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ch12.indd 429 11/12/15 6:32 pm

C R O O M , D O N A V A N 4 6 4 5 T S

430 Unit 4: The Dynamic Animal Body

N ia

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Chapter 12: Nutrition and Digestion 431

DOES VitAMiN C PREVENt COlDS?

Upper respiratory tract infections, such as the common cold, invade mucous membranes through the nose and mouth. They are caused by a virus that is quite delicate but, when it enters the body, leads to mucous and inflammation symptoms of the common cold.

The Mayo Clinic conducted a series of studies on the effect of taking vita- min C on the duration and prevention of colds. They discovered that there were no differences between those people taking vitamin C and those taking a placebo (sugar pill).

Linus Pauling, a famous chemist of the 1930s, who discovered aspects of atomic structure, claimed that vitamin C boosts immunity. In Linus Pauling’s book “Vitamin C and the Common Cold,” he suggested that 1,000 mg of vitamin C per day would ward off the common cold. However, over 11,000 research studies have failed to find data to support his claim about the effects of vitamin C on prevention of colds.

It is true that vitamin C is an antioxidant, and foods containing vitamin C, such as fruits and vegetables like oranges, broccoli, have large amounts of antioxidants. Thus, diets high in these vitamins tend to improve one’s overall health. A large glass of orange juice contains about 100 mg of vitamin C, and it is certainly better than many soft drinks. The relationship between vitamin C and health may emerge, however, from the association of vitamin C with other healthy foods. Figure 12.6 shows the innocent tablets of vitamin C, which stim- ulated all of this research and debate.

u tt

h ic

h a

i/ Sh

u tt

e rs

to c

k. c

o m

Figure 12.6 Vitamin C tablets, are they helpful or useless?

Minerals They are inorganic substances that form ions in the body, which help to perform many functions. Calcium strengthens bones and teeth, iron is central to the transport of oxygen in the blood, and iodine is needed for thyroid hormone manufacture, as some examples. Minerals in the body are shown in Figure 12.7.

Minerals

Are inorganic substances that form ions in the body, which help to perform many functions.

ch12.indd 431 11/12/15 6:32 pm

C R O O M , D O N A V A N 4 6 4 5 T S

432 Unit 4: The Dynamic Animal Body

F ig

ur e

12 .7

in er

al s in

t he

b od

y an

d th

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Diets high in vitamins and minerals help carry out life functions and are associated with good health. Over 50% of Americans take vitamin and mineral supplements. But is there really a need for these additions to our diets? Most nutritionists agree that ade- quate amounts of vitamins and minerals, especially antioxidants, are a key to a healthy lifestyle. However, most also agree that supplements are not necessary for most adults. Few adults suffer from diseases associated with lack of micronutrients, such as goiter (thyroid malfunction due to lack of iodine) and rickets (bone weakness due to lack of calcium), which are found more frequently in the developing world. A diet properly bal- anced with whole foods provides an adequate supply of micronutrients, without the need for regular vitamin or mineral supplements.

Water The longest period of time a person has ever survived without the intake of water is 17 days, by a prisoner sentenced to death in Italy in the early 1900s. Water is an essential nutrient, comprising between 60 and 80% of the volume of cells, and is the medium in which all cell reactions take place.

Water is needed in almost every function carried out by organisms. All chemical reactions occur in a watery environment. Water is the medium that transports nutrients and wastes through the body. It lubricates joints, the brain, spinal cord, and eyes. Body temperature is regulated, as discussed in the last chapter, in part by sweating, which requires a large amount of water. A human can sweat up to 8–12 L (2–3 gallons) of sweat in a day. The need for water is continual to replenish it.

Water must be taken in the right amounts. The USDA recommends that an aver- age adult person, requiring 2,000 calories of energy per day, needs between 2 and 3 L (roughly a half gallon) of water. Intake also depends upon age and different health condi- tions. Pregnant women require at least 1 additional liter of fluids per day. Water is found in many foods, such as milk, juice, and even many types of bread.

Excessive intake of water may lead to disruption in mineral balance (Figure 12.8). In a recent radio game show, called “Hold Your Wee for a Wii,” a caller was dared to drink several liters without urinating. The caller, 28-year-old mother of three, Jenni- fer Strange, was found dead after trying to win one of Nintendo’s Wii game consoles.

Water

An essential nutrient, comprising between 60% and 80% of the volume of cells, and is the medium in which all cell reactions take place

Figure 12.8 Person drinking water on radio talk show.

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Ms. Strange may have suffered from water intoxication caused by a decreased concen- tration of sodium called hyponatremia. In cases of hyponatremia, sodium levels become so diluted that they do not function properly in nerve transmission, and heart and brain activity are disrupted. The radio show was under investigation for endangerment of health by the FCC.

Macronutrients Macronutrients hold, within their bonds, the energy that drives life’s processes. Macro- nutrients including proteins, lipids, and carbohydrates each store energy. The National Academy of Sciences has recommended intakes for our diets to include all of the macro- nutrients in accordance with a MyPlate guided diet. The MyPlate nutrition guide empha- sizes only sparing amounts of dairy and fats, with guidelines shown in Figure 12.9a. It also emphasizes less meat and dairy and promotes more fruits and vegetables to be

Food Plate (MyPlate guided diet)

A nutrition guide modeled for healthy eating in the United States. Food pyramid

A pyramid-shaped graphic representation that represents the optimal number of serving to be taken each day.

Figure 12.9 a. Guides to eating right by the National Academy of Sciences: the “MyPlate” Food Guide. b. The old USDA Food Pyramid gives guidelines for obtaining recommended daily allowances for vitamins and minerals. USDA.

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consumed every day. The food plate is in greater agreement with most nutrition studies, and replaced older food guides, such as the Food Pyramid, which emphasized higher intakes of carbohydrates (Figure 12.9b).

Let’s review how macronutrients drive life’s processes.

proteins Proteins compose many structures and functional chemicals in the human body, as you may recall from Chapter 2. Muscles are composed of almost 50% protein; bones and other body structures are also constructed with proteins. The Food and Nutrition Board of the National Academy of Sciences’ Institute of Medicine report Dietary References Intakes for Energy, Carbohydrate, Fiber, Fat, Protein, and Amino Acids (Macronutri- ents) recommends daily protein intake of 10–35% of total calories. A slight increase in protein intake is recommended for athletes engaged in muscle-building programs. However, proteins alone do not build up muscles; muscle building requires resistance training, and proteins only act as raw materials.

How do proteins act as building materials? First, as described in Chapter 2, pro- tein molecules are composed of long chains of amino acids, held together by peptide bonds. Amino acids may be compared to bricks in a house, which the body rearranges to build other structures. These “bricks” are reordered based on what foods we eat and the structure we require.

Second, proteins form specific shapes to enable then to perform multiple func- tions in the body. Proteins, in the form of the hemoglobin, carry oxygen gas in the blood. Proteins form enzymes that break down foods in our digestive system, a topic that will be discussed later in this chapter. Proteins also work as enzymes to break and form bonds. Enzymes are used in almost every chemical reaction within our bodies, from changing fat into energy to storing water and building new cells.

Finally, proteins are found in many types of foods. Animal sources of protein include meats such as chicken, fish, and beef, and dairy products such as cheeses and milk. Veg- etable sources include mostly seeds, nuts, beans, and grains, which are used by plants for growing their new offspring.

All animals require each of the 20 amino acids that compose proteins. Only eight of the amino acids are considered essential, meaning that they must be taken in by diet. The essential amino acids are not able to be synthesized by the body. The other 12 non- essential amino acids may be produced from other forms of amino acids and thus are not required in a diet to survive. Many combinations of foods have all of the amino acids required for survival. In other words, the components of a nutritious meal complement each other by providing all of the essential amino acids. Meals such as rice and beans have amino acids in each food that together constitute a full set of proteins. Some foods, such as a slice of beef or an egg, contain all of the needed amino acids and are said to be complete protein meals. Vegetarians must be particularly careful to choose foods that provide the needed sources of proteins. Vegetarian diets are great alternatives to tradi- tional cooking, as long as one chooses the right set of foods to yield a complete protein meal. Vegetarian diets are beneficial in that they are often healthy, low in fats and are able to provide all of the needed nutrients.

lipids Lipids, including fats, waxes, and oils, are the focus of many weight management and nutrition studies. Lipids contain more than twice the energy per gram of other macro- nutrients and are therefore cited as a culprit in the obesity epidemic. A gram of fat has

Essential amino acids

Amino acids that are not synthesized by the body.

Nonessential amino acids

Amino acids made by the human body and thus are not required in a diet to survive.

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9 calories, compared to 4 calories per gram for carbohydrates and protein. Fat stores a great deal of energy. A person’s stored energy in the form of fat lasts them roughly 4 to 5 weeks when deprived of food.

A normal intake of fat is about 20–35% of one’s total daily intake. Lipids are necessary for life functions, ranging from the cushioning provided by adipose tissue to maintaining the integrity of cell membranes within the fluid mosaic structure. How- ever, excess lipid intake is related to greater risks for heart disease, stroke, and many other illnesses. Alternatively, when there is a lack of calories (as occurs in eating dis- orders such as anorexia nervosa) the body taps into its fat energy reserves. The break- down of fats produces ketones, an acid responsible for the ketone breath alluded to in the story.

Lipids are composed of long-chained molecules of fatty acids and glycerol, which contain many bonds, all holding energy. Foods are, in part considered “good” or “bad” based on their fat content, with some examples shown in Figure 12.10. As classified in Chapter 2, saturated fats, with multiple single bonds, are associated with heart disease, and unsaturated fats, containing double bonds, with better health.

Trans-fats, or those lipids created by adding hydrogen to oils to make them solids, such as margarine, have the strongest links to heart disease and premature dying. Both saturated fats and trans-fats increase levels of LDL (bad) cholesterol in the blood, a substance that is thought to build up on artery walls. This leads to higher risks for stroke and heart attack.

Figure 12.10 The different kinds of fats in our foods. Trans-fats and saturated fats are most harmful to a person’s health. Unsaturated fats are linked to healthy hearts.

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Carbohydrates Access to quick energy in the body is provided by carbohydrates. Carbohydrates are composed of single molecules called simple sugars or monosaccharides, as discussed in Chapter 2. Carbohydrates are transformed into sugar and then into energy, in processes described in Chapter 4. They provide structure in cell membranes, enable growth and fuel movement. The Food and Nutrition Board suggests that 45–65% of our diets should draw from carbohydrates.

Just as all fats are not the same, all carbohydrates do not have the same contribu- tion to rises in sugar levels in the blood. The glycemic index gives a numerical value to carbohydrates depending upon their spike in blood-sugar levels. Foods with a high glycemic index more rapidly increase sugar levels than those with a low glycemic index. For example, a donut with a high proportion of simple sugars has a high glycemic index because its sugars are quickly released into the bloodstream. Whole grain breads, which have longer chained carbohydrates, must be broken down to release simple sugars into the blood stream and thus have a lower glycemic index.

Foods with lower glycemic indices are advised because they take longer to pro- cess and do not spike levels of sugars and thus insulin in the body. Spikes in sugar levels contribute to increased risks of diabetes, or excess sugar in the blood (discussed in Chapter 14). Diets containing low glycemic index foods include fruits, vegetables, whole grain cereals and breads, whole grain rice, wheat. Processed foods such as white breads, candy, cookies, cakes, and donuts have a high glycemic index. It is best to

ARE FAtS REAlly thE CulPRit iN hEARt DiSEASE?

In addition, recent studies published in the Journal Nature Medicine, and the New England Journal of Medicine, link the dangers of red meat to bacteria in human guts. In the first study, l-carnitine, found in high proportions in processed red meat, provoked bacteria to produce trimethylamine N-oxide (TMAO). TMAO is an organic substance that alters cholesterol processing in the liver. In the second study, lecithin, also found in high amounts in eggs and red meats, led to the formation of TMAO by gut bacteria.

TMAO is associated with heart disease and strokes. The effects of TMAO have been demonstrated in a Cleveland Clinic study of over 4,000 people, in which those having higher levels of TMAO were more likely to have a heart attack or stroke over a three-year period. The findings show that other chem- icals, l-carnitine and lecithin, and perhaps not saturated or trans-fats, might be the cause of heart disease and premature death — not the fats in foods directly.

It is possible that those foods containing saturated fats also contain sub- stances causing bacteria to form TMAO. In the Cleveland Clinic study, those subjects eating two eggs per day had increased levels of TMAO, but those subjects adding an antibiotic to kill gut bacteria did not have increased levels of TMAO and did not suffer the same risks as those not taking the antibiotic. Use of antibiotics to kill gut bacteria and improve health is not recommended due to the need for bacteria in our digestive system (discussed later in this chapter). Those wishing to avoid the negative effects of TMAO on their health should increase their vegetable and fiber intake, and limit red meat and eggs.

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choose foods with a low glycemic index, along the lines of those examples given in Figure 12.11.

The storage form of glucose in our bodies is glycogen, found in the liver. When energy is needed, glycogen is broken down into simple sugars and transformed into energy by cellular respiration. Large amounts of water are stored along with glycogen; in fact up to four pounds of water are associated with every one pound of glycogen. This is the reason why a diet almost always initially works well, as glycogen is used up and water is excreted through the kidneys; water weight is lost but not fat. As a diet enters the fat-usage stage, weight loss slows dramatically because fat burning is a slow process in contrast to the water-weight loss associated with glycogen. If a person stops their diet, the weight is rapidly gained back because glycogen restores in the liver along with the water weight.

All carbohydrates are not created alike and therefore diets addressing these dif- ferences are essential for good health. Whole, unprocessed foods that contain higher amounts of larger, complex carbohydrates such as fruits, vegetables, and whole grains will limit risks for disease. Our physiology is based upon over 90,000 years of adapta- tions to diets of hunter and gatherers. They did not have processed foods, and our bodies are therefore not adapted to properly process these kinds of foods.

Figure 12.11 a. Choose foods with a low glycemic index. Foods with a lower glycemic index give less of a sugar rush after eating. b. Fruits and whole grain cereals have a lower glycemic index.

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iS thE NEOlithiC (CAVEMAN) DiEt A GOOD GuiDE tO EAtiNG RiGht?

Proponents of the Neolithic or “Caveman” diet propose that eating like a caveman or cavewoman is the right way to obtain nutrients and keep within a normal weight range. They argue that Homo sapiens developed digestive processes over the past 150,000 years based on the hunter/gatherer lifestyle that characterized early humans. These processes thus resulted from over 180 million years of mammalian evolution, 65 million years of primate evo- lution, 5 years of hominid evolution, and 2 million years of our genus Homo.

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The idea of the Neolithic diet is that it took a long time to develop our digestion and, in an evolutionarily short period of time, our diets have made radical changes.

Some nutritionists argue that to more closely parallel the diets to which we are adapted, people should follow the prehistoric nutrition system called the Neolithic diet. This diet includes the kinds of foods that were eaten by pre- historic humans. They claim that the MyPlate guidelines conflict with the Neo- lithic diet; and thus they collide with a diet type that our metabolism requires because of many years of evolution.

Prehistoric diets likely included mostly whole grains, fruits, nuts, and veg- etables, as recommended in the previous sections. In cave-era times, there were few opportunities to eat meat and fish because they are more difficult to capture and hunt. Thus, human digestion was adapted to greater proportions of plant foods. Obviously, proteins and fats were therefore less a part of the Neolithic diet, far less than most Americans consume today.

The Neolithic diet most likely contained not only a large amount of fresh fruits and vegetables, but also many whole-grain (unrefined) starches such as rice, tubers, acorns, and grasses. Early humans likely ate small game meats such as frogs, birds, snakes, fish, and even insects to obtain most of their fats and proteins. It would have been extremely rare (and probably coveted) to find refined sugars in the form of honey.

On the other side, our modern diet is laden with refined sugars and high-fat foods, never encountered by our ancestors and thus not well adapted by our genes. Americans regularly consume too much refined sugars and fats, and not enough micronutrients from lower calorie foods such as fruits and vegetables.

Neolithic diet supporters contend that modern society is at odds with genetic predispositions of digestion emanating from the past. First, they cite our activity levels. We are less active today than compared with our ancestors and even peo- ple from 100 years ago. This, they cite, is contributing to the modern obesity epi- demic. Preagricultural people led more active lifestyles with caloric needs of about 3,000 calories per day. Nomadic lives required hunting of game and gathering of vegetables, as well as fighting the elements and caring for young. However, they consumed fewer calories from fat. Corn-fed stock today contains approximately 29% fat as compared with wild game of our ancestors, which had only 4% fat.

Critics of the modern American diet often cite the prevalence of pizza. Pizza has become rapidly integrated into our diets within the past three decades. Perhaps consider when was the last time you ate pizza? It may be alarming to you that the components of pizza are drizzled cheese and oils. An average slice of pepperoni pizza contains 298 calories, with 37% fat, 47% carbohydrates, and only 14% protein. A serving of deer meat, for which our bodies are more adapted, contains only 32 calories per ounce and has 18% fat, 0% carbohydrates, and 82% protein (Figure 12.12). A mismatch between modern day food choices and our physiologic origins are possible contributors to the current obesity epidemic, according to proponents of the Neolithic diet.

Neolithic diet

The prehistoric nutrition system.

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how is Weight Gained and lost?: Food, Energy, Metabolism, and Weight Energy is measured in Calories Food energy is measured in small units commonly known as calories (cal), which are defined as the amount of energy required to raise 1 gram of water by 1°C. However, food calories are actually kilocalories (kcal) of energy, each of which equals 1,000 calories. We use kcal to measure food energy quantities because food contains much more energy than single calories. Thus, a yogurt with 100 calories on its label is really 100 kcal or 100,000 calories.

Calories

The amount of energy required to raise 1 gram of water by o1 Celsius.

Figure 12.12 a. Caveman diet is filled with fruits and vegetables; and b. Modern person eating pizza.

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Chapter 12: Nutrition and Digestion 441

As we have said before, macronutrients provide different amounts of energy. One gram of lipids provides 9 calories of energy, while 1 g of carbohydrate and 1 g of protein each contain only 4 calories of energy. However, a diet low in fat may not lead to less intake of energy. Intake of energy is based upon the total calories in one’s diet.

A simple rule applies to gaining and losing weight: calories in vs. calories out. The body may be compared to a meticulous accountant – it measures how many calories are coming into the body and how much is leaving it. If a person takes in more calories than are expended in a day, then that person will gain weight. If a person takes in fewer calories than are expended in a day, then the person will lose weight. To gain a pound of weight, a person needs to take in 3,600 more calories than he or she uses. Thus, to lose a pound of weight, a person must take in 3,600 calories less than is used.

Basal Metabolic Rate Of course, weight gain and loss depend upon how well those calories in one’s diet are burned off. The energy needs of an individual are calculated based on a base level of energy needs, doing nothing but survive in a sitting position within a single day. This energy requirement is known as the basal metabolic rate (BMR), for a person who is at rest, with no energy requiring digestion and only minimal energy needed for movement. The BMR for a human is roughly 1 calorie per hour per gram of body weight. This trans- lates into a need for 1,700 calories per day for a person weighing 170 pounds. In reality, calorie needs are about 50% higher for most people, who are involved in some physical activity such as walking and conducting daily activities. The same 170-pound person would therefore need about 2,550 calories per day to maintain their weight.

Basal metabolic rate differs for different species of animals. Generally, the smaller ani- mals have faster heartbeats and a faster metabolic rate, requiring more energy. For exam- ple, a tiny shrew has a heart rate of more than 500 beats per minute (humans average only 80 beats) and a BMR 35 times higher than humans. An elephant, large in size and stature, has a heart rate closer to 40 beats per minute and has a BMR only 4% that of a shrew.

Different people have differing BMRs based on their genetics, muscle composition, and hormonal factors. The greater the number of muscle cells, which use more energy than an average cell, the higher one’s BMR. Some people burn calories better than others and are said to have a faster metabolism, or total set of cellular reactions. Some have a slower metabolism.

A recent set of research studies reports that BMR may not be the best measure of overall health. Instead, a person’s waist-to-height ratio is more important in predicting heart health and longevity than BMR. It is recommended that the waist-to-hip ratio should not exceed 0.5. In other words, a person’s waist circumference should not be more than half of his or her height in inches or centimeters. Thus, a person at a height of 6 feet, or 72 inches, should have a waist 36 inches or smaller to be considered healthy. Abdominal fat, indicated by a larger waist size, is associated with stroke, heart diseases, and various cancers. People with an apple shape, or those carrying fat around their mid- sections, are thus at greater risk for developing disease than those with a pear shape, who carry extra weight around their hips. Figure 12.13 depicts the two body types.

Some studies on fat distribution point to body fat percentage as the best measure of a person’s risk for disease. In these calculations, folds of fat are measured at various locations on a person’s body. Measurements are taken at the waist, back of the upper arm and at the back regions. To be considered healthy, a male should have a body fat percentage less than 15%, and females should have not more than 24% body fat. Women require more body fat due to hormonal and childbearing influences. Young adults who are healthy should range between 12 and 15% total body fat for men and between 20% and 25% for women.

Basal metabolic rate (BMR)

The minimal rate of energy used by an organism at complete rest.

Metabolism

Chemical processes occurring in a living organism that are necessary for life maintenance.

Apple shape

A body shape that is characterized by excess body fat in the abdominal region.

Pear shape

A body shape characterized by extra weight around the hips.

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The obesity epidemic described in the earlier section reflects a change in diets to fast foods and prepared meals as one factor causing increasing weight. These foods have higher numbers of calories and thus increase the amount of energy taken in, on average, by people.

Of course, there are many factors leading to the increasing average weight in our populace. As average weights go up, the appeal of a thin body grows. Eating habits and therefore weight have strong social and psychological components, a theme of our story of Paulo and Jenny. First, to fully consider these factors, let’s review how the energy is released from the macromolecules by our digestive system.

the Digestive system: how humans Break Down and absorb Food the alimentary Canal: a tour of the Digestive system The alimentary canal is the tube and associated organs of digestion, which includes all of the parts of the digestive system that contribute to the breakdown of food. It is composed of about 24 feet of tubes and as such, it is referred to as a “tube-within-a-tube” arrange- ment within our tube-like bodies. The structure of the digestive system in humans is given in Figure 12.14.

The alimentary canal comprises a series of tubes from mouth to anus including a mouth chamber surrounded by a tongue and teeth; a pharynx or back of the throat; a food tube called the esophagus; which empties into a flexible compartment, the stom- ach; which brings food into the small intestines where most of it is absorbed; and emp- ties into the large intestines, after which it is eliminated through the anal canal and rectum. Food is propelled through the alimentary canal through rhythmic contractions of its muscular walls, called peristalsis.

The alimentary canal is connected with associated organs, called accessory organs, which produce, store, and/or release chemicals to carry out the processes of the break- down of food. Accessory organs include the salivary glands of the mouth, which secrete saliva; a gallbladder, which stores bile, a juice released within the canal; the liver and pancreas, which both make enzymes to break down food.

Alimentary canal

The tube and associated organs of digestion, which includes all of the parts of the digestive system that contribute to the breakdown of food.

Pharynx

A tube that starts behind the nose and mouth connecting to the esophagus.

Mouth

An opening in the lower part of the face.

Esophagus

Food tube.

Anal canal

Terminal part of the large intestine.

Rectum

The final part of the large intestine.

Peristalsis

The involuntary muscular contractions of the digestive tract by which contents are forced onward.

Accessory organs

Associate organs that produce, store and/ or release chemicals to carry out the processes of the breakdown of food.

liver

A large glandular organ found in the abdomen of vertebrates.

Figure 12.13 Apple vs. pear shapes. It is better to be a pear than an apple. Abdom- inal fat located around the organs in the abdomen is linked to cardiovascular disease and increased cancer risks.

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Pancreas

A diffuse gland located near the stomach.

Salivary glands

The gland that secretes saliva.

Stomach

An internal organ sac that holds and digests food before entering the small intestines.

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Digestion The alimentary canal, also called the digestive tract, carries out the process of digestion. Digestion is defined as the mechanical and chemical breakdown of food. It readies food for absorption into the body. Digestion does not provide instant energy because the food is not broken down into ATP. Instead, digestion breaks down food particles into a size that is able to be absorbed by the alimentary canal at certain points. After food particles

Oral Cavity

Duodenum

Small Intestine

Anus

Transverse colon

Figure 12.14 The human digestive system. The alimentary canal in humans is composed of several com- partments that mix and digest food.

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are absorbed, they are transported into cells and broken down to release adenosine tri- phosphate (ATP) energy through cellular respiration (see Chapter 4).

Digestion occurs mechanically and chemically. Mechanical digestion changes only the size of food particles, making them smaller and easier to digest. Smaller particles have a greater surface area on which digestive enzymes can work to break the parti- cles down. This process is shown in Figure 12.15. Mechanical digestion first occurs in the mouth. Through chewing food, particles become smaller and easier for enzymes to attach to. After the mouth, food moves through the esophagus to the stomach, where it is further mechanically digested. Through the churning of muscles on the walls of the stomach, food further breaks into smaller bits.

Chemical digestion changes the structure of substances being digested. Enzymes are produced in the mouth, stomach, and small intestines to cleave food at certain points, breaking them into smaller compounds. The smaller substances are able to be absorbed by the lining cells of the small intestines. Let’s give a look at the processes and structures along the alimentary canal.

Figure 12.15 Surface area increases after mechanical digestion. Food is broken down into smaller pieces, increasing the surface area on which enzymes can act to aid in food digestion. These smaller pieces of Belgian cheese will be easier to digest than a large piece.

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DOES DiGEStiON CAuSE CRAMPiNG iF yOu DON’t WAit tO SWiM AFtER yOu EAt?

There is no need to wait to swim after you eat, as digestion does not interfere with swimming. Muscle cramps while swimming do not occur as a result of eat- ing a meal. No measurable changes in peristalsis occur while a person swims.

This myth might have originated because the parasympathetic nervous sys- tem becomes activated during and after eating. The parasympathetic nerves activate digestion and slow messages to other body parts. However, no evi- dence has shown muscle dysfunction or heart problems during exercise simul- taneous with digestion.

Digestion

The process in which food breaks down mechanically and chemically. Mechanical digestion changes only the size of food particles, making them smaller and easier to digest, while chemical digestion changes the structure of the substances being digested.

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Chapter 12: Nutrition and Digestion 445

Mouth

The first part of digestion, called ingestion, requires food to be brought into your stom- ach. Ingestion typically takes about one minute, the time to chew and swallow food. It involves the mouth, tongue, teeth, and esophagus. Figure 12.16 shows the process of swallowing and the rhythmic motion of muscles in the throat that propel food into the stomach. Figure 12.16 also gives an overview of the digestive organs alongside their enzymes produced and the foods absorbed in those different regions. Peristalsis is defined as this set of digestive muscle contractions, which begins with smooth muscle bringing food into the stomach. Because the muscles carrying out peristalsis act invol- untarily once food is swallowed to move the bolus (ball) of food through the alimentary canal, a person could drink and eat upside down.

Food, and sometimes the smell or thought of food, stimulates the production of saliva in our mouths. When food enters the mouth, it stimulates a nervous reflex, leading to saliva release by the salivary glands. Over 1 L of saliva is produced by the salivary glands per day and released into the mouth. The salivary glands of the mouth are iden- tified in Figure 12.17.

While mechanical digestion is accomplished by the tongue and teeth, breaking food into smaller bits, saliva contains the enzyme salivary amylase which chemically breaks down starch into smaller polysaccharides. About 20% of the starch ingested into the alimentary canal is broken down by salivary amylase. Digestion of carbohydrates is completed later in the small intestines.

Buffers within the saliva also neutralize the acids in the mouth and limit damage to the teeth. A flora of bacteria lives in our oral cavities; they produce acids that cause den- tal caries (cavities) and gum disease. Certain bacteria, such as Streptococcus mutans and Streptococcus sobrinus, are particularly good producers of acid when sweet foods enter the mouth cavity. These bacteria are closely linked to tooth decay, but their populations are greatly reduced in the presence of fluoride toothpaste.

ingestion

Consumption of a substance by living organisms.

Figure 12.16 Ingestion of food. Food moves quickly from the mouth (via the esophagus) to the stom- ach. It then takes 24–48 hours to move through the rest of the digestive tract, with enzymes released and absorption of nutrients in different regions. BSCS by Doug Sokel. Corel.

Bolus

A rounded mass of food. Salivary amylase

An enzyme present in the saliva that chemically breaks down starch into smaller polysaccharides.

Cementum

A glue-like substance holds the ligament that connects the dentin to the underlying bones of the face.

Dentin

The bony tissue of a tooth.

Enamel

The strong covering protecting the teeth.

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Teeth, as shown in Figure 12.18, are protected by a strong covering called enamel, composed of calcium salts. These calcium salts are not replaced, so wearing of enamel results in bacteria’s access to tissues beneath. The bony tissue of a tooth, called dentin, lies below the enamel layer. Dentin is connected to the underlying bones of the face via a ligament held together with glue-like substance called cementum.

A cavity within the dentin contains blood vessels and nerves. This cavity is known as the pulp cavity or root canal, a name that scares many people from the dentist’s chair. In order to deaden the nerve and remove infected tissue from the pulp cavity, a “root canal” is performed, which is often associated with pain at the dentist. Teeth are sur- rounded by the gingiva or gums, composed mostly of connective tissue providing a blood supply to the region. Gum disease, also known as periodontal disease, is a leading cause of tooth loss.

The front teeth, called incisors and canines, are long and narrow; both types evolved to tear and pull foods. Premolars and molars at the back of the mouth are suited for grinding and chewing foods, such as vegetables and fruits. A look at an animal’s teeth indicates its diet. For example, meat eaters such as cats and bats have sharp teeth while those eating plants have flat, wide teeth.

Esophagus

As the tongue brings food from the mouth it first enters the pharynx. The bolus of food passes the pharynx at the back of the throat, and the pharynx opens into two passage- ways: the trachea and the esophagus. The trachea, also known as the windpipe, connects to the lungs, and the esophagus travels to the stomach. The trachea is covered with a flap of elastic cartilage called the epiglottis, which prevents food from entering into the trachea.

Pulp cavity

A cavity within the dentin containing blood vessels and nerves. incisors

The four front teeth evolved and adapted for cutting and tearing. Canines

The front teeth on the side, long and narrow, evolved to tear and pull foods.

Molars

A grinding tooth found at the back of the mouth and suited for grinding and chewing foods. Epiglottis

The flap of elastic cartilage covering the trachea.

Figure 12.17 Salivary glands in the mouth release saliva for digestion of starches. Saliva also buffers the mouth, limiting damage to teeth from its often caustic acidity.

Parotid duct

Masseter muscle

Mucosa (cut)

Sublingual ducts

Parotid salivary gland

Submandibular duct

Submandibular salivary gland

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Pre-molars

Teeth situated between canine and molar teeth and suited for grinding and chewing foods.

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Chapter 12: Nutrition and Digestion 447

When food arrives at the pharynx, the voice box or larynx moves quickly upward, pushing the epiglottis over the trachea. When a person is choking, the bolus of food becomes lodged in between the epiglottis and the larynx. Choking victims can be helped by the Heimlich maneuver, which forces air out of the trachea to dislodge the food blockage. The steps of the Heimlich maneuver are given in Figure 12.19.

The esophagus, also known as the food tube, is a muscular tube that propels food down into the stomach. The superior part of the esophagus is composed of striated mus- cle, enabling voluntary movement of food downward. The inferior portion of the esoph- agus is composed of smooth muscle, which is not under conscious control.

larynx

The part of throat containing the vocal cords.

Incisors Central (7 yr) Lateral (8 yr)

Canine (eyetooth) (11 yr)

Premolars (bicuspids)

First Premolar (11 yr)

Second Premolar (12-13 yr)

Molars First Molar

(6-7 yr) Second Molar

(12-13 yr)

Third Molar (Wisdom Tooth)

(17-25 yr)

Permanent Teeth

Incisors Central

(6-8 mo)

Canine (eyetooth) (16-20 mo)

Molars First Molar (10-15 mo)

Second Molar (about 2 yr)

Deciduous (Milk) Teeth

Lateral (8-10 mo)

Figure 12.18 Tooth anatomy and types of teeth in humans. Molars are best adapted to grind foods such as vegetables and fruits. Canine and incisors are better adapted for pulling and tearing foods such as meats.

trachea

A tube-like portion of the respiratory tract that connects to the lungs.

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Crown

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Root

Blood Vessels and Nerves in

Apical Foramen

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448 Unit 4: The Dynamic Animal Body

Figure 12.19 The Heimlich Maneuver is vital in saving choking victims.

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Stomach

No digestion occurs in the esophagus, through which food is transported quickly into the stomach, a flexible and muscular J-shaped organ. Proteins and fats are not broken down up to this point. The walls of the stomach are quite muscular with three layers and a compartment within is able to hold up to 4 L (one gallon) of food and fluids. Food remains in the stomach for up to 2 hours as it is digested. Figure 12.20 shows the struc- ture of the stomach.

The top region of the stomach, where it connects to the esophagus, is guarded by the cardiac sphincter or gastro-esophageal sphincter. The cardiac sphincter opens and closes as a circular muscle. It prevents stomach fluids, which are acidic, from back flow into the esophagus. In the stomach, folds called rugae churn food to mechanically break it down. The bottom region of the stomach, which empties into the small intestines, is controlled by the pyloric sphincter.

When food enters the stomach through the gastro-esophageal sphincter, stomach-lin- ing cells found within gastric pits in the stomach wall produce hydrochloric acid (HCl) and pepsinogen. Pepsinogen is an inactive enzyme and unable to break down nutrients. After it is released into the stomach cavity, pepsinogen is quickly transformed into an active enzyme called pepsin. Pepsin requires the acidity created by HCl in the stomach cavity to become active and digest proteins. When a pepsinogen molecule is released into the stomach, HCl in the stomach cavity cleaves the tail off the molecule, revealing an active site that enables pepsin to break down protein. This action occurs in open areas in Figure 12.21.

The pH of the stomach ranges between 2 and 3. Acids break down plant materials such as fiber, and structures that otherwise are not digested such as cellulose and bind proteins. This process enables food to more easily move through the digestive tract. The acids of the stomach also serve to destroy the many bacteria in our foods. Even cooked, bacteria – which number more than 100 million per cubic centimeter – enter into the stomach. Most bacteria die when entering such an acidic condition. However,

Cardiac sphincter

The muscle surrounding the opening between the stomach and esophagus.

Rugae

Series of folds produced by folding the wall of an organ.

Pyloric sphincter

Muscle fibers around the stomach opening between it and the duodenum.

hydrochloric acid (hCl)

An aqueous solution of hydrogen chloride.

Pepsinogen

The inactive precursor to pepsin.

Pepsin

An enzyme produced in the stomach.

Figure 12.20 Stomach anatomy. a. The stomach muscle layers help propel food (by peristalsis) from the gastro-esophageal sphincter to the pyloric sphincter. b. Micrograph of stomach.

Cardiac Sphincter

Body of the Stomach

Pyloric Sphincter

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Gastric Pit

Simple Columnar

Epithelium

Surface Mucous Cell (secretes mucin)

Mucous Neck Cell (secretes acidic mucin)

Parietal Cell (secretes hydrochloric acid and intrinsic factor)

Chief Cell (secretes pepsinogen)

Gastric Pit

Gastric Gland

Mucosa

Submucosa

Muscularis

Myenteric Nerve Plexus Artery Vein

Opening to Gastric Pit

Gastric Pits

(b)

Figure 12.20 (continue)

some food-borne illnesses, such as Staphylococcus aureus and Salmonella are resistant to the acidic environment of the stomach. Acidity from the stomach has powerful effects. In our story treating eating disorders, many bulimics suffer damage to their oral cavity from stomach acids. In bulimia, which involves purging of food, stomach acids regur- gitate to damage teeth and gums. Acidity from the stomach also damages the linings of the esophagus in its victims.

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Chapter 12: Nutrition and Digestion 451

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Figure 12.21 Cells in the pits of the stomach secrete pepsinogen and HC1. Pepsino- gen is inactive when produced but is transformed into the active enzyme pepsin. The enzyme action of pepsin on proteins breaks these substrates down into amino acids.

DOES PuttiNG hOt FOOD iN thE REFRiGERAtOR RuiN thE FOOD?

Hot foods should be immediately placed into the refrigerator to avoid food- borne illnesses. There is little truth to leaving out a dish of food to “bring out its flavors.” The same flavor will develop, perhaps more slowly, in the refrig- erator. Moreover, the increased risk of dangerous bacteria multiplying when food is left at room temperatures far outweighs any minimal loss of flavor from refrigerating cooked foods immediately.

The cooling down phase from hot food (57°C or 135°F) to room tem- perature (15°C or 41°F) is known as the danger zone because certain types of bacteria, Salmonella, Pseudomonas and E. coli, for example, grow well at 37°C, and Staphylococcus (often found on skin surfaces) thrives at 25°C.

Some bacteria, such as Pseudomonas, are also able to grow at refrigerator temperatures, but the cold slows their growth drastically. Placing hot food in the refrigerator does require more energy since it takes more electricity to bring a meal from a higher temperature than from room temperature, but the tradeoff in added safety is well worth the extra expense.

Small Intestine

The acidic ball of food, called the chyme, passes into the small intestines through the pyloric sphincter. The small intestines are narrow, thin tubes roughly 20 feet in length. The name “small” emanates from its narrow width, but it is actually a very long tube winding around abdominal organs. Peristalsis moves food slowly through the small intestines, taking up to 8 hours. The liver and pancreas are connected to the small intes- tines via a common duct.

Chyme

Acidic ball of food.

Small intestine

The portion of intestine that lies between the colon and stomach.

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The walls of the small intestines are covered in villi, which are small folds or pro- jections. On these small projections are thousands more smaller villi called microvilli. Together, villi and microvilli increase the surface area of the small intestines to aid in digestion and absorption of nutrients. Figure 12.22 successively shows the smaller and smaller folds of the small intestines.

Villi

Small folds or projections lining the walls of the small intestine. Microvilli

Smaller villi.

Figure 12.22 The layers of the digestive system. Folds of the small intestines form villi and microvilli. Villi contain capillaries and lymph vessels that absorb and transport nutrients to the rest of the body.

Circular muscle layer

Muscularis Esterna

Myenteric Plexus

Submucosal Plexus

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In Celiac disease, a malfunction of villi creates cramping and intestinal discomfort. There are many forms and levels of severity of Celiac disease. An inability to digest glu- ten is blamed on increasing cases. The causative effect of gluten on intestinal efficiency is still being researched.

Complete digestion of all of the macronutrients occurs in the small intestines. Intes- tinal cells produce enzymes that complete the digestion of all of the macronutrients. Food becomes small enough to be absorbed through the cell membranes of intestinal lining cells.

How is this done? As chyme enters into the top portion of the small intestines, called the duodenum, it stimulates the release of enzymes. Some enzymes are made by the intestinal lining cells and others are made by the pancreas and the liver. As food moves through the small intestines, it enters a middle region called the jejunum in which diges- tion continues. Accessory organs, discussed below, aid in the digestion of the macronu- trients. After this point, food is small enough to be absorbed, as shown in Figure 12.23. It reaches the end region of the small intestines, called the ileum. Absorption occurs in the intestinal cells of the ileum. By the end of digestion in the small intestines, all of the macronutrients are absorbed into the body.

Major Accessory Organs: Pancreas. Acidic chyme entering from the stomach stimulates intestinal cells to make the hormone secretin. Secretin causes the pancreas to release bicarbonate (HCO3−) and pancreatic juice. Bicarbonate is a buffer and neu- tralizes the acidic chyme entering the intestines. For enzymes to work in the small intes- tines, a basic pH of roughly 8 is required. Pancreatic juice also contains enzymes that digest all of the macronutrients: proteins, carbohydrates, and lipids are broken down into their smallest units – amino acids, simple sugars (monosaccharides), fatty acids, and glycerol – to be absorbed by the intestines.

intestinal cells

Cells lining the GI tract.

Duodenum

The top portion of the small intestine.

Jejunum

The second part of the small intestine.

ileum

The third portion of the small intestine.

Secretin

A digestive hormone secreted by the duodenum.

Bicarbonate (hCO3

A buffer that neutralizes the acidic chyme entering the intestines.

Pancreatic juice

A secretion of the pancreas that contains enzymes that digest all of the macromolecules.

Figure 12.23 Digestion of the three macronutrients in the small intestines: Almost all nutrient absorption occurs across the lining cells of the small intestines. Villi help to increase surface area for absorption in the small intestines.

Amino acids

Fatty acids

Simple sugar

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Figure 12.24 a. Fat emulsification. The way in which bile works. Bile breaks down larger globules of fat into smaller ones. When fat is in the small intestines, bile is released from the gall bladder to break it down. b. Functions of the liver. From Biological Perspectives, 3rd ed by BSCS. c. The liver.

Fat globule

Bile

(a) (b)

Right Lobe Left Lobe

Cystic Duct

Right Lobe Left Lobe

Hepatic Portal Vein Common Hepatic Duct Hepatic Artery Proper

Gallbladder

Gallbladder Quadrate Lobe

Caudate Lobe

Anterior View Posteroinferior View

Anterior Inferior

Vena Cava

Inferior Vena Cava

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Major Accessory Organs: Liver. When fats arrive at the duodenum, intestinal cells make the hormone cholecystokinin (CCK), which slows peristalsis. This gives the small intestine more time with fatty foods to complete their digestion. CCK also stimulates the liver to produce bile, a salt that emulsifies fats. Emulsification breaks fat globules into smaller globules, helping their digestion by enzymes. Bile is not an enzyme and serves to mechanically break down fat by pulling apart the hydrophobic and hydrophilic regions. The way bile works is depicted in Figure 12.24a.

Cholecystokinin (CCK)

A hormone that slows peristalsis.

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Like the pancreas, the liver is an accessory organ, and both aid in the digestion of macronutrients. Bile is made in the liver but is stored in the gall bladder, a small organ on the underside of the liver. Bile is released only when fat arrives at the duo- denum. The liver has a number of functions within the body in addition to its role in digestion:

1) Detoxification of harmful substances such as alcohol and drugs 2) Storage and packaging of fat into cholesterol: HDLs and LDLs 3) Deamination of proteins by removing amino groups and forming urea in the

urine 4) Transformation of amino acids into carbohydrates 5) Regulation of glucose levels in the blood by storing glycogen 6) Production of plasma proteins, clotting factors, and bile; and storage of

fat- soluble vitamins 7) Inactivation of hormones

While the liver is only an accessory organ in the digestive system, it plays a major role in our life functions. The digestive and accessory organs work together to accom- plish the complex task of digestion. An overview of the principal digestive enzymes and their regions of activity in the body are given in Figure 12.25.

Gall bladder

A small organ on the underside of the liver.

Figure 12.25 Principal digestive enzymes. Enzymes digest macromolecules in differ- ent regions of the alimentary canal. Ed Reschke.

WhEN COMBiNiNG CERtAiN FOODS, CAN DiGEStiON BE SlOWED, AiDiNG WEiGht lOSS?

Some diets argue that eating separate macromolecule meals (proteins, lipids, or nucleic acids) or combining certain foods with one another, helps people to lose weight. They claim that some combinations of foods poison the body and lead to weight gain and other ailments. It is true that certain foods, such as vitamin C, help the ileum to absorb more iron from foods. However, the small intestines make enzymes for all of the macronutrients at the same time. The macronutrients are digested independent of one another, with combinations irrelevant to digestion or absorption. As long as a macronu- trient is broken down into small enough particles, it is absorbed in the small intestines. There is no truth to this myth.

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Large Intestine

The final phase of food processing occurs in the large intestines, also known as the colon. The large intestines are much wider (3 inches) than the small intestines (1 inch) but they are shorter, at only 3–6 feet in length. The large intestines form a loop around the abdominopelvic cavity, surrounding the small intestines. They attach to the small intestines at the ileum and receive remaining wastes. They then ascend, travel across the body, and descend into the rectum. Feces or final waste products are expelled through the anus. The human large intestine is shown in Figure 12.26.

It takes between 12 and 24 hours for food to travel through the large intestines. In the 1980s, the Mayo clinic measured the time it takes for digestion in 21 healthy people. It estimated that the transit time for food moving throughout the alimentary canal is 33 hours for men and 47 hours for women.

The large intestines are excellent recyclers of the micronutrients: they absorb over 90% of the water needed for the body, along with dissolved minerals, salts, and vitamins from feces. The colon concentrates wastes, drying them out as water and these vital micronutrients are absorbed. The last part of the colon, the rectum acts a storage com- partment for our final waste products.

Figure 12.26 The human large intestine. A wide tube, which houses bacteria and is responsible for most of the water absorption in the human body. It is also known as the colon and carries food to the rectum and anus.

Transverse Colon

Descending Colon

Sigmoid Colon

Rectum

Ascending Colon

Cecum

Appendix

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The composition of feces is about 95% bacteria by dry weight. A flora of bacteria normally resides in the large intestines. These bacteria are useful to humans. They guard against other, more harmful bacteria that would otherwise take hold of the area. Large intestinal bacteria provide nutrients such as vitamin K and a type of vitamin B (biotin) as they break down wastes. Anorexia nervosa, as pointed to in our story, can have drastic effects on heart and nerve functions, as minerals such as sodium and potassium are not absorbed in adequate amounts. This disruption of mineral balance is a frequent cause of death in anorexics.

The large intestines provide an oxygen-free environment. They house bacteria that break down wastes to produce nonoxygen gases as by-products: methane, hydrogen, sulfur, carbon dioxide, and water (also the composition of any flatulence – intestinal gas).The gases found in the large intestines of humans are very similar those found on early Earth. Thus, the bacteria within our intestines also resemble those found on Earth over 4 billion years ago. Often, environmental cleanliness is measured by track- ing certain bacteria in soils and water, namely coliform and E. coli, normal intestinal bacteria.

DO VEGEtABlES CAuSE GAS?

Bacteria break down plant and animal materials that are undigested in humans. Undigested feces move en masse into the large intestines, where bacteria transform feces into gas vapors. Vegetables, particularly beans and legumes, have high amounts of these materials, such as cellulose, which only bacteria can consume. Raffinose oligosaccharides, found in high doses in beans, cab- bage, and Brussels sprouts produce larger volumes of gas as they are broken down by bacteria. The gases cause the commonly associated intestinal pains. Abdominal muscles contract to move the gas bubbles through the intestines more quickly.

The Role of Fiber. Diets high in fiber, long chained carbohydrates, help to cleanse the digestive system. Fiber, found in grains, vegetables, and fruits, is not digested or absorbed in the alimentary canal. It adds bulk and speeds the movement of food through the digestive tract. In chronic constipation cases, a long term treatment plan is to increase fiber intake to prevent constipation by softening feces and making it easier to move through the many convolutions of the digestive tract.

Diet changes are always the best first strategy to improve one’s digestion. Laxatives are also used to soften stools. Laxatives often contain magnesium salts, which increase the salt concentration in the feces. Since water follows solute, salt draws more water out of the body and into the large intestines. The added water softens feces, making it easier to expel.

Fiber is also related to lower risks for colon cancer and heart disease. Some forms of fiber, which dissolve in water called soluble fiber, attach to cholesterol in the digestive tract and thus eliminate fat from the body. Diets high in soluble fiber are associated with lower risks of heart disease and stroke. Insoluble fiber, which does not dissolve in water, serves as roughage to cleanse the intestines.

Soluble fiber

Fibers that dissolve in water.

insoluble fiber

Fibers that do not dissolve in water and serve as roughage to cleanse the intestines.

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Common Diseases of the Digestive system Heartburn

Heartburn. Heartburn occurs when pain along the esophagus results from acids of the stomach leaking out of the upper regions through the gastro-esophageal spinchter. Leak- age from either sphincter in the stomach leads to damage in adjoining organs. Indiges- tion due to leakage of acidic stomach contents into the esophagus causes damage to linings and may result in serious discomfort for its sufferers.

It may occur when someone eats too much or too quickly, propelling food upward into the esophagus. Antacids can alleviate the discomfort of indigestion. However, antac- ids interfere with digestion because the stomach functions best when its acidity is normal.

When acids continue to escape into the esophagus, a chronic condition called gas- tro-esophageal reflux disease (GERD)can develop and continual damage to the esophageal lining may lead to Barrett’s esophagus, characterized by a change into precancerous cells. In 10% of cases of Barrett’s esophagus, GERD leads to esophageal cancer, a very danger- ous disease claiming over 95% of its victims (discussed in chapter 2). GERD is treated by stronger medications to reduce acidity in the stomach and by surgery to repair the sphincter.

Ulcers and stomach Cancer Ulcers. A species of bacteria called Heliobacter pylori thrive in acidic conditions and can cause forms of stomach (peptic) ulcers. Ulcers are open sores in the lining of mucous membranes that can develop into infections. It is estimated that one-third of all people have H. pylori in their bodies. In 1985 Barry Marshall, a young physician and scientist, demonstrated that H. pylori caused ulcerations in the stomach lining by drinking a vial of H. pylori to prove that it was the cause of, rather than a result of, ulcers. Indeed, he developed numerous irritations after drinking the vial. However, H. pylori are only active in some people, for reasons that are not fully understood.

Stomach Cancer. Peptic ulcers are a risk factor for developing stomach cancer. Stom- ach cancer has a low survival rate because it is often found too late and metastasizes to other parts of the body. As we saw in Chapter 5, cancer when found early, is usually cur- able. Some cancers, such as stomach cancer, are not screened regularly or found early enough. Stomach cancer occurs at a high incidence in Japan, where adults are regularly screened for the disease. An open or bleeding peptic ulcer is obvious in Figure 12.27.

Gastro-esophageal reflux disease (GERD)

A chronic condition caused when acids continue to escape into the esophagus.

Figure 12.27 Ulcers are not caused by stress alone but by some forms of bacteria. From Biological Perspectives, 3rd ed by BSCS.

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Colon Cancer Colon Cancer. Diets high in insoluble fiber are related to lower risks for colon cancer, the third highest cause of cancer deaths in the United States. Colon cancer develops from a small polyp, which grows larger and becomes cancerous over time. A colonoscopy places a flexible tube into the colon to detect polyps and colon cancer (Figure 12.28). If removed early, colon cancer has a 90% survival rate. Polyps are removed during a rou- tine colonoscopy. Surgery may be required upon detecting colon cancer. A controversial limit to screen for colon cancer recommends an end to screening after age 75 because a person is statistically likely to die from other causes by that age. Is this a fair recommen- dation by the American Medical Association? Are seniors being deprived of screening tests that could save their lives in the name of statistics?

Figure 12.28 A colonoscopy examination checks the topography of the large intes- tines to detect signs of colon cancer. In this image, a polyp (small growth of cells) is removed within the colon.

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DOES BlACKENED (OR SEARED) MEAtS CAuSE CANCER?

Whenever a meat is smoked or grilled (especially when it is blackened), it has been shown to develop chemicals that are cancer causing (carcinogenic). High temperatures convert normal chemicals in meats into heterocyclic amines (HCA’s), which have been shown to cause a variety of cancers. The smoke ema- nating from grilling contains polycyclic aromatic hydrocarbons (PAHs). PAHs are known carcinogens that attach to meats as they are grilled or smoked. Salami, smoked fish, bacon, hamburgers, and hot dogs contain PAH levels asso- ciated with cancer.

However, limited research has been conducted on human subjects to make these claims. Animal studies act as a model for possible links between grilled and smoked meats and cancer (Figure 12.29). One recommendation is to remove the skin on smoked or grilled meats, which is to likely contain the majority of the PAH chemicals. As in our opening story, food is a source of health and disease.

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summary Eating disorders and obesity are illnesses influenced by societal factors centering on people’s focus on body image and food. While food is needed to survive, with micronu- trients and macronutrients required in the right amounts, food is also a source of disease. Eating too many calories leads to obesity and eating too few calories, to a point of being seriously underweight, also leads to health problems. A person’s healthy body weight may be determined using the BMI. Nutrients are broken down and absorbed through digestive processes. Digestion and its related diseases occur throughout the alimentary canal and its accessory organs. Eating disorders and obesity, both leading causes of health hazards, are a result of disruption in normal nutrition and digestion.

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Figure 12.29 Grilling meats and PAHs, does charred meat cause cancer?

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summary: key points

• Psychological and societal factors both influence what foods a person chooses. • Changes in diet and exercise in the past century have led to both the obesity epidemic and eating

disorders in our society. • Nutrients, both micronutrients (water, minerals, and vitamins) and macronutrients (proteins, lipids,

and carbohydrates), are essential for the proper workings of the human body. • Calories taken in vs. calories used by the body determines whether a person gains, maintains, or

loses weight. • While mechanical digestion physically breaks down food into smaller pieces, chemical digestion

changes food by rearranging bonds, into smaller substances. • The alimentary canal transports food through the mouth, pharynx, esophagus, stomach, small intes-

tines, large intestines, rectum, and anus. • Digestive cancers, such as stomach, esophageal and colon cancer, and ulcers, along with eating dis-

orders, impact proper digestive processes.

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accessory organs alimentary canal anal canal anorexia nervosa antioxidants apple shape basal metabolic rate (BMR) bicarbonate (HCO3-)bolus bulimia calories canines cardiac sphincter cementum cholecystokinin (CCK) chyme dentin digestion, mechanical, chemical duodenum enamel epiglottis esophagus essential amino acids fat-soluble vitamins food plate food pyramid free radicals gall bladder gastro-esophageal sphincter, or pyloric sphincter gastro-esophageal reflux disease (GERD) hydrochloric acid (HCl) ileum incisors ingestion insoluble fiber intestinal cells

jejunum large intestines or colon larynx liver macronutrients metabolism micronutrients microvilli minerals molars mouth Neolithic diet nonessential amino acids nutrients obesity pancreas pancreatic juice pear shape pepsin pepsinogen peristalsis pharynx premolars pulp cavity rectum rugae salivary amylase salivary glands secretin small intestines soluble fiber stomach trachea villi water water-soluble vitamins

KEy tERMS

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Multiple Choice Questions

1. Which disease is MOST influenced by the role food plays in body image society? a. Colon cancer b. Herpes c. Ulcers d. Anorexia nervosa

2. A characteristic of modern society that has resulted in changes in the rates of obe- sity over the past century is: a. less physical activity in jobs. b. more varied food choices. c. decreases in HFCS use in foods today. d. decreased productivity by workers.

3. Which term is best associated with metabolism? a. BMR b. BMI c. BMO d. BBB

4. Vitamin A belongs to the_____ group of nutrients. a. smallest b. largest c. macronutrient d. micronutrient

5. When dieting, the most weight is lost during the first few weeks. This weight loss is attributed to loss of: a. lipids b. proteins c. minerals d. water

6. Which represents a logical order, from start to finish, in the movement of food along the alimentary canal? a. esophagus ➔ pyloric sphincter ➔ stomach ➔ large intestines b. pyloric sphincter ➔ esophagus ➔ large intestines ➔ stomach c. esophagus ➔ large intestines ➔ stomach ➔ pyloric sphincter d. esophagus ➔ stomach ➔ pyloric sphincter ➔ large intestines

7. Which is NOT a function of the liver? a. Production of bile b. Storage of glycogen c. Absorption of nutrients d. Elimination of wastes

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8. Mechanical digestion is carried out by: a. teeth b. pepsin c. pancreatic juice d. amylase

9. Which organ does NOT produce enzymes that digest nutrients? a. Liver b. Stomach c. Pancreas d. Small intestines

10. Heliobacter pylori is most closely associated with: a. tooth decay b. acid reflux disease c. colon cancer d. ulcers

short answers

1. Describe two ways in which society influences the foods people choose to eat. Define and describe one digestive disease that is influenced by the food in one’s diet.

2. Define the following terms: anorexia nervosa and bulimia. List one way the terms differ from each other in relation to their a. symptoms; and b. prevalence in the U.S. population. Explain how the terms are similar.

3. Explain how BMI is used in determining healthy weight. Is it always a reasonable measure of a person’s health? Why or why not?

4. Which micronutrient is the most important in maintaining ion balances within the body? Which organs are most affected by micronutrient imbalance?

5. Mechanical digestion plays an important role in breaking down foods. Define mechanical digestion and give an example of it within the alimentary canal. Is a human able to survive using only mechanical digestion?

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Chapter 12: Nutrition and Digestion 465

6. Colon cancer is a major killer. List two ways a person may limit their risks of dying from colon cancer.

7. Trace the movement of sugar water through the alimentary canal. Be sure to list 1) each region it is digested and 2) each region it is absorbed.

8. For question #7, how would the answer change if the food were a large slice of fatty bacon?

9. Explain how GERD is affected by both diet and anatomy.

10. Describe a plan for best improving weight loss in a client. Be sure to include the terms BMI, BMR, muscle mass, insoluble fiber, and water.

Biology and society Corner: Discussion Questions 1. Fast foods, such as McDonald’s and Kentucky Fried Chicken, are becoming more

common in many countries in Western Europe, including Greece. Research and explain the changes in diet and obesity rates in Greece over the past 25 years.

2. The growing obesity epidemic is particularly concerning among children. What changes (if any) would you suggest to parents to help their children eat healthy. Do you think it is ethical to mandate your suggestions in, for example, school lunches?

3. Roughly half of Americans take vitamin supplements. It is a multimillion-dollar industry. Yet, most nutritionists agree that the majority of these vitamin takers do not need them. Should the government limit their consumption? Why or why not?

4. Barry Marshall, to show that H. pylori causes (and is not a result of) ulcers in the stomach, went to extreme measures, drinking a vial of the bacteria. Do you think it was ethical for him to put his life in danger with an untested hypothesis? Would an animal model have been a good enough evidence for the research question? Why or why not?

5. This chapter focuses on many diseases associated with digestive illnesses. The sur- vival rate for many digestive cancers, such as colon cancer, is high when caught early in its onset. Would you recommend mandatory screenings at certain ages? Do you agree with limiting screening after certain ages, as for colon cancer, as recom- mended by the American Medical Association?

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Figure – Concept Map of Chapter 12 Big Ideas

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467

The Heart-Lung Machine: Circulation and Respiration

A father and daughter

A heart and lungsA father is alone

A heart transplant surgery

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A car accident

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The Case of his Daughter’s Heart 2014: Charles’ heart beat ever so gently, with a regularity that reminded him every moment that Peggy was still with him – in him – all the days of his life.

Flashback 15 years: It would be her first trip away from home. Peggy looked for- ward to her weekend camping trip, high in the mountains of the Adirondacks. Charles’ daughter, Peggy was a lively and driven teen but she wanted to be a little more indepen- dent. It would be her first trip away from home and the first time she spent a night away from her father. Charles had a strange feeling about the day. He felt worse than usual, as if life would soon end. He was quite ill, after all, and struggled to walk around the house; even a trip across the room had become a breathless chore.

Charles’ heart was weak, with a condition called congestive heart failure. He had a series of heart attacks, which weakened his heart muscle to about 15% of its normal strength. The doctors checked his left ventricle ejection fraction, which is the amount of blood pumped out of the heart by its strongest muscle, the left ventricle. Charles would need a new heart but it would be hard to find a matching one. The doctors leveled with Charles, informing him that if he did not find an organ within the next year, he would die.

Charles felt a horrid chill after hearing the doctor’s news that he would soon die – an ominous loneliness that he and his Peggy would part. He looked through old pictures of his daughter, tracing each event as she grew up through the years. Their years together would stay with them forever.

Charles was both a father and a mother to Peggy. After her mother died, when Peggy was only 8 years old, they had only each other. Charles had not ever spent a night away from his daughter since she lost her mother. They had a closeness about which they never spoke, but was deeply felt between them. Some people told Charles that he was overprotective.

Nevertheless, Charles was pleased that Peggy travelled with her friends to the Adirondacks. Peggy might soon be alone, without Charles to care for her, if biology had its way. So, Charles knew that he had to let go. The trip would be good for Peggy and for him. “She needed to be with other people; to have a good time,” Charles thought. “Peggy always gave a part of herself to everyone she met.”

This is what made the phone call so ironic: “Your daughter is in a coma. She had a car accident on the Northway. I am very sorry sir,” spoke the voice on the phone. Charles was numb and his horror was immense.

CHECk in

From reading this chapter, you will be able to:

• Explain how medical treatment advances and prevention help improve heart and lung health in society.

• Describe the functions and components of the blood. • Trace the movement of blood within the heart and blood vessels and the electrical activity that cor-

responds to an ECG. • Connect the role of high blood pressure with cardiovascular diseases in society. • Trace the movement of air through the respiratory system. • Explain how gases are exchanged within the lungs • Describe the cardiovascular and respiratory diseases and their current treatments.

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Chapter 13: The Heart-Lung Machine: Circulation and Respiration 469

At the hospital, doctors emphasized that his daughter would die shortly. She was an organ donor and she had offered her heart to you in her donation paperwork.

Charles could not do it: “Was it ethical?”; “How macabre.”; “Who could take their own daughter’s heart?” thought Charles. But it was the right decision or Charles too would soon die.

The doctor explained that it was his daughter’s wish that he live on through her. It was a gift of the deepest love. Charles took his daughter’s heart.

CHECk Up sECTion

Organ donation is a key to survival for many people facing serious illness, like Charles in the story. But obtaining a donor for a needed transplant can be difficult. About 6,500 people die each year while waiting for a transplant.

Many organs are able to be transplanted after a person dies, while some organs may be trans- planted while a person is alive. Research the organs used in both deceased and live organ transplants. Explain the risks associated with organ transplants.

Owing to the shortage of organs, should the government require all people to donate their organs upon death? Why or why not?

Blood: Life’s Force Early religions viewed blood as a life force, with special healing and magical powers. Many religions integrated these views into their beliefs and customs, from sacrifices and blood bonding to specific uses of foods containing blood. The Mayan Indians, for exam- ple, believed that blood sacrifices needed to be offered to keep the cosmos in balance. Figure 13.1 depicts an image of their ceremonies.

Figure 13.1 Mayan Indian sacrifices. Blood sacrifices were used in many rituals throughout human history. In this figure, a Mayan Lord runs a rope through the tongue of its subject.

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Blood has a mystique, perceived by the ancients, that also intrigues us today. This chapter answers some of the ancients’ questions: How does blood heal us? Why do we die when we lose too much blood? How is blood able to carry our nourishment? Science discovered the chemical components of blood to better understanding its role within our bodies. In this chapter, we will first look at how blood functions. We will then study how the heart and lungs work together to transport gases, nutrients, and wastes.

What is Blood? Blood is a viscous fluid, composed mostly of water, with dissolved salts, proteins, and cells within the liquid. The blood comprises almost 8% of the body weight of most adults. Males, on average have between 5 and 6 L (1.5 gallons) of blood and females have 5–6 L. Males have slightly more red blood cells than females, to enable more oxygen transport to muscles. When blood travels within its vessels, it is dark red with less oxygen than when it is exposed to the air, appearing bright red due to the enhanced oxygen content. Blood is carried throughout the body to perform many tasks: healing, waste removal, temperature regulation, nutrient transport, and acid–base balance. Blood is slightly basic, with a pH of about 7.4. Its pH must remain within strict limits for the body to function properly.

The composition of blood is mostly water but contains cells and solutes within it. Roughly 55% of the blood is made of a straw-colored liquid, called the plasma. Blood plasma is 90% water and contains more than 100 dissolved solutes, which include calcium, potassium and urea. Dissolved solutes are often included in blood tests to diagnose a person’s health. A high amount of urea indicates kidney malfunction, for example, because this solute should be removed from the blood through the kidneys. The rest of the blood is composed of the formed elements, which are those cells and cell fragments “formed” by the body. About 45% of the blood is composed of the formed elements. When blood is centrifuged, as shown in Figure 13.2, heavier materials such as the formed elements, move to lower parts of the test tube.

The formed elements of the blood include white blood cells, red blood cells, and platelets:

1) White blood cells (also called leukocytes) play a role in protection from disease and illness. When a pathogen or disease-causing agent, such as a bacterium or virus enters, white blood cells are the first line of defense for the body to guard itself. As you might recall from Chapter 8, there are many microbes surrounding us. They are kept at bay by our body’s defenses.

Each white blood cell plays a different role in the defense our bodies, which will be elaborated upon in Chapter 15. There are five types of white blood cells: neutrophils, lymphocytes, monocytes, eosinophils, and basophils. However, all of them patrol the blood vessels to search for signs of an invasion. Normal white blood cell numbers range between 4,800 and 10,800 cells per cubic millimeter. When these readings increase, infection or other illnesses are indicated.

2) Red blood cells (also called erythrocytes) carry oxygen and carbon dioxide gases. They are the most numerous of blood cells, comprising over 95%. Red blood cells are flexible, biconcave cells, fairly small in size at 7.5 µm in diame- ter. They are quickly made and swiftly disposed of, lasting only about 120 days. (Other cells can last a lifetime, such as nerves and heart cells). Red blood cells are destroyed in the spleen and liver, as discussed in Chapter 12. Red blood cells are filled with hemoglobin molecules, each able to transport oxygen and carbon dioxide gases.

Blood

A viscous fluid composed mostly of water, with dissolved salts, proteins and cells within the liquid.

Plasma

The straw-colored liquid that makes up 55 percent of the blood.

Formed elements

The cells and cell fragments formed within the blood and have a definite shape.

White blood cells

Large blood cells that help the body fight infections.

Pathogen

Any disease causing organism.

Red blood cells

Blood cells that contain hemoglobin and carry oxygen to and from the tissues.

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Figure 13.2 The components of human body: white and red blood cells, and platelets. When centrifuged, the lighter layer of watery plasma sifts to the top of the tube and the denser red blood cells migrate to the bottom. A thin layer of white blood cells forms in the middle of the two other layers.

Albumin 58%

Globulins 38%

Fibrinogen 4%

Ions

Nutrients

Waste products

Gases

Regulatory substances

Neutrophils 60%–70%

Lymphocytes 20%–25%

Monocytes 3%–8%

Eosinophils 2%–4%

Basophils 0.5%–1%

White blood cells

Percentage by Body Weight

Blood 8%

Formed Elements

45%

Plasma 55%

Percentage by Volume

Plasma (percentage by weight)

Proteins 7%

Other solutes 2%

Water 91% Other Fluids

and Tissues 92%

Proteins 7%

Other solutes 2%

Platelets 250–400 thousand White blood cells

5–9 thousand

Red blood cells 4.2–6.2 million

Water 91%

Platelets 250–400 thousand White blood cells

5–9 thousand

Red blood cells 4.2–6.2 million

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Porphyria, as you may recall from our story in Chapter 6, is an example of a blood disorder in which abnormal hemoglobin causes symptoms similar to that of a vampire. Red blood cells are unable to properly transport gases in porphyria.

There are other types of red blood cell disorders, each of which may have serious health consequences. When hemoglobin is abnormal, it affects a red blood cell’s oxygen-carrying capacity. In thalassemia, for example, a faulty or absent hemoglobin chain makes the molecule fragile and less able to carry oxy- gen. A more serious disease, sickle-cell anemia, was described in Chapter 5. Here, the red blood cell forms a sickle shape under conditions in which there is less oxygen, such as during physical exertion. Then, sickle-shaped cells jam up within blood vessels, causing clots, often affecting organs.

When blood lacks normal oxygen-carrying capacity, it is called anemia. The most common form of anemia is iron deficiency anemia. Iron holds oxygen within a hemoglobin molecule within its heme group of the hemoglobin mole- cule. When iron is lacking, often due to low amounts in the diet, blood is unable to carry sufficient oxygen.

Thalassemia

The condition in which a faulty or absent hemoglobin chain makes the molecule fragile and less able to carry oxygen. Sickle cell anemia

A serious condition that affects the RBCs

Anemia

The condition in which blood lacks normal oxygen carrying capacity. Iron deficiency anemia

A condition characterized by lack of healthy RBCs in blood.

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472 Unit 4: The Dynamic Animal Body

Another form is pernicious anemia, which presents itself when a patient lacks vitamin B-12 in her or his diet. Sometimes people with anemia feel run down. They lack energy due to the low levels of oxygen in their blood. Many times, pernicious anemia develops during pregnancy. Pernicious anemia is treated with vitamin supplements or vitamin B-12 injections.

3) Platelets are chips of cells that form clots within vessels to prevent blood loss. Within them, platelets contain granules filled with clotting factors. Clotting factors are proteins that undergo a series of chemical reactions that halt bleeding.

Platelets work by latching onto roughened surfaces where a break or tear occurs within the body. They stick to the collagen fibers along the damaged walls of vessels. Platelets first work by causing vasoconstriction of blood ves- sels, which lessens blood flow to the area. This slows bleeding. Platelets and damaged cells release chemicals that activate a chain of over 200 clotting factors and other proteins. These factors lead to the forming of a clot.

An important enzyme at the end of this series of chemical reactions is thrombin. Thrombin mediates the last steps of the reactions, and is measured by a blood test to determine the rate at which blood clots. This rate is commonly called its protime, or time to clot: it is the time it takes for the reactions to form thrombin. Thrombin causes the formation of fibrin threads, which trap platelets and red blood cells within a clot, as shown in Figure 13.3. Also note that calcium ions are important in mediating the end steps of clotting.

When blood clots too slowly, a condition of uncontrolled bleeding occurs, called hemophilia. Hemophilia is a disorder of certain clotting factors within platelets. There are three types of hemophilia: A, B, and C; each lacking a differ- ent clotting factor. In hemophilia, a prolonged bleeding in skin and within body organs occurs. Genetically engineered clotting factors are an effective treatment for hemophilia, eliminating the need for blood transfusions.

Sometimes clots form in the wrong places. In an unbroken vessel, such a clot is called a thrombus or thrombosis. A thrombosis in the heart (coronary)

Platelets

Are chips of cells that form clots within vessels to prevent blood loss.

Clotting factors

Are proteins that undergo a series of chemical reactions that halt bleeding.

Thrombin

An important enzyme in blood that facilitates clotting of blood by converting fibrinogen to fibrin.

Protime

A blood test that measures the rate at which blood clots.

Hemophilia

A condition of uncontrolled bleeding when blood clots occur too slowly.

Thrombosis

Clots forming in the wrong places (an unbroken vessel).

CRITICAl ReASonIng: WHy ARe Red Blood CellS MAde So CHeAPly?

Red blood cells are inexpensively produced by the body, lacking most of the organelles and containing no nucleus at maturity. The first reason for this is that a lack of organelles gives red blood cells physical space – to be filled with over 250 million molecules of hemoglobin. Hemoglobin is the oxygen carrying molecule of the blood, as described in Chapter 2. Almost all of the oxygen and 20% of the carbon dioxide in the blood is transported attached to hemoglo- bin. This will be discussed later in the chapter. Red blood cells are like supply trucks, carrying large amounts of gaseous materials. These include oxygen and carbon dioxide gases, moved constantly to and from all cells of the body.

A second reason for the way a red blood cell is constructed lies in its usage of oxygen. As a supply truck, it would be a problem if the supplies were used by those transporting them. Similarly, the presence of mitochondria within red blood cells would use up the very oxygen needed by cells that depend upon them. Thus, cells lacking organelles serve the unique purposes of fast transport and efficiency.

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Chapter 13: The Heart-Lung Machine: Circulation and Respiration 473

Figure 13.3 A blood clot also called a thrombus. Over 200 steps lead to the forma- tion of a clot. Red blood cells get caught in a mesh of fibrin strands during the formation of a clot.

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arteries is known as a heart attack. A thrombosis in the brain causes a stroke. In many cases, after sitting too long, in an airplane or after an operation, blood pools within the legs and may form a deep vein thrombosis.

The danger of a thrombus is in its ability to break apart and travel to other parts of the body, causing obstructions. A floating thrombus is dan- gerous and known as an embolus. When an embolus lodges in the lungs, a common pathway for its travel from the legs, it is a pulmonary embolism. Treatments for thrombosis and embolism cases include blood thinners such as warfarin and heparin. These are two strong blood thinners used to treat and prevent clots.

Blood cells are produced in the bone marrow, a compartment within bones that stores stem cells. Stem cells are specialized cells that are able to develop into many types of cells, given particular conditions. For example, under some conditions stem cells become skin and in other conditions, stem cells become a heart muscle. Stem cells are also referred to as pleuripotential stem cells, because they have multiple potentials to become any types of cell depending upon the environment. Blood cells form from stem cells within the bone mar- row. This is a reason why damage to the bone marrow cavity, as in cancer treat- ments, often leads to anemia (low red blood cell production) and infection (low white blood cell production) (Figure 13.4).

Why Blood? Why is blood, and its movement within the body, laden with historical and religious con- notations in society? Because blood performs so many tasks that satisfy our immediate needs, vital to our survival. Without oxygen, a cell dies in less than 4 minutes, as men- tioned in a previous chapter. In our story, Charles suffers from a weak heart that cannot pump the blood sufficiently. Let’s give a look at the primary roles for blood in the body. The functions of the blood include:

1) Transport: Blood contains nourishment for every cell in the form of nutri- ents (macromolecules) and oxygen and removes unwanted wastes, including

Heart attack (myocardial infarction)

The condition in which heart muscle is damaged from the sudden blockade of coronary artery by blood clot.

Stroke

The sudden diminution of brain cells due to lack of oxygen caused by obstruction or rupture of a blood vessel of brain.

deep vein thrombosis (dVT)

The condition that occurs when a blood clot forms in one of body’s large veins, most commonly in legs.

embolus

A floating thrombus.

Pulmonary embolism

The condition in which an embolus lodges in the lungs.

Bone marrow

A compartment within bones that stores stem cells.

Stem cells (Pleuripotential)

Are specialized cells that are able to develop into many types of cells, given particular conditions.

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474 Unit 4: The Dynamic Animal Body

Proerythroblast Myeloblast

Progranulocyte

Eosinophilic myelocyte

Neutrophilic myelocyte

Basophilic myelocyte

Lymphoblast

Stem Cell (hemocytoblast)

Monoblast Megakaryoblast

Megakaryocyte

Megakaryocyte Breakup

PlateletsMonocyte

Lymphocyte NeutrophilEosinophil

Granulocytes Agranulocytes

White Blood Cells

(a)

BasophilRed Blood Cell

Reticulocyte

Late Erythroblast

Intermediate Erythroblast

Early Erythroblast

Nucleus Extruded

Basophilic Band Cell

Eosinophilic Band Cell

Neutrophilic Band Cell

Figure 13.4 a. Cells of the blood and their origins. All cells emerge from pleuripotential stem cells. b. White blood cells: a close up look.

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Chapter 13: The Heart-Lung Machine: Circulation and Respiration 475

carbon dioxide gas. Every cell needs a continual supply of nutrients and a con- stant removal of wastes. Nutrients are brought through the blood as dissolved particles, as described in Chapter 12. After macromolecules are digested and absorbed into the alimentary canal, they are transported, used, and removed as wastes through the blood.

As nutrients are processed in metabolism, wastes accumulate and are toxic if not removed by the blood. Many wastes contain nitrogen, such as urea, and are removed immediately as they are formed. Nitrogen wastes build up in serious cases of kidney failure, called uremia. If uremia is left untreated, death is certain. Car- bon dioxide gas is also a waste product of metabolism, but is removed through the lungs. Carbon dioxide is a product of cellular respiration, described in Chapter 4.

Hormones are also moved through the body. These chemical messengers stimulate cells to use nutrients for growth, development, and reproduction. Hor- mones help tissues and organs communicate through a chemical message sys- tem, described in the next Chapter 14.

2) Defense: The blood is used for the protection of the body. White blood cells within the blood carry out phagocytosis to removed microbes and harmful sub- stances, such as cancer cells and pathogens. Antibodies, or specialized proteins, disable, destroy, and reveal harmful organisms that have invaded the body. Blood serves a role in defending the body from infection and disease in ways that will be discussed in Chapter 15.

In defense of body damage, clotting factors within the blood form a clot to prevent blood loss. An abrasion on the skin, for example, is healed by a series of steps started by clotting factors. This process was described earlier in the chap- ter, leading to a solid clot along the wall of a blood vessel.

3) Temperature Regulation: Blood is also able to store heat as it moves through the body. When blood vessels expand or contract, they change the amount of blood and heat reaching body surfaces. This regulates heat arriving at different areas. When blood vessels expand (or vasodilate), more blood goes to the skin, causing heat loss. When blood vessels constrict (or vasoconstrict), it causes less to blood movement to the skin and thus heat conservation. Blood movement

Figure 13.4 (Continued)

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helps to maintain body temperature, a vital goal for all homeotherms. As described in Chapter 11, homeostasis keeps body temperature set around 37°C (98.6 °F) for optimal enzyme functions.

4) Acid–Base Balance: Blood contains a set of reactions that regulate its pH called the carbonic acid–bicarbonate buffering system. The pH of blood cannot vary more than .1 pH unit without serious health consequences. Thus, the carbonic acid–bicarbonate buffering system absorbs and releases hydrogen ions. In this way, the number of hydrogen ions is regulated and the pH of the blood is buff- ered or maintained. Usually, blood pH is held strictly at 7.4 in healthy people. Even small variation from this set point, a symptom of congestive heart disease described in the story, may lead to death.

Stabilizing blood pH depends on many factors, but includes the role of car- bonic acid. Carbonic acid is a part of the buffering system that prevents the movement of the acid–base level to veer too far from its set point. When it gives up a hydrogen ion, blood becomes more acidic. When it absorbs a hydrogen ion, blood becomes more basic. The buffering system will be discussed in greater detail later in the chapter, in relation to respiratory gases.

Cardiovascular system: Heart and Vessels Heart Blood is propelled through the body of vertebrates using a specialized muscular organ called the heart. The heart in humans is a fist-sized organ, weighing about one pound. It is very strong, with cardiac tissue beating about 70 times each minute, functioning as the most reliable pump that has ever been developed. In fact, the heart beats 1 billion times in a person’s lifetime. The heart muscle, called myocardium, is thick and flexible.

Some organisms, such as the earthworm use a series of small hearts to pump blood. Mammals and birds have a four-chambered heart to transport blood through a series of connected blood vessels. Together, the heart and blood vessels are called the cardiovascular system.

Carbonic acid- bicarbonate buffering system

A set of reactions that regulate the pH of blood.

Heart

A specialized muscular organ that propels blood through the body of vertebrates.

Cardiovascular system

The system comprising the heart and blood vessels

Figure 13.5 The heart and it blood vessels: arteries are colored red and veins are colored blue.

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Chapter 13: The Heart-Lung Machine: Circulation and Respiration 477

The human cardiovascular system acts as a heart–lung machine, with blood vessel connections between the two organs. The heart pumps blood and the lungs trade differ- ent gases with the blood. Lungs exchange gases to remove carbon dioxide wastes from it and infuse needed oxygen. In our story, Charles’ breathing was also affected by his weakened heart. It was unable to pump blood through the lungs adequately, making him short of breath. Let’s trace the movement of blood between the heart, lungs, and body to study how heart functioning affects one’s overall health.

Movement of Blood in the Heart and Vessels The center of the cardiovascular system is the heart. The heart consists of four chambers: right and left atrium and right and left ventricle; and a number of vessels connecting the heart with the body and the lungs. In humans, the chambers and blood vessels are lined with simple squamous tissue, which appears smooth to the touch, called endothelium. The chambers and vessels of the heart are shown in Figure 13.6.

When blood is received from the body, it travels through the superior and inferior vena cava into the right atrium of the heart. Let’s trace the movement of blood through the heart and the rest of the body using Figure 13.7. The right atrium, a small cham- ber with little pumping ability, moves blood through the tricuspid valve and into the right ventricle. The right ventricle pumps blood out of the heart through the pulmonary arteries to the lungs. In the lungs, blood exchanges its gases.

The connection between the heart and lungs is known as the pulmonary circuit. So far, the blood in the vessels mentioned has been deoxygenated. Deoxygenated blood has a lessened amount of oxygen within it after exchanging with body cells. As such, the lungs are said to oxygenate blood within it, adding oxygen for the body. Carbon dioxide, built up by body processes, leaves the blood through the lungs. Oxygenated blood then travels back into the left side of the heart, through the pulmonary vein and into the left atrium.

When blood returns from the lungs through the pulmonary veins, it completes its travel through heart on the left side. Blood makes its way through the bicuspid or mitral valve into the left ventricle. The left ventricle is a very powerful, thick muscle which pumps blood out through the aorta to the rest of the body. The vessel connection between the heart and body cells is called the systemic circuit. The systemic circuit connects the heart with the whole of the body systems. When the aorta forks, it sends blood to the body in two ways: to the head and arms in one direction and to the lower body and legs in another direction.

Some vessels branch off and resend blood toward the heart in what is called the coronary circuit. The coronary circuit supplies the heart walls with oxygenated blood. Why does a blood supply need to return to the heart, when there is ample blood within the heart? The reason is: blood within the heart is unavailable to it for use by its cells. Blood within the heart travels through it but the heart’s endothelial lining prevents the transfer of nutrients. Instead, the coronary circuit is comprised of coronary arteries which branch into capillaries along the surface of the heart, allowing exchange of oxy- gen and nutrients.

In our story Charles had congestive heart disease, in which the heart is too weak to pump blood efficiently. Charles had shortness of breath in this condition, because blood could not sufficiently move out of the lungs through the left side of the heart. Thus, his pulmonary vein backed up, leading to fluid buildup in his lungs. This presents as breathing difficulty during exertion. Symptoms may also include fluid accumulation in the legs and abdomen, because the left side of the heart is weak. When the heart cannot sufficiently pump out fluid from the body, it accumulates in lower regions.

Coronary circuit

The system in which some vessels branch off and resend blood toward the heart.

Systemic circuit

The vessel connection between the heart and body cells.

Mitral (bicuspid) valve

A heart valve located between the left atrium and left ventricle.

Pulmonary vein

A vein that carries oxygenated blood from lungs to the heart’s left atrium.

deoxygenated blood

Blood that lacks oxygen.

Pulmonary circuit

The connection between the heart and lungs.

lungs

A pair of breathing organs.

Pulmonary artery

The artery that carries blood from the right ventricle to the lungs.

Tricuspid valve

A heart valve between the right atrium and ventricle and keeps blood from flowing back into the atrium.

Vena cava

A large vein that carries deoxygenated blood into the heart.

endothelium

The squamous tissue lining the chambers of heart and blood vessels.

Ventricle

A chamber of heart that receives blood from the atrium.

Atrium

An entry chamber of the heart from which blood is passed to the ventricles.

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Pulmonary trunk semi-lunar valve

(to head and upper extremities)

Aorta

Superior vena cava (from head and arms)

Pulmonary arteries (to right lung)

Pulmonary veins (from right lung)

Right atrium

Tricuspid valve

Right ventricle

Inferior vena cava (from trunk and legs)

Papillary muscles Interventricular

septum

Left ventricle

(to aorta)

Mitral valve

Aortic semi-lunar valve

Pulmonary veins (from left lung)

Pulmonary arteries (to left lung)

(from right lung)

Aorta (to trunk and lower extremities) (a)

Chordae tendineae

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Figure 13.6 a. The heart and its chambers. The four chambers of the heart pump blood through the lungs and the body. b. Anterior view of external heart. Illustration by Jamey Garbett. c. Posterior view of external heart. Illustration by Jamey Garbett.

Right Atrium

Left Atrium

Right Ventricle

(b) (c)

Right Atrium

Right Ventricle

Left Ventricle

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Chapter 13: The Heart-Lung Machine: Circulation and Respiration 479

Tissue capillaries Circulation to

tissues of head, neck, and upper limbs

Systemic circulation (through the body)

Tissue capillaries

Lung

Lung capillaries

Right side of heart

Circulation to tissues of thorax, abdomen, and lower limbs

Pulmonary circulation

(through the lungs)

CO2 O2

CO2

Left side of heart

Figure 13.7 Cardiovascular system: tracing the traveling of blood through the heart, lungs, blood vessels. The systemic and pulmonary circuits are linked by the heart. Illustration by Jamey Garbett.

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Heart Beats: Electricity activity The heart beats because of a control center, called the Sinoatrial (SA) node, which reg- ularly sends an electrical message initiating a heart muscle contraction. Cells of the SA node are found in the wall of the right atrium and send out a message to cause the heart to beat. They are said to be autorythmic, meaning that they beat independent of the ner- vous system (on their own).

Each time the heart beats, the SA node sends its message, causing a wave-like elec- trical dispatch leading to both atria beating at the same time. This message hits another region, called the atrioventricular (AV) node. The AV node sends another electrical mes- sage down a set of nerves in the heart called the Bundle of His and into the left and right ventricles along Purkinje fibers, causing the ventricles to contract. The rhythmic contractions of the heart keep blood flowing through all of the circuits in a regular man- ner. An electrocardiogram (ECG) traces the conduction of electricity through the heart per heartbeat, as shown in Figure 13.8. An ECG detects an abnormal rhythm, called an arrhythmia. A common type of arrhythmia, atrial fibrillation is found in over 2% of the population.

Sinoatrial (SA) node

The center that controls the heart beats.

Autorythmic

Cardiac muscle cells that beat independent of the nervous system.

Atrioventricular (AV) node

Small mass of neuro muscular fibers located at the base of the interatrial septum.

Purkinje fibers

Specialized heart muscle fibers that carry electrical impulses controlling the contraction of ventricles.

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480 Unit 4: The Dynamic Animal Body

Diseases of the Cardiovascular system

Heart attack: Myocardial infarction As a person ages, though, the heart parts wear and weaken, leading to cardiac disease. Heart or cardiac disease is the leading cause of death in the United States and the devel- oped nations.The most common cause of cardiac disease is a heart attack or myocardial infarction (MI). An MI leads to death of myocardial tissue and therefore poorer func- tioning of the heart. One third of MIs lead to instant death because it disrupts the elec- trical beating of the heart just described. The heart becomes functionless in these cases, with no pumping of blood. Many victims can be saved with a shock to bring the beating back into a normal rhythm.

The health of survivors of MI is determined by the amount of damage to the myo- cardium. The greater the myocardial damage, the poorer the outcome for the patient. The amount of damage to heart muscle after an MI is measured by troponin levels, which are muscle proteins of the heart which show up after tissue is destroyed. The higher the troponin levels, the greater the extent of damage to heart muscle.

Figure 13.8 Electrical conduction in the heart and a normal ECG. Depolarization occurs in step-like waves along the muscle of the heart.

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A collection of heart muscle cells that transmit electrical impulses from the AV node to the interventricular septum and ventricles.

Arrhythmia

A condition in which the heart beats in an abnormal rhythm.

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Chapter 13: The Heart-Lung Machine: Circulation and Respiration 481

arteriosclerosis In our story, Charles was an end-stage cardiac patient, with a heart weakened enough to require a transplant. There are many effective treatments for heart disease to prevent or slow progression to the degree of congestive heart failure that Charles experienced.

A major cause of heart attack and heart damage is a buildup of plaques in coronary arteries called arteriosclerosis (also referred to as atherosclerosis). Plaque buildup is strongly associated with cholesterol and bad fats in the blood, such as LDL described in Chapter 12. When blood flows through a plaque laden area on a coronary artery, blood flow becomes more turbulent. This disruption from a smooth flow causes plate- lets to initiate clotting. Platelets recognize rough surfaces, in part by detecting turbu- lent blood flow. Thus, wavy walls of coronary arteries caused by plaques constitute a high risk for MI.

When plaques are detected, diet changes and/or medicines may be recommended to lower a patient’s cholesterol. If the condition is more serious, with plaques blocking more than 60% of arteries, surgery may be required. A less invasive surgery is angioplasty, in which a tube called a catheter is inserted into the coronary artery to the area of plaque buildup. The tube expands, sometimes placing a hollow metal tube in place, called a stent to hold the area open. Sometimes, a replacement of the diseased artery is required, in open heart surgery called coronary artery bypass graft (CABG). The surgery takes a health artery or vein from another area on the body, such as the chest or leg, and uses it to replace the diseased artery.

Arteriosclerosis

A chronic condition characterized by abnormal thickening of vessel walls.

Artery

A vessel that carries oxygenated blood away from the heart to cells, tissues, and organs.

Angioplasty

A surgical procedure to widen obstructed arteries or veins.

Coronary artery

An artery supplying blood to the heart.

Coronary artery bypass graft (CABg)

A type of surgery that improves blood flow in the heart.

We ARe WHAT We TAke InTo uS! Choosing nutritious foods to eat is a daunting task. There are so many ingredi- ents that are hard to pronounce and chemicals that are unfamiliar, in processed foods. This is a reason why people have a hard time choosing the right foods. To start, eating foods that are not processed, such as fresh vegetables and fruits or meats that you cook yourself, is healthier than those that contain many of the chemicals added in the processing of meals. Fats in food contribute to heart disease, a leading cause of death.

In considering foods and other substances entering your body, consider their components. Figure 13.9 shows the many substances found within ciga- rettes and yet more than 20% of Americans smoke. Tobacco companies used research by the Tobacco Research Council showing that there is no basis for its link to lung cancer for years. How is this so when so many dangerous chem- icals make up cigarettes? Some statistics were used for years to give a pass to smoking and its link to disease.

What is inhaled, such as chemical in the air alos affects our health. For example, a recent study points to increased risks of heart attack when jogging along roads with high traffic. It is surmised that the pollutants inhaled by jog- gers stimulate changes in the heart to elicit an attack. We are what we eat as well as the air we breathe into our bodies.

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482 Unit 4: The Dynamic Animal Body

Heart Valve Disease Another wear-and-tear problem in the heart emanates from the valves. Heart Valves prevent backflow of blood into chambers of the heart. There are four valves in the heart, as shown in Figure 13.6: the mitral and tricuspid, which prevent backflow into the atria; and the semilunar valves, which prevent backflow into vessels.

The most common valve problem is backflow or regurgitation, detected by auscul- tation as a murmur, described in Chapter 11. Most often, the mitral valve, due to high pressure from the left ventricle, is the culprit. When the backflow is bad enough, the heart repumps the same blood over and over, weakening the myocardium. This enlarges the heart and creates a smaller chamber within. Smaller chambers are not able to pump as much blood as a normal-sized chamber. This results in less efficient heart pumping ability. In these cases, surgical replacement with a cadaver, pig, or artificial valve is rec- ommended. Murmurs are very common and usually do not require intervention. In fact, over 80% of people over age 65 have a leaky valve.

Semilunar valves

A valve of heart that prevents backflow into vessels.

Regurgitation

The most common valve problem.

Murmur

An abnormal sound made by blood during the heartbeat cycle.

Figure 13.9 Cigarettes and their many harmful chemical components. The harmful substances found in cigarettes are linked to many chronic diseases.

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Chapter 13: The Heart-Lung Machine: Circulation and Respiration 483

Cardiovascular Disease: Treatment progress Treatment and surgery for cardiovascular disease has advanced greatly over the past 25 years. While it still afflicts over 30 million people each year, the death rate and quality of life for cardiovascular patients has improved greatly. In the past half-century, medical developments have cut deaths from cardiovascular disease by 80% for strokes and 70% for heart attack, between 1950 and 2000. Many heart diseases link to a buildup of plaques of fat in vessels. Figure 13.10 shows the development of atherosclerosis or clogging of the vessels. Medical procedures and drugs have helped patients with atherosclerosis.

Blood Vessels Blood is carried to and from the heart by different types of blood vessels. The cardio- vascular system consists of three sets of vessels: arteries, veins, and capillaries. Let’s compare the three types, with a look at their differing structures and functions:

1) Arteries are the set of vessels that transport blood away from the heart, to all parts of the body. (You can remember that the word “artery” starts with “A” and “away” also starts with “A”.) Arteries contain oxygenated blood, obtaining oxy- gen from the lungs and transporting it to body cells. The only exception to this rule is in the pulmonary arteries, which carry blood away from the heart to the lungs to become oxygenated. Blood within the pulmonary arteries is deoxygen- ated, the only artery to have this.

There is a great deal of pressure within arteries because they are nearer to the heart, the source of that pressure. Walls of arteries are thick to withstand the extra pressure, containing smooth muscle. The aorta is the largest and thickest artery in the human body, receiving the highest pressure blood because it is so near to the heart. Smooth muscle allows for changes in the diameter of arteries, in vasoconstriction and vasodilation. Thick arteries branch into smaller ones,

Figure 13.10 Atherosclerosis and heart disease. The development of plaques in the blood vessels is a major cause of stroke and heart attack.

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484 Unit 4: The Dynamic Animal Body

eventually into arteries only a few cells thick, called arterioles. Arterioles lead into all of the organs and tissues of the body until they branch into capillaries.

2) Capillaries connect arteries and veins and are much smaller than both vessels, with a 10 µm diameter the size of a red blood cell. The walls of capillaries are thin enough (only one cell layer thick) to allow exchange of materials. These walls are porous, with holes sometimes large enough for whole cells to move through. In capillaries, blood exchanges wastes and nutrients through diffusion with body cells.

Free trade between capillaries and body cells is rapid and extensive, with 50,000 miles of capillaries in an average human adult. Capillaries form a capillary bed, in which the many capillaries branch out, slowing the movement of materials within them. Capillary walls create friction against the blood mov- ing through them. This slows the speed of blood, enabling exchange to occur more completely.

Capillaries are the first vessels to carry deoxygenated and nutrient-poor blood back to the heart. Capillaries converge into larger vessels called venules, which combine to form into veins.

3) Veins carry deoxygenated blood back to the heart after it has picked up wastes and carbon dioxide from body cells. The only exception to this rule is in the pul- monary veins, which carry oxygenated blood toward the heart from the lungs. Pulmonary veins are oxygenated because they have just picked up oxygen from the lungs. The pulmonary veins are the only veins to carry oxygenated blood. The vena cava, discussed earlier in the chapter, is the largest vein in the human body, returning blood from all parts of the body back to the heart.

Vein structure is similar to arteries, both lined with an endothelial layer and both contain thick walls compared to the single layer of capillaries. Owing to their distance from the heart, veins have less pressure than arteries, about one- tenth that of arteries. Veins therefore also have walls that are thinner than arter- ies, with a lessened pressure not requiring thick walls. Walls of veins therefore have much less smooth muscle than arteries.

Recall that capillaries, with their porous walls and extra resistance, slow the blood and reduces its pressure. With less pressure, veins could lack fast enough movement of blood through it. In fact, over 60% of blood remains within veins at any one time. However, veins are adapted against the backflow of blood and blood pooling. They contain valves, which are one way doors interspersed throughout the vein system.

When valves are incompetent within the legs, blood pools in a condition called varicose veins. These may be painful and are associated with extended periods of standing, such as for nurses, cashiers, and teachers or due to extra pressure caused by pregnancy. Varicose veins are treated by laser surgery or injections that fade or remove them.

The three vessel types each have different functions with structures to enable them to perform them. A comparison of the structure of arteries, veins, and capillaries is given in Figure 13.11.

Blood pressure High blood pressure is a root cause for many of the diseases of the cardiovascular sys- tem. Blood pressure is defined as the amount of force per unit area on blood vessel walls. It is measured in millimeters of mercury using a blood pressure cuff, usually against the brachial (upper arm) artery. It is a measure of artery pressure within the body.

Arteriole

A small branch of artery leading to a capillary.

Capillary

A tiny blood vessel that connects arteries and veins.

Capillary bed

The whole system of capillaries of the body.

Venules

Small veins connecting capillaries with larger systemic veins.

Vein

A blood vessel that carries deoxygenated blood back to the heart after it has picked up wastes and carbon dioxide from body cells.

Varicose veins

The condition in which valves are incompetent within the legs leading to the formation of blood pools.

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Chapter 13: The Heart-Lung Machine: Circulation and Respiration 485

When ventricles contract, there is a greater force exerted against the walls of arter- ies. This is known as a person’s systolic pressure. When ventricles fill, less force is exerted against artery walls. This is known as the diastolic pressure. Two numbers are given in a blood pressure reading. The higher number or systolic pressure is the top num- ber and the lower number, or diastolic number, is the bottom number. Thus, a reading of 120/80 indicates that there is 120 mmHg of pressure against a person’s artery when their ventricles are contracting and 80 mmHg of pressure against that person’s artery when their ventricles are relaxing. A normal adult blood pressure reading should not exceed 120/80 mmHg.

High blood pressure is defined as a chronic elevation of pressure above the nor- mal 120/80, for a consistent period of time. This period ranges from a month to sev- eral months. Pressures between 120/80 and 140/90 mmHg are considered borderline cases. These individuals are considered prehypertensive and should be monitored more closely. Roughly three quarters of prehypertensive adults will develop high blood pres- sure. Hypotension occurs when blood pressure is below 100/60 mmHg and is (when not caused by disease) related to longevity. Of course, high blood pressure, along with other factors such as diet, family history, and older ages, leads to cardiovascular disease. Figure 13.12 shows the multiple factors causing cardiovascular disease.

High blood pressure itself may be caused by several factors: stress, anxiety, smok- ing, excess weight, or it may simply be inherited. Excess salt in one’s diet is also related

High blood pressure

A chronic elevation of pressure above the normal 120/80, for a consistent period of time.

Figure 13.11 Comparison of the structure of arteries, veins, and capillaries. Arteries are thick-walled while veins have large lumen. Capillaries are adapted for exchange, with walls only one cell layer thick. Illus- tration by Jamey Garbett.

Tunica externa

Elastic artery

Muscular artery

Tunica media

Tunica intima

Tunica externa

Arteriole

Continuous capillary

Tunica media

Tunica intima

Smooth muscle

Venule

Medium-sized vein

Large vein

Fenestrated capillary

Endothelial cells

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486 Unit 4: The Dynamic Animal Body

Figure 13.12 High blood pressure and heart disease are linked to many factors. Blood pressure is a major contributor to cardiovascular disease.

Table 13.1 Blood Pressure Ranges. Normal Blood Pressure is Below 120/80 mmHg.

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to high blood pressure. As described in Chapter 2, water follows solutes. When added salt enters the bloodstream, water follows, increasing its pressure.

Regardless of the cause, high blood pressure, over time, damages vital organs, and the linings of arteries. For example, damage to vessels may result in plaque buildup, stroke, and heart attack. This damage is irreversible but, if high blood pressure is treated before damage occurs, its effects are limited.

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Chapter 13: The Heart-Lung Machine: Circulation and Respiration 487

Regular exercise helps to reduce the risk of high blood pressure. It reduces weight and therefore the number of blood vessels in each pound. Each blood vessel gives resis- tance, so weight loss reduces resistance from blood vessels. When exercising, muscles are used to breathe and to move. When skeletal muscles contract during exercise, for example, it propels blood through veins back to the heart. This movement of blood is termed the muscular pump. The muscular pump helps pump blood through the vessel system, reducing the workload on the heart. Thus, each time a person exercises, muscles help to move blood. Its action is shown in Figure 13.13.

During breathing, other muscles contract in the chest and abdominal cavity. This mus- cle movement is termed the respiratory pump, which forces blood back to the heart as well through the veins. Both the respiratory and muscular pumps reduce strain on the heart.

The Respiratory system What is Respiration? The most pressing need for body cells is the uptake of oxygen and the release of carbon dioxide gas. Our bodies are in constant need of these two processes, accomplished by respiration. Respiration is defined as the taking up of oxygen gas from the environment

Muscular pump

A collection of skeletal muscles that aid the heart in blood circulation.

Respiratory pump

The movement of blood when other muscles contract in the chest and abdominal cavity.

Respiration

The process of taking up of oxygen gas from the environment and the release of the waste gas, carbon dioxide.

Figure 13.13 Muscular pump: skeletal muscles contract, moving blood back to the heart. One-way valves allow the blood to move toward the heart but not backward. This reduces the workload of the heart with blood movement without a need for the heart’s pumping.

Valve Closed

Valve Opened

Valve Closed

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and the release of the waste gas, carbon dioxide. It is a mechanical process and differs from cellular respiration, discussed in Chapter 4, a chemical process.

During its movement through the pulmonary circuit, blood exchanges gases in the lungs. Therefore, circulation and respiration are coupled together, as described earlier in this chapter. Needed oxygen is obtained by the blood within the lungs and carbon diox- ide waste is removed into the air. The heart pumps blood through lungs, which gives it oxygen and removes carbon dioxide from it.

Respiration uses muscles within the chest cavity to bring air into the lungs for gas exchange. However, in cellular respiration, the oxygen taken in is used for obtaining energy. Cellular respiration results in the breakdown of sugar from the use of oxygen through several chemical processes. Both processes are related; each involving oxygen and carbon dioxide transport. The subsequent sections describe the mechanical act of respiration.

Gas exchange in most land vertebrates occurs within lungs, which are specialized organs with branched and moist respiratory surfaces. Humans have a pair of lungs, which both rest within the chest cavity. Gases are exchanged in two places in the body: 1) between the external environment and the air sacs or alveoli of the lungs; and 2) between oxygenated blood and body cells. The movement of gases in each area is depicted in Figure 13.14.

The process of moving air into and out of the lungs is called mechanical breathing. The act of breathing involves the taking of air into the lungs, known as inspiration and expelling air to the outside world, called expiration. The lungs are like balloons, with very little pumping capacity on their own. They inflate and deflate based on the pres- sures surrounding them in the chest cavities. During inspiration, the ribs move upward

Air sacs (alveoli)

Tiny sacs within the lungs where exchange of oxygen and carbon dioxide takes place.

Mechanical breathing

The process of moving air into and out of the lungs

Inspiration

The process of taking of air into the lungs.

expiration

The process of expelling air to the outside world.

Figure 13.14 Gas exchange in cells occur in air sacs of the lungs and between body cells and the circulatory system. From Biological Perspectives, 3rded by BSCS.

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and outward, and a sheet of muscle at the bottom of the chest moves downward. These movements open up the chest cavity, forcing air into the lungs. In expiration, the oppo- site occurs, with the ribs moving downward and inward and the diaphragm moving upward, decreasing the size of the chest cavity. The smaller size forces air out of the lungs during expiration. The process of mechanical breathing is given in Figure 13.15.

Humans take 12–20 breaths per minute, on average. Count the number of times you breathe in 15 seconds and multiple that by four. This will give your number of breaths per minute. The more carbon dioxide in the blood, the greater the number of breaths a person needs to take per minute. Rapid breathing blows off carbon dioxide and can be a sign of diminished oxygen in the blood. Air can also be moved in and out of the lungs very rapidly, reaching over 100 mph, in some coughing fits. This speed is important in the ability of a cough to dislodge food from one’s respiratory passageways.

anatomy of the Respiratory system Humans use a respiratory system to uptake oxygen from the environment and eliminate carbon dioxide. The respiratory system includes all of the organs used to move air into the body. The system resides within the thoracic (chest) cavity. Air moves from the nose and mouth through the pharynx, larynx, trachea (windpipe), and into the bronchial tubes within the lungs.

Let’s trace the route air takes as it moves through the respiratory system. As air is inhaled, or brought into the body through the nose, it is filtered by small hairs called cilia. Dust, microbes and other particles larger than 4 µm are removed as air moves through the convoluted nasal cavities.

Respiratory system

The system by which oxygen is taken into the body from the environment and carbon dioxide is eliminated.

Pharynx

A tube that starts behind the nose and mouth connecting to the trachea.

Bronchial tubes

Tubes that let air in and out of the lungs.

Inspiration

Ribs expand up, out, and widen

Diaphragm contracts (a) (b)

Expiration

Ribs move down and in

Diaphragm relaxes © Ke

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Figure 13.15 Mechanical breathing: inspiration and expiration are accomplished by movements of muscles of ribs and the diaphragm.

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Let’s trace the movement of air as it flows through the body. Figure 13.17 shows the anatomy of the human respiratory system. First, when air moves to the back of the throat or pharynx, it shares the area with food until it reaches the larynx or voice box. The larynx sits at the start of the trachea, creating sounds as air rushes through its folds. It is composed of a set of cartilage structures. At the top of the larynx, two elastic cords stretch across the upper end, called the vocal cords. When the vocal cords tighten, the pitch of a sound created increases and when it loosens, the pitch decreases.

As air rushes over the larynx, it travels through the trachea, or windpipe. The epi- glottis, discussed in Chapter 12, remains in an open position, allowing air into the tra- chea. The trachea is about 4 or 5 inches long, held open by rings of hyaline cartilage. It branches into two primary bronchi, which enter into the two lungs, branching further into smaller secondary bronchi and finally within the lungs into bronchioles. There

larynx

Voice box.

Vocal cords

Two elastic cords stretching across the upper end in the larynx.

Trachea

A tube-like portion of the respiratory tract that connects to the lungs.

Figure 13.16 Asbestos fibers are linked to lung diseases, including lung cancer, particularly mesothelioma. This photo shows natural asbestos fibers, mined from rocks.

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ASBeSToS: THe WondeR MATeRIAl . . .?

Some particles are so small that they cannot be caught by our nasal canals. Asbestos is a material that is smaller than 4 µm, able to enter into our lungs. It is a wonder substance – able to be molded into any size or shape and is therefore used in insulation, siding, and fire resistant materials – but also has a deadly link to lung cancer. Even a brief exposure to asbestos in the air can greatly increase one’s chances of getting a type of lung cancer called mesothe- lioma (Figure 13.16).

It might surprise you that evidence of the ill effects of asbestos on human health has been around for a long time. Some governments were quick to outlaw or limit its use. Even Nazi Germany limited the use of asbestos in the 1930s, based on damaging data about the substance. At the same time, the United States unfortunately continued using asbestos up until the 1980s in many facets of building. Government agencies later admitted that the use of asbestos, due to its ability to enter and irritate the lungs, should be banned.

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Figure 13.17 Human respiratory system a. An overview of major respiratory organs. b. The bronchial tree.

Respiratory centers in the brainstem

Laryngopharynx

Right lung

Bronchus

Diaphragm

Nasal cavity

Oral pharynx

Epiglottis

Larynx

Lower respiratory tract

Trachea

Left lung

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are hundreds of thousands of tiny bronchioles in the lungs, each ending in an air sac or alveolus. There are about 300 million alveoli in a human lung. Each is composed of squamous epithelial cells, thin enough to allow for easy transport of gases.

Exchange in the Lungs Blood enters the lungs from the heart. As blood moves into the lungs, through the pulmo- nary artery, the vessels branch into smaller and smaller sizes until they become capillar- ies, reaching the lung’s alveoli. The alveoli are delicate sacs surrounded by a network of vessels, called pulmonary capillaries. This network completely surrounds the air sac. Alveoli are a perfect place for gas exchange, because transport of gases occurs over a short distance between vessels surrounding the sac and the air in the sac.

Oxygen and carbon dioxide gases are traded between blood in the lungs and the atmosphere, through diffusion. Diffusion, as you may recall from Chapter 3, occurs when particles move from higher to lower concentrations.

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Right Primary Bronchus

Right Superior Secondary Bronchus

Right Middle Secondary Bronchus

Right Inferior Secondary Bronchus

Right Tertiary Bronchus

Smaller Bronchi

Left Primary Bronchus

Larynx

Trachea

Left Superior Secondary Bronchus

Left Tertiary Bronchus

Left Inferior Secondary Bronchus

Smaller Bronchi

Bronchial Tree Up-Close

(b)

Figure 13.17 (Continued)

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Gases are no exception to this rule, except that they move according to partial pres- sures of the gases. They are composed of particles in differing concentrations and pres- sures within the lungs. Oxygen gas, for example is in a high concentration within an air sac and a lower concentration within pulmonary capillaries surrounding the air sac. Thus, oxygen gas moves (from a higher to lower partial pressure) into pulmonary cap- illaries. The opposite occurs for carbon dioxide gas. Respiring cells cause higher pres- sures of carbon dioxide to accumulate within pulmonary capillaries, creating a diffusion pressure out of them and into the air sac. Thus, carbon dioxide gas moves from pulmo- nary capillaries into the alveoli and out of the body as waste. The movement of both oxygen and carbon dioxide gases within the lungs are shown in Figure 13.18.

Figure 13.18 a. Terminal bronchioles. Alveoli gas exchange. Oxygen and carbon dioxide gases are transferred between the air and the blood within the air sacs of the lungs. The accompanying figure shows the air sac (alveolus). Carbon dioxide and oxy- gen gases are exchanged across the alveolus membrane. Oxygen enters red blood cells where it attached to hemoglobin within the capillaries. b. Exchange of gases in air sacs and in tissue cells.

Terminal bronchiole

Pulmonary vein

Smooth muscle

Respiratory bronchiole

Capillaries

Elastic fibers

Pulmonary artery

Alveolus

Alveolar sac

Macrophage

Connective tissue and elastic fibers

Septal cell

Alveolar epithelium

Capillary with red blood cells

Macrophage

Capillary endothelium

Capillary lumen

Alveolus

Alveolar fluid layer

Alveolar epithelium

Connective tissue

Nucleus of capillary endothelium

Alveolar duct

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Lung Compliance The ability of the lungs to properly inflate and exchange gases is termed lung compli- ance. Several factors affect a lung’s compliance. First, the passages of the respiratory system, namely the bronchial tubes, determine the amount of air reaching the lungs. When the bronchial tubes are wide open, there is enough air to reach the lungs. However, in some conditions, such as asthma and in allergies, lung compliance is compromised because the diameter of the air passageways becomes smaller. This limits the amount of needed gases reaching and leaving the lungs.

Second, the lungs must inflate and deflate continuously to function properly. This ability is called its resilience. Lung resilience is limited when parts of the lung are not flexible, as occurs in emphysema, when lung tissue becomes stiff or fibrosis (filled with fibers).

Finally, in order for gas exchange to occur, the lungs are normally filled with fluid to keep its cells moist. Healthy lungs contain surfactant, a special chemical that helps to keep the alveoli open despite this fluid. Surfactant decreases the surface tension of fluid within the lungs. As you may recall in Chapter 2, surface tension causes a liquid to “stick” to itself. Surfactant interferes with the surface tension of water in the lungs, preventing alveoli from collapsing into each other. In premature births, usually more than one month early, surfactant-producing cells are too immature to make surfactant. This may result in troubled breathing, in a condition called infant respiratory distress syndrome (IRDS).

Gas Transport in Blood Oxygen is carried within the blood in several ways. Only a small portion of oxygen is dissolved within the blood in its transport. Instead, over 98% of the oxygen carried within the human body is carried on the hemoglobin molecule in red blood cells. As discussed earlier in the chapter, hemoglobin is a small molecule composed of four poly- peptide chains, each holding a heme group with iron at its center.

Resilience

The ability of the lungs to inflate and deflate continuously to function properly.

Surfactant

A special chemical that helps to keep the alveoli open by reducing the surface tension of fluid within the lungs.

Tissue CellsAlveoli (air sacs)

(b)

Red Blood Cell

Loading of O2

Unloading of CO2

O2 CO2

CO2 CO2

CO2

Plasma Plasma

Loading of CO2

Unloading of O2

Pulmonary Capillary Systemic Capillary Red Blood Cell

Figure 13.18 (Continued)

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Hemoglobin holds on to oxygen at its iron core, bound in a form called oxyhemoglo- bin. Each hemoglobin molecule is able to carry up to four oxygen molecules. With over 250 million hemoglobin molecules per single red blood cell, 1 billion oxygen molecules are carried per red blood cell! The ability of blood to move large amounts of oxygen in a short period of time is enormous.

Hemoglobin is not permanently affixed onto an oxygen molecule. Oxygen moves off of hemoglobin based on the pressure difference it encounters as it moves through the body. When there is a high pressure difference, oxygen moves quickly away from hemo- globin. When there is less of a need, oxygen is slower to move. Figure 13.14 shows the sites at which oxygen moves off of hemoglobin in the body.

Hemoglobin is much like a parent who gives money only when it is most needed, saving some for a rainy day. Hemoglobin conserves some oxygen, at some points to give to tissues when they need it most, as in cases of strenuous exercise. At these times, there is a decreasing in hemoglobin’s affinity for oxygen. Hemoglobin becomes less able to hold onto oxygen during exercise and when a need for oxygen presents itself.

Carbon dioxide is also transported through the body to be eliminated as a waste product. About 20% of carbon dioxide in the blood is bound to hemoglobin, in the form of carbaminohemoglobin. About 7% is dissolved and over 70% is carried as the bicar- bonate (HCO3−) ion. When carbon dioxide dissolves in the blood, it rapidly forms into carbonic acid. Carbonic acid (H2CO3) is a weak acid, and rapidly breaks into bicarbonate (HCO3−) and hydrogen ions:

CO2 + H2O ➔ H2CO3 ➔ HCO3− + H+

This equation is reversible, meaning that it also moves in the opposite direction depending upon the amount of bicarbonate and carbon dioxide present. If there is a large amount of bicarbonate in a system, it will drive the reaction to the left, producing more carbon dioxide. When carbon dioxide builds up in the blood, the reaction shifts to the right and blood becomes acidic.

Diseases of the Respiratory system Respiratory acidosis During respiratory acidosis, when the lungs and heart do not sufficiently transport needed gases within the body, acidic blood develops. A buildup of carbonic acid and hydrogen ions lowers the pH of the blood in this situation. As you may recall from ear- lier in the chapter, pH of the blood must be held within stringent conditions. Veering too far from the set point may result in serious health consequences. The end stages of ketosis, lung and heart disease often result in acidosis of the blood and death. In our story, Charles was saved by his daughter’s heart transplant. Otherwise, he faced death by respiratory acidosis. His blood would not have sufficiently pumped out carbon dioxide from his lungs, and would have made his blood acidic by his final weeks. As a result, changes in the pH would have ceased his life functions. Hemoglobin gives off more oxygen when blood is acidic. This helps the situation but acidic blood is a serious health hazard (Figure 13.19).

oxyhemoglobin

A bright red complex of oxygen and hemoglobin present in oxygenated blood.

Carbaminohe moglobin

One of the forms in which carbon dioxide exists in blood.

Respiratory acidosis

A condition that occurs when the lungs and heart do not sufficiently transport needed gases within the body, leading to the development of acidic blood.

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The Bends Usually carbon dioxide and oxygen are the only gases transported within the blood. However, during deep-sea diving, nitrogen gas may accumulate in a diver’s blood in a condition known as the bends. When a diver ascends too quickly to the surface, nitrogen gas bubbles come out of solution too quickly. This leads to air pockets that interfere with proper blood flow. As a result, blockages act like clots, to prevent blood flow to needed areas. Placing a victim in a compression chamber in order to slowly equalize the pressure treats the bends. The deep-sea diver in Figure 13.20 needs to be very careful to ascend from the water slowly to prevent the bends.

Carbon Monoxide poisoning In cases of suffocation due to car exhaust, carbon monoxide is the culprit. Carbon monoxide poisoning occurs when carbon monoxide (not carbon dioxide) binds to hemo- globin, replacing oxygen. This occurs because carbon monoxide (CO) more easily binds to hemoglobin than oxygen. CO is 200 times stickier to hemoglobin than oxygen. Thus,

The bends

The condition in which nitrogen gas accumulates in a diver’s blood.

Carbon monoxide poisoning

A potentially fatal condition that occurs when carbon monoxide binds to hemoglobin, replacing oxygen.

Figure 13.19 A patient is breathing poorly, using oxygen tanks to supplement low oxygen levels in the blood.

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Figure 13.20 Deep-sea diver. This diver is exploring a wreck.

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when carbon monoxide poisoning occurs, treatment with 100% oxygen or a hyperbaric compression chamber works best. The hyperbaric chamber, shown in Figure 13.21 works to force it off of the affected hemoglobin molecules.

altitude sickness When altitude affects a person’s ability to breath, it is called altitude sickness. Usually after a person travels from a low altitude to one that is over 8,000 feet, there are some health consequences. There is a decreased pressure of oxygen at such heights. Therefore, with air density too low for sufficient oxygen levels, the body needs to acclimatize to lower oxygen conditions. Acclimatization occurs when more red blood cells are formed and when the lungs develop more capacity to hold more air to compensate for the new conditions. Athletes often train in higher altitudes to naturally acclimatize, giving them an advantage when they return to normal altitudes.

Blood is able to carry oxygen based upon the number of red blood cells that it has. In blood doping, red blood cells are added to an athlete’s blood. One way is to store her or his blood and then inject it before a competition. This increases the number of red blood cells and hemoglobin a person holds. Blood doping, banned by the Olympics today, enhances an athlete’s performance and is considered unethical. Lance Armstrong, an Olympic medal winner, lost his awards due to allegations of blood doping.

Blood doping also has negative health consequences. It adds red blood cells to the blood, thus increasing the thickness or viscosity of it. Thicker blood may initiate clots and increase risks for heart attack and stroke. Olympic cyclist Lance Armstrong, in Figure 13.22 was accused of using blood doping to improve his performance.

Lung Cancer The leading cause of death in the United States from cancer is a result cancer of the lungs. One-third of all cancer deaths are due to lung cancer. In lung cancer, a bleeding mass or growth blocks the normal passage and exchange of gases in the lungs. It is often a painful disease, with a poor prognosis; survival is less than 20%, 5 years after diagnosis.

Altitude sickness

The condition in which the altitude affects a person’s ability to breath.

Figure 13.21 High oxygen hyperbaric chamber. A treatment for the bends, which slowly brings nitrogen gas out of solution and prevents it from forming large bubbles in blood vessels.

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What are the causes of lung cancer? Smoking is cited as the number one cause of lung cancer, while a distant by second asbestos exposure. However, what percentage of people actually gets lung cancer if they smoke? You might guess 20% or even 50% . . . but the actual number is much lower. Only 1% or 1 in 100 smokers ever gets lung cancer in his or her lifetime.

So, is smoking really linked to lung cancer? Consider the alternate data: on any lung cancer floor in the hospital, over 90% of lung cancer patients were smokers. Most lung cancers are related to smoking, given this set of data. Tobacco companies in the 1930s through to the 1980s manipulated these statistics to give the public the impression that lung cancer was not caused by smoking. Smoking is now accepted as the leading cause of lung cancer, among other illnesses including other respiratory diseases, cancers, stroke and heart disease. The lungs of a smoker are shown in Figure 13.23.

Figure 13.23 Smoking damages the tissues and conducting tubes of the lungs. a. The accompanying images show evidence of a lung tumor linked to smoking. b. Smoking destroys healthy lung tissues.

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Figure 13.22 Lance Armstrong Cycling

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Chronic obstructive pulmonary Disease In chronic obstructive pulmonary disease (COPD), limitations in sufficient breathing occur. One form of COPD is emphysema, which manifests as deteriorated alveoli. In emphysema, lungs lose their elasticity and air sacs are hardened, unable to properly exchange gases. Sufferers therefore are required to breathe more frequently and with more exertion. It can be an exhausting disease, with great effort expended to improve lung compliance. Emphysema is treated with increased oxygen and lung reduction surgery.

Asthma, another form of COPD, is an inflammation of the respiratory passageways. Gas exchange is harmed because the smaller size of the respiratory passageways limits the amount of air moving in and out of the lungs. Asthma is treated with steroids to relax muscles around the respiratory passages. An asthma sufferer is shown in the photo in Figure 13.24.

Controls of Heart and Lung actions The heart and lungs are controlled by hormones and nerves that direct them to work faster or slower. When certain nerves are activated, called the sympathetic nerves, they cause the heart to beat faster and the force of its contraction to be stronger. An opposing set of nerves, called the parasympathetic nerves, slow the heart down. Hormones are also released to speed up and slow down the cardiovascular system. Epinephrine and thyroxin both speed up the heart while acetylcholine slows it down. At times the needs of the body require changes in the rate at which the cardiovascular system works. When a need to run away from a scary situation arises, the heart rate must change to accommo- date changing conditions. The role of nerves and hormones in regulating body functions will be discussed in more detail in Chapter 14.

The rate of breathing is determined by a number of factors within our internal environment. The respiratory system is controlled by hormones and nerves much like the cardiovascular system. Our brains, particularly a region called the medulla oblongata, detect carbon dioxide levels. When the levels are too high, the medulla sends nerve messages to the ribs and diaphragm to stimulate more breathing. This eliminates the increased carbon dioxide detected in the blood and simultaneously adds oxygen for cellular use.

emphysema

A condition in which lungs lose their elasticity and air sacs are hardened, unable to properly exchange gases.

Asthma

A respiratory condition characterized by inflammation of the respiratory passageways.

Medulla oblongata

The inner part of the brain.

Figure 13.24 Asthma sufferer

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Pons

Apneustic and Pneumotaxic Centers

Ventral Respiratory Group

Dorsal Respiratory Group

Medulla Oblongata

Spinal Cord

Intercostal Nerves

Internal Intercostal Muscles (involved in expiration)

External Intercostal Muscles (involved in inspiration)

Diaphragm (involved in inspiration)

Phrenic Nerve

Figure 13.25 Respiratory controls of breathing. The medulla oblongata of the brain detects carbon diox- ide levels. The brainstem is linked via nerves to communicate blood gas information to other parts of the body.

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Other factors also change one’s rate of breathing. Consider a situation in which a person gets excited, as before an exam; her or his heart rate and breathing rate increases so that more oxygen can be transported around the body. This excitement is then brought back to normal breathing levels after the situation subsides. Some nerves slow respi- ration, as occurs when the Pons of the brain is stimulated. Emotion, as detected in the hypothalamus of the brain, affects respiration. The controls of breathing are shown in Figure 13.25.

ARe SCARIng A PeRSon, eATIng SugAR, BReATHIng InTo A BAg oR dRInkIng A glASS oF WATeR ReAlly THe BeST WAyS To SToP HICCuPS? It is only a myth that scaring a person, eating sugar, breathing into a bag and drinking a glass of water stops hiccups. A look at nerve anatomy indicates the best cure. As shown in this chapter, nerves are sent from the brain to the heart and lungs to cause their movements. The phrenic nerve, sent from the fourth cervical plexus in the neck sends impulses to the diaphragm muscle below the lungs to stimulate breathing. When the diaphragm contracts, it changes pres- sure in the thoracic cavity, which we know from the chapter readings, creates a gasp of air to move inward.

When pressure or damage to the phrenic nerve occurs at any point along its pathway, hiccups may occur. Hiccups are rapid gasps of air, producing a sound in the larynx. Imagine yourself hiccupping for 68 years: Charles Osborne, an Iowa farmer hiccupped from 1922 until his death in 1991. Mr. Osborne hic- cupped every few seconds, with the only relief occurring when he slept. He had the longest attack of hiccups in recorded history.

The best cure for hiccups was discovered by accident. When a 60-year old man was admitted to the hospital with acute pancreatitis, the man developed hiccups lasting two days. By accident, a new treatment for chronic hiccups was discovered. After doctors attempted a variety of treatments, they found no success. However, during a routine rectal examination the hiccups quickly stopped. While his hiccups resumed again within a few hours, the rectal exam- ination was repeated, and the hiccups did not return. The rectal examination, was surmised, massaged the phrenic nerve to stop its firing and its stimulation of the diaphragm muscles. This cure ironically came a year too late in 1992 . . . Charles Osborne did not live to see his cure.

summary The circulatory and respiratory systems are linked together with a common goal: Trans- port of needed materials throughout the body. The heart and lungs are linked by a set of blood vessels known as the pulmonary circuit. Blood is the fluid used to accomplish transport as well as protection, temperature and pH regulation. As blood moves through the pulmonary circuit, it forms oxygenated blood ready for the body to use. Blood moves through different types of vessels – arteries, capillaries, and veins – as it makes its way to needed cells and back to the heart. The respiratory organs function together to transport to and from the blood. A lung’s ability to function is measured by its compliance. There are many diseases related to the cardiovascular and respiratory systems, with emerging treat- ments, such as organ transplants, improving survival, and quality of life for its sufferers.

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CHECk oUT

summary: key points

• Medical treatments, such as organ transplants described in the story and prevention of disease such as diet and exercise have improved life expectancy and quality of life for cardiovascular and respira- tory illnesses.

• Blood is composed of plasma, which is mostly water and dissolved solutes and the formed elements, which are cells and cell fragments in the blood.

• Blood serves to transport materials within the body; it also regulates body temperature, internal pH, and protects the body from pathogens.

• Blood returns to the heart via the vena cava; is pumped from the right side to the lungs, back to the left side of the heart, and is propelled to all parts of the body through the pumping activity of the left ventricle, all based on electrical messages sent from the sinoatrial (SA) node.

• High blood pressure damages heart vessel linings and other organs, increasing risks for stroke and heart attack.

• When air enters the nose and mouth, it is conducted through the pharynx, larynx, trachea, bronchi, and into the air sacs of the lungs.

• The alveoli exchange oxygen and carbon dioxide gases, based on the partial pressure of each gas, between air in its sacs and pulmonary capillaries surrounding them.

• Numerous treatments for cardiovascular and respiratory diseases have helped improve survival and the quality of life of many people including: angioplasty, heart bypasses, surgery, steroids, oxygen, and hyperbaric compression chambers.

air sacs (alveoli) altitude sickness anemia angioplasty arrhythmia arteriosclerosis arteriole artery atrioventricular (AV) node atrium asthma autorythmic the bends blood bone marrow bronchial tubes Bundle of His

capillary capillary bed carbaminohemoglobin carbonic acid–bicarbonate buffering system carbon monoxide poisoning cardiovascular system clotting factors coronary artery coronary artery bypass graft (CABG) coronary circuit deep vein thrombosis (DVT) deoxygenated blood embolus emphysema endothelium expiration

key TeRMS

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formed elements heart heart attack (myocardial infarction) hemophilia high blood pressure inspiration iron deficiency anemia larynx lungs mechanical breathing medulla oblongata mitral (bicuspid) valve murmur muscular pump oxyhemoglobin pathogen pharynx plasma platelets protime pulmonary artery pulmonary circuit pulmonary embolism pulmonary vein Purkinje fibers red blood cells

regurgitation resilience respiration respiratory acidosis respiratory pump respiratory system semilunar valves sickle cell anemia sinatrial (SA) node stem cells, pleuripotential stroke surfactant systemic circuit thalassemia thrombin thrombosis trachea tricuspid valve varicose veins vein vena cava ventricle venules vocal cords white blood cells

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Multiple Choice Questions

1. Which treatment uses a tube to open clogged coronary arteries? a. Angioplasty b. Bypass grafting c. Lung-reduction surgery d. Hyperbaric compression chambers

2. Which term does NOT fit with the others? a. Plasma b. Erythrocyte c. White blood cell d. Platelet

3. A disease in the _________ would MOST affect blood cell production? a. blood b. bone marrow c. heart d. lungs

4. Carbonic acid functions to: a. protect blood from pathogens. b. buffer blood from pH changes. c. transport carbonated liquids. d. exchange carbon dioxide and oxygen gases.

5. Which transmits electrical signals through the left ventricles, during a heartbeat? a. Sinoatrial (SA) node b. Atrioventricular (AV) node c. Mitral valve d. Purkinje fibers

6. Which represents a logical order, from start to finish, in the movement of blood through the heart and lungs? a. right atrium➔pulmonary artery➔lung➔left ventricle b. pulmonary artery➔right atrium➔left ventricle➔lung c. left ventricle➔right atrium➔pulmonary vein➔lung d. right atrium➔pulmonary vein➔lung➔left ventricle

7. Which traps particles, larger than 4 µm, during respiration? a. Epiglottis b. Nasal cavities c. Trachea d. Echinoderm

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8. Which is NOT a part of the region that exchanges gases within the respiratory system? a. Alveoli b. Trachea c. Pulmonary capillaries d. Air sacs

9. If pressure of oxygen within an alveolus is 40 mmHg and within pulmonary capil- laries is 35 mmHg, which is expected to occur? a. Oxygen will move into the capillaries b. Carbon dioxide will move into the capillaries c. Oxygen will move out of the capillaries d. There is no net movement of gases in the alveolus under these conditions

10. Which increases a person’s risk for developing high blood pressure? a. Smoking b. Being overweight c. Genetics d. All of the above

short answers

1. Describe two treatments in which cardiovascular life expectancy have been improved upon since the 1950s.

2. Define the following terms: vein and artery. List one way each of the terms differ from each other in relation to their 1) anatomy; 2) function in blood transport; and 3) placement between the heart and lungs.

3. The formed elements make up an important part of the blood. Choose one of the formed elements and 1) explain how it is used in the body and 2) what diseases are linked to the malfunctioning of that formed element.

4. Draw a sketch of the heart, using arrows to trace the movement of blood through the sketch. Which is vessel is the most likely to be damaged by high pressure from the heart?

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5. How does the muscular pump aid in the prevention and treatment of high blood pressure?

6. Describe the anatomical changes that occur during inhalation and exhalation. Use the following terms in your description: diaphragm, ribs, chest cavity, lungs, inflate, deflate.

7. Define lung compliance. Explain three factors that contribute to lung compliance.

8. For question #7, which factor is most affected in infant respiratory distress syndrome?

9. Where does sound get produced in the respiratory system? How do the vocal cords create higher pitched sounds?

10. Describe three ways that carbon dioxide is transported in the blood. How is carbon dioxide buildup dangerous to a person’s health? Be sure to discuss the role of respi- ratory acidosis in your answer.

Biology and society Corner: Discussion Questions 1. Organ donation is a voluntary option exercised by a small percentage of people in

the United States. Over 10% of people will die each year while waiting for an organ transplant. As shown in our story, however, it can be life-saving. Should the govern- ment mandate all citizens to donate their organs upon their death? Why or Why not?

2. In the above question, consider that there is a black market for organs, traded ille- gally throughout the world. The average price paid for a kidney was $150,000 USD. It is estimated that 11,000 organs were traded illegally in 2010. Would mandatory organ donation, if implemented, affect patient healthcare? What is the likelihood that people will be allowed to die (or be killed) in the hospital to obtain their organs, because they are so valuable? What safeguards could be implemented, if any, to prevent such as problem?

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3. Smoking is a health hazard, yet more than 20% of adults in the United States smoke. Smoking is also on the rise in other nations, especially in the developing countries. The Tobacco Institute and Council for Tobacco Research continues to present data to question the link between smoking a lung cancer. Should the government inter- vene to make laws restricting or banning the use of tobacco products, considering that it is harmful to us? Why or why not?

4. While air quality has improved in cities over the past 20 years, air pollution is still a risk factor affecting heart and lung health. For example, studies show that jogging near a polluted highway increases the risk of heart attack by more than four times. Children who grow up in a city are also more likely to develop asthma than those in rural areas. How might this information impact whether you or your family’s choice in where to live? Would you rather live in a city or in a rural area, based on this information?

5. Blood doping has been banned by the Olympics because it gives unfair advantage to players. Lance Armstrong, Olympic gold medal winner in cycling, has been stripped of his medals due to his alleged use of blood doping. Construct an argu- ment against the banning of blood doping, defending Lance Armstrong. What other factors, besides blood doping, give one athlete an advantage over another? Should these be considered in your argument?

Figure – Concept Map of Chapter 13 Big Ideas

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509

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ESSENtialS

Lifting large objects, especially the wrong way, can cause injury

Neck pain is a common ailment but may indicate anatomical causes

The discs in the neck: herniated discs usually cause pain

Nerves go to muscles, transmit pain, and conduct messages

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Pain from the back and neck can emerge in other areas of the body. A burning and painful arm is caused by discs compressing on the nerves of the neck going down the arm

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ChECk iN

From reading this chapter, you will be able to

• Explain how medical treatment compares with alternative medicine in the treatment of pain and musculoskeletal injuries.

• Describe the organization of the nervous system and explain the chemistry of the nerve impulse. • Describe and compare the different sense systems in humans. • Trace the evolutionary development of the brain, describing its parts and their functions. • Connect the functions of the muscles alongside the sliding filament theory. • Identify the bones of the human skeleton and their associated diseases. • Identify the glands of the endocrine system and match them with the hormones they produce.

the Case of the Burning arm The pain was intense – it shot like an electric shock, moving through his living tissues – along his arm, with a burn all across his upper back and neck. “I should never have lifted that heavy rock . . . . these rocks will rip the very flesh off of my body,” sighed Richard.

It had been weeks since Richard worked to build his stone wall on the upper part of his land. The farmers built beautiful stone walls, and Richard prided himself on con- tinuing in their tradition. It was his hobby and Richard needed one; he was so ener- getic and healthy that the diversion of stone wall building was always a great feeling of accomplishment.

However, this last time was different. Richard knew that he had taken on too much for his body to bear. The rocks were larger and heavier and Richard was not accustomed to such strenuous lifting. He was a determined fellow, however, and he would build a new and larger wall than he had ever constructed. At the very moment that Richard lifted the corner rock on his land, he knew that something had gone terribly wrong. He felt a burn down his arm and a weakness in its muscles.

Richard waited in pain for days until he decided to go to his doctor. While Richard explained to the doctor that he must have pulled a muscle in his shoulder, his doctor knew the diagnosis right away. “Richard, I think you have a herniated disc in your neck. We will order an MRI to check it out.” Richard was perplexed. “If the pain is in my left arm, what does the neck have to do with it?” he asked. The doctor explained that a slipped or ruptured disc was pressing on the nerves coming out of his neck that stimulate his arm muscles. Nerves leave the neck as a group of nerves called the cervical plexus, giving messages to muscles throughout the arm.

The prognosis was as confusing as the cause of the symptoms. The doctor explained that in most cases, for roughly 80%, the slipped disc retracts back into place and no fur- ther treatment is needed. When the disc does not stop causing pain, drugs for pain and steroid shots can be given to reduce swelling and help buy time until it heals. In serious cases, neck surgery is needed. It all depends on Richard’s pain level.

Richard certainly did not want surgery but he was in pain. The doctor recommended that Richard wait a while, perhaps months, to see if the pain gets better. Surgery would be a last resort and was dangerous because they would need to go into his neck. Sur- geons would clip or remove the disc and they would be very close to all of his nerves,

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including his spinal cord. There was even a chance of total paralysis. Richard was given an anti- inflammatory and sent home. Richard was in severe pain.

The most difficult part of this problem for Richard was that he did not know what would happen to him because of this malady. He had read that over 90% of people expe- rience regular back and neck pain and get better, but he was not. He could not work for the past two months and, in this condition, Richard could barely move his arm.

“How surprising that it was all simply because of this small disc, a piece of cartilage that cushions the vertebrae of the back,” Richard thought to himself. How could some- thing so small and moveable still be causing him pain after merely moving rocks? What a disaster; Richard needed to do something; he needed to get back to work and earn a living. Would Richard get better, face surgery, or live a life of pain?

Richard repeated to himself, “I should never have lifted that heavy rock . . . .”

ChECk Up SECtioN

Neck and back pain afflict many people. They are sometimes driven to alternative medicine, often when traditional medical approaches fail.

Research the types of alternative medical approaches to treating pain. Be sure to describe the tech- niques and philosophy used by chiropractors and acupuncturists to treat pain. How does it differ from the traditional medical community?

Most medical doctors do not work with nor recognize alternative medicine practitioners. Would you recommend that Richard try an alternative medicine practitioner, such as a chiropractor? Why or why not?

the Nervous System Regulation Whether shooting pain down the arm, as shown in our story, or a change in blood pres- sure described in other chapters, the changes that occur in the body require regulation. Regulation, or control over functions of the body, is accomplished by a combination of the nervous (nerves), muscular (muscles), skeletal (bones), and endocrine (hormones) systems working together. Each plays a role in responding to changes and adapting to those changes. These systems work toward the common goal: to maintain homeostasis. In this chapter, we will survey the four systems to study how they regulate processes in the human body.

pain Pain is a response to some malfunction, sensed by the nervous system. It indicates that something is wrong – a cancer or an inflamed nerve, for example – which manifests as a symptom. Symptoms are studied by doctors to determine the cause and course of treatment. The philosophy that the medical community uses to approach each case is based on pre- vious outcomes and treatments of other patients. Many times a diagnosis changes or a prognosis (expected outcome) is uncertain in medicine. For example, in the story, some- times a herniated disc retracts and sometimes it does not. Some people (5% of cases)

Regulation

Control over functions of the body.

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have MRIs that show herniated discs but do not have any symptoms and experience no pain. Some people have extreme back pain and have almost no disease in their medical imaging.

Medicine treats the person and the case, but not the image. Each patient reacts dif- ferently to treatments and diseases in their outcome. Sometimes it is difficult to predict who will do well and who will not, although there are indications based again, on prior cases. Medical treatments always have uncertainty in their outcomes, for these reasons.

Our story described the suffering of Richard, like many people, who lives in pain every day because of a disorder of the musculoskeletal or nervous systems. Sometimes pain is at the site of its cause and sometimes it is referred pain, sent to another site away from its cause. In Richard’s case, the neck problem sent shooting pain down his arms instead of his neck, a common symptom of herniated discs. The pain was referred to another area of the body besides the neck.

More than 14 million people in the United States live with chronic pain. Many of these cases involve back and neck problems, because nerves emanate from the back in many areas, each of which sense pain. Others are diagnosed with diseases such as fibromyalgia (inflammation of the nerves), arthritis (inflammation of the joints), and endometriosis (inflammation in the reproductive system). Pain is personal – no one can see it or feel it but the sufferer – but pain is real for people and is it felt.

Should a person turn to alternative medicines, such as chiropractic help and acu- puncture? Medical treatments, such as surgery, physical therapy, and drugs, seek to repair anatomical problems. Alternative medicines do not intervene in injuries, and instead rely on holistic strategies for pain relief. There are many studies supporting the use of alter- native medicines. However, the medical community does not officially endorse nor work with these practitioners. More research needs to be done and more collaboration with traditional medicine to improve outcomes for alternative medicine pain patients.

Many famous people suffer with chronic pain due to back injuries, such as George Clooney and Jennifer Grey shown in Figure 14.1. Clooney fell while filming the thriller Syriana in 2005, which resulted in a tear in his dura mater that surrounds and contains the fluid of the spinal cord. After multiple surgeries to repair the tear, he continues to suffer from pain, and considered “ending it all,” at points due to the severity of his pain. Grey was in a car accident in 1987, causing her neck injury and pain. She treated it using

Referred pain

Pain that is not at the site of its cause.

Figure 14.1 George Clooney (Venice Film Festival, 2012).

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ice packs and Advil. Grey eventually had surgery to place a metal plate into her neck to stabilize her vertebrae, which eased her pain.

Nerves Almost all animals except the sponges, including vertebrates and invertebrates, have a nervous system and nerve cells or neurons. Neurons were described in Chapter 11, and their general structure is shown again in Figure 14.2. Neurons are specialized cells that receive information in the form of a sensation, which brings information to the brain and spinal cord. That information is processed in the brain and is then called a perception.

Neuron

A nerve cell.

Sensation

Information received by the neurons.

Figure 14.2 a. Neuron (nerve cell) Structure: The cell body contains most of a neu- ron’s organelles. b. Impulses are received by dendrites and travel along the axon to terminal branches. They jump from node to node bypassing the myelin sheath, a neu- ron’s insulation. Impulses reach terminal branches ready to travel to another nerve cell, muscle, or gland.

Motor Neuron

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Perceptions elicit a response to the information. Sensation, perception, and response constitute a process of responding to environmental changes, forming the nervous sys- tem’s role in regulation.

A neuron has two choices: to fire a message or not to fire a message. If a fly lands on a person’s arm, a neuron may or may not fire; depending on how much the fly disrupts the neurons on the skin. When the strength of the stimulus is strong enough, a message by a nerve is sent.

Neuron message signals are called nerve impulses and are actually a flow of charged ions. Long axons in neurons, as shown in Figure 14.2, enable them to transmit nerve impulses over relatively long distances. The sciatic nerve, our longest, is about 1 m (3 feet) in length traveling down the legs. Sciatica is pain down the leg along the sciatic nerve, a common ailment when the sciatic nerve is pinched or touched by bone or carti- lage. Let’s review the neuron’s structure in Figure 14.2.

Richard’s pain described in our story is an example of a stimulus, or any change in the environment that causes a response. A stimulus is picked up by neurons. The start of a nerve response process begins with receptors. Receptors are specialized structures that sense stimuli. There are several types of receptors, each specific to the type of stim- ulus it receives. Each also performs a special function, with select receptors given in Figure 14.3. For example, a Meissner’s corpuscle is a receptor on the skin. This receptor fires when mechanical changes (e.g., pressure) from a stimulus (in the example above, the fly) are sufficient enough to warrant a receptor’s firing.

When receptors fire, they send a nerve impulse along a sensory neuron (also called afferent neurons). Sensory neurons bring information from the external environment, toward the brain and spinal cord. Within the brain and spinal cord, interneurons organize and connect those messages. Motor neurons (also called efferent neurons) bring nerve

Nerve impulse

Neuron message signals that are actually a flow of charged ions.

Stimulus

Any change in the environment that causes a response.

Sensory neuron

Neurons that bring information from the external environment, toward the brain and spinal cord.

Interneuron

A neuron that transmits impulses between other neurons.

Motor neuron

A nerve cell that brings nerve impulses from the brain and spinal cord to a muscle.

Figure 14.3 Types of Sense Receptors (aka corpuscles) on the skin.

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impulses away from the brain and spinal cord to elicit a response by an animal. In our example of the fly sitting on an arm, the stimulus or mechanical changes brought out by the fly need to be strong enough to cause a receptor to fire. The message would then be sent via a sensory neuron to the brain to perceive the fly’s presence. After it is inte- grated using interneurons, the brain is likely to send a motor neuron message to the arm muscles, directing them to swat the fly. The passage of nerve impulses along the three different types of neurons is shown in Figure 14.4.

Figure 14.4 Neurons Work Together in the Nervous System. Sensory neurons, interneurons, and motor neurons. Note that sensory and motor neurons have a myelin sheath that allows for rapid transmission of impulses along axons. From Biological Perspectives, 3rd ed by BSCS.

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The DollaR BIll DRop: CaN a peRSoN CaTCh a DollaR BIll wheN IT IS DRoppeD IN BeTweeN FINgeRS?

Place a dollar bill in-between another person’s thumb and middle fingers, with their fingers extending around the face picture on the bill. Drop the dollar bill at a random time. Keep the catcher’s hand stationary. This prevents the catcher from lunging forward toward the bill.

You will see that the catcher’s nervous system is always too slow to catch the bill. The dollar bill drop is a measure of a person’s reaction time. Reaction time is the time it takes for a person to react to a stimulus. In this case, the stimulus is the dropping of the dollar bill.

The reaction to the dollar bill dropping takes too long for the sensory neuron, interneuron, and motor neuron to work together to elicit a response in time. The nerve message is sent from the brain, after seeing the dollar drop. There are too many nerve cells and too many gaps in-between the nerve cells for a person to consistently catch a bill.

Through only random chance, roughly 1 in 1,000 people, some will inevita- bly luck out and catch the bill – but usually the catcher is too slow. Figure 14.5 shows that it is a clever bar trick that can win some money in betting – but also a black eye!

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organization of the Nervous System The example above shows that the branches of the nervous system have differing roles. The different branches of the nervous system and their interactions are clarified in Figure 14.6. The brain and the spinal cord function as the center of the nervous system and are together called the central nervous system (CNS). The brain is the command center of the body, interpreting stimuli and capable of higher-order thought. This will be discussed later in this chapter. The spinal cord nerves are surrounded by a series of protective membranes called the meninges, within the vertebrae (neck and back bones). The spinal neurons conduct impulses up and down the spinal cord.

All of the other nerves outside of the CNS are part of the peripheral nervous system (PNS). Peripheral nerves may be classified within the somatic nervous system, which is under voluntary control, such as those motor neurons, directing muscles to swat a fly; or they may be part of the autonomic nervous system, which are involuntary nerves.

Central nervous system (CNS)

The part of the nervous system consisting of the brain and the spinal cord.

Brain

A part of central nervous system that functions as the command center of the body.

Spinal cord

A long cord of nerve tissues that connect the brain to the other parts of the body.

Meninges

A series of protective membranes that surround the spinal cord nerves.

peripheral nervous system (pNS)

The portion of the CNS that is outside the brain and the spinal cord.

Somatic nervous system

Part of the PNS that controls the voluntary movements in the body.

autonomic nervous system

System of involuntary nerves.

Figure 14.5 Catching a Dollar Bill Is Not Easy!

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Figure 14.6 Organization of the Nervous System: the CNS (brain and spinal cord) and PNS (all other nerves). Receptors of the PNS send nerve impulses to the CNS. The brain sends messages via motor neurons to effectors (muscles or glands). From Biological Perspectives, 3rd ed by BSCS.

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Autonomic nerves are those that control involuntary activities, such as smooth muscles of the alimentary canal or heart muscle, discussed in Chapters 12 and 13.

Autonomic nerves may be stimulated during times of excitement or fear, in a set of neurons comprising the sympathetic nervous system. Sympathetic nerves increase heart rate, stimulate muscles, and raise blood pressure. They also slow digestion because energy is directed instead to the muscles and the heart. Sympathetic nerves carry out the “fight or flight response,” which is characterized by an energetic reaction to fearful or exciting stimuli. A student getting handed an examination paper or confrontation with a friend, both stimulate sympathetic nerves and a sympathetic nervous system response.

The opposing set of nerves is termed the parasympathetic nervous system, which are stimulated when the body calms down, under relaxing conditions. The parasympathetic nervous system acts in opposition to sympathetic responses. They instead slow down the heart rate, relax the muscles, lower blood pressure, and speed up digestion. When you had a frightening event, did you feel that you would never calm down? Parasympathetic nerves brought your body back to normal; back to homeostasis. In Richard’s case in our story, relaxation is a technique used to improve pain, which we might recommend to him despite the stresses of a herniated disc.

Do Nerves Use Electricity? Regulation by the nervous system is fast and efficient. Neurons fire, and a flow of ionic charges move along them. In our story, Richard felt the effects of nerve impulses because a disc compressed his cervical neurons, sending pain and heat sensations down his arm along their axon paths. While it felt like electricity to Richard; what really is a nerve impulse?

A nerve impulse is similar to an electric current because both consist of a flow of charged particles. Anyone who has touched a live wire knows the feeling that Richard felt down his arm: burning pain and numbness due to the flow of charged particles along the stimulated nerve.

However, a nerve impulse differs from electricity in several ways. First, a nerve impulse is actually a wave of positively charged ions, namely sodium and potassium ions. Electricity is the flow of negatively charged electrons within copper wire. Impulses are much slower than electricity, moving only 2 m/s; while electricity rapidly travels mil- lions of meters in 1 s. The strength of a nerve impulse also stays the same, but electricity weakens over a distance. This is why powerhouses cannot be too far from the homes they supply; the electrical strength would be too weak.

Nerve impulses Neurons are said to be “at rest” when they are not carrying a nerve impulse. How- ever, nerve cells are really active, even when they are not firing impulses. They con- duct cellular activities, mostly within their cyton. Across the membrane of the neuron, a difference in the numbers and types of ions exists. Recall from Chapter 3 that the sodium–potassium pump actively transports sodium out of and potassium into the cell. The sodium–potassium works continually to create a difference in charge across the neuron membrane. This difference in charge is called the neuron’s resting potential. Its inside is more negatively charged than the outside because more Na+ is pumped out than K+ is pumped into the cell. The resting potential of a neuron is -70 millivolts (mV) because its inside is relatively more negative (due to the positive sodium ions pumped outside) compared with the outside. Figure 14.7 gives the cutaway of an axon to show the resting potential of a neuron.

Sympathetic nervous system

A part of the nervous system that increases heart rate, stimulates muscles, and raises blood pressure.

parasympathetic nervous system

Opposing set of nerves that are stimulated when the body calms down, under relaxing conditions.

Resting potential

The potential of a cell that does not exhibit the activity resulting from a stimulus.

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A stimulus may cause a disruption of that resting potential. Much like an earth- quake, a stimulus causes openings, in this case in the neuron’s membrane, to leak sodium ions into the cell. The stimulus must be strong enough to disrupt the resting potential. When the potential rises to -55 mV, called the critical threshold potential, the entire neuron fires a nerve impulse across its membrane. A fly, for example, would disrupt the resting potential if it bites or walks on a person’s arm. It requires enough detectable force to hit the -55 mV threshold. The stimulus then opens up channels in the dendrite’s membrane, allowing Na+ ions to flow into the cell. Some K+ ions leak out at roughly the same time. This forms a wave of ion flow called an action potential. The flow of sodium and potassium ions creates a moving charge in Figure 14.8, which is an action potential.

The action potential travels through a neuron, down the axon, which is covered in pads of insulation called the myelin sheath, which prevents the action potential from weakening. The action potential continues until it reaches the terminal branches at the end of the axon. Here, another shake-up occurs, with sacs along the terminal branches sent off to cross a gap to reach another neuron or muscle cell. The gap or region sep- arating the neurons from the other cells is called its synapse. A picture of the synapse is given in Figure 14.9. Nerve impulses travel across synapses and require extra time, slowing their transmission. These slow-downs cause people to fail to “catch” the dollar bill described earlier.

Neurotransmitters Sacs traveling through the synapse are filled with neurotransmitters, which are special chemicals that carry a nerve impulse to new cells. Roughly 25 types of neurotransmitters have been identified, each of which serves an important role in nervous system regula- tion. Table 14.1 gives selected neurotransmitters, their actions, and structure. These are the most important to know for a working knowledge of human biology and health study.

Neurotransmitters are important in memory, mood, and pain perception. Acetylcho- line is a neurotransmitter that is associated with good memory skills. It is found in

Critical threshold potential

The critical level (-55mV) at which the entire neuron fires a nerve impulse across its membrane.

action potential

A change in the electric potential across the plasma membrane that occurs when a cell is stimulated.

Myelin sheath

Pads of insulation that prevent the action potential from weakening.

Synapse

The gap or region separating neurons from other cells or each other.

Neurotransmitter

Special chemicals that carry a nerve impulse to new cells.

Figure 14.7 Resting Membrane Potential. The sodium–potassium pump works to maintain a charge difference across the cell membrane. This action (by the presence of negatively charged proteins within the cell) causes the inside of a nerve to be more neg- ative by -70 mV, called its resting potential. From Biological Perspectives, 3rd ed by BSCS.

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Figure 14.8 a. Formation of an action potential. Nerve impulse transmission along the axon: ions flow into and out of the neuron forming a wave-like current, called the action potential. b. Action potential changes in membrane polarity associated with the action potential corresponding to chemical movements in part (a).

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decreased amounts in Alzheimer’s patients, as you may recall from Chapter 1. Several other neurotransmitters influence mood and even personality. Serotonin and endorphins, for example, are both types of neurotransmitters that improve mood and inhibit pain and depressive feelings. They are found in increased amounts in happier people and decreased in depressed people. There are ways to improve mood and decrease pain. Some manu- factured drugs, such as some antidepressants, work by increasing the amount of these neurotransmitters in the blood. Prozac, for example, blocks the normal reabsorption of

Serotonin

A type of neurotransmitter that improves mood and inhibits pain and depressive feelings.

endorphins

A type of neurotransmitter that improves mood and inhibits pain and depressive feelings.

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Figure 14.9 a. The Synapse and Traveling Nerve Impulse. Nerve impulses must travel across synapses, which are gaps between nerves through which ionic charges are carried. Neurotransmitters (nerve chemicals) carry the charge across the synapse. From Biological Perspectives, 3rd ed by BSCS. Reprinted by permission. b. Steps for transmission of action potential across synapse.

serotonin, increasing it within the body and lessening feelings of depression. A more natural way is to use physical exercise and training. Both serotonin and endorphins also increase after physical activity, such as regular aerobic exercise. Medical doctors are increasingly recommending exercise for patients with depressive mood disorders, for these reasons.

Special Senses While the mechanics of nerve impulse transmission explains communication and reg- ulation within the body, a look at our special senses – smell, taste, touch, vision, and hearing – gives us a better view of how our nervous system helps us to respond to the

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1 The action potential reaches the synaptic knob.

The synaptic knob releases neurotransmitter into the synaptic cleft.

Neurotransmitter crosses the synaptic cleft.3

Neurotransmitter attaches to the post-synapse4

Ion channels on the post- synapse temporarily open.5

Ions diffuse into the post-synapse6

(b)

Figure 14.9 (continued)

world around us. Some people have a more keen sense of smell than others. It is also reported that failure in one of the senses, such as blindness, results in development of another sense, such as improved hearing.

Different organisms also have heightened senses: dogs are able to hear pitches much higher than humans; dogs also have a sense of smell 40 times more powerful than humans, able to detect drugs and track suspects; ants are able to see very little but are able to sense chemicals that are one-billionth of a gram in weight; and nocturnal owls have excellent eyesight and depth perception, able to detect their prey very easily. A photo of an owl, seriously focused on its prey, is given in Figure 14.10.

Even different humans have differing sense abilities. Children are able to sense more frequencies of music than adults, whose hearing is diminished as a result of age. If a group of school kids set their cell phones to ring at a certain range of pitches, their teacher will not hear it! Our differences are based on our individual physiology. What one person is able to hear may not have access to another due to the differing sensitivity of their senses.

Gustation The ability to taste or gustation starts by chemoreceptors in the mouth, tongue, and cheeks. Specialized receptors are called taste buds, which fire when chemicals from food attach to them. Gustatory receptors are thus chemoreceptors because they

gustation

The ability to taste.

Chemoreceptor

A sensory cell that is stimulated by chemicals.

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Table 14.1 Selected Neurotransmitters in the Body

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are stimulated by chemicals. Gustation is stimulated most strongly by taste buds on the tongue.

There are roughly 10,000 taste buds in the human mouth and on the tongue. The sides of the tongue pick up sour tastes and the front senses sweet. The front and sides overlap with other taste buds to sense sour chemicals and the back of the tongue pick

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up bitter sensations. Different regions of the tongue detect different tastes in foods, as shown in Figure 14.11. Studies report that men and women, on average, differ in their taste preferences, with men preferring salty treats more often and women preferring sweets.

Taste has strong nerve responses that remain in one’s memory. Do you know someone who has had food poisoning? They are likely to have lost interest in what- ever food they ate at the time, due to the association of that food with the experience. Taste is a strong force in society. Cultures are built around food, and more than half of a hunter-gatherer’s time was spent obtaining it. Our modern culture also centers on eating, a need for survival. When taste is associated with satiety from hunger, the food becomes more desirable. Many Europeans, as in Germany, eat pig brains for breakfast. While Americans may consider it distasteful, pig brains probably satisfied hunger in these nation’s people.

Figure 14.10 An Owl Watches Its Prey before Attacking. Visual clues help many organisms locate and obtain food.

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Figure 14.11 The Tastes of the Tongue: taste buds for different stimuli are in dif- ferent regions of the tongue. While more receptors for sour (acidy) substances are located mostly on the sides of the tongue, as shown in this figure, receptors of all types are found strewn throughout the mouth.

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olfaction A keen sense of smell or olfaction is great for culinary students and chefs. Try cooking without a good sense of smell and try eating with your nose plugged. You taste is com- promised and you cooking skills diminish greatly. Figure 14.12 points out the relation- ship between the brain and the olfactory receptors in our noses.

Olfactory receptors are located in the superior portion of the nasal cavity, covering an area of about 5 cm2. Smells are a result of chemicals diffusing through the air. Thus, olfac- tory receptors are also chemoreceptors. When chemicals attach to olfactory receptors, nerve impulses are sent to a special region of the brain, the olfactory bulbs. Olfactory bulbs are located at the front part of the brain. Nerves travel through a thin bone separat- ing the brain from the nasal cavity, called the cribriform plate, covered in holes for which nerves may travel. Damage to the frontal parts of the brain may inhibit smell. A famous chef sued for damages after a car accident damaged his sense of smell. He received mil- lions of dollars because his cooking suffered with the loss of his olfactory senses.

olfaction

The sense of smell.

Figure 14.12 Olfactory (smell) Receptors Are Linked to the Brain by Running Nerves across the Nasal Bones. There are small holes in these bones that allow the passage of nerves to the brain. The olfactory bulbs in the brain interpret smells. Adapted from Anatomy I and Physiology Lecture Manual by John Erickson and C. Michael French.

Olfactory Bulb

Cribriform Plate of the Ethmoid Bone

Olfactory receptors

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A young boy was admitted to the hospital in central Texas in August 2007. He had fever, felt poorly, had transient pains, and lost his sense of smell. Instead, he smelled a burning odor despite there being none in his surroundings. He had been swimming in a lake during his days at summer camp. Doctors could not identify the cause of his symptoms until a sample of his cerebrospinal fluid showed that he had amoebas in his CNS. The boy received aggressive treat- ment for the amoeba but he died five days after being admitted to the hospital.

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Vision Human use of vision is well developed as compared with many other animal species. It is our sharpest sense, used for hunting, reading, writing, and fine movements. Our eyes are developed to take in light rays and convert them into a nerve impulse to be registered within the brain. Let’s trace the movement of light as it travels from the outside world and into our brains, using Figure 14.13.

The outermost tunic (covering) of the eye is called the sclera. When light travels into the eye, it first hits the cornea, which covers the anterior (front) chamber of the eye. Light moves through the cornea and into the front chamber, known as the aqueous humor. The aqueous humor contains fluid through which light passes until it is focused by the lens. The colored iris surrounds the opening to the lens, called the pupil. The lens of the eye is very hard in structure but flattens to focus the rays of light passing through it. The ciliary body surrounds the lens, which regulates the lens’ shape. After passing through the lens, light moves as a focused beam through the eye’s posterior chamber called the vitreous humor. The inside of the eyeball is lined with a thin, tanned coat called the retina.

Light strikes the retina, which contains receptor cells called photo-pigments. Photo-pigments come in two forms: rods and cones, which send impulses to the brain when they are stimulated by light waves. Rods are sensitive to low levels of light, allowing sight at night. Cones are more sensitive to light and used to see during the daytime. There are three types of cones: red-, green-, and blue-sensitive. Using a combination of cones enables us to see colors. (Both cone and color start with “C” to help you remember). Some people (usually males) are color-blind because their green or red cones do not function properly. It is a sex-linked trait, as you may recall from Chapter 6. Recall that waves are energy, and light waves transfer that energy to ionic impulses because of photoreceptors.

Cornea

Transparent part of the eye.

aqueous humor

The clear fluid present between the cornea and lens of the eyes.

Iris

The colored part found around the pupil of the eye.

pupil

The opening in the center of iris.

lens

A very hard structure of the eye but flattens to focus the rays of light passing through it.

Ciliary body

A part of the eye located between the choroid and iris.

Vitreous humor

Posterior chamber of the eyes.

photo pigments

Special pigments found in the retinal rods and cones.

Rods

One form of photo pigment that sends impulses to the brain that give black-and- white perception.

Cones

A form of photo pigment that sends impulses to the brain that give color perception.

The story above reveals a case in which an amoeba, a single-celled protist discussed in Chapter 8, caused a fatal infection of a child’s brain: amoebic menin- goencephalitis. When the amoeba, Naegleriafowleri, enters the brain through the nasal passages, it travels through the cribriform plate. It first attacks the olfactory bulbs of the brain. Thus, the first symptom is loss of smell or a sense that something is burning or rotting. Olfactory tissue is instead being attacked and in a sense “burned” away by the amoeba. Later symptoms include a loss of balance, seizures, and confusion and hallucinations. The entire course of the disease takes under two weeks, almost always resulting in death. It is difficult to treat and even detect early, over 98% of people die within this short period. From 1995 to 2004, the amoeba has killed 23 people only in the United States, according to the U.S. Centers for Disease Control and Prevention.

While this is a rare illness, it has been associated with swimming in warm water lakes and ponds. More recently, two cases are thought to have arisen from water wells and municipal water supplies. Naegleria fowleri was found in the home water supply of both victims. Neti pot, a device used to irrigate (clean) nasal systems, may be the cause. Water is poured from the neti pot through one nostril and then it flows out of the other. While it is an ancient technique, it is now being recommended by the medical community for allergy, cold, and sinusitis treatment. The use of sterile water is therefore recom- mended when using a neti pot.

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Changing light into Nerve impulses Rods and cones are shown in Figure 14.14, in which the process of forming a nerve impulse from light is described. One type of photo-pigment found in rods for example, called rhodopsin, responds to light by changing shape and generating a nerve impulse and sending it to the brain. Rhodopsin is composed of two parts: opsin, which is a gly- coprotein, and retinal, a derivative of vitamin A. Absorption of light by photo-pigments occurs as energy from light waves strikes them. Photo-pigments change their structure upon light absorption. The retinal part of rhodopsin converts from a bent or cis-retinal form to a trans-retinal form, which is straight in its shape. The shape change causes an earthquake-type response in the retina, stopping Na+ from flowing into the adjacent nerve cells. These nerve cells are inhibitory, so that when they cease to function, other nerve cells are triggered.

Thus, nerve impulses are sent from receptors within the retina. First, bipolar cells fire sending impulses to ganglion cells, and eventually, via the optic nerve to the brain.

Rhodopsin

One type of photo- pigment found in rods that responds to light by changing shape and generating a nerve impulse and sending it to the brain.

Bipolar cells

A neuron that has two processes.

Figure 14.13 Eyeball Anatomy. Light’s movement through the structures of the eyeball cause vision. Light passes through the eye to the photoreceptors in the retina along the backside. Nerve impulses are sent via the optic nerve to the brain to be processed.

Pupil

Aqueous Humor

Optic Disc

Optic Nerve - CN II

Vitreous Humor

Lens

Iris

Retina

Sclera

Choroid

Fovea Centralis

Cornea

Ciliary Body

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In the brain, visual messages are sensed and interpreted. The brain’s functions will be discussed in the next sections; however, the movement of impulses through the retina is shown in Figure 14.15.

hearing The human ear is adapted to transform sound wave energy into mechanical energy. The ear is a funnel through which waves are concentrated more and more, strengthening them. Have you ever seen old movies, with hearing aids that were simply funnels placed up against an ear? The principle applies to modern hearing aids as well: concentrating sound waves enables hearing. Different species have differing abilities to hear: Dogs hear high pitches well and some even hear echoed sound, in echolocation used by bats. However, they all hear using the same process, with sound waves moving through the ear structure shown in Figure 14.16.

First, sound waves are funneled in the outer ear, which consists of a pinna and an eardrum. The pinna acts as a funnel to concentrate sound to the eardrum, which vibrates. At this point, the traveling sound transforms into a physical entity: a vibration in the

outer ear

Pinna and eardrum.

pinna

Projecting part of the external ear.

ear drum

The membrane separating the outer ear from the middle ear.

Figure 14.14 a. Photoreceptors in the eye, rods, and cones contain photo-pigments stacked in discs along their top regions. b. Vitamin A (retinol) is important in regenerating retinal.

Vitamin A Retinol

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eardrum. Vibrations travel along the middle ear, which consists of three ear bones: the hammer (malleus), anvil (incus), and stirrup (stapes) or (HAS, to help you remember).

The oval window is the start of the inner ear, which consists of two parts: the semicircular canals and the cochlea. The semicircular canals are responsible for balance. As the stirrup vibrates, the oval window passes energy along the vibrations to the fluid within the cochlea. The oval window is much smaller than the eardrum. Why? Well, what is better to walk with in a muddy field: boots or high heels? Of course, high heels will sink much faster than boots. This is because the surface area of the high heels is so small that it concentrates the weight of a person to press down into the ground. The oval window thus concentrates sound strongly into the cochlea.

This concentration of sound waves transmits into the liquid of the cochlea, appear- ing as liquid waves. Waves in the cochlea bend tiny hairs sitting atop receptors, along its membranes. Each time a hair bends, receptors fire a nerve impulse up the auditory nerve and to the brain. When sound travels, it either has many waves, making it a higher pitched sound, or it has waves that are high, making it louder. As we age, hearing usu- ally changes, decreasing in the range of sounds we are able to hear. There are numerous causes of hearing loss, from viral infections and arthritis to deterioration of the mem- branes in the cochlea. For example, when ear bones develop arthritis or joint disease, it can impair hearing. Hearing aids are useful but often do not return one’s hearing suc- cessfully to its full capacity. Different parts of the membrane within the cochlea detect different pitched sounds, as identified in Figure 14.17.

Middle ear

Middle ear bones found inside the eardrum.

hammer

A bone that is the outermost of the three small bones in the middle ear.

anvil

A tiny bone in the middle ear.

Stirrup

The innermost bone of the middle ear.

Semicircular canals

Part of the inner ear filled with a fluid substance.

Cochlea

A spiral-shaped cavity of inner ear.

oval window

An oval-shaped opening that is the start of the inner ear.

Figure 14.15 Nerve Messages Sent through the Retina Are Organized by a Network of Neurons; bipolar cells and ganglion cells each help light’s message to pass to the optic nerve and onto the brain.

Cone Rods

Pigmented retina

Main photoreceptor cells

Bipolar cells

Ganglion cells

Fibers to optic nerve

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Figure 14.17 a. Distinguishing Pitch Occurs within the Cochlea. Different parts of the membrane within the cochlea detect different pitches of sound waves. b. If unwound, the cochlea would form a U shape. c. The cochlea has a spiral shape, with fluid and hair cells that are attached to the tectorial membrane.

Stapes

Cochlea Unwound

Tectorial Membrane

Cochlear Duct

Spiral Organ

Spiral Organ Cochlear Duct

Hair Cells

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Figure 14.16 Structure of the Human Ear; vibrations are transmitted through the ear to bend hairs within the cochlea, forming nerve impulses.

Auricle

External Auditory Meatus

Semicircular Canals

Labyrinth

Vestibulocochlear Nerve (Cranial Nerve VIII)

Cochlea

Vestibule

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Auditory Tubes

Canal

Tympanic Membrane

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touch Human touch, the last of the five senses, is studied as an important treatment in sick- ness and recovery. Massage therapy, acupuncture, and osteopathic medicine use touch to alleviate symptoms of pain and help in a patient’s recovery. We began the chapter with a reflection on alternative medicines and whether they would help Richard in our story. All of those medicines focus on the efficacy of touch.

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Touch is classified into several categories, based on the types of receptors that are stim- ulated: pressure by mechanoreceptors, temperature by thermoreceptors, and pain by nociceptors, described earlier in the chapter. Most of these are found on our skin and are used to respond to internal or external cues. When we have pain, for example, in our elbow, it indicates that there is damage and we should be careful with it. Some drugs, such as morphine, block the nerve impulses transmitted from the site of pain to the brain. It is a cut in the communication between the two areas, a way to treat pain. Painkillers are addictive and a leading cause of substance abuse in our society.

the Brain All of the senses are interpreted by the brain, a complex organ capable of great thought, but only about 1300 g (3 pounds) in weight. It is gray in color and mushy in texture, resembling a ball of bumpy play dough, just a bit softer though. However, the appearance of the brain merely skims its great functions: the brain is very much a fantastic organ. When holding a brain, it is amazing that all of our emotions, thoughts, intelligence, and even spirituality arise from this small yet complex set of tissues.

The brain is composed of three regions: (1) the cerebrum, or the largest part of the brain, which is divided into two hemispheres, (2) the cerebellum, the posterior part of the brain, and (3) the brain stem, which consists of the midbrain, pons, and medulla oblongata.

The brain and spinal cord are both protected by three coverings, together called the meninges. The outer layer of the meninges is the dura mater (“tough mother”), made of strong fibrous tissue. The middle layer is known as the arachnoid (spidery) layer, which has vessels that appear spidery. The inner layer is called the pia mater (“delicate

Mechanoreceptors

A sense organ responding to physical changes.

Thermoreceptors

A sense organ responding to temperature.

Nociceptors

A sense organ responding to pain.

Cerebrum

The largest region of the brain.

Cerebellum

The posterior part of the brain, involved in coordination.

Dura mater

The outer layer of meninges.

arachnoid

The middle layer of meninges.

Do huMaNS haVe oNly FIVe SeNSeS?

Many pieces of data are sensed by receptors other than through the five tra- ditional senses. Many organisms, for example, are able to navigate based on the Earth’s magnetic field. Birds, whales, eels, and sharks migrate using metal within their brains to align with the magnetic fields. Snakes are able to sense heat or infrared energy in other organisms, and jellyfish have sensory cells to sense gravity.

Other data are detected internally by the human body. For example, pro- prioceptors are used to help us balance based on gravity. Proprioceptors are found in our muscles, tendons, and joints and send information about body positioning to the brain. Damage to these areas can lead to balance problems. Some studies report that cholesterol-reducing drugs, called statins, may dam- age these regions.

The sensing of pain, described in our story of Richard, uses special recep- tors called nociceptors. Pain is perceived differently by different people. This is because it has many aspects to how it is perceived and felt. Sometimes there is a mind–body connection, allowing some people to relax and reduce their pain while not working for others. There is also a cultural component to pain, with some cultures showing more or less reaction to the same pains. Because so many people suffer from pain, whole areas of medicine and research are dedicated to pain management.

pia mater

The inner layer of meninges.

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Figure 14.18 Brain Anatomy. The brain and its protective coverings, the meninges.

Cerebrospinal Fluid Structures and Flow

Arachnoid Villas

Lateral Ventricle

Choroid Plexus

Interventricular Foramen

Third Ventricle

Cerebral Aqueduct

Fourth Ventricle

Central Canal

Choroid Plexus

Dura Mater

Pia Mater

Arachnoid

Subarachnoid Space

Superior Sagittal Sinus

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mother”), which contains capillaries that nourish underlying brain tissue. The brain and its coverings are shown in Figure 14.18.

Below the meninges, many structures are visible on the surface of the brain. The corpus callosum is an obvious attachment area, connecting the two hemispheres of the cerebrum. The rounded area underneath the corpus callosum is called the thalamus. It is like the grand central station of the brain, receiving all of the sense information from the body. The rest of the brain interprets that information. The region below the thalamus is the hypothalamus, which has many functions in the body (e.g. thirst, hunger, and tem- perature regulation). Attached to the hypothalamus is the pituitary gland. It regulates the hormonal system, which will be discussed in the last section of this chapter.

The regions of the brain that are responsible for basic survival are shown in Figure 14.19. At the front of the brain there are two olfactory bulbs, described earlier as important in sensing smell. The pons and medulla and midbrain and cerebellum are also visible, which comprise the central core or the brainstem (Figure 14.21). The brain- stem carries out the basic functions of life: breathing, heart rate, and blood pressure are controlled by the medulla; and hearing, seeing, and pain perceptions are functions of the midbrain. The thalamus is shown transmitting messages to multiple parts of the brain.

Corpus callosum

An attachment area that connects the two hemispheres of the cerebrum.

Thalamus

The rounded area underneath the corpus callosum.

hypothalamus

The region below the thalamus.

pons

Part of the brainstem that helps relay impulses from cortex to cerebellum.

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Figure 14.19 Different Regions of the Brain Are Responsible for Basic Living Functions. The brainstem controls breathing and blood pressure. The major lobes of the brain control different life functions. The cerebrum is the largest part of the brain, controlling higher-level thinking, such as reasoning and language. The cerebellum controls balance and coordination, located as a sphere in the posterior region of the brain. From Biological Perspectives, 3rd ed by BSCS.

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The thalamus is the “grand central station” of the brain because it is the first to receive information from the body. It quickly sends out nerve messages to be interpreted by other brain structures.

The cerebellum controls balance and coordination. A great basketball player usually has a more developed cerebellum to enhance motor (movement) skills. The cerebellum is located toward the posterior region of the brain.

We might recommend to Richard that there is a mind–body connection to pain per- ception that occurs within the central core. It is believed that smaller diameter nerve fibers transmit pain up to the brain, but large diameter fibers carry other nonpain infor- mation. Acupuncture claims to work by stimulating large diameter fibers. This blocks the sensations of small nerve fibers and pain messages.

The central core is our most primitive part of the brain, developed first evolution- arily as shown in part in Figure 14.19. The next set of structures to develop in the animal kingdom was the limbic system. In humans, the limbic system consists of the thalamus, which transmits messages to the hypothalamus, hippocampus, and amygdala, and other limbic structures. Each limbic structure controls behaviors related to emotional situa- tions such as sexual drive and evaluating threatening situations. The inner portion of the brain holds the limbic system, as shown in Figure 14.20. The three most important limbic structures direct many of our basic needs and desires:

1) The hypothalamus is responsible for our basic drives: hunger, thirst, sex, and sleep. Sleep is a strange phenomenon. It is a needed function, but encompasses almost one-third of our lives. The longest a person has gone without sleep has been 264 hours, after which the person, a volunteer in an experiment, began hallucinations and showed physical problems such as heart rhythm effects. Mice kept awake indefinitely always die, but first develop heart disease, high blood pressure, and cholesterol problems.

limbic system

A group of brain structures found on both sides of the thalamus.

amygdala

A section of brain associated with fear, panic, and aggression.

Midbrain

The short part of the brainstem above the pons.

Central core

The foundational part of an organism that helps regulate basic life processes.

Brainstem

The portion of brain that consists of pons, midbrain, and medulla oblongata.

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Figure 14.20 The Limbic System (shown in red): important are emotional responses such as evaluating threatening situations, sexual behavior, and aggression. It evolved earlier than the cerebrum in animal evolutionary history.

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2) The hippocampus is involved in short-term memory inputs, acting as a conduit to long-term memory storage in the cerebrum. When the hippocampus is dam- aged, a person cannot recall recent events. In the movie 50 First Dates, the main character is afflicted with damage to her hippocampus, falling in love with the same person over and over.

As we age, the hippocampus decreases in its size and ability to function. A 75-year-old loses more than 50% of their hippocampus functionality in tests comparing them with 17-year-olds. This is why learning a language, such as anatomy, at a younger age is easier than at older ages.

3) The amygdala is associated with fear, panic, and aggression. Recent studies show different activity levels in the amygdala of violent criminals as compared with nonviolent people. However, where are the nerve impulses most associated with our personality and temperament?

Our higher thoughts and actions – visual memory, speech, reasoning, and love – manifest within the neurons of the cerebrum. The cerebrum is the largest region of the brain, with two hemispheres (right and left) and four lobes: frontal, parietal, temporal, and occipital, shown in Figure 14.21. The regions of the brain are associated with dif- ferent, higher-level activities. For example, the ability to understand language is accom- plished by a small area between the parietal and temporal lobes called Wernicke’s area. Different regions of the brain work together to accomplish complex tasks and thoughts.

Electroencephalography (EEG) experiments show that the frontal lobe is responsible for much of our personality, intelligence, and skeletal movements. Activity in the left fron- tal lobe is associated with social and friendly demeanor, while activity in the right frontal lobe is most active in people who are depressed, argumentative, and crabby. Is personality that simple? Of course not but, the other regions of the brain contribute to higher levels of thought: speech, sensation, and sensory integration occurring in the parietal lobe; hearing and visual sensing as well as language comprehension in the temporal lobe; and receiving and processing visual cues in the occipital lobe. The left and right sides of the brain control functions on their opposite sides. For example, the right side of the brain controls the left side of the body. Different regions of the brain also control different sensing and motor activities in the body. Figure 14.22 maps the right and left functions.

Frontal lobe

The anterior part of the brain that is responsible for much of human personality, intelligence, and skeletal movements.

parietal lobe

One of the four major lobes of the brain that contains an area concerned with higher levels of thought (speech, sensation, and sensory integration).

Temporal lobe

One of the four major lobes of the brain that contains an area concerned with hearing and visual sensing as well as language comprehension.

occipital lobe

The posterior lobe of the brain.

hippocampus

Part of the brain involved in short term memory inputs, acting as a conduit to long term memory storage in the cerebrum.

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Brain function is complex, and each person is unique in his or her personality and abilities because of this complexity. Figure 14.22 shows that damage to one area of the brain affects particular abilities and normal functions. Consider the case of Phin- eas Gage. In 1848, Mr. Gage, a railroad worker, was injured while packing explosives. A three-and-a-half foot iron bar was driven through his face just beneath his left eye. Shockingly, he walked to the doctor and made what appeared to be a complete recovery. Soon, however, his personality changed, going from a friendly and hard-working man to a vulgar, hostile, and lazy vagrant. He drifted job to job and after he died 13 years later, his brain was preserved. It showed that he damaged portions of his frontal lobe, affecting his personality.

As a person ages, the size of her or his brain also shrinks. Most people lose about 10% in their lifetimes. The frontal lobe, associated with personality, decreases by over 50% by the age of 90 years. Altered levels of acetylcholine and decreased numbers of neurotransmitters in general are responsible for cognitive impairments in aging. How- ever, there is a natural cell death, called apoptosis, which is a necessary process. Normal losses in cells are needed to make room for new ones and to grow and properly develop. In schizophrenia, normal apoptosis of dopamine-producing neurons does not occur. This leads to excesses in the neurotransmitter dopamine, causing fragmented thoughts and actions, classic symptoms of the disease.

apoptosis

Cell death that occurs as a part of an organism’s growth.

Dopamine

A neurotransmitter type that plays an important role in a number of different brain functions.

Figure 14.21 General Structure of the Brain.

Precentral Gyrus

Corpus Callosum

Cerebrum Central Sulcus

Parietal lobe

Temporal lobe

Postcentral Gyrus

Fornix

Lateral Fissure

Thalamus

Pineal Body

Transverse Fissure

CerebellumPons

Medulla

Pituitary Gland

Mammillary Body (2)

Infundibulum

Optic Chiasma

Olfactory Bulb (2)

Hypothalamus

Cerebrum

Occipital lobe

frontal lobe

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the Muscular System Characteristics of Muscles Nerves stimulate muscles, attached to the bones of the skeleton, to move the body. Mus- cles are the workhorse of the body. They respond to directives from nerves to cause them to move. The three types of muscles were described in Chapter 11: skeletal, cardiac, and smooth. Each muscle type has a nerve that is attached to it to stimulate its movement. We will focus on the skeletal muscles in this chapter, as they respond to nerves.

Muscles make up over 50% of a human body’s mass. Muscle cells are specialized to transform ATP energy into mechanical movements. They function in moving different bones of the skeleton, maintaining posture, and in stabilizing the joints. Muscles also generate a great deal of heat in their actions, maintaining body temperature. In Chapter 12, sphincters also guarded entrances and exits within the alimentary canal.

Muscle cells have the unique ability to both contract when stimulated by a nerve and also extend back into their original shape. The ability of a muscle cell to resume its original length after a contraction is called its elasticity.

When muscles contract, the direction in which they move is called their action. An action is based on two places: the location at which a muscle is attached to a bone that moves, called its insertion and the location at which it is attached, the origin. The origin of a muscle is usually another bone onto which the muscle is secured. A muscle action causes the movement of a bone in a certain direction or set of directions. These move- ments are always stimulated by a nerve, called the innervation.

Two sets of muscles frequently act in opposition to each other: while one is contract- ing, the other is relaxing during an action. The biceps of the arm, for example, contract at the same time that the triceps relax, both contributing to coordinated movement of the arm. An example of this antagonistic muscle movement is illustrated in Figure 14.23.

elasticity

The ability of a muscle cell to resume its original length after a contraction.

action

The direction in which muscles move when they contract.

Insertion

Movable end of a muscle.

origin

The location (bone) at which muscles attach.

Innervation

The distribution of nerves to an muscle.

Figure 14.22 Specialized Hemispheres of the Human Brain. The left and right sides of the brain each control opposite sides of the body. The left side controls the right side of the body and the right side of the brain controls the left side of the body. Each side of the brain has greater control of certain characteristics. In addition, there is a dif- fering amount of control each body region has within the brain. The lips, for example, occupy a much larger part of the brain than the arm. Thus, the lips are more sensitive to feeling than an arm. Pinch your lips and then pinch your elbow. Which has greater sensation? Even if you pinch your elbow as hard as possible, it will be difficult to elicit a pain response.

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Figure 14.23 Muscles and Bones Work Together to Pull Bones and Rotate Limbs Around Joints. Muscle groups are antagonistic with each other, with one muscle often contracting, while another relaxes. Action of biceps and triceps work antagonistically to cause movement in the arm.

Extension

Flexion

Humerus

Biceps brachii (belly)

Ulna

Radius

Insertion, or mobile end, of biceps brachii

Tendon

Origins, fixed ends, or heads of biceps (two heads) brachii on scapula

Scapula

Origins, fixed ends, or heads of triceps (three heads) brachii on scapula and humerus ©

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Muscle Cell organization Whole muscles, such as the biceps, are actually composed of smaller strands of muscle fibers. Bundles of these muscle fibers are known as fascicles, which are further comprised many smaller muscle cells called muscle fibers. Muscle cells are made of thousands of intertwining myofibrils. Myofibrils are individually made of a series of contractile units called sarcomeres. The sarcomere is the fundamental contractile unit of muscles. They contract inwardly like an accordion, after they are stimulated by nerve impulses. When a muscle cell contracts, either all of its sarcomeres contract together, or none at all. This principle of muscle contraction is known as the all-or-none response. Richard’s pain resulted from his nerves firing into muscles along his arm, neck, and back, making them contract and tense up. This causes pain. The structure of muscle fibers is given in Figure 14.24.

Sliding Filament theory Over 80% of sarcomeres are made of two types of proteins: actin and myosin. This is why proteins are so important in building strong muscles. Actin and myosin slide past each other folding upon itself and expanding much like an accordion. When sarcomeres contract, the sliding filament theory explains the steps of the process. These steps may be traced using Figure 14.25:

1) A nerve impulse changes the ionic potential along the muscle cell membrane, called the sarcolemma.

2) Changes in the membrane potential of the sarcolemma cause calcium ions to flow into the muscle cell.

Fascicle

Bundle of muscle fibers.

Muscle fibers

The functional muscle cell.

Myofibrils

A rod-like protein structure in a muscle cell.

Sarcomere

A series of contractile units that make up the myofibrils.

all-or-none response

All sarcomere contract in a muscle fiber or none at all.

Sliding filament theory

The theory that explains muscle contraction.

Sarcolemma

A nerve's cell membrane.

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Figure 14.24 Muscle Anatomy. Muscles are composed of many fibers running alongside each other. Orien- tation of muscle fibers into parallel bundles causes movement of muscles along only a single plane.

Axon Branch

Myofibrils

Sarcoplasmic Reticulum

Capillary

Presynaptic Terminal

Muscle Fiber Sarcoplasm

Mitochondrion

Presynaptic Terminal

Synaptic Vesicles

Synaptic Cleft

Postsynaptic Membrane

Sarcolemma

Neuromuscular Junction

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3) Calcium ions combine with a protein, troponin (as you recall in Chapter 13, troponin is tested to see the extent of a heart attack), which changes shape and causes its attached tropomyosin to slide. Tropomyosin looks like ropes covering binding sites on actin. When these sites are revealed, they allow myosin heads to attach to them.

4) When myosin heads attach, ATP is used to cause the heads to swivel. This is known as the powerstroke because the sarcomere contracts inward using energy or power.

5) Relaxation occurs when another ATP molecule is used to release myosin heads from their attached positions.

Rigor Mortis Because relaxation takes energy, both contraction and relaxation during exercising a muscle are important. During rigor mortis, after a person dies their muscle stiffen. There are old horror stories, before embalming, which tell of people sitting up in their coffins after a few hours from their death. A particularly scary scene of rigor mortis is shown in Figure 14.26.

When the dead begin deteriorating, calcium ions flow through the holes formed and into the muscle cell. This changes troponin shape and starts the sliding of filaments. The problem arises during relaxation, which requires ATP energy. After death, there is no new energy and so the muscles remain stiffened for up to 12 hours.

Fast vs. Slow twitch Fibers The time period comprising a contraction and relaxation is called a twitch. Some mus- cles twitch faster than others. Fast-twitch muscles contract up to 10 times faster than slow-twitch muscles (Figure 14.27). Some athletes have more of each type, contributing to their specialized skills in a sport. Long-distance runners, for example, have greater

Troponin

A protein found in all muscle.

Tropomyosin

A protein rope that plays an important role in muscle contraction.

powerstroke

Movement of filaments using ATP during the contraction of muscle.

Relaxation

A state of freedom from skeletal muscle tension and anxiety.

Rigor mortis

Stiffening of the body that happens a few hours after death.

Twitch

The time period comprising a contraction and relaxation.

537

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538 Unit 4: The Dynamic Animal Body

Figure 14.25 a. Sliding Filament Theory: sarcomere contraction follows specific steps to cause muscle movement. When motor neurons send impulses to the muscle, calcium ions cause actin and myosin to attach. ATP is used in the powerstroke to move the muscle filaments. b. Sarcomeres. Illustration by Jamey Garbett.

Sarcomeres Side by Side

Thin Filaments

(b)

Thick Filaments

Sarcomeres End to End

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ADP

ATP

ADP P

Ca2+

Calcium flowing into a muscle cell

Nerve going to muscle

ATP used

Myosin head binding to actin

Swivel of myosin head and actin

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Figure 14.26 A Deceased Person Sitting Up in a Coffin Was Commonplace (before Embalming) in Days Gone By. Rigor mortis sets in within hours of death, causing mus- cle contractions, but there is no energy to relax the corpse. Movement results in rigid contractions found only in the dead.

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proportions of slow-twitch fibers than sprinters. Sprinters have more than 70% classi- fied as fast twitch. Each person may develop their muscle fibers, but will not change their proportion nor their inclination for a particular type of sport. Someone who is physiologically meant for long-distance running will probably never be a great sprinter and vice versa.

Exercise has many benefits to muscles. It increases the size of muscles called hyper- trophy. It also increases the number of blood vessels that supply it as well as the number of mitochondria from which it derives its energy. Exercise does not, however, affect the number of muscle cells we have; it only improves what we are genetically given.

Of course, disuse of muscles leads to its rapid loss. Have you ever had your arm or leg in a cast or sling for a few weeks? It probably resulted in a very skinny arm with a lot of muscle loss. Humans lose about 5% of their muscle mass per day in those that are not used! There are over 200 muscles in the human body, with some superficial muscles shown in Figure 14.28.

0 10 20 30 40

Untrained

Middle distance runner

Elite sprinters

50 60 70 80 90 100

Fast twitch

Slow twitch

Figure 14.27 Fast vs. Slow Twitch Percentages in Different Athletes. Fast-twitch muscles enable sprinters to move in quick spurts and slow-twitch muscles best suit long-distance runners to endure long periods of less-intense exercise.

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540 Unit 4: The Dynamic Animal Body

Figure 14.28 Muscles of the Human Body: anterior (left) and posterior (right).

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Figure 14.28 (continued)

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Skeletal System Skeletons There are three types of skeletons in the animal kingdom: a hydrostatic skeleton, found in earthworms and jellyfish, which uses water and muscles for support and movement; an exoskeleton, which is composed of hardened materials on the outside of the body, such as chitin covering insects; and an endoskeleton, which is a living, internal but hard inner structure found in animals such as humans. Our focus will explore the endoskel- eton of humans.

Functions of Bones The endoskeleton, composed of our bones, works with the muscle system for (1) sup- port and (2) movement of the body. The bones also provide (3) protection from outside forces, with the skull protecting the brain and the vertebrae, the spinal cord, for example. The bones are hard structures, mineralized with calcium salts and embedded with multi- ple layers of fibers. As such, its salts act as (4) storage for minerals such as calcium and phosphorous. Within the bone marrow, we discussed in Chapter 13 the importance of the skeletal system’s role in (5) blood cell production. Usually in the soft or spongy parts of the bone’s blood cells are made. In hollow cavities within the bones called the yellow marrow, (6) energy is stored as fat. Have you ever broken a chicken bone and pulled out its yellow marrow to eat? Many cultures consider yellow marrow a delicacy because it is filled with fat and energy.

Morphology of Bones While there are 206 bones in the human skeleton, bones are classified into four general categories based on their shape or morphology: long, short, flat, and irregular. Within these bones, their tissues include: (1) spongy bone and (2) compact bone. Bone tissue anatomy was touched upon in Chapter 11, if you wish to review. Spongy bone is com- posed of many small spindles or trabeculae of bone with many open spaces. Compact bone is dense and contains very little open space. Some examples from each bone clas- sification are given in Figure 14.29.

Long bones (e.g., femur, fibula, and phalanges) are longer in length than in width. They contain a shaft with heads at either end. Short bones (e.g., tarsals and carpals) are cube shaped and contain spongy tissue. Flat bones (e.g., skull bones) are thin and contain two layers of compact bone sandwiching a spongy internal area. Bones that are not classified within these categories are called irregular bones (e.g., vertebrae). For examples, see Figure 14.29.

Many of the bones connect with each other to enable movement. The areas of connection between two bones are called a joint or articulation. There are numerous articulations of the skeletal system, which will be pointed out in the next sections.

Human bones also have distinctive features on their morphology called surface markings, which include either projections (sites for muscle attachment or joint connec- tions) or depressions (blood or nerve openings). Each of the surface markings serves a purpose for human body functions. Projections often attach to a muscle or ligament, and depressions such as small holes (or foramen) act as opening for blood vessels and nerves. Some examples of surface bone markings are shown in Figure 14.30.

hydrostatic skeleton

A type of skeleton found in earthworms and jellyfish, which use water and muscles for support and movement.

exoskeleton

An external covering that is composed of hardened materials on the outside of the body.

endoskeleton

A living, internal but hard inner structure found in animals and humans.

yellow marrow

Hollow cavities within bones filled with fat.

Morphology

A particular structure or shape.

Spongy bone

Tissue found inside the bones that resemble a sponge.

Trabeculae

Small spindles that make up the spongy bone.

Compact bone

A portion of bone that is dense and contains a very little open space.

articulation

The areas of connection between two bones.

Surface markings

The distinctive features found on human bones.

projection

Sites for muscle attachment or joint connections.

Depression

Blood or nerve openings in human bones.

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Figure 14.29 The Four Types of Bones: Long, Short, Flat, and Irregular. Each shape is suited for its function. A flat bone (e.g., skull bone) is often used to protect the underly- ing organs and tissues. a. long; b. short; c. flat; d. irregular. Illustration by Jamey Garbett.

(a)

(d)

(c)

(b)

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the human Skeleton The human bones are a part of the axial skeleton, which comprises the skull bones, ribs, sternum, and vertebrae, and the appendicular skeleton, which consists of bones of the limbs, the pelvic girdle, and the pectoral girdle (shoulder). Both skeletal categories are important to learn, as shown in Figure 14.31, which gives just a few of the major bones of the human skeleton.

The axial skeleton holds the center of gravity for the human body. It resists the many pressures placed upon it by gravity. Walking, running, and working in a garden require a strong resistance by the axis of the vertebrae and supporting bones of the axial skeleton. The axial skeleton contains skull bones, the ribs, and the bones of the vertebrae.

The skull is composed of two sets of bones: cranial bones (cranium), which enclose the brain, and the facial bones, which is attached to the muscles of the face. There are eight bones that make up the cranium, which are curved around the skull: The frontal

axial skeleton

The portion of skeleton that consists of the skull bones, ribs, sternum, and vertebrae.

appendicular skeleton

The portion of skeleton that consists of bones of the limbs, the pelvic girdle, and the pectoral girdle.

Cranial bones

The bone that encloses the brain.

Facial bones

The bones that attach to the muscles of the face.

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544 Unit 4: The Dynamic Animal Body

bone make up the anterior part of the cranium; the two parietal bones are along the sides of the cranium; the two temporal bones are inferior to the parietal bones, placed along the lateral part of the skull; the two zygomatic bones form the cheeks; and the occipital bone is at the back of the head. Note that the names of the bones generally correspond with the names of the underlying parts of the brain. For example, the occipital bone cov- ers the occipital region of the brain.

There are 14 facial bones, all paired except for the vomer bone (inside the nose) and the mandible (jaw). Palpate the following areas on your own body to discover these bones and surface markings using Figure 14.32.

1) Mastoid process: the roughened area behind your ears. 2) Temperomandibular joints: open and close your mouth to hear these click. 3) Superior orbital foramen: apply pressure in the middle of your eyebrow and feel

for the indentation. 4) Nasal bones: feel the bridge of your nose. 5) Mandibular angle: feel the angle of your jaw. 6) External occipital protuberance: feel the back, inferior portion of your skull – it

is the bump back there. 7) Zygomatic bone and arch: feel your cheekbone and its bridge toward the ear. 8) Hyoid: squeeze medially just below the mandible.

The axial skeleton consists of the vertebrae of the spine (24 single vertebrae bones plus two fused bones, the sacrum and coccyx) and the thorax (ribs and sternum). The ver- tebral column extends from the skull to the pelvis (hip bones) and is the main axial sup- port. Of the 24 single vertebra of the spinal column, 7 are in the neck, which are called

Zygomatic bone

Bone that forms an important part of the cheeks

Vomer

A small bone found inside the nose.

Mandible

Jawbone.

Sacrum

A large, wedge-shaped bone located between the two hip bones of the pelvis.

Coccyx

A small triangular- shaped bone located at the base of the spine.

Figure 14.30 Bone Markings: Every Bump, Groove, or Hole on Our Bones Has a Name and a Function. The figure shown is an example of the many surface regions of one of our vertebrae (back bones).

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Chapter 14: Regulation: Nervous, Musculoskeletal, and Endocrine Systems 545

Thoracic Cage (ribs and sternum)

Skull

Vertabral Column

Humerus

Rib

Sternum

Scapula

Clavicle

Facial Bones

Cranium

Bones of Pectoral Girdle

Upper Limb

Bones of Pelvic Girdle

Lower Limb

Phalanges

Metacarpals

Femur

Patella

Tibia

Fibula

Tarsals

Metatarsals

Phalanges

Carpals

Ulna

Radius

Vertebra

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Figure 14.31 Major Bones of the Human Skeleton. There are 206 bones found within humans. Illustration by Jamey Garbett.

cervical vertebrae, 12 are along the thorax, which are referred to as thoracic vertebrae, and 5 make up the lower back, known as lumbar vertebrae. You can remember this by when you eat: BREAKFAST at 7 a.m., LUNCH at 12 noon, and DINNER at 5 p.m. The vertebrae are shown in Figure 14.33.

Cervical vertebrae

The top seven vertebrae of the spinal column that form the neck.

Thoracic vertebrae

The 12 vertebrae along the thorax.

lumbar vertebrae

The five vertebrae that make up the lower back

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546 Unit 4: The Dynamic Animal Body

Zygomatic

Maxilla

Temporal Bone

Occipital Bone

Parietal Bone

Mandible

(b)

Frontal Bone

Figure 14.32 Skull Bones Are Flat and Curved, Forming a Covering Around the Brain. a. b and c: Illustration by Jamey Garbett.

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Chapter 14: Regulation: Nervous, Musculoskeletal, and Endocrine Systems 547

Figure 14.32 (continued)

Parietal Bone

Frontal Bone

Sphenoid

Zygomatic

Maxilla

Mandible

Occipital Bone

Temporal Bone

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Figure 14.33 Vertebral Bones Are Irregularly Shaped and Contain Holes to Allow the Spinal Cord through It. Adapted from Anatomy I and Physiology Lecture Manual by John Erickson and C. Michael French.

Spinous Process

Vertebral Foramen

Body of the Verebra

Transverse Process

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548 Unit 4: The Dynamic Animal Body

Figure 14.34 Carpal Bones in the Wrist Glide Past Each Other to Create Movement.

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Vertebrae are separated by pads of fibrocartilage called intervertebral discs. As a person ages, they lose water from the disc. This makes the disc less able to with- stand compressive forces. It makes a person more prone to a ruptured disc, the cause of Richard’s pain in the opening story. When this happens, the disc herniates (bulges) backward and compresses adjacent nerves. Richard’s cervical nerves were compressed, giving him shoots of pain along his muscles.

The appendicular skeleton is composed of 126 bones that help humans to move and respond to their environment. The arms, legs, hips, and shoulder contain all of these bones to support movement. The pectoral bones, for example, rotate to move the arm and shoulder to throw a ball. The scapula, or shoulder blades, are triangular and are called “wings” of the human. The main joint in the shoulder girdle is flexible, but it comes at a price: the humerus (upper arm bone) dislocates easily (inferiorly and anteriorly), espe- cially in car accidents.

Another example showing our flexibility is in the wrist joints. The wrist has many moveable bones, with joints in-between them. There are eight carpals arranged in two rows of four bones each. The carpals are shown in Figure 14.34. In the proximate row are (lateral to medial) the scaphoid, lunate, triangular (aka triquetrum), and pisi- form bones; in the distal row are (lateral to medial) trapezium, trapezoid, capitate, and hamate. A naughty little saying, but an efficient way to remember these bones, might be: “Some Lovers Try Positions That They Can’t Handle” with each first letter

Intervertebral disc

Pads of fibrocartilage that separate individual vertebrae.

humerus

Upper arm bone.

Carpals

Any bone of the wrist.

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Figure 14.35 Long Cut of a Femur and Wolff ’s Law. The area in which a bone expe- riences the most stress is often the thickest. Bone remodeling, according to Wolff ’s law, adds bone to the area it is most needed.

Articular surface covered with cartilage

Red marrow in spongy bone

Periosteum

Yellow marrow

Compact bone

Articular cartilage Epiphysis

Diaphysis

Metaphysis Epiphysis

Thickest here

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corresponding to a carpal, in that order. The carpals are held very closely together by ligaments, which restrict joint movement between them.

Carpal tunnel syndrome is an inflammation of the joints in-between the carpals due to, primarily, repetitive movements such as using a computer keyboard. The damage of the cartilage and/or ligaments between the carpals can require physical therapy, anti- inflammatory medications, or surgery.

Bone Remodeling and Disease Bones grow and change over a person’s lifetime. Have you ever experienced growing pains at night, when most of our bone growth occurs? It can wake a person from even a deep sleep. Bones grow and remodel according to the forces placed upon them. This phenomenon is called Wolff ’s law. When a person exercises, for example, it stimulates bones to grow stronger in certain areas. Bones remodel and add material to areas that are more likely to break. For example, in the femur, the area most likely to buckle is the thickest, as shown in Figure 14.35. Euler’s buckling equation, an engineering formula to show where a cylinder is most likely to fail, when applied to a femur, shows a thicker area in the region predicted to break. (Euler’s equation from which this information is derived is: Pcr = pi2E/L2, with L equal to the length of the tube, E the elasticity of the sub- stance, and Pcr the critical load amount to cause buckling.) This phenomenon is shown in Figure 14.35.

wolff ’s law

The phenomenon which states that bones grow and remodel according to the forces placed upon them.

euler’s Buckling equation

An engineering formula to show where a cylinder is most likely to fail, when applied to a femur, shows a thicker area in the region predicted to break.

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Bones recycle and replace themselves – compact bones every 10 years and spongy every 3–5 years – so that we are made of all new bones in these periods. Replacement occurs slowly, and regular exercise helps to keep bones strong.

Bones have tremendous strength: Long bones have half as much compressive strength as steel of the same size and the same tensile (pulling) resistance as steel! The arrangement of the calcium salts and the fibers within bone gives it great hardness.

While fractures (breaks) in bones are the most common injury, other disorders involve a long-term problem in many people. Osteoarthritis is a disease in which bones and their joints deteriorate, usually because the cushioning cartilage in-between these bones wears out. It is not merely a disease of the elderly. A high proportion of runners experience arthritis in their knees because of chemicals, called metalloproteases, pro- duced during their runs. These chemicals wear out their joints. Arthritis forms bone spurs or projections that inflame joints and cause pain. More than 85% of people will get osteoarthritis in their lifetime. The key to healthy joints is strengthening the ligaments, muscles, and tendons surrounding the bones. This gives the joints stability and limits its wear and tear.

Osteoporosis, a thinning and weakening of bones, occurs most often in the elderly, particularly in females. It is believed that decreased estrogen levels are associated with osteoporosis. Osteoporosis is due to a higher amount of osteoclast, or bone-destroying cell activity, and a lower amount of osteoblast, or bone-building cell activity.

Soda is especially bad for osteoporosis. Not only does soda replace other, more nourishing beverages such as milk or orange juice, which contain calcium to build strong bones and teeth, but phosphorous in many sodas causes a leaching effect of cal- cium out of the bones. Phosphorous is an essential component of bones in the form of calcium phosphate salts and hydroxyapatite ((Ca3(PO4)2 * (OH)2). As can be observed from the equation, both calcium and phosphorous are needed in these bone-building materials. However, when phosphorous is added to our diets in large amounts via soda consumption, it combines with calcium in the blood and leaches it out. Research at Tuft’s University studied a large number of both men and women, and discovered that women who drank three or more phosphorous-containing sodas had a 4% lower bone mass density than women who drank non-phosphorous-based soda or less soda. We are not entirely sure of the mechanism, but soda is linked to osteoporosis. Regular exercise and diets rich in calcium and vitamin D are the best strategy to fight the effects of thinning bones. Figure 14.36 shows osteoporotic bone and its weak trabeculae compared with normal bone.

osteoarthritis

A disease in which bones and their joints deteriorate, usually because the cushioning cartilage in between these bones wears out.

osteoporosis

Thinning and weakening of bones.

osteoclast

Bone destroying type cell.

osteoblast

Special bone building cells.

hydroxyapatite

An essential component and major ingredient of normal bone.

IS a BRokeN BoNe STRoNgeR ThaN The oRIgINal?

Because bones remodel according to the forces placed upon them, special bone-building cells called osteoblasts build new bone tissue when pressure is applied or when there is a break in the bone. Bones will overcompensate and build even more material in areas of breaks. Therefore, yes a broken bone is indeed often stronger and thicker than its original form.

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Figure 14.36 a. Soda b. Osteoporotic bone trabeculae are thin and fragile compared with normal bone.

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Endocrine System Glands and Basics Controls over bone growth and remodeling are due to, in part, hormones. Hormones (from the Greek “to arouse”) are chemical messengers that cause change or direct activity in another area of the body. Any cell that secretes a hormone is an endocrine cell. Hor- mones arouse the functions of another area of the body, called the target cells.

Some hormones, such as steroid (fat-based) pass easily through cell membranes. Other hormones must have receptors to enter a cell. Many target cells have specifically shaped receptors on them to attach to the shape of their respective hormones. This is called the receptor–hormone match. The methods by which hormones enter a cell and cause changes are illustrated in Figure 14.37.

The endocrine system includes all of the groups of cells, called endocrine glands, which produce hormones. It is much slower to act than the nervous system because its messengers are chemicals that diffuse through the circulatory system. Nerves fire like electricity, but hormones travel slowly like cargo ships.

There are seven major glands of the endocrine system. Figure 14.38 gives the major endocrine glands in the human body: the hypothalamus, the pituitary gland, the thyroid, the parathyroid, the pancreas, the adrenal glands, and the pineal gland. These glands pro- duce an alphabet soup of hormones, with names given alongside their glands in Figure 14.38.

The hypothalamus, in the brain, is connected to and controls the activity of the pituitary gland. The pituitary gland is considered the master gland of the endocrine sys- tem because it sends messages to stimulate all of the other glands. We will take a look at some of these glands to study how they regulate life functions. An overview of the glands and the hormones they produce is in Figure 14.38.

hormones

Chemical messengers that cause change or direct activity in another area of the body.

endocrine cell

Any cell that secretes a hormone.

Target cell

Any cell having a specific receptor for an antibody, hormone, or antigen.

Receptor-hormone match

Match making between the receptors of target cells and their respective hormones.

pituitary gland

The master gland of the endocrine system that sends messages to stimulate all of the other glands.

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Figure 14.38 a. Major Glands of the Endocrine System and their Hormones. b. Functions of Endocrine Glands. From Biological Perspectives, 3rd ed by BSCS. c. Pituitary control over other glands. From Biological Perspectives, 3rd ed by BSCS.

Testis (male)

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Pancreas

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Thymus gland

Parathyroid glands (on dorsal aspect of thyroid gland)

Thyroid gland

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Pineal gland

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Figure 14.37 The Hormone Communication Process. Some hormones (steroids) pass right through a membrane, while other hormones (peptide) require a receptor protein. These hormones dock specifically to receptors, bringing them into the cell. Hormones often work within the nucleus of a target cell, eliciting a cellular response.

Hydrophilic Hormone (First Messenger)

Enzyme

Second Messenger

Effect on Cellular Function, Such as Glycogen Breakdown

Plasma Membrane of Target Cell

Receptor Protein

Cytoplasm

ATP

cAMP

Lipophilic Hormone Cytoplasm

Nucleus

Hormone Receptor Complex

Receptor Protein

DNA

mRNA

New Protein

1 2

Plasma Membrane of Target Cell

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554 Unit 4: The Dynamic Animal Body

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Figure 14.38 (continued)

hormones Regulate homeostasis Calcium and Bones

Almost every activity in the body involves hormones. Bones grow, as described in the previous section, when calcium levels are sufficient within the blood. Bones store 99% of calcium in the body, so that one hormone called parathyroid hormone (made by the parathyroid gland) directs it to give up calcium. Back in the blood, calcium is then avail- able for a body’s use. When calcitonin, another hormone made by the thyroid, directs calcium ion uptake by the bones, it can again be used for strengthening the bone tissue. The control of calcium in the blood is an example of how hormones regulate the aspects of our body. Blood calcium is kept at a balance of 9–11 mg/100 mL. The process of calcium homeostasis is traced in Figure 14.39.

Blood Sugar and Diabetes

Normal levels of blood sugar (glucose) in the blood (80–120 mg of glucose/100 mL blood) are maintained by two hormones: insulin and glucagon. When carbohydrates are consumed in an animal’s diet, special beta cells of the pancreas release insulin. Insulin causes the direct uptake of glucose into body cells. Insulin also stimulates the liver to store glucose in the form of glycogen.

As sugar levels decrease, alpha cells of the pancreas release glucagon, which stim- ulates the liver to release glucose from its stored glycogen reserves. This is a nega- tive feedback mechanism, described in Chapter 11, which maintains the homeostasis of sugar to around 90 mg/100 mL blood consistently through a lifetime.

Diabetes is a disease in which glucose levels remain higher than normal in the blood and urine. It may lead to numerous health problems including nerve damage, heart dis- ease, blindness, and death, if untreated. There are two types of diabetes: Type I and Type

parathyroid hormone (pTh)

Hormone produced by the parathyroid glands help in regulating the amount of phosphorous and calcium in the body.

Calcitonin

A hormone made by the thyroid directs calcium ion uptake by the bones. Insulin

A hormone produced in the pancreas that regulates the amount of glucose in blood.

glucagon

A hormone that raises blood sugar level.

Beta cells of pancreas

Cluster of cells found in the pancreas, which makes the insulin.

alpha cells of pancreas

Cluster of cells found in the pancreas, which makes glucagon.

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Figure 14.39 Calcium Homeostasis Is Accomplished by the Action of Two Hormones: calcitonin and PTH (parathyroid hormone).

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II. Type I diabetes is an autoimmune disease resulting from an attack on the pancreatic cells making insulin. Type II diabetes is a result of resistance to insulin by cells.

Diabetes is associated with diets high in refined sugars because excess sugars “wear out” insulin receptors. This wearing down process is known as down regulation. The receptor–hormone match wears out due to overuse.

Metabolism

Regulation of the sum of chemical activities, called metabolism, is a large task. It involves several endocrine glands: When the hypothalamus activates the anterior pituitary to

Diabetes Type I

An autoimmune disease resulting from an attack on the pancreatic cells making insulin.

Diabetes Type II

A medical condition as a result of resistance to insulin by cells.

Down regulation

Decrease in the number of effective receptors on cell surfaces.

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556 Unit 4: The Dynamic Animal Body

IS DIaBeTeS a gooD aDapTaTIoN?

New research shows that diabetes may have once been useful to humans in our evolutionary history. The genes associated with diabetes are termed “thrifty” genes because they keep sugar levels high in the blood. “Thrifty” genes evolved for millions of years, it is thought, to maintain higher sugar levels during starva- tion conditions that occur between meals for hunter-gatherer tribes. Diabetes is a result of a mutation that prevents the conversion of glucose to glycogen. Thus, “thrifty” genes spare sugars in the blood, keeping it available for use in times of need.

Consider the Neolithic diet, discussed in Chapter 12, in which calories are hard to find. Someone with “thrifty” genes would benefit because normal cir- culating levels of sugar would be maintained longer. James V. Neel, a geneticist at the University of Michigan, discovered this “thrifty gene” sequence in several human populations. He looked at the Pima Indians of Arizona, who were more apt to be diabetic and store fat. About one-half of the Pima Indians have diabe- tes and about 95% are obese.

Both of these tendencies would have helped the Pima endure longer peri- ods of starvation conditions in evolutionary history. In modern society, with food readily available, people with “thrifty” genes are more prone to obe- sity and diabetes. Are diabetes and obesity on the rise due to a dissonance between evolved thrifty genes and modern diets? Can lifestyle changes improve these modern-day maladies?

Studies show that things are not hopeless for those predisposed to diabe- tes: Pimas practicing traditional lifestyles of hunting and gathering, in isolated parts of the Sierra Madre mountains of Mexico, have significantly lower rates of diabetes (8%) and obesity (rare) as compared with the modern US Pima Indian population. If people with thrifty genes are more aware of their predisposition through genetic testing, they could alter their diets to avoid diabetes and obe- sity. A diet rich in variety and whole grains, fresh vegetables, and fruit and low in fat and protein sources is thus recommended.

produce thyroid-stimulating hormone (TSH), the process starts. TSH stimulates the thy- roid to manufacture and release thyroxine, which increases metabolism throughout the human body. If a problem arises at any point in the process, disease occurs. The process of thyroid-regulating metabolism is shown in Figure 14.40.

Hyperthyroidism is an overactive thyroid, which results in too much thyroxine, caus- ing nervousness, excess energy, sometimes enlarged eyes (exophthalmos), and irregu- lar heart rates. In the long term, it can lead to cardiovascular disease. Hypothyroidism results from an underactive thyroid and insufficient amounts of thyroxin, causing weight gain, intolerance to cold and higher cholesterol, and in the long term also cardiovascular disease. Both can be treated successfully with drug therapy, or in the case of hyperthy- roidism, destruction of part of the thyroid.

Control atop the Kidneys

The adrenal glands sit atop both the kidneys, controlling a variety of body functions. The adrenal cortex, the exterior portion of the gland, secretes steroid (fatty-based) hormones

Thyroid stimulating hormone (TSh)

Hormone produced by the pituitary gland and stimulates the thyroid gland.

Thyroxin

A hormone that increases metabolism throughout the human body.

hyperthyroidism

An overactive thyroid, which results in too much thyroxine, causing nervousness, excess energy, sometimes enlarged eyes and irregular heart rates.

hypothyroidism

An underactive thyroid, which results in weight gain, intolerance to cold and higher cholesterol.

adrenal glands

Glands that sit atop both kidneys and control a variety of body functions.

adrenal cortex

The exterior portion of the adrenal gland that secretes steroid hormones.

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Figure 14.40 Thyroxine Production Flowchart: Hypothalamus -> Anterior Pituitary -> Thyroid. Thyroid hormones limit their own production by a negative feedback mech- anism. Any problem in one process within the thyroxine production sequence may lead to a thyroid disorder.

Environmental stimuli (e.g., cold, stress)

Hypothalamus

TRH

TSH

Thyroid gland

Thyroid hormones (T3 and T4)

Metabolism Growth

Anterior pituitary

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including mineralocorticoids that control mineral and water balance; glucocorticoids that help regulate glucose levels; and gonadocorticoids that contribute to female sex drive. All of these activities are under the control of the pituitary gland that directs the activities of the adrenal cortex.

The adrenal medulla, the inner part of the gland, is like a knot of nerves, connected with the sympathetic nervous system described earlier in this chapter. When its nerves are activated, the cells secrete epinephrine and norepinephrine, both of which initiate a fight-or-flight response. Stimulation of the sympathetic nervous system increases the heart rate, blood pressure, and short-term available energy. It is the fastest acting of the endocrine glands because it is partially nervous tissue. The adrenal glands and their actions are shown in Figure 14.41.

Pineal Gland

Have you ever wondered why babies are so sleepy? Why do you become more tired at night instead of during daylight? The pineal gland, found deep within the brain, produces melatonin. Melatonin is a hormone that makes a person sleepy. The more active the pineal gland is, the more melatonin is produced.

adrenal medulla

The inner part of the adrenal gland.

epinephrine

A hormone secreted by adrenal medulla.

pineal gland

A small gland located deep within the brain.

Melatonin

A hormone produced by the pineal gland that makes a person sleepy.

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Figure 14.41 Adrenal Glands and Their Actions. Blood sugar levels are controlled, in part, by the action of the adrenal glands.

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Babies have very active pineal glands. Pineal glands also become activated in dark- ness, producing more melatonin. As we age, our pineal glands decrease in activity, with a person of age 80 requiring only 5 h of sleep compared with a growing child, who needs over 12 h. The chart in Figure 14.42 shows how sleep needs change with age.

Reproduction

The gonads, ovaries, and testes are also endocrine glands. Each gland secretes hor- mones: male testes produce androgens, the class of male hormones responsible for male sex characteristics and sex drive; female ovaries produce estrogens, the class of female hormones responsible for female characteristics and sex drive. Both males and females have androgens and estrogens, just in different amounts. Males have more androgens and females have greater proportions of estrogens. Reproductive hormones will be discussed in greater detail in Chapter 16.

Pheromones

Communication between organisms rather than within them occurs frequently in nature. Chemicals called pheromones travel between different organisms to interconnect them. Ants communicate with each other, and conduct complex wars and food recruitment, through use of pheromones. Human females, within the same dorms, have been shown to exhibit reproductive cycles in tandem with each other, due to pheromones. Consider the complex actions of ants, shown in Figure 14.43, all directed by pheromones.

pheromone

A chemical that travels between different organisms to interconnect them.

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Pain and Paracrine glands

Many tissues produce substances that diffuse from one tissue into another tissue. These chemicals are called paracrine regulators, which bind to receptors on neighboring cells to elicit a response. Prostaglandins are a type of paracrine regulator that affects inflam- mation and pain in tissues. Prostaglandins were discussed in Chapter 11 and its role in pain perception.

Aspirin and other pain medications inhibit the enzymes that help to produce pros- taglandins, reducing pain and inflammation. These drugs can damage linings of the stomach and cause bleeding. In Richard’s case, weighing the pros and cons of pain med- ication is a difficult task.

paracrine regulators

Chemicals that bind to receptors on neighboring cells to elicit a response.

Figure 14.43 Ants Move in a Line to Carry Out Activities, such as Food Procurement. Pheromones are used to communicate and coordinate activities in ants.

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Figure 14.42 The Amount of Sleep a Person Needs Decreases with Age. In the course of a lifetime, human sleeping time decreases by more than 50%. The pineal gland becomes less active as we age, causing less melatonin and fewer hours of sleep.

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560 Unit 4: The Dynamic Animal Body

Summary The nervous, musculoskeletal, and endocrine systems work together to regulate life pro- cesses. Homeostasis occurs when the concert of systems maintains balance within the human body. The nervous system acts rapidly to send ionic messages through the body and ultimately to the brain. The brain interprets these messages, sending impulses to the muscles and bones for movement and to the endocrine glands to direct cellular activity in target cells. Pain, a type of sensation, is a result of one of the many stimuli experienced by humans. Humans have five special senses with associated sense systems to perceive and respond to the world. They utilize the other systems to accomplish regulation.

ChECk oUt

Summary: key points

• Medical treatments, such as surgery, physical therapy, and drugs, seek to repair anatomical problems, but alternative medicines do not intervene in injuries, and instead rely on holistic strategies for pain relief.

• The nervous system is organized into central and peripheral divisions, with several subgroups. Nerve impulses are a flow of positively charged ions, transmitted by neurotransmitters across synapses.

• The five senses: gustation, olfaction, vision, hearing, and sensation each begin by stimulation of spe- cial receptors sending nerve impulses to the brain for interpretation.

• The brain developed from the simple central core, then a more complex limbic system and then higher brain centers in the cerebrum.

• The sliding filament theory shows that muscle fibers slide past each other when stimulated by nerves, resulting in a muscle contraction.

• The bones of the human skeleton are divided into an axial and appendicular skeleton. • Endocrine glands produce hormones that regulate various activities in the human body.

action action potential adrenal glands, cortex-, medulla-, all-or-none response amygdala anvil apoptosis appendicular skeleton aqueous humor arachnoid space articulation autonomic nervous system axial skeleton bipolar cells brain brainstem

calcitonin carpals cerebellum cerebrum central core central nervous system (CNS) chemoreceptor ciliary body coccyx cochlea compact bone cones cornea corpus callosum cranial bones critical threshold potential

key TeRMS

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depression diabetes, type I, type II dopamine downregulation dura mater ear drum elasticity endocrine cell endorphins endoskeleton epinephrine Euler’s Buckling equation exoskeleton facial bones fascicle frontal lobe glucagon gustation hammer hippocampus hormones humerus hydrostatic skeleton hydroxyapatite hyperthyroidism hypothalamus hypothyroidism innervation insulin interneuron intervertebral disc iris insertion lens limbic system mandible mechanoreceptors medulla melatonin meninges midbrain middle ear morphology motor neuron muscle fibers myelin sheath myofibrils nerve impulse neuron

neurotransmitter nociceptors occipital lobe olfaction origin osteoblast osteoclast osteoarthritis osteoporosis oval window outer ear pancreas, alpha cells-, beta cells-, paracrine regulators parasympathetic nervous system parathyroid hormone (PTH) parietal lobe peripheral nervous system (PNS) pheromone photo-pigments pia mater pineal gland pinna pituitary gland pons powerstroke projection pupil receptor–hormone match referred pain regulation relaxation resting potential rhodopsin rigor mortis rods sacrum sarcolemma sarcomere sensation sensory neuron semicircular canals serotonin sliding filament theory somatic nervous system spinal cord spongy bone stimulus stirrup surface markings

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sympathetic nervous system synapse target cell temporal lobe thalamus thermoreceptors thyroid-stimulating hormone (TSH) thyroxin trabeculae

troponin tropomyosin twitch vertebrae, cervical-, thoracic-, lumbar- vitreous humor vomer Wolff ’s law yellow marrow zygomatic bone

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Multiple Choice Questions

Reflection questions:

1. It is hypothesized that acupuncture works by stimulating: a. sensory neurons b. motor neurons c. large diameter nerve fibers d. small diameter nerve fibers

2. Which term(s) does NOT fit with the sympathetic nervous system? a. Fight-or-flight b. Somatic c. Autonomic d. Peripheral

3. A nerve fires when it hits _________, which is defined as the _______ threshold potential. a. -55 mV; critical b. -70 mV; resting c. +70 mV; impulse d. 0 mV; resting

4. Changing from wave energy to mechanical energy, by movement of hairs, is accom- plished in: a. vision b. hearing c. gustation d. olfaction.

5. Which type of receptor triggers gustation sensation? a. Thermoreceptor b. Mechanoreceptor c. Chemoreceptor d. Photoreceptor

6. Which represents a logical order, from oldest to most recent, in the development of the brain over evolutionary time? a. Cerebellum ➔ medulla ➔ hippocampus ➔ cerebrum b. Medulla ➔ cerebellum ➔ hippocampus ➔ cerebrum c. Hippocampus ➔ medulla ➔ cerebellum ➔ cerebrum d. Cerebrum ➔ medulla ➔ hippocampus ➔ cerebellum

7. Which swivels in the powerstroke step, during the sliding filament theory? a. Actin b. Troponin c. Myosin d. Tropomyosin

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8. Which bone is NOT a part of the axial skeleton? a. Frontal b. Humerus c. Occipital d. Temporal

9. Which correctly MATCHES an endocrine gland with its hormone? a. Adrenal medulla –- thyroxin b. Thyroid – parathyroid hormone c. Epinephrine – adrenal cortex d. Pineal – thyroid-stimulating hormone

10. Which decreases as person ages and is associated with sleepiness? a. Melatonin b. Thyroxin c. Mineralocorticoids d. All of the above

Short answers

1. Medical treatments, especially in the treatment of pain, always have uncertainty in their outcomes. Give two reasons for this uncertainty in medicine.

2. Define the following terms: sympathetic and parasympathetic nervous system. List one way each of the terms that differ from each other in relation to their: a. organi- zation in the nervous system; b. function; and c. relationship with each other.

3. What is the point of the corpus callosum in brain functioning?

4. Draw a sketch of the brain, using arrows to show five structures (or regions) of the cerebrum, central core and limbic system. What does the medulla oblongata regu- late. Can a person live without one?

5. How does vitamin A help in the prevention and treatment of poor eyesight?

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6. Pretend you are a light wave. Describe the pathway that you take after entering into the human eyeball. Name five structures that you pass through. What do you become, at the end of the vision process? Where is your final place in the body?

7. Define rigor mortis. Explain the role of ATP in this phenomenon.

8. For question #7, how do calcium ions affect rigor mortis? Why?

9. Describe the steps of calcium regulation in the body. Be sure to use the following terms in your explanation: calcitonin, PTH, thyroid, parathyroid, and osteoblasts?

10. Describe the symptoms of osteoarthritis and osteoporosis. How are the two condi- tions similar? How are they different? Which would you rather have?

Biology and Society Corner: Discussion Questions 1. The research presented in this chapter shows that amygdala activity in the brain is

associated with criminality. Should convicts, who are more prone to criminality, be treated differently (more leniently) because of their underlying predispositions? Why or Why not?

2. The use of night shifts is vital for many professional services: nursing, air traffic control, airline pilots, and military personnel, to name a few areas. Considering that the pineal gland acts to make us tired in the night, is it ethical to keep people awake every week on night shifts? To answer this, consider: What are the effects on the body of keeping someone on long-term night shifts? Does medical care quality suf- fer at night time hours? What could be done, if anything, to the problems associated with night shifts?

3. Bert’s son, Bob, is short for his age. Bob is only 13 years old, but Bert wants his son to be taller than he was? He experienced a great deal of stress and bullying in school due to his height. The doctor predicts that Bob is projected to grow to 5 ft 4 in as an adult. Bob wants Bert to try Human Growth Hormone (HGH) to help him grow. Research the uses and side effects of HGH. Should Bob take HGH, given his case? Why or why not?

4. Creatine is used as a supplement to improve muscle mass building and endurance training. It is thought to add extra phosphate for ATP to aid in training. The Inter- national Olympic Committee, most professional sports leagues, and the National

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Collegiate Athletic Association do not prohibit the use of creatine. Research the biology of creatine, its effect on training, and the side effects. On the basis of your research, would you take creatine in your own training? Would you recommend restrictions in creatine use by professional athletes? Why or why not?

5. Steroids mimic testosterone, a type of androgen hormone normally produced in the body. Steroids are banned in the Olympics and in professional sports. Steroid use builds muscle mass rapidly, giving energy and bulk to aid in muscle-building exer- cises. Construct an argument for and against the banning of steroids. Which factor gives you the most certainty in your argument?

Figure – Concept Map of Chapter 14 Big Ideas

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567

A War against the Enemy – Skin’s Defenses and the Immune Attack

A college student has a cold sore

College stress can be overwhelming

Antibodies do protect usAntibodies attack viruses, such as herpes

Students studying organic chemistry

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the Case of the Recurring Chemistry nightmare We all met in the Commons, the name for our cafeteria at the college. The Commons was the center of social life, where we would eat all our meals, have coffee, and plan the parties for the week. It was also a place where you were on stage and where you were watched – studied, looked at, and analyzed – by your fellow students. It was a rumor mill, in short.

Rumors started with my smell. In organic chemistry laboratory, we used chemicals that left a scent on me. Whenever I went to the Commons after the lab session, I felt peo- ple noticed my odor. I remember the day when we produced amines in the lab; amines were one of the worst smelling functional groups of all the chemicals.

I had a dinner date that evening right after lab (no time to shower). I had looked forward to it for weeks. When the smell of amines sifted through the air in the Com- mons, I knew something was wrong. My date hurried home after eating very little of the dinner. We usually got along well, but we had not much to say to each other after- wards; and a rumor spread that I smelled. That smell rumor stuck with me through the years.

The larger problem of rumors for me spun out of the organic chemistry class, every time there was an exam. There were four exams in the class plus a final, each of which elicited the same recurring nightmare. But the nightmare was real and it cost me my social life. It should have been no big deal, except for the rumors.

Organic chemistry exams were stressful for me. It is true that I was strained when an exam came. While studying, I encountered reduction reactions, functional group move- ments, I had to keep track of electrons; but the worst were synthesis reactions: which required us to figure out how to make an organic compound from its constituents. I think the fear of these exams caused my recurring nightmare – herpes!

I would develop a fever blister on the same spot on my lips with every test. People watched me at the Commons, with my large lip blisters . . . rumors spread throughout

ChECk In

From reading this chapter, you will be able to:

• explain how individuals with a contagious infection have been treated through history in society. • list and describe the three lines of defense provided by the immune system. • connect the structure and functions of skin with immune defense. • describe and compare three general types of white blood cells of the immune system and connect

them with the events of inflammation. • compare and contrast cell-mediated and humoral immunity, connecting the events of each to defense

against pathogens. • explain the process of tissue regeneration and list, in a hierarchy, the tissues according to their ability

to regenerate. • list and explain the four types of acquired immunity. • define and describe the functions of the lymphatic system. • list the diseases occurring when the immune system malfunctions.

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campus that I had contracted herpes. It is true that the organic chemistry exam gave me herpes – but not the kind that was sexually transmitted, herpes simplex II. An organic chemistry exam cannot cause a sexually transmitted disease . . . although it can cause lots of other issues. Instead my cold cores were a result of the other form: herpes simplex type I, which is not sexually transmitted. Many people have it and it is obtained through touch or even when we are in our mother’s womb. Stress can bring out the virus.

Herpes simplex I presents as a fever blister or cold sore at the edge of the lips. It is always within the body but rears its painful and ugly effects at certain times – during stress, illness, sunburn, for example – any weakening of the immune system. Usually the immune system – the white blood cells, antibodies, interferon chemicals – keeps the virus dormant. A herpes virus recognizes and attacks nerve cells at the skin of the lips, causing them to fire and give pain. Herpes, in me, remains quiet until my immune sys- tem weakens during organic chemistry exams.

Most people at the college did not know about the difference between the two types of herpes. I tried to explain it over and over that more than 80% of people have herpes type I. I don’t think anyone was listening. Being on stage at the Commons led to unknown rumors about me; but is it all in my head? I am not sure of it, but am I being discriminated against because of my illness? I am hoping that this note may clear my name.

ChECk Up SECtIon

Was the watchfulness of the college community real or imaged by our character in the story? It is diffi- cult to know. However, often throughout history, it is true that when illness spreads in a society, those who are deemed contagious are shunned. The plague, leprosy, and more recently AIDS sufferers have experienced discrimination due to their illness.

Research the types of illnesses spread in the past two centuries, in which its victims also felt social discrimination. Choose one of these illnesses and (1) describe how people suffered physically, (2) describe how ill people suffered due to society, and (3) make recommendations on how to prevent society-based discrimination due to illness in modern society.

the Immune System’s War The story of herpes at the start of this chapter illustrates not only how our body is sus- ceptible to pathogens for a long time but also how the society responds to those of us with these illnesses. The media and people are animated by stories of disease and conta- gion. But how do these stories affect our perceptions of disease in society?

In the news, a flu epidemic or a new strain of virus captures the headlines and public interest almost each day. Billions of pathogens including the viruses, bacteria, fungi, and parasitic protists (described in Chapter 8) continually inhabit the surfaces of our bodies and the items we touch. There are many agents of infection to talk about (and fear) from the news. A 2010 media report showed that 72% of shopping carts had fecal bacteria! But how susceptible are we?

The immune system acts as a very effective bulwark against all of these pathogens. The immune system has several layers in its line of defense. It should be thought of as a fight against invaders, using strategies and military operations similar to war. The battle is often bloody and pus filled, much like the results of a cold sore described in our story,

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or worse infections. Figure 15.1 paints the picture: infectious diseases surround us but are fought by the immune system traveling within our blood.

The human immune system includes the set of disease-fighting factors that protect against pathogens. These include three general lines of defense against the invading enemy. First, the physical barriers of the body provide protection by preventing patho- gens from gaining entrance into the body. The skin and mucous membranes comprise most of this first line of defense.

After entering the body, pathogens encounter the second line of defense called non- specific immunity. Most multicellular organisms have a nonspecific immune system. In this second line of defense, inflammation, fever, and chemical defenses operate to gen- erally attack the invader. The name “nonspecific” denotes the fact that these processes do not target any particular intruders. For example, when Staphylococcus aureus, a com- mon bacterium causing skin infections, occupies an area of the body, general inflamma- tion and fever often occur. The immune system does not produce any substances aimed directly against S. aureus. Instead, it fights off the invaders by stimulating fever, inflam- mation, and phagocytosis, for example. These general strategies are employed by the immune system to kill any and all intruding pathogens without a specific targeting.

Immune cells do specifically attack certain pathogens in their last line of defense. They make cells and chemicals especially for certain invaders. The third line of defense is called specific immunity, during which the body employs methods to specifically target patho- gens. It directs proteins called antibodies to bind with specific microbes. Antibodies stim- ulate white blood cells, produced and geared only for a particular pathogen. In our example of S. aureus infection, specific immunity produces specialized agents to target and destroy the bacterium. The three lines of immune defenses are delineated in Figure 15.2.

physical Barriers: First line of Defense Border patrol: the Skin and Mucous Membranes In our story, the skin is depicted as a site for attack from the inside, by the herpes virus. The skin usually functions as a defense from pathogens and other damaging agents on the outside of the body. The skin is the physical barrier, like “barbed wire” in trench warfare, which stops the battle before it begins.

Immune system

A system that includes the set of disease- fighting factors that protect against pathogens.

Figure 15.1 Immune Cells Are Actively Protecting Us in the Blood. The immune cell in the image is engulfing a number of enemy antigens. Defense of the body is much like a war, with tactics and troops (cells) defending their home turf.

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Preventing war is the best form of defense, so pathogens that are kept out do not cause harm. Skin has multiple layers through which pathogens need to travel before gaining access to the body. The skin also has an acidic pH, roughly 3–4, which drives away most infectious microbes.

Saliva, tears, and mucous act as a border patrol. These secretions contain antibodies and other special chemicals that attack pathogens. Secretions are produced from mod- ified areas of the skin, especially in regions most vulnerable to attack – our openings: eyes (tears), ears (wax), mouth (saliva), and the nose (mucous). The anus has resident bacterial defenders, discussed in Chapter 12. Openings are an easy conduit for patho- gens to enter, but these secretions and bacteria both act as border patrol. Figure 15.3 shows some of the body’s vulnerable orifices.

Figure 15.2 Three Lines of Defense against Pathogens: Physical Barriers, Nonspe- cific Immunity, and Specific Immunity.

Immune response

Pathogens (bacteria, virus,

fungi, etc.)

Life

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defense (nonspecific)

Mechanical

Chemical

Skin

Third line of defense

specific (acquired) immunity

Cell-mediated

Humoral

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defense (nonspecific)

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Phagocytosis

Protective proteins-cytokines

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Figure 15.3 Orifices of the Human Body: Nose, Mouth, Eyes, Ears, and Anus. These are the vulnerable regions that may be breached during the first line of defense (nonspecific immunity) of the immune system. This one-week-old baby has a sensitive immune system, with orifices that may be easily breached.

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the Border’s Construction: Skin Structure and Function The skin is not simply a sheet of beauty upon which to gaze. It is a vibrant, active organ system and the most expansive of the body systems. Our college student’s cold sore in this story shows that there is more going on in the skin than aesthetics.

Skin has a surface area of 15–20 square feet, a weight of 9–11 pounds, and a thick- ness of 0.5–4.0 mm. It is expansive and also contains many specialized structures, with one square inch of skin holding: 15 feet of blood vessels, 12 feet of nerves, 100 oil glands, 650 sweat glands, and thousands of circulating white blood cells. Within these layers, immune cells work to stave off infections such as herpes. First, the phys- ical layers prevent microbes from gaining a footing into the human body. Figure 15.4 shows the structure of the skin with its dead cells continually being produced in its surface.

Human skin has three layers: the epidermis, which is on the surface of the skin; the dermis, which is directly below the epidermis; and the hypodermis, the deepest layer. The layers are held together tightly by cell junctions, as described in Chapter 3. However,

Epidermis

The outer layer of the skin.

Dermis

The middle layer of the skin, containing most of its organs and sense receptors.

Hypodermis

The deepest layer of skin.

Figure 15.4 General Structure of the Skin Is Continually Renewing and Dead Cells Are Constantly Sloughing Off.

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in some situations, such as wearing poorly fitting shoes while walking, a blister forms due to a separation of the three skin layers. Blisters from cold sores, as described in our story, break apart the layers of the skin due to the pressure from battle between herpes and the immune system.

the outside Border: Epidermis The epidermis contains a series of five layers of flattened cells (Figure 15.4). Epidermal layers mostly contain dead cells filled with keratin, especially the outer layers. These cell layers become filled with granules of keratin protein, which is protective. From outside to inside, epidermal layers include the: stratum corneum, stratum lucidum, stratum gran- ulosum, stratum spinosum, and stratum basale. You may remember them with a saying: “cells like getting sun burnt”; with the start of each word in the sentence also starting with the same letter as the layer names. Figure 15.5 gives a micrograph of the layers of the epidermis.

The outmost layer, the stratum corneum serves as the best protection from patho- gens, with 20–80 cell layers. The cells in this layer are water repellant and easily flake off, making those inexpensive cells to lose or to protect us. The stratum basale is the only fully living cell layer. It is also mitotic and gives rise to the other epidermal layers. It gives rise to so many cell layers, and so continuously, that the skin would be six feet in diameter if stratum corneum cells did not flake off by the time we are 80 years old.

the Inside Border: Dermis and hypodermis The dermis lies directly beneath the epidermis and contains most of the organs and living cells of the skin. It is separated from the epidermis by the dermal papillae, a wavy layer of the skin, which is also responsible for our fingerprints. Use Figure 15.6 as a guide to integumentary anatomy: the hair root and its hair follicle are used to detect insects and the arrector pili muscle helps hair to stand on end. Four enlarged receptors called corpuscles act to sense stimuli: the Pacinian corpuscle looks like an onion and senses deep pressure, Meissner’s corpuscle is another receptor that senses light touch,

Keratin

A protein that is the principal constituent of nails, hair, and skin tissues. Stratum corneum

The outermost layer of the epidermis. Stratum granulosum

A thin layer of granular cells in the epidermis located between stratum lucidum and stratum spinosum.

Stratum basale

The deepest layer of the epidermis, mitotic.

Dermal papillae

A wavy layer of the skin which is also responsible for human fingerprints.

Hair follicle

A structure from which hair grows.

Arrector pili muscle

Small muscles attached to hair follicles in skin.

Pacinian corpuscle

A receptor that senses deep pressure.

Meissner’s corpuscle

A receptor that senses light touch.

Figure 15.5 Layers of the Epidermis. Each layer has specific functions and character- istics. The outer layer, the stratum corneum is thickest and visible to the eye.

Stratum Lucidum

Stratum Corneum

Stratum Spinosum

Stratum Granulosum

Stratum Basale

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Hair root

Part of hair embedded in a hair follicle.

Stratum lucidum

A clear layer of dead skin cells in the epidermis located between stratum corneum and stratum granulosum. Stratum spinosum

A layer in the epidermis located between stratum granulosum and stratum basale.

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574 Unit 4: The Dynamic Animal Body

Hair Shaft

Free Nerve Ending

Sebaccous (oil) Gland

Dermal Papillae

Meissner’s Corpuscle

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Dermis Papillary Layer

Reticular Layer

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Vein Sensory Nerve Fiber

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(a)

Ruffini’s corpuscle (ending) senses heat, and Krause’s corpuscle (bulb) senses the cold. Sweat glands and sebaceous oil glands produce their secretions, and blood vessels and nerves carry materials and cells through the skin to parts of the body.

Deep to the dermis, the hypodermis layer is primarily composed of adipose (fat) cells. Stored fat acts as a protection to absorb shock and cushion tissues it surrounds. Along the layers of the skin there are also special cells of the skin. Special white blood cells called Langerhans cells reside in the stratum spinosum are able to defend the layer if invaded. Keratinocytes produce keratin granules that infuse the layers of the epidermis to aid in protection. Melanocytes make the skin pigment called melanin, which gives the skin its darker tones and protects from ultraviolet light, as you might recall from Chapter 5. All of these cells work to provide the first line of defense in immunity.

Ruffini’s corpuscle

A receptor that senses heat.

Krause’s corpuscle

An bulbous cell that senses cold.

Sweat glands

A tubular gland that secretes sweat.

Langerhans cell

Special white blood cells that reside within the skin.

Keratinocyte

An epidermal cell that produces keratin granules.

Melanocyte

Cells that make the skin pigment melanin.

Figure 15.6 a. The Human Integumentary System: Epidermis, Dermis, and Hypodermis Structure, along with Specialized Components. The dermis of the skin contains most of the organs and is responsible for many of its varied functions. Adapted from Anatomy I and Physiology Lecture Manual by John Erickson and C. Michael French. b. Sensory receptors of the skin.

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Chapter 15: A War against the Enemy – Skin’s Defenses and the Immune Attack 575

Ruffini’s corpuscle

A receptor that senses heat.

Krause’s corpuscle

An bulbous cell that senses cold.

Sweat glands

A tubular gland that secretes sweat.

Langerhans cell

Special white blood cells that reside within the skin.

Keratinocyte

An epidermal cell that produces keratin granules.

Melanocyte

Cells that make the skin pigment melanin.

(b)

Figure 15.6 (continued)

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IS A tAn HEALtHy?

Skin color denoted social status since ancient society. In the time of Cleopatra, lighter skin tones were admired. However, by the 1920s, tanned skin became in style. A tan is a sign of good health and attractive in our society. Most of us know that it is associated with skin cancer but accept that aspects of darker skin tones are considered appealing. After all, celebrities show off their tanned bodies at the beach and the media is quick to give them attention.

Skin darkens when ultraviolet (UV) light strikes melanocytes in the skin. This stimulates melanocytes to make more melanin, a response to give protec- tion. Melanin shields the nucleus of skin cells from the damaging effects of UV light. It was believed that tan skin protects from the effects of UV light and this is true. However, the way to get tanned skin is by exposure to the dangerous effects of UV light in the first place.

Thus, the more one is exposed to UV light, a source of radiation, the greater the damage to the integumentary system. UV light is clearly associ- ated with an increased rate of aging of the skin. As you might recall from Chapter 11, collagen is a protein giving support to most areas of the body. Skin has an abundant amount of collagen ropes holding it together. When UV light strikes the collagen fibers, they form cross-linkages and become brittle. Collagen cross-linkages break apart, decreasing their amounts. Less and brittle

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collagen leads to skin wrinkling and sagging. It may only be appearance but UV light also links closely with skin cancer. Figure 15.7 shows identical twins, one who tanned and other who did not tan regularly. Note that here will be a dif- ference in skin features and the effects of sunlight between the identical twins if one stops tanning but the other continues.

UV light is also associated with skin cancer, the abnormal growth of cells of the skin. The rate of skin cancer incidence has increased markedly in the last 80 years. There are three types of skin cancers: basal cell carcinoma, which is relatively common (almost one third of the US white population will develop this type of skin cancer) but very rarely kill its victims; squamous cell carcinoma, which appears as a flaky reddened area and is able to spread and kill; and mela- noma, which is very dangerous and rapidly spreads (a few months) in its victims.

The incidence rates of malignant melanomas are on the rise in populations all over the world. This trend is alarming: they occurred for 1 person in 1,500 in 1930, to 1 in 250 in 1981, to 1 in 87 in 1996, to 1 in 79 in 1999. Projections from this pattern predict increases by roughly 7% more cases per year. Amer- icans now spend almost $400 million each year on suntan lotions and other cosmetic products for tanning. However, a tan is nothing more than destroyed collagen and changing cells into cancer. Malignant melanoma may be detected by using the ABCD (asymmetry of moles, border irregularity, coloration differ- ences, and diameter - larger than a pencil eraser makes a mole suspicious) rule for identifying suspicious moles.

Skin cancer

A condition characterized by the abnormal growth of cells of the skin.

Basal cell carcinoma

A type of cancer, which is relatively common, but very rarely kills its victims.

Squamous cell carcinoma

A type of cancer characterized by a flaky, reddened area.

Melanoma

The most dangerous form of skin cancer.

Figure 15.7 If One of These Twins Stops Tanning, She Will Likely Have Less Wrin- kles and a Decreased Risk of Skin Cancer in Years to Come.

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the Role of the Border: Skin Functions Protection is not the only function afforded by the skin. The skin is considered an organ system because it is complex and performs numerous functions for the body. It is known as the integumentary system because it maintains the integrity of the body, covering it

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but also managing many aspects of homeostasis. As shown in the previous section, the skin contains all of the tissue types as well as a variety of smaller organs. Together, these parts comprise the integumentary system and play a central role in:

1) regulation of body temperature: The skin contains blood vessels that are able to expand and contract, changing the amount of heat and blood to skin surfaces. When blood vessels dilate, more blood is brought to the surface, losing heat and lowering body temperatures. Humans also are capable of sweating, sometimes profusely. An average person sweats out 500 mL (a cup) per day but is able to sweat up to 12 liters (3 gallons)!

2) excretion of wastes: Nitrogen-containing wastes are removed from the kidneys, which will be discussed in Chapter 16. However, some nitrogen-containing wastes are excreted via sweat, with urea, uric acid, and ammonia components of sweat and all containing toxic nitrogen.

3) blood regulation: About 5% of blood remains in the integumentary system at any one time. The skin acts as a blood reservoir, sending blood to needed areas depending on a person’s activities. For example, after eating or exercising, blood is sent to the digestive system or to the muscles, where it is needed.

4) sensation of stimuli: The corpuscles of the skin sense different stimuli. They are adapted to respond to the environment to send these messages to the brain, in ways described in Chapter 14.

5) vitamin D synthesis: When cholesterol present in the skin layers is exposed to UV light, it forms vitamin D, which is needed in the digestive tract to absorb cal- cium. When people are deprived of sunlight, their intake of calcium is impaired because of a lack of vitamin D. This problem is especially noticeable in the elderly population who are restricted to the indoors. Sunlight helps them to increase their levels of vitamin D and thus calcium needed for strong bones and teeth.

HoLD tHE SHowER, PLEASE! . . . IS BAtHIng oR SHowER- Ing EvERy DAy REcoMMEnDED?

Our first line of defense, the skin and its related membranes, are covered by a normal skin flora of bacteria and other microbes. Most of these bacteria are not harmful and in fact, fight off other more harmful strains of microbes.

Although most adults in the United States bathe or shower every day, it may not be necessary or recommended. First, compared with the past in which farming lifestyles required physical strength and sweating, modern society has led to more passive lifestyles and people get much less dirty. Second, bathing too frequently reduces the population of protective Staphylococcus-type ben- eficial bacteria on the skin surface. Staphylococcus occurs normally as a part of the skin microbiome, which includes over 1,000 species of bacteria covering our two square meters of skin surface. Staphylococcus makes up only 5% of the skin microbiome, with many other defending microbes protecting us. Protect- ing our skin by bathing and showering is vital in staving off infections. However, can we bathe too much?

Some studies claim that daily bathing may make people more susceptible to skin infections, including MRSA, mutant-resistant S. aureus. Figure 15.8 shows the superbug MRSA and an infection caused by its invasion of the skin.

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Skin that is too frequently cleansed with soaps and shampoos removes protective oils from the surface. This causes dry skin, cracking, and openings through which microbes, such as the herpes virus in our story, may enter the body. Although bathing and showering are not ecofriendly and wastes valuable water, its effects on our health should also be considered. Is this a good case for being dirty?

(a)

(b)

Figure 15.8 MRSA and Its Invasion of the Skin. a. MRSA first appears like a spider bite. b. As MRSA progresses, it creates an inflammation with pus oozing.

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Malfunctions of the Border: Skin and Disease Besides skin cancer, other skin changes also indicate illness. For example, the skin requires constant supply of blood for nutrients. When that supply is cut off, which occurs when lying in bed for too long, bed sores often develop. Bed sores, called decubitus ulcers, form dead tissue rather quickly when the blood supply is pinched by pressure from lying down.

Skin color is also important an indicator of a patient’s health. When a yellow color- ation of the skin is noted, as seen in jaundice, it indicates that the liver is not functioning properly. Bilirubin a substance produced by the digestive system should be broken down

Jaundice

A disease characterized by yellow coloration of the skin.

Bilirubin

A substance produced by the digestive system during the breakdown of RBCs.

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by the liver. When the liver malfunctions, bilirubin accumulates in the skin layers and results in the yellow coloration. When a liver disease occurs or when a baby’s liver is temporarily immature upon its birth, jaundice is presented in a patient. Bronzing of the skin indicates that a person’s adrenal glands are hypoactive, a symptom of Addison’s disease.

Internal Borders: Stomach and Respiratory tract Defenses When pathogens pass through the skin’s protective borders, they encounter harsh con- ditions in the stomach and in the respiratory tract. The stomach, as you recall from Chapter 12, has a very acidic pH of between 2 and 3, killing most bacteria on foods. The respiratory tract is also lined with cells containing cilia, which beat upward to move pathogens out, as described in Chapter 13. When microbes do enter our lungs, special- ized immune cells are able to phagocytize them in the next line of defense, nonspecific immunity. Let’s take a closer look at the immune cells and their tactics during nonspe- cific immunity.

IS tHERE REALLy A 3-SEconD RuLE FoR FooD?

You should not pick up food after it falls to the floor, even if it is less than 3 seconds. When food touches the surface, either the floor or the other areas suspected of increased microbes, pathogens attach easily. Research from 2003 and 2006 studies showed that all of the foods falling to the ground have some level of contamination by microbes. Whether in 2 or in 10 sec- onds, all of the foods had significant amounts of Escherichia coli and Salmo- nella contamination.

Our surrounding surfaces have 108 = 100,000,000 per square centime- ter (about the size of your fingernails) of bacteria along with large num- bers of protists, viruses, and fungi, all described in Chapter 8. Many of these microbes are associated with illnesses such as food poisoning and intestinal sicknesses. Stomach acidity and antibodies in our saliva fight off pathogens, but not always. That said, eating food from any floor or dirty surface is not recommended, even after an overview of the immune system defenses.

nonspecific Immunity: the Second line of Defense When the first line of defense fails, nonspecific immunity procedures take over the defense of the body. Immune cells called specific white blood cells (introduced in Chapter 13) conduct a military operation to (1) identify the invading pathogen, (2) recruit new immune cells to the infected area to help in the fight, and (3) attack and destroy the invaders. Tissue injury due to pathogens (but also physical trauma and harmful chemicals) causes necrosis or tissue death. When cells die as they are invaded by pathogens, they release chemical messengers to trigger white blood cells to respond to the invasion.

necrosis

Death of tissue.

white blood cells

Blood cells that help body fight infections.

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the Start of Warfare: Inflammation Do you recall stepping on a nail or getting a paper cut? Any disturbance of the bor- der of our bodies, whether damage by a pathogen or due to a physical injury, elicits an inflammatory response. Inf lammation is a series of events that identify, recruit, and attack invading cells. It results not only in the pathogen’s destruction but also in red- ness, heat, swelling, and sometimes, pain. Figure 15.9 describes the steps in eliciting an inflammatory response to pathogens.

When an intruder, such as the herpes virus mentioned in the story, enters through the first lines of defense, damage to the cells occur. The start of warfare follows when dam- aged fibers are recognized by a type of immune cell called a mast cell. Circulating mast cells patrol the border looking for damaged fibers. When contacting out of place fibers, mast cells release two types of chemicals: histamines and heparin. In our story, the area of infection led to a cold sore, which felt inflamed and swollen due to this process.

Histamines are chemicals that bring more blood to a site of infection by vasodilation of the blood vessels surrounding the area. This causes more blood flow (and heat and swelling) in infected areas. More blood flow serves the purpose of increasing transport to the area. If more blood is directed to the site of infection, then more immune cells will arrive as well. Any military operation requires more troop transport to a region of attack, through roads and rails. Similarly, histamines open up the area to bring in more troops or in our example, immune cells.

Heparin is a chemical that acts as a blood thinner. It is also found in rat poison and medicines that slow blood clotting. When heparin is released into the site of infection in an

Inflammation

A series of events which identify, recruit and attack invading cells, causing swelling.

Mast cell

A type of immune cell.

Histamines

Chemicals that bring more blood to a site of infection by vasodilation of the vessels surrounding the area.

Figure 15.9 (a) Nonspecific Immunity: Identifies, Recruits, and Attacks Pathogens. White blood cells (phagocytes) arrive at the site of infection and histamine and heparin are released simultaneously. (b) White blood cells (also called macrophages or phagocytes) attack pathogens at the site of infections. (c) White blood cells clean up the infection site by gobbling up dead cells and debris. (d) Mitosis replaces dead tissues.

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Fluid and clotting factor

release

Invading Organisms

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Capillary

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area, the region is less able to clot blood. It might seem strange to slow clotting in an area of a cut, which would require a clot to stop its bleeding. However, the external area of the cut does continue to clot, in which there is little heparin. Instead, the site of battle, where the pathogen combats its immune cells, remains free from clots. This area allows free movement for immune cells to carry out their defense operations. Free mobility is vital in a battle, in which immune cells acting much like tanks are able to attack their enemy.

the tanks: Cells of the Immune System

neutrophils White blood cells are phagocytes that attack in nonspecific immunity. They gobble up the invading pathogen by phagocytosis, as described in Chapter 3 and white blood cells shown in (Table 15.1). As seen in Figure 15.9, phagcytosis of pathogens is accomplished by cells that are the first to arrive at a site of infection, neutrophils. Neutrophils are white blood cells that quickly ingest pathogens. They push through the endothelial layers of capillaries and enter the site of battle. Neutrophils attempt to contain the invader before it has time to divide and colonize an area.

Neutrophils act like “fast tanks,” with rapid speed in an area of infection (they arrive within 1–2 hours after an invasion). They are cheaply built and rapidly made – and they are self-destruct units, destroying themselves after they ingest pathogens. Neutrophils only live 3–5 days and are found in high numbers during bacterial infections. Neutro- phils make up between 50% and 70% of white blood cells. High counts of neutrophils in the blood indicate an acute bacterial infection.

Macrophages Macrophages are the largest (from the term “macro”) of the white blood cells, devel- oped from monocytes (both shown in Table 15.1). They are expensive to build and slow to arrive at the site of infection. They are the slow moving but “powerful tanks” of the immune system. Although they are slow to arrive, they make a big impact, carrying out large-scale phagocytosis to engulf their enemies.

Macrophages engulf whole pathogens and display the pathogen’s parts, called anti- gens, on their surface. Antigens are any molecule or cell part that initiates an immune response. The display of antigens is called macrophage presentation. Presentation of

Macrophage

The largest of the white blood cells.

Antigens

Any molecule or cell part that initiates an immune response.

table 15.1 Types of White Blood Cells, the “heros” of immune battles

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The display of antigens by a white blood cell.

neutrophils

A type of WBC that are the most abundant in mammals and are first to arrive at an invasion.

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the pathogen helps other immune cells to identify the invader. For example, in our story, the narrator’s herpes simplex I viruses would be ingested by macrophages and their antigens displayed on the surface. All other immune cells would “see” this as an example of what to search for and destroy as an enemy in the body. This process will be discussed further in the next section on specific immunity in this chapter.

Macrophages do not die upon phagocytosis of their enemy. They live for months or even years, circulating through the blood to ready for the next encounter. They are often engaged in heavy battle, phagocytizing invading cells. Macrophages make up only 5% of white blood cells.

Macrophages are often found in pus, a yellow fluid emerging from a site of infec- tion. Pus indicates that a battle was serious and contains parts of damaged pathogens and macrophages. In our story, the character’s blisters form from a heavy battle between herpes viruses and macrophages. The pus within cold sores is composed, in part of giant cells, which are enlarged macrophages. Giant cells become so large, filled with their enemy, hence their name. The process of phagocytosis by neutrophils is shown in Figure 15.10.

When defense against an intruder fails, the body walls off an area called an abscess. Abscesses can break apart and become dangerous when its infection spreads. The way to treat any abscess is to drain the pus within it and administer antibiotics. Pimples

Pus

A yellow fluid emerging from a site of infection.

giant cells

Enlarged macrophages.

Abscess

Collection of pus that builds within the tissue of the body.

Figure 15.10 Phagocytosis by a Neutrophil. The process of engulfing pathogens involves their digestion by lysosomes in vacuoles within neutrophils. Digestive enzymes break down pathogens within internal vacuoles and eventually expel them from the cell.

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on the skin are examples of minor abscesses, in which Staphylococcus (discussed in Chapter 8) bacteria invade hair follicles. An example of a skin abscess is shown in Figure 15.11.

lymphocytes Neutrophils and macrophages work in the nonspecific immunity division, gobbling up whatever pathogens they encounter. However, lymphocytes are white blood cells that work to specifically target invaders. Lymphocytes are thus classified as specific immu- nity. They are the “special forces-type tanks” of the immune system able to specifically target pathogens.

Lymphocytes are the smallest of the white blood cells but contain the largest nucleus. They are the brains of the immune cell operation; their nucleus directs complex specific-immunity methods. They are in the last line of defense and are protected from the rigors of battle along the border of the body. Lymphocytes are expensive to build and remain in the body for many years, giving long-term immunity to illnesses.

There are two types of lymphocytes: B cells and T cells (both shown in Table 15.1). Both types of white blood cells are produced in the bone marrow. T cells leave the bone marrow to mature in the thymus (hence the name “T” cell) and B cells remain, maturing in the bone marrow (standing for “B” cell). B cells, T cells, and antibodies, along with their attack strategies, will be discussed in the subsequent sections of this chapter.

Chemical Warfare Both neutrophils and macrophages secrete chemicals to attack the invading pathogens. The secreted chemicals, hydrogen peroxide (H2O2) and hypochlorous acid (both com- ponents of household bleach), are deadly to bacteria and fungi. When H2O2 is secreted from neutrophils during the height of its battle with a pathogen, it releases small spears along with the chemical in what is termed a respiratory burst. The spears cut into a pathogen’s cell membrane creating damaging holes. Figure 15.12 will help you visualize the defense strategies of neutrophils.

Chemical warfare also occurs when interferons are released from dying cells. Inter- ferons are small proteins that bind with receptors on neighboring cells. It is released in small amounts by the dying cells and is the chemical weapons used in immunity.

Specific-immunity

The third line of defense in the human immune system.

Respiratory burst:

The rapid release of hydrogen peroxide and superoxide radical from neutrophils.

Interferon

Small proteins which bind with receptors on neighboring cells.

Figure 15.11 Abscesses and Pus. Abscesses are walled off infections and the body isolates it to fight it.

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White blood cells that work to specifically target invaders.

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Interferons cause neighbor cells to produce antimicrobial proteins and also recruit more white blood cells to the site of invasion.

Some chemicals called pyrogenes cause fever, a natural and needed response by the body. Fever increases the average body temperature in response to disease or illness. Pathogens such as bacteria work best at body temperature. When pyrogenes activate, warmer body temperatures slow growth and inhibit their survival. Pyrogenes initiate a “slash-and-burn strategy” to defense, by raising temperatures to destroy pathogens and sometimes our own body cells as collateral damage. A very high fever (105°F) is dan- gerous because our own proteins may denature (unfold) and cease functioning.

Taking anti-inflammatory medicines and aspirin help to lower a fever. But do they also interfere with the military operations of the immune system? A study showed that those patients taking aspirin took longer to recover from chicken pox than those taking a placebo.

Specific Immunity: the third line of Defense The final line of defense operates carefully to match their substances with invaders. Spe- cific immunity occurs when the immune system specifically targets certain types of pathogens. It directs the body to make materials and gear them for attack against a particu- lar antigen. Specific immunity is the final and most precise phase of the immune response.

Macrophage presentation (shown in Figure 15.13), introduced in the previous sec- tion, starts specific immunity. The macrophage holds antigens from their engulfed invader, on the surface of its cell membrane. The macrophage acts much like a flag-car- rier during a battle. The flag is the enemy antigen, shown on the macrophage membrane. Its specific shape informs all other immune cells to target specific pathogens. Immune cells can then search for and destroy only those cells. For example in our story, if the her- pes virus antigens are presented, a specific, tailored immune response will be initiated.

There are two types of specific-immunity strategies:

1) Cell-mediated Immunity. Macrophages that present immediately attach to other immune cells. The attachment is mediated by the specific fit of the shape of the presented antigen and the receptors on these immune cells. A specific type of T cells, called a T-helper cell, attaches to the macrophage to start specific

Pyrogene

A chemical that causes fever.

t-helper cell

A specific type of T-cell that attaches to the macrophage to start specific-immunity.

Figure 15.12 H2O2 (Hydrogen Peroxide) Released from a Neutrophil. Many terms describe the vicious attack by the respiratory burst. In this image, peroxide shoots out of a neutrophil like a gas stream hitting the enemy antigen.

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immunity, as shown in Figure 15.15 and 15.17. T-helper cells stimulate other cells to target invaders.

The use of T cells in specific immunity is called cell-mediated immunity because cells drive the processes. In cell-mediated immunity, T-helper cells send out chemical messen- gers when binding to macrophages. T-helper cells stimulate other T cells, called cytotoxic T cells (or killer T cells) to kill specific invaders. T-helper cells are shown attaching in Figure 15.15. Cytotoxic T cells also attack cancer cells in our body. (see Figure 15.17 for an overview of cell-mediated immunity). Our immune system plays a role in fighting off many diseases – perhaps more than we know – which affects our health. Direct evidence for the role of the immune system in suppressing cancer is shown in Figure 15.14. In this figure, a T cell directly attacking a cancer cell is shown.

cell-mediated immunity

An immune response that is based on on antigen-specific T lymphocytes.

Figure 15.13 A Macrophage “Presents” the Antigen That It Engulfs. It then places the antigen on its cell surface, which attract T-helper cells. T-helper cells activate other cells of the immune system to initiate both cell-mediated and humoral immunity.

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Figure 15.14 A Cytotoxic T Cell (shown in grey) Attacks Cancer Cell. This is direct evidence for the importance of the immune system in fighting and preventing cancer.

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cytotoxic t-cells

Killer T-cells stimulated by T-helper cells to kill specific invaders.

t-cell

A type of lymphocyte that matures in the thymus.

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T-helper cells also cause other T-helper cells to divide more quickly, forming new ones. They also stimulate B cells, which serve in specific immunity. When T or B cells encounter an antigen, they divide rapidly to produce large numbers of their own type of immune cells. This process is called clonal selection because clones of the specifically needed T and B cells are rapidly produced. It is a massive tank production process, with many of the same type of lymphocytes developing all at once. This way, very few T and B cells need to be circulating at any one time, saving the body energy to produce them.

clonal selection

The process by which T-cells or B-cells divide rapidly to produce large numbers of their own type of immune cells on encountering an antigen. MHc PRotEInS: Know tHy EnEMy!

All cells of our body have antigens on them called MHc (major histocom- patibility) proteins. These are indicators to tell immune cells the difference between invading cells and those of our own. It tells the immune system who thy enemy is and who is a friendly “self” cell (or cell of the body).

If a foreign cell has a different set of MHC proteins, the immune system will attack it; using T-helper cells. In Chapter 13, organ donation and rejection was discussed. MHC proteins in donated organs need to match those of the recipient. In our chapter 13 story, Charles was able to obtain his daughter’s heart because they were genetically close enough in their MHC compatibility.

MHC proteins have also been shown to determine mating behavior between organisms. Mice will evaluate each other’s MHCs to find a suitable mate. By smelling potential mates, they base their choice on how different a mate’s MHC is from their own. Studies show that mice are choosy; selecting only those mates with different MHC proteins. This avoids inbreeding and its negative effects, described in Chapter 6.

2) Humoral Immunity. When T-helper cells combine with presenting macro- phages, they send out chemical messengers. These messengers activate B-cell lymphocytes to become plasma cells. Plasma cells may also become memory cells, which are lymphocytes that continue to defend against pathogens. They may circulate in blood for years and even a lifetime to defend after exposure to an illness. Figure 15.15 describes how B cells develop to contribute to our immune response. How do these two cell types – plasma and memory cells – function to accomplish such a feat?

The answer is that they use antibodies to attack invaders. Humoral immunity occurs when plasma cells produce antibodies or proteins that bind with and attack invading antigens (antibodies are also called immunoglobulins). An overview of humoral immu- nity is given in Figure 15.17. They are the “fighter jets” of the immune system, specif- ically targeting their enemies. They also look like airplanes, with a set of wings and a cockpit. Unlike other methods, which harm many cell types, antibodies attack only those pathogens for which they are specifically made to fight against. They pursue certain targets much like military airplane searches for specific enemies.

The name humoral immunity originates from the Greek and Roman words for liquids in the body, also called “humors.” Blood, phlegm, yellow bile, and black bile were the four humors of the ancients. Oddly, the ancients were on the right track – all of our humors including sweat, tears, milk, saliva, and blood – contain antibodies within them to defend us.

Antibodies specifically target pathogens and have a “Y” shape that, mentioned ear- lier, resembles a fighter plane. Antibodies have a specific shape on their “wings,” onto

B-cell

A type of white blood cell that produces antibodies.

Plasma cell

A type of lymphocyte produces antibodies.

Memory cell

Type of lymphocytes that continue to defend against pathogens long after they are gone.

Humoral immunity

A form of immunity where plasma cells and B lymphocytes produce antibodies.

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which antigens attach. Memory cells circulate in the body long after an infection ends, producing antibodies whenever they are needed. Memory cells are antibody factories. When a new pathogen invades our bodies, it takes 7–9 days to start humoral immunity. When there are memory cells already in the blood for pathogens, it takes only 1–2 days to obtain enough antibodies to defend ourselves.

Antibodies are not really fighter jets – they are instead composed of four polypep- tide chains, joined together by sulfur bridges. The wings of the airplane are made of variable regions, which vary from antibody type to antibody type, and constant regions, which are the same across antibodies. Constant regions allow the body to mass produce antibodies cheaply with the same parts. However, a variable region is necessary to give antibodies their specific fit with antigens. Antibodies have a three-dimensional shape, which attaches to specific antigens. The antibody structure and it functions are given in Figure 15.16.

When they attach to an invader, antibodies harm the pathogen by using a series of possible mechanisms. First, antibodies often coat the invading pathogen, to enable mac- rophages to attach more easily. This process is called opsonization, which also means “to make tasty.” The four mechanisms of antibody action are to: (1) neutralize antigens, which cover their harmful parts (like muzzling a dangerous animal), (2) agglutinate (or clump) antigens together to help them be “seen” by white blood cells, (3) precipitate out antigens, which brings them out of dissolved form, also allowing immune cells to identify them, and (4) initiate a complement cascade of chemicals. Complement does not mean a positive remark (like you have a nice shirt on) but instead is a series of chem- ical reactions that blow holes in a pathogen’s cell membrane. The goal of all four mech- anisms of antibodies is pathogen cell lysis. In our story, the way in which the herpes cold sore virus is combatted is partially through the strategies employed by antibodies: they are clumped and neutralized to prevent their spread. Specific antibodies are made against herpes simplex I to conduct this immune-specific process.

Figure 15.15 Humoral Immunity. T-helper cells stimulate B cells to specialize and make antibodies and memory cells. Humoral immunity uses antibodies to specifically attack invading pathogens.

Macrophage

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opsonization

The process by which antibodies often coat the invading pathogen to enable macrophages to attach more easily.

variable region

Regions that vary from antibody type to antibody type.

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Inactivates By

Antigen Antigen-Antibody Complex

Neutralization (masks dangerous parts of bacterial

exotoxins; viruses)

Agglutination (cell-bound antigens)

Precipitation (soluble antigens)

Complement

Antibody

Fixes and Activates

Enhances

Phagocytosis Inflammation

Chemotaxis

Histamine Release

Cell Lysis

Enhances Leads To

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Figure 15.16 (a) Antibody Structure and (b) Function. Antibod- ies are able to perform a number of strategies to attack antigens.

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When an immune response ends, T-suppressor cells enter the field of battle. T- suppressor cells turn off the activities of the immune system. It acts to “demilitarize” the area, shutting down cells and chemicals that cause immune responses. T-suppressor cells end the immune response in an area and ready it for regeneration of new tissue to rebuild. Much like peace-keeping troops after a war, T-suppressor cells serve only to maintain order as rebuilding of the area takes place. Macrophages phagocytize final debris and white blood cells migrate out of the area. T-suppressor cells guide the final phase of the immune response to pathogens. Figure 15.17 shows the many interactions between cells of humoral and cell-mediated immunity.

Rebuilding after the War: Regeneration of tissues The scars of battle lead to necrotic tissue and tissue injury. Regions affected are repaired and rebuilt after T-suppressor cells calm the immune response. There are two ways to rebuild damaged areas in the body: regeneration and fibrosis. Both require specialized cells called fibroblasts to lay down a network of collagen fibers on which to add replace- ment materials and cells. Then, capillaries invade the area, adding nutrients to bring further construction materials. However, regeneration and fibrosis differ in the kinds of cells reoccupying the damaged region.

Regeneration

Replacement of damaged tissues with an original tissue type.

Fibrosis

The scarring or thickening of connective tissue.

Fibroblast

Specialized cells that produce and maintain connective tissue.

Figure 15.17 An Overview of Specific Immunity. Macrophages, B cells, and T cells carry out immune func- tions in concert with each other. From Biological Perspectives, 3rd ed by BSCS.

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Type of immune cells “demilitarize” an immune response when an immune response ends.

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When scar tissue, composed of fibrous connective tissue, replaces damaged regions, fibrosis occurs. Scar tissue does not carry out the functions of the original tissue replaced. For example, scar tissue that replaces heart muscle after a heart attack does not pump blood as its original cardiac cells would have.

Scar tissue can be harmful when it occupies areas of the body and gets in the way of normal functioning. In the example of scar tissue in the heart, it may occupy space in ventricles and limit the holding capacity of the heart. However, scar tissue does have

(b)

Figure 15.17 (continued)

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benefits – it is infection resistant – which prevents further intrusion by pathogens in the areas it replaces. But, scar tissue is not desirable because it does not function as the original cells.

However, regeneration is the most desired strategy, which replaces areas with the same type of tissue that was destroyed. Regeneration occurs because cells that were lost are regrown or newly added with the same functioning tissue. This is optimal because the damaged area returns to its previously functioning state. Of course, regeneration depends on the extent of the damage to tissues and tissue type affected. When there is extensive damage to any tissue, regeneration is limited and areas are instead replaced with scar tissue. These incidences are obvious because they leave a scar, as with many surgical cuts and accidents.

Some tissues are less able, inherently because of their type, to regenerate. In heart damage, for example, cells do not readily regenerate and recovery is therefore limited. Some tissues easily regenerate, such as the skin that contains epithelial cells. Recall, when you last got a cut on your hand; it probably did not take more than a few days to note marked healing. But when a nerve gets damaged, as seen in our story of Richard in Chapter 14, its effects are seen for years and sometimes permanently. Figure 15.18 gives a hierarchy of regeneration based upon tissue type affected.

Epithelial and many connective tissues, such as bone and blood, readily regenerate given the proper nutrients and conditions. These are constructed of materials that are easier to build than those tissues that have poorer regeneration capacity. In our story, the cold sore victim heals quickly, after her epithelial regenerates. How do her other tissues fare?

Smooth muscles in organs and dense regular connective tissues, such as ligaments and tendons, have regularly arranged fibers. These are more difficult to lay down during replacement than the scattered cells of skin, for example. Cartilage, with no blood vessels to give them direct nourishment and to bring immune cells, is unable to regenerate and does worse than smooth muscles and regular connective tissue. In the story, none of these tissues were damaged, which is why healing is so quick from cold sores.

Figure 15.18 Hierarchy of Regeneration of Tissues. The most regenerative tissues are at the bottom of the hierarchy (epithelial [skin] and connective [bone, areolar, and blood]), then dense regular connective (tendon and ligaments) and smooth muscle (e.g. on the stomach walls), then cartilage and skeletal muscle, and finally, the least regener- ative tissues are on top (nerve and heart muscle).

Nervous

Regeneration depends on tissue

Skeletal, cartilage

Dense regular connective smooth muscle

Epithelial, bone, areolar, dense irregular, blood

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Of course, the most difficult to regenerate are cardiac and nerve cells. In our story, the narrator’s nerves were inflamed, causing pain associated with cold sores. However, nerve damage does not usually occur in herpes simplex I. When brain damage occurs, as in strokes, recovery requires retraining of remaining cells rather than regeneration of damaged nerves. Both cardiac and nerve cells are complex and difficult to build, in the first place. Thus, their regeneration is very limited.

Recent studies indicate, however, that some regeneration occurs in the heart and along nerves but very slowly. A peripheral nerve cell heals at a rate of one millimeter a month, cold comfort for Richard, our nerve pain sufferer in the story in Chapter 14.

preventing Future Attacks: Acquired Immunity A vaccine is a medicine containing a weakened or dead pathogen or piece of a pathogen, which is injected into our bodies to start an immune response. Vaccines do not cause the disease but instead stimulate the body to produce antibodies to prevent from future attack. Vaccination is the series of medicines that are administered to prevent various illnesses and their spread through society.

Before vaccinations, the rate of death from infectious diseases were profoundly higher than today: In 1900, the infant mortality rate was upwards of 30% and today it is below 5%; in 1920, there were upwards of 200,000 cases of diphtheria and today only one; in 1952, polio paralyzed more than 20,000 people and today no one; and in 1985, there were 20,000 cases of children infected with Haemophilus influenzae type b, causing meningitis (12,000) and pneumonia (7,500) and in 2002, only 34 cases. Chicken pox, an infection that caused over 4 million cases per year, caused suffering with pus- tules and painful itchiness throughout the body. In 1995, a vaccine for chicken pox was introduced, cutting cases by over 75%. It saves people from more than 100,000 hospital- izations and some deaths every year. All of these advances are due to immunity derived from modern medicine: vaccines acting as aids to our immunity.

table 15.2 The effects of vaccines on Rubella incidence in the US. From Biological Perspectives, 3rd ed by BSCS.

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Acquired immunity occurs when an organism obtains a prior-set of immune defenses to a pathogen before that pathogen enters the body. It is the immune system’s military preparation for war before it happens.

There are four types of acquired immunity, depending upon the way in which the immunity was acquired. When a vaccine activates the immune system to produce anti- bodies in a response to it, it is termed active artificial acquired immunity. The chicken pox vaccine, in the example earlier, gives active acquired immunity to patients. Vacci- nations are a part of artificial acquired immunity because a medical treatment (the vac- cine) stimulates an immune response. It is not a natural process and is therefore called “artificial” immunity. Most vaccines carry out active acquired immunity, such as polio, measles, and influenza vaccines.

When a medicine gives immunity to a patient without stimulating their immune system, it is called passive artificial acquired immunity. In passive acquired immunity, medicines are composed of antibodies, which simply pass into the body. Rabies vaccina- tion, the discovery described in the story in Chapter 8, uses passive acquired immunity to fight off rabies and prevent its infection. The patient’s immune system does nothing, merely receiving the antibodies needed to combat the rhabdovirus.

Natural acquired immunity occurs without intervention from the medical profession – in other words, naturally and using the body’s normal processes. In our story, the her- pes infection leads to natural reactions but no long-term immunity. The story’s narrator remains infected with herpes for life. Although this is often the case after an infection, sometimes immunity for the longer term may be acquired.

When the immune system defends itself and enables future defense against patho- gens, it is termed active natural acquired immunity. The immune system actively pro- duces memory cells and/or antibodies to guard against future attack. It engages in the battles described in this chapter, which ultimately leads to memory cells and circulat- ing antibodies. Some natural immunity is long-term, such as chicken pox and measles, with memory cells lasting for years. Other illnesses, such as the gastrointestinal illness caused by the Norovirus, have an immunity lasting for only a few days.

Passive natural acquired immunity occurs when immunity is obtained naturally but without the work of the immune system. During nursing, for example, a child passively receives antibodies from mother’s milk, giving immediate defense against pathogens. It is passive because the child’s immune system does not activate to make antibodies; and it is natural because it is from a normal process, lactation.

Active artificial

The condition that occurs when a vaccine activates the immune system to produce antibodies in a response to.

Passive artificial

The condition that occurs when a medicine gives immunity to a patient without stimulating their immune system.

Active natural

A type of immunization that occurs when the immune system defends itself and enables future defense against pathogens.

Passive natural

The condition that occurs when immunity is obtained naturally but without the work of the immune system.

DoES DRESSIng wARM In coLD wEAtHER PREvEnt tHE coMMon coLD?

The rhinovirus is spread from person to person through contact or through airborne means. Chapter 8 showed that the common cold is caused by the rhinovirus. Staying warm does not physically prevent the rhinovirus from touching and attaching to our skin and mucous membranes. However, when a person takes care of their health, by eating right and dressing warm, the overall immune system stays stronger to fight off infections. Some studies show that cold weather may suppress the immune system. Suppressed immunity gives the rhinovirus better chances to gain a foothold in our bodies and invade cells. However, there is no direct link between keeping warm and preventing the common cold.

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Defense Stations: the lymphatic System Lymph is the fluid of the body that carries excess liquids and cells not normally trans- ported by the circulatory system. The series of vessels and their organs carrying lymph is called the lymphatic system. The organs of the lymphatic system include: the spleen, lymph nodes, small intestinal areas, and thymus, depicted in Figure 15.19. Lymph nodes

During cold weather, however, more people are driven indoors. Thus, the population density increases – as in the mall, in schools, or in dorms – which leads to a more rapid spread of the rhinovirus. Thus, during the winter, com- mon colds (and other sicknesses such as influenza) occur at higher rates in the population.

Figure 15.19 (a) The Lymphatic System: Vessels and Organs of the System Are Found throughout the Human Body. (b) Lymph nodes are sites of immune defenses by white blood cells against invaders. White blood cells migrate between blood and lymph to defend areas of the body. From Biological Perspectives, 3rd ed by BSCS.

Subclavian Trunks

Right Lymphatic Duct

Right Subclavian Vein

Thymus Gland

Broncho- mediastinal Trunks

Cisterna Chyli

Intestinal Trunks

Jugular Trunks

Left Subclavian Vein

Thoracic Duct

Spleen

Lumbar Trunks

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The fluid of the body that carries excess liquids and cells not normally transported by the circulatory system.

Lymphatic system

The series of vessels and their organs carrying lymph.

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act like “defense stations,” strewn throughout the body and filled with defending white blood cells. Movement of lymph through lymphatic vessels does not occur with the pumping of a heart. Instead, muscle movements in the body push lymph fluids through toward the chest.

The lymphatic system plays a role in (1) immunity and (2) transport of fluids and nutrients.

Immunity and Lymph. White blood cells pack lymph nodes, as shown in Figure 15.19. These white blood cells phagocytize bacteria, viruses, and cancer cells removing them. Although lymph nodes serve as defense stations, white blood cells may defend against invaders at any point in the lymph vessels. Lymph nodes are armed at all times. During an illness, lymph nodes enlarge because heavy battle occurs at these defense sta- tions. The tonsils, the largest lymph nodes in humans, enlarge to become swollen when the body fights a throat infection. In our story, herpes simplex I does not get noticed by white blood cells in lymph nodes, a reason there is little swelling of nodes during cold sore infections.

Lymph nodes serve to fight against cancer cells. When a cancer cell travels into a lymph node, white blood cells attempt to kill it before it can spread to other parts of the body. A failure at the lymph nodes leads to the spread of cancer.

When diagnosing stages at which cancer has spread, lymph nodes are removed to determine if cancer cells have entered the lymph. Classifying cancer into different stages is based on the size and location of the tumor as well as the extent of its spread. However, generally, if cancer cells remain localized and do not spread to lymph nodes it is classi- fied as Stage I. If cancer enters the lymph nodes, cancer is at Stage II. This means that some of the cancer cells of the tumor invaded the blood, through which they travelled across lymph tissue. When cancer is at Stage III, it is found extensively in the lymph nodes. When it is classified as the highest Stage IV, it is discovered in distant areas of the body. The higher the stage, the more difficult a cancer is to treat. The stages, as applied to breast cancer, are given in Figure 15.20.

Transport of Fluids and Nutrients. As cells exchange materials with capillaries, diffusion occurs. When some fluid is lost to the interstitial (in-between cells) areas of the body, they are collected by the lymphatic system. When lymph vessels do not work prop- erly, lymphedema may occur. For example, in deep vein thrombosis cases, described in Chapter 13, roughly 45% of patients experience damage to valves in their lymphatic vessels.

(b)

Figure 15.19 (continued)

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In an extreme case, mostly in the tropics, parasitic worms carried by mosquitoes cause infection leading to elephantiasis, or swelling of the extremities. In these cases, extremely large swellings of the arms and legs occur, as shown in Figure 15.21.

Lymph vessels also extend into the villi within the small intestines, in the form of lacteals. From lacteals, lymph vessels transport fats from the small intestines to the liver, where fats are further processed.

Lacteal

A lymphatic vessel of the small intestine that absorbs digested fats.

Figure 15.20 Breast Cancer, Stages I through IV. All cancer follows a similar classifi- cation scheme based on the extent to which it has travelled.

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Figure 15.21 Lymphedema Patient: Leg Swelling. It occurs because lymph nodes that are damaged cannot transport excess fluids back to the blood vessels. As a result, swelling results from water retention in lymph vessels. CDC photo

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Malfunctions in our Immune Defenses our Immune System Attacks its own troops: Autoimmune Disease When the immune system overreacts to its own cells, it is called an autoimmune disease. Antibodies attack their own cells during an autoimmune attack. Antibodies normally recognize foreign antigens, separating “self ” from “nonself ” in the way they identify structures. Recall that normally, antibodies attach to antigens and stimulate immune responses. However, when antibodies attach inappropriately to our own body cells, an immune response is initiated at the wrong time. Multiple sclerosis, rheumatoid arthritis, lupus, Graves’ disease of the thyroid, and sarcodiosis all involve an autoimmune attack. Each is characterized by inflammation and tissue damage as a result of the immune system attacking normal body cells. Figure 15.22 depicts the deformations of joints in rheumatoid arthritis shows how disabling the disease can become.

Figure 15.22 Rheumatoid Arthritis. Symptoms of joint damage include swelling, inflammation, and even dislocation of joints within affected areas.

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A disease in which the immune system overreacts to its own cells.

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In multiple sclerosis, for example, hardened plaques form along oligodendrocytes. Figure 15.23 shows a normal and attacked oligodendrocyte. You may recall from Chapter 11, oligodendrocytes are neuroglia in the nervous system. Plaques prevent normal trans- mission of nerve impulses to the brain because this neuroglia is destroyed. Cell destruc- tion leads to symptoms such as abnormal vision and sensations across the body. In later stages, there is muscle weakening and possible death. Some studies indicate that a virus may initiate multiple sclerosis, causing cytotoxic T cells to attack oligodendrocytes.

our Immune System overreacts to terror: Allergies When the immune system overreacts to a “nonself ” antigen, such as pollen, peanuts, or chemicals in latex gloves, an allergic reaction occurs. An allergy is an inappropriate immune reaction to antigens that are otherwise not harmful. Antigens that cause aller- gies are called allergens. They occur when the body encounters an antigen that should be recognized as normal. An allergy is like an overreaction, in politics, which leads to a war.

Basophils are a type of white blood cell associated with allergies (shown in Table 15.1). They send out histamines and heparin to cause the swelling, inflammation, and runny nose common in allergies.

Basophils determine whether or not a cell is one of its own or a foreign cell to be attacked. In the determination of “normal” and “foreign,” childhood exposure is shown to be associated. When a person experiences pine pollen, for example, as a child, he or she is less likely to be allergic. Studies also show that very clean households for children are more likely to result in higher rates of allergies for them as adults. It is surmised that the cleanliness of the house prevents their normal exposure to antigens as a child. When adults raised in a clean household encounter allergens, their immune system mistakenly views the antigens as foreign, initiating an immune response.

Spies and Corruption of our Immune Defenses The most serious malfunction of the immune system occurs when it does not work effi- ciently, called immunodeficiency. There are numerous examples of diseases character- ized by weak immune systems. Some of these are a result of viruses, which invade and

Allergy

An inappropriate immune reaction to antigens that are otherwise not harmful.

Allergen

Antigens that cause allergies.

Basophil

A type of white blood cell associated with allergies.

Immunodeficiency

The most serious malfunction of the immune system occurs when it does not work efficiently.

Figure 15.23 Multiple Sclerosis (MS): Plaques on Oligodendrocytes Disrupt normal Nerve Transmissions. MS causes abnormal symptoms in patients such as double vision, odd sensations, and muscle weakness.

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destroy our defenses. Viruses, as described in Chapter 8, act like spies, which take over a cell’s defenses. They corrupt the normal processes of a host cell. A weakened immune system makes a cell susceptible to invaders.

In our story, stress weakened the immune system of the main character. It resulted in the eruption of herpes along the lips. Sometimes, the immune system is weakened not because of stress, but due to other illnesses such as lung disease, neutropenia, as well as many cancers. Other weakened immune systems result due to viral infection, as in HIV and AIDS.

When only one of the immune system strategies is compromised, all of its defense mechanisms are threatened to fail. The results can be devastating, with the many microbes ready to invade, as described in Chapter 8.

Consider AIDS, or Acquired Immune Deficiency Syndrome, the most widely known immunodeficiency. AIDS as viral illness was introduced in Chapter 8 as well, which described its lysogenic life cycle akin to a spy operation. The HIV virus invades a cell and remains dormant, like a spy, to attack a cell from the inside at any time.

The HIV virus attacks and destroys T-helper cells, which in turn limits humoral and cell-mediated immunity in its sufferers. This spy-like virus leaves only the first two lines of defense, the skin and nonspecific immunity, to fight off diseases. When T-helper cells fail to stimulate plasma cells, antibodies cannot be produced in sufficient amounts to fight off other infections. AIDS victims succumb to infectious illnesses such as pneu- monia as well as cancers such as Kaposi’s sarcoma.

HIV infection affects less than 1% of the U.S. population, representing about 1 mil- lion people. However, only 40,000 of those infected with HIV actually get symptoms of AIDS. In developing nations, the infection and death rates are much higher; with a lack of adequate access to the expensive AIDS cocktail of medicines. In sub- Saharan Africa in nations such as Namibia and South Africa, infection rates from HIV are 25% or more in the adult population. AIDS patients have new treatments to stave off the effects of weakened immunity, but a cure to save T-helper cells is still not realized. At this time there is no effective vaccination for HIV because the virus mutates so rapidly and there is no cure for AIDS. A map of HIV infection rates across the world is shown in Figure 15.24.

Figure 15.24 Map of HIV Infection Rates across the World. The highest rates are found in sub-Saharan and South Africa. The darker the shade purple, the higher per- centage affected within that nation.

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Summary The immune system defenses include: a protective border of skin and mucous mem- branes; a nonspecific immunity including white blood cells and chemicals; and a specific immunity that utilizes antibodies and specialized cells to specifically target invading pathogens. The skin or integumentary system serves several purposes in the human body. It maintains a protective border to defend against pathogens. When the skin defenses are breached, a series of nonspecific and specific immune responses take place. There are malfunctions of the immune system including allergic reactions, auto- immune diseases, and immunodeficiency such as AIDS.

cAn A PERSon AcquIRE wARtS FRoM toADS oR FRogS?

Warts are acquired after a papillomavirus enters body cells and seizes control of its machinery. Viruses, as you recall from Chapter 8, are intracellular spies, which take control of cells. There is no evidence that toads or frogs act as vectors for human papillomavirus.

A wart is actually a benign tumor, which is defined as an abnormal cell growth that does not spread. A wart is not a malignant cancer and is not life endangering. However, warts are troublesome and do spread from person to person. Viruses are species-specific, meaning that they cannot spread from one species to another species (there are exceptions, discussed in Chapter 8). However, if a human papillomavirus enters into an open or delicate area of the skin of another human, the virus may spread.

Thus, you cannot generally get warts from other species, such as frogs. Figure 15.25 shows a toad kissing a woman with a cold sore. The toad cannot get a cold sore from the woman he is kissing. Also, while a toad may appear to have wart-like features, it does not mean that it has warts. Toads often have only roughened skin.

Figure 15.25 A Toad Kissing a Woman with a Cold Sore.

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Summary: key points

• People who suffer from contagious diseases such as herpes, leprosy, and AIDS have been shunned by many in society. Understanding about the nature of these illnesses dispels many fears.

• The immune system has three lines of defense: the skin and mucous membranes; nonspecific immu- nity; and specific immunity.

• The skin and mucous membranes have multiple layers and secretions, which act as a strong border; skin serves other functions, such as blood storage and vitamin D synthesis.

• Neutrophils, macrophages, and lymphocytes not only ingest pathogens but also play a role in initiat- ing inflammation and specific immune defenses.

• Cell-mediated immunity uses cells in hand-to-hand combat to battle pathogens. Humoral immunity uses antibodies to specifically target pathogens.

• Some tissues regenerate well, such as skin, bones, and blood; while others have little or no regener- ation capability, such as nerves and cardiac tissues.

• The lymphatic system comprises the lymph nodes and other organs, serving as defense stations to battle invading pathogens.

• The immune system malfunctions when (1) it attacks itself, as in autoimmune disease; (2) it overre- acts to antigens, as in allergies; and (3) it is weak, as in AIDS.

abscess acquired immunity, -active artificial, -passive artificial, -active natural, -passive natural agglutination allergy allergen antibody antigens arrector pili muscle autoimmune disease B cell basal cell carcinoma basophil bilirubin cell-mediated immunity clonal selection cytotoxic T cells dermis dermal papillae epidermis fibroblast fibrosis giant cells

hair follicle hair root histamines humoral immunity hypodermis inflammation interferon immune system immunodeficiency keratin keratinocyte Krause’s corpuscle jaundice lacteal Langerhans cell lymph lymphatic system lymphocyte macrophage macrophage-presentation major histocompatibility proteins (MHC) mast cell melanocyte melanoma

KEy tERMS

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Meissner’s corpuscle memory cell necrosis neutralization neutrophils nonspecific immunity opsonization Pacinian corpuscle plasma cell pyrogene pus regeneration respiratory burst Ruffini’s corpuscle sebaceous glands

skin cancer specific-immunity squamous cell carcinoma stratum basale stratum corneum stratum granulosum stratum lucidum stratum spinosum sweat glands T cell T-helper cell T-suppressor cell variable region white blood cells

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Chapter 15: A War against the Enemy – Skin’s Defenses and the Immune Attack 603

Multiple Choice Questions

Reflection questions:

1. Contagious diseases are difficult to cope with because of: a. pain b. recurrence c. fear of rejection in society d. all of the above

2. Which term(s) does NOT fit with nonspecific immunity? a. macrophage b. pyrogene c. neutrophil d. antibody

3. Which part of the skin acts as a border with many layers of defense? a. dermis b. epidermis c. hypodermis d. sudoriferous sweat gland

4. To begin specific immunity, antigens are presented by: a. macrophages b. neutrophils c. antibodies d. fibroblasts

5. Which directly leads to the formation of antibodies? a. humoral immunity b. nonspecific immunity c. cell-mediated immunity d. autoimmunity

6. Which represents a logical order, from MOST to LEAST able to regenerate, for tissues of the human body? a. epithelial ➔ cartilage ➔ ligaments ➔ nerve b. epithelial ➔ ligaments ➔ cartilage ➔ nerve c. ligaments ➔ epithelial ➔ nerve ➔ cartilage d. nerve ➔ cartilage ➔ ligaments ➔ epithelial

7. A mother nurses her child, giving her baby vital antibodies through the milk. This is an example of: a. natural active acquired immunity b. natural passive acquired immunity c. artificial active acquired immunity d. artificial passive acquired immunity

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8. Which is NOT a function of the lymphatic system? a. transport of fats b. transport of carbohydrates c. transport of excess fluids d. immune defenses

9. Which correctly MATCHES an immune system disease with its classification? a. allergy – thyroxin b. autoimmune – allergen c. immunodeficiency – rheumatoid arthritis d. multiple sclerosis – autoimmune

10. White blood cells are found in all of the following places EXCEPT: a. lymph nodes b. lymph vessels c. dermis d. stratum corneum

Short Answer

1. Contagious diseases are often recurring. Give one reason for why they recur and one reason for why they are socially taboo in some societies.

2. Define the following terms: heparin and histamine. List one way each of the terms differ from each other in relation to their (a) function, (b) role in inflammation, and (c) relationship with each other.

3. List the three lines of defense of the immune system. Which uses antibodies to tar- get pathogens? Which uses lymphocytes to defend against pathogens?

4. Draw a sketch of the inflammatory response, using arrows to show the role of the two chemicals in inflammation. Be sure to include the white blood cells involved in inflammation. How does a mast cell begin the inflammatory response?

5. How do memory cells play a role in natural active acquired immunity? Do they play a role in natural passive acquired immunity? Why or why not?

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6. Pretend you are an antibody. Describe the four pathways that you take to destroy a pathogen. Which pathway most directly damages your enemy?

7. Sketch a hierarchy of tissues, in terms of their ability to regenerate from damage to them. Explain the role of mitosis in tissue regeneration.

8. For question #7, explain the role of scar tissue in tissue repair? Give the pros and cons of scar tissue to answer this question.

9. Describe the steps of macrophage presentation in the immune response. Be sure to use the following terms in your explanation: antigen, pathogen, T-helper cell, plasma cell, and antibody. How do lymph nodes play a role in this process?

10. Describe the symptoms of multiple sclerosis. How does the disease progress? What does the latest research show is the cause? How is the disease classified?

Biology and Society Corner: Discussion Questions 1. Is taking anti-inflammatory and fever reducer drugs good or bad for fighting patho-

gens? Why or why not? Discuss the role of society in its expectations of doctors to provide relief from illnesses.

2. The following statement was made in a courtroom in a medical malpractice suit: “This doctor is often accused of treating the condition and its symptoms and not the whole patient” as a reason for the malpractice. This case involved the mistreatment of a person with HIV infection, who is shunned in some societies. Without knowing the details of the case, construct an argument for the plaintiff, the patient. Construct a counterargument in favor of the defendant, the medical doctor.

3. The treatments for AIDS and HIV infected individuals are very expensive, tallying several thousand dollars a month. People in developing nations die at much higher rates than those infected in the United States. Research this disparity and plan a strategy to lessen the gap between survival rates between these two groups. List three specific ways that you would attempt to accomplish your task. List the draw- backs to each of your strategies.

4. Allergies are on the rise in populations all over the world. Some scientists blame changing climate and others claim that there is simply better diagnosis of allergies compared with the past. Research the biology of allergies and its changing rates in

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the population. Based on your research, which factor do you think is most important linking to the rise in allergies?

5. Jim Carey, a prominent U.S. movie actor, has campaigned against the negative effects of vaccines on childhood health. Based on the information in this chapter, construct an argument against stopping the use of vaccination. Which factor gives you the most certainty in your argument?

Figure – Concept Map of Chapter 15 Big Ideas

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607

Urogenital Functions in Maintaining Continuity

A normal childbirth

An embryo (center of circle) develops in the wrong place (within the fallopian tube) called an ectopic pregnancy

Portrait of a Victorian lady, Mrs. Eddy

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the Case of the stone Baby The autopsy was attended by over 20 persons. In the year of our Lord, 1851, Dr. William H. H. Parkhurst, the friend and attending physician of the deceased, presented a short history of an unusual and rare case. The widow of Amos Eddy of Herkimer County, New York died after a long and unusual set of symptoms. After the autopsy was complete, Dr. Parkhurst shuffled his papers and began: “I present to you the most unusual case I have ever encountered . . . Mrs. Eddy, my former patient, it appears has been pregnant for 50 years!”

The audience whispered loudly in a show of disbelief. “It is not possible,” one doctor called out, “for a mother to go beyond 45 weeks gestation and live.” “Aha” replied Dr. Parkhurst, “if you let me explain the case, you will see how it was and is possible.”

He went on, “Ladies and gentlemen, I met Mrs. Eddy in 1842, 40 years after her first signs of pregnancy. She described her marriage to Mr. Eddy in 1795 and her days as a new bride for their first happy years together. Then, this woman became pregnant with child. Her early months passed with the usual symptoms of pregnancy: the catamenial secretion ceased; a recurrent nausea occurred and normal feelings of pregnancy through to the last eight and one half months gestation.”

Dr. Parkhurst paused, sadly in memory of his patient, and then continued, “But in the last month of her pregnancy, Mrs. Eddy, while preparing supper with a large pot sus- pended over the fire, received a shock when it gave way due to the weight of the meal. This stimulated labor contractions about two hours later. Mr. Eddy readied the horse and buggy to bring her to the doctor. Birth was thought to be imminent. But the labor pains subsided and Mr. Eddy kept his horse and buggy ready for the next month . . . but no baby came. More weeks went by and Mrs. Mrs. Eddy felt the pains of bloat and labor contractions but no doctor could deliver a baby for her.”

“Mrs. Eddy’s health deteriorated.” The doctor explained that months passed and Mrs. Eddy did not feel well and was near exhaustion and death. “But after about one year and one half, Mrs. Eddy’s health began to slowly improve. Her abdomen remained swollen except for the reabsorption of adipose.” The doctor, however, described her con- dition as chronic pregnancy, explaining that “forty years after her pregnancy, I still saw her undergo periods of labor contraction. I tried to deliver the baby, and it would have been a 40-year-old newborn.”

The audience was dismayed at the images of the newly deceased Mrs. Eddy. Dr. Parkhurst began the autopsy to verify his suspicions. He described how he came to

ChECk in

From reading this chapter, you will be able to:

• explain how developments in medical technology play an important role in changing women’s health. • define excretion and describe how it is accomplished in human kidneys. • explain a urinalysis, analyze its results and connect it to urinary diseases. • compare asexual and sexual reproduction and external and internal fertilization. • trace the movement of sperm and egg from production to fertilization and identify the organs in the

reproductive system. • describe the changes in structure during embryology. • identify and describe the diseases of the reproductive system.

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ChECk Up sECtion

The story above depicts the true case of the result of an ectopic pregnancy in the early 1800s in Her- kimer, New York. Ectopic pregnancy occurs when a fetus develops outside of the uterus. Its extreme results were due to a lack of knowledge about ectopic pregnancy. There were only 300 documented cases of lithopedians diagnosed in history.

Research the types of problems that occur during an ectopic pregnancy. Be sure to describe the techniques and methods now used to help women with ectopic pregnancies.

A battery of prenatal tests is soon becoming available to detect over 1,500 diseases before a fetus is born. How might the emergence of these tests affect decisions to terminate a pregnancy? Would you consider using the technology to find out, for example, if your newborn is likely to have a disease?

believe in Mrs. Eddy’s pregnancy: “I had suspected Mrs. Eddy of this unusual condition but I dared not tell her, so many years after the start of her pregnancy. I became aware of another lithopedian (calcified fetus) when reading about a similar case in Cooperstown, New York.”

The autopsy then confirmed the case of the stone baby. Everyone in the audience was astonished to see the opened pelvic area showing a baby, six pounds in weight and facing his mother’s spine. The fetus was fully grown, wrapped in a bony and cartilagi- nous casing. One leg, one foot and one elbow were fused together. The baby was almost completely ossified – it was now a stone baby!

The problem that the stone baby had, which caused the abnormal condition, was then discovered. There were no connections to the uterus by way of an umbilical cord. Instead, the baby’s nourishment was obtained by mesenteric arteries. It had been grown in the fallopian tubes of its mother instead of the uterine wall, which would be normal. Growth of an embryo in any other place (abdominal cavity; fallopian tube) is known as an ectopic pregnancy. Often it is painful and if left without surgical intervention, as in days of the past, it may be deadly for the expecting mother.

Dr. Parkhurst made his final remarks: “Believe it or not . . . the baby turned to stone.”

*Based on a true story from Transactions of the American Association of Obstetricians and Gynecologists for the Year 1888, Volume 1, p. 305. The Association, 1888.

the Urinary system Within the pelvic region described in our story, a lithopedian formed within Mrs. Eddy. The story shows some of the changes in this area of the body related to pregnancy. The reproductive system includes all of the pelvic structures and it products related to the forming of new organisms. In humans, the pelvic region is also home to the urinary sys- tem, which is responsible for eliminating wastes.

The two systems are studied together because they are located in the same region. They comprise what is called the urogenital system, shown in Figure 16.1. The urinary and reproductive systems will be discussed in separate sections of this chapter. Although found close together, they each work to accomplish distinct goals – the urinary system produces urine and the reproductive system produces babies – but both are the focus of this chapter. Both maintain continuity: reproduction helps the species endure and the urinary system stabilizes water and ion balance.

Reproductive system

The system that includes all of the pelvic structures and it products related to forming new organisms.

Urinary system

The system that is responsible for eliminating wastes.

Urogenital system

The system comprising of the reproductive organs and the urinary system.

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Regulating Water Balance First, let’s look at the way organisms regulate their water and ion levels. All organisms, whether on land or in the sea, control the amount of water they take in and lose using a process known as osmoregulation. Osmoregulation is the process by which organisms control their fluid intake along with dissolved solute balances. Organisms have adapted structures in order to work with their environments to maintain water balance.

In freshwater systems, for example, water is in excess and solutes within organ- isms need to be brought inward. Some organisms have special structures within cells to help control water balance. The Paramecium described in Chapter 8, for example, has contractile vacuoles, which displace water as it enters. In another example, freshwater fish have gills that take up salt from their surroundings and excrete large amounts of dilute water. In salt water, the opposite situation happens. Saltwater organisms conserve water and prevent salts from entering into them. Salt water fish, for example, drink large amounts of water to compensate for the solutes and produce small amounts of very con- centrated urine to rid the solutes. This helps them to conserve water. Some saltwater fish gills also excrete salt back into the environment.

The removal of wastes from organisms is known as excretion. The main waste prod- ucts are: urea, which contains nitrogen; carbon dioxide (eliminated through the lungs); salts; and water. There are four organs responsible for excretion of these waste products in humans (Figure 16.2): (1) the liver processes nitrogen wastes by combining them to form into urea and removes bile from red blood cell breakdown via intestines and feces, detailed in Chapter 12; (2) the lungs remove carbon dioxide waste and some water vapor, in processes described in Chapter 13; (3) sweat glands, shown in the previous Chapter 15, remove water and salts in the form of sweat; but (4) the kidneys are the main organ of excretion in vertebrates.

Osmoregulation

The process by which organisms control their fluid intake along with dissolved solute balances.

Excretion

The process of eliminating wastes from organisms.

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Figure 16.1 Sketch of the Male Urogenital System. The reproductive and urinary systems lie mostly within the pelvic region.

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kidneys Water is a scarce commodity on land, where animals need to conserve water. Water balance and water scarcity in the environment are topics discussed in Chapter 18. Terres- trial organisms require systems adapted for their lives on land. Animals, therefore, must remove the nitrogen wastes produced during metabolism while also conserving water. This is a conundrum – wastes accumulate in the body’s fluids and yet they cannot be simply removed because the land organism must conserve its fluids.

To solve this dilemma, terrestrial vertebrates developed urinary systems adapted for limited water conditions. In humans, there are two organs called the kidneys, which filter blood, remove wastes, and at the same time, conserve needed materials including water. The kidneys are bean shaped and fist-sized, lying in the posterior region of the lumbar area on either side of the spine.

Any structure or function referring to the kidneys is known as “renal.” So, the name renal arteries indicate that they are entering the kidneys. The renal capsule covers the kid- ney, affording it some protection. The outer portion of the kidney is known as the renal cortex and the inner portion is the renal medulla. The medulla empties into the renal

Kidney

Organ that filters blood, removes wastes, and at the same time conserves needed materials including water.

Renal capsule

A fibrous layer surrounding the kidney, affording it some protection.

Renal cortex

The outer portion of the kidney.

Renal medulla

The inner portion of the kidney.

Liver

Kidney

Digestive system Skin

Lungs

Urine

Wastes produced

Wastes

Organs of excretion

Deamination of amino

acids

Breakdown of nucleic acids

Hemoglobin breakdown

Excretion

Feces Sweat

Exhaled air containing water

vapor and carbon dioxide

Urea

Uric acid

Bile pigments Carbon dioxideWater

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Figure 16.2 Organs of Excretion: Humans dispose of their metabolic wastes through four major organs: the kidneys, lungs, liver, and sweat glands.

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pelvis. There are pyramid-shaped structures oriented around its pelvis called medullary or renal pyramids. The renal pelvis removes liquid from the kidney (Figure 16.3).

Let’s trace the flow of urine from the kidney to the outside of the body (Figure 16.4). Each kidney is connected to a tube called a ureter, which transports urine from the renal pelvis to a holding tank called the urinary bladder. Urine is stored in the urinary bladder until it is removed from the body through a final tube, the urethra. The urinary system connects with the reproductive system within the urethra in males. It remains separate from the reproductive system in females. We will explore these systems more closely in the next sections.

However, pregnancy places pressure on the urinary system. Many pregnant women experience bladder leak and swellings, for example. In our story, Mrs. Eddy’s fetus grew to six pounds. As you may see in Figure 16.4, this placed pressure on her urinary bladder and other organs. Obviously, in normal cases, pregnancy is a temporary condition and the urinary system fortunately returns to normal functioning. This was not the fortune of Mrs. Eddy, however.

Functions of the kidneys The kidneys perform five functions for the body, besides excretion; they: (1) regulate blood volume and the pH of the blood; (2) remove toxic nitrogen- and sulfur-containing compounds; (3) make erythropoietin, a hormone that regulates red blood cell formation; (4) make renin, a hormone that regulates blood pressure; and (5) maintain Ca++ ion bal- ance, which activates vitamin D in the body.

Renal pelvis

A hollow funnel that removes liquid from the kidney.

Ureter

A tube connected to each kidney responsible for transporting urine from the renal pelvis to the urinary bladder.

Urinary bladder

An organ that holds the urine.

Urethra

The duct by which urine is removed from the body.

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Figure 16.3 Kidney Anatomy. The nephron is situated within the renal cortex and medulla. The kidney is the organ of filtration of wastes in the excretory system.

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Although excretion of wastes and water conservation are key goals of the kidneys, they have an intricate connectedness with other systems of the body. For example, if blood volume is not properly regulated by the kidney, the heart will have problems func- tioning. Too much liquid in the blood might be too difficult for the heart to pump. The kidneys are often discussed at the end of a unit in human anatomy and physiology. This is because they link to all other systems of the body through their multiple functions.

special Cells of the kidneys: nephrons The kidneys filter up to 2,000 liters of blood per day. A person’s urine output varies as well day-to-day, with 0.5–2.0 liters of urine excreted daily, depending upon the amount of liq- uids taken in. Kidneys are composed of specialized cells called nephrons, the functional unit of the kidneys. Each kidney contains 1 million nephrons, all of which produce urine.

As shown in Figure 16.5, nephrons are composed of (1) long tubes and (2) blood vessels surrounding those tubes. The blood vessels at the start of a nephron form a ball of capillaries called the glomerulus. The glomerulus is surrounded by Bowman’s capsule, (the glomerular capsule) which receives substances from the glomerulus.

Nephron

The functional unit of the kidney.

Glomerulus

A ball of blood vessels at the start of a nephron.

Bowman’s capsule

A cup-like sac surrounding the glomerulus.

Left kidney

Ureter

Aorta Inferior vena cava

Renal artery and vein

Urinary bladder

Ureteral opening into bladder

Common Iliac artery and vein

Urethra

Internal and external urethral sphincters

Adrenal gland

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Figure 16.4 Urinary System Anatomy. The kidneys produce urine, which passes through the ureters and into the bladder, in which it is temporarily stored. At urination, the bladder releases urine through the ure- thra to the outside.

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These capillaries contain blood from the body. Vessels then leave the glomerulus (a long with its blood) moving through and surrounding the nephron tubes. A large tube in the nephron, descending and then ascending, is called the Loop of Henle. The Loop of Henle transports its contents into the collecting duct, after which it is removed from the kidneys. The glomerulus is found in the cortex of the kidneys, while the Loop of Henle and collecting duct are located in the renal medulla.

The nephrons work by filtering out some substances from the blood. Those sub- stances enter nephron tubes. Materials that remain in nephron tubes eventually become urine. Those materials remaining in the blood are returned to the body. In this way, the kidney controls which materials are kept and which are removed from the blood.

Loop of Henle

A large tube in the nephron that descends and then ascends.

Collecting duct

A collecting tube that receives urine from several nephrons.

Glomerular Capsule

Proximal Convoluted Tubule

Descending Limb of the Nephron Loop

Ascending Limb of the Nephron Loop

Arcuate Vein

Arcuate Artery

Glomerulus

Distal Convoluted Tubule

Collecting Duct

Interlobular Artery

Interlobular Vein

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Figure 16.5 Nephron Structure. There are three steps to urine formation in the kidneys: filtration, reab- sorption, and secretion. Much reabsorption of water from the collecting ducts concentrates urine by con- serving water.

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the kidney has a three-step process to Make Urine Blood enters the kidneys so it can pick up urea from the liver, and ions, salts, and water from body cells. The kidneys carry out a three-step process to produce urine, using the structures shown in Figure 16.5.

1) Filtration. When blood enters the kidneys, it is first filtered in the glomerulus. The glomerulus has tremendous pressure exerted on its capillary walls. When blood flows through the glomerulus, small substances such as water and salts pass through the filter and large substances remain in the blood. Filtration is strictly based on size. Large proteins should not be found in the urine, for example, because normally they are too large to pass through the glomerulus. Holes in the capillar- ies of the glomerulus determine whether or not a substance will pass through it. Substances that pass through and into the nephron tubes are called filtrate. Water, salts, glucose, urea, and small amino acids are normally found in the filtrate. Red blood cells, white blood cells, and large proteins should not be found in the filtrate.

The kidneys concentrate liquids from the blood as they flow through. High pressure in the glomerulus sends filtrate into Bowman’s capsule. Materials within Bowman’s capsule move along the nephron through the Loop of Henle and the collecting duct.

2) Reabsorption. As indicated, filtration is unselective and removes all small items while keeping large ones in the blood. Some materials that were filtered out need to be returned back into the blood by the process of reabsorption.

Over 2,000 liters of blood pass through the kidneys each day, and yet only 1.5 liters of urine are produced. This means that 1998.5 liters are reabsorbed by the kidneys every day. How does this much liquid return to the blood and body? It begins by the nephrons actively transporting Na+ ions out of the neph- ron tubes by active transport (out of the ascending limb of the Loop of Henle in Figure 16.5). This creates a hypertonic environment outside of the tubes. The blood vessels that surround the nephron thus also become hypertonic. As described in Chapter 3, water follows solute. So, water travels back into the blood from the tubes to be reabsorbed by the body.

The filtrate in the nephron is modified all along its path through the neph- ron. Valuable items are reabsorbed; they include water, macromolecules (such as carbohydrates and amino acids), and ions (such as potassium and sodium) which all serve important roles in the body. They are reabsorbed at certain points along the tubes of the nephron due to the osmotic differences across the nephron.

3) Secretion. Some materials that are not filtered from the blood still need to be removed. The removal of unwanted or unneeded substances from the blood is called secretion. Substances are actively and passively transported out of the blood (and into the nephron tubes) by secretion. For example, to maintain pH balance, H+ ions are actively transported into the nephron tubes (and out of blood vessels) to increase the pH of the blood.

One point in the nephron, the collecting duct, is particularly permeable to water but not to salt. Here, a large amount of water diffuses into the collecting duct and is removed from the body. To recap, the environment around the collecting duct is hypertonic, draw- ing water from the tubes back into the blood. Active transport of ions by the nephron creates a hypertonic environment surrounding tubules. This pulls most of the water out of the tubules and back into the blood. Animals adapted to conserve water usually have long Loops of Henle. Cats, for example, have very long Loops of Henle, concentrating their urine. This is the reason why cat urine is so smelly: the solutes remaining in the filtrate cause odor and there is very little water within its urine. Some animals are so

Filtration

The process by which substances in blood are separated out by pressure through kidneys.

Reabsorption

The process by which some materials that were filtered out are returned back into the blood.

Secretion

The removal of unwanted or unneeded substances from the blood.

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efficient at concentrating their urine, such as kangaroo rats, that they never need to drink any water. They obtain all of their fluids from only the foods that they eat.

In summary, as filtrate moves along the tubules of the nephron, it becomes more and more concentrated, losing water to a hypertonic environment. Because regions surrounding the tubules are high in solutes due to active transport, water follows sol- ute out of the nephron. Concentrated filtrate is produced and water is conserved for the body. Excretion by the kidney is an excellent adaptation to water conservation by land-dwelling animals. The movement of water, ions, and urea along a nephron is shown in Figure 16.6.

Urine indicates a person’s health The end result of kidney function is to conserve water and needed substances but also to excrete wastes and harmful products. This produces healthy urine with normal sub- stances found within it. The kidneys are very effective and over 99% of water is returned to the body, along with glucose and amino acids. Urine normally contains any wastes and unwanted materials made by the body or taken into the body. Drugs and toxic chemicals are removed efficiently by the kidneys. A urinalysis tests urine for normal and abnormal substances in the urine. Normal values for various substances, including whole cells (leukocytes) and a battery of ions in the urine, are given in Figure 16.7.

The kidneys are excellent processors, able to efficiently remove wastes and toxic substances from the blood. As such, most drugs (legal and illegal) ingested are found during drug testing through a urinalysis. Metabolized products of Ecstasy, cocaine, and marijuana are easily detected in drug screenings. In the case of the fat-soluble drug,

Urinalysis

An analysis that tests urine for normal and abnormal substances.

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Figure 16.6 How Do Nephrons Work? Movements of materials along the nephron. Water passes through the nephron tubules, becoming more and more concentrated. Active transport of Na+ ions out of the thick filament of the ascending segment of the Loop of Henle drives water out of the nephron tubules (passively) and back into the blood. The three-step process is shown here.

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Figure 16.7 Urinalysis. A test strip is used to show a patient’s urine results. The values are compared with a normal reading. The figure shows abnormal constitu- ents that may be found in urine and their associated pathology.

Substance Found Potential Causes for its Presence

Glucose Pathological: diabetes mellitus Nonpathological: excessive sugar intake

Blood Pathological: bleeding in the urinary tract as a result of bacterial infection or kidney stone; chronic sympathetic stimulation

Protein Pathological: kidney disease—glomerulonephritis, hypertension Nonpathological: excessive exercise, pregnancy

Pus, White Blood Cells Pathological: urinary tract infection

Bilirubin Pathological: if excessive, liver malfunction

Ketones Nonpathological excessive breakdown of lipids

marijuana, it remains in body cells much longer than most drugs. Marijuana can be detected for a month or longer after its last use. Drug testing in the workplace is a com- mon practice, which screens employees for illegal drugs (Figure 16.8).

Excretion is Expensive However, kidney processes come at a high price – they are very expensive. Active trans- port taking place in the kidneys conserve water but take a great deal of ATP energy. It is, therefore, a costly tax on the body. However, excretion is a necessary strategy to employ in order for organisms to live on land.

Excretion is essential because it removes nitrogen wastes. For all organisms to stay alive, nitrogen wastes must be found in low concentration. Nitrogenous wastes are toxic and interfere with normal life functions. Have you ever sniffed ammonia, a cleaning product? It is actually very dangerous and in an unventilated room may lead to disorien- tation and health problems.

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Figure 16.8 Drug Testing at the Workplace. Should people be required to take drug tests as a condition for their employment?

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Ammonia

Urea

Uric acid

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Figure 16.9 Types of Excretory Products in: Fish (ammonia), Birds (uric acid), and Cats (urea). Nitrogenous wastes are excreted differently by each animal, with humans producing a less toxic form, urea. Humans, just like cats, excrete small amounts of ammonia and uric acid alongside mostly urea.

Ammonia (NH3) is the first by-product made from the metabolism of proteins and nucleic acids. Ammonia is converted into urea in the liver by combining it with carbon dioxide, as described in Chapter 12. This process takes a great deal of energy, but ammo- nia is so toxic that it would kill humans if it remained in the system for more than a few minutes. Urea is able to remain in the body longer, without causing as much harm. Our kidneys are the human adaptation to solving the problem of conserving water while also removing nitrogen wastes.

Some organisms do not have the problem of processing nitrogen wastes. Aquatic organisms, such as fish and aquatic snails, are able to directly excrete ammonia into their watery environment. They do not require the energy needed for processing nitrogen wastes.

Other organisms go a step further than humans, transforming ammonia into the pasty white precipitate, uric acid. It is a more energy-consuming process than forming urea or simply excreting ammonia. Birds, insects, terrestrial snails, and some reptiles produce uric acid as a waste product. Some nitrogenous waste products from different organisms are seen in Figure 16.9.

Why Uric acid? But why would an organism go through the extra work of making uric acids? Why do birds, for example, bother producing uric acid, instead of other substances? Ammonia made by fish is less expensive to process. We know that uric acid is more expensive to make but there must be some evolutionary benefit. In other words, why did different systems of excretion develop differently in organisms?

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Let’s consider bird droppings, which are mostly uric acid. You may recall your first ice cream cone, vanilla, topped while you were not looking with uric acid . . . and it does not taste like chicken. Then why would a bird excrete it? We stated earlier that uric acid is a precipitate, meaning that it is in semi-solid form. This is different from urea, the human substance of excretion, which dissolves in water.

How are birds different from humans? One way is that they lay eggs in which their embryos develop. Human embryos develop in a watery amniotic sac. What would hap- pen in a bird’s egg, if birds instead excreted urea? Urea, dissolved in water, would diffuse throughout a bird’s egg. It would therefore travel into the bird embryo and its toxicity would kill it. Instead, uric acid precipitates out at the corner of an egg and does not harm the chick embryo. Birds would end as a living unit if urea were its excretory product. In humans, the wastes of a fetus are removed by blood vessels connections with its mother. Thus, we do not need to form uric acid as our main excretory product.

Controlling kidney Functions As discussed in Chapter 14, hormones play an important role in regulating processes in the body. The three hormones that help control our urine output are: aldosterone, angiotensin II, and antidiuretic hormone (ADH). Each of these works to conserve water in our bodies. All three hormones work by reabsorbing water into the capillaries surrounding the nephron tubules. This increases water levels within the blood. Recall from Chapter 14 that ADH is produced in the hypothalamus of the brain and stored in the pituitary gland just below it. When the hypothalamus detects that the blood has become too salty (too much solute; too little water), it produces ADH. This increases the amount of water in the blood. By ADH increasing the permeability of the collect- ing duct (and other tubules) to water, it then moves freely back into the capillaries and is therefore conserved. This decreases urine volume output and increases blood pressure.

Malfunctions of the kidneys Sometimes the kidneys fail to work properly, resulting in impaired kidney function. The rate at which a kidney filters blood is measured to determine kidney impairment. If the filtration rate drops to 50% or less, a person is classified as being in kidney failure. The top two causes of kidney failure are high blood pressure and diabetes. Both of these diseases damage delicate blood vessels in the kidneys.

During impaired kidney function, improper filtering of the blood often leads to ris- ing pH values and solute concentration changes. In total kidney failure, ionic balances are more disrupted and toxic substances accumulate within days leading to death. For

Aldosterone

A hormone produced by the cortex of adrenal gland.

Angiotensin

A hormone that promotes aldosterone secretion in blood and causes blood pressure to rise.

Antidiuretic hormone (ADH)

A hormone released by the pituitary gland that helps in water retention in the body.

Impaired kidney function

The failure of kidneys to function properly.

Kidney failure

A medical condition in which the filtration rate falls to 50 percent.

DOES DRINKING ALCOHOL mAKES yOU URINAtE?

Alcohol is a depressant, slowing down all of the processes in humans. It also slows the hormones and nerves in the brain. The hypothalamus and the hor- mones controlling the kidney also slow in their actions. When ADH acts more slowly, for example, more urine output results. This is why “breaking the seal” is not a myth after drinking alcohol. Alcohol stimulates a person’s need to uri- nate and it remains in effect for many hours.

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Mrs. Eddy in our story, the pressure and changes associated with her stone baby probably damaged her kidneys and led to her poor initial health in the first years after fertilization.

The treatment for kidney impairment is dialysis, which filters the blood and restores normal ion concentrations. There are two types of dialysis (Figure 16.10 show hemodi- alysis): hemodialysis, which carries a patient’s blood through semi-permeable tubes that filter it; and peritoneal dialysis, which pumps dialysis solution into a patient’s abdomi- nal cavity to exchange nutrients and wastes. Hemodialysis is performed three times each week in the hospital and peritoneal dialysis is done at home each night.

When kidney failure is permanent, dialysis must be continued lifelong or until a kidney transplant is performed. A person may live healthy life with only one kidney. However, for a transplant to be successful the proper MHC match must be found. The National Kidney Foundation estimates that each day, 17 people die from kidney failure. Organs from living donors have a better chance at success than those from dead donors. Organ donation was discussed in Chapter 13, showing the many sides of the matter.

Some advocate allowing people to sell their kidneys for money to alleviate the donor shortage. Others find the sale (and endangerment of health of the donor) of organs an unethical temptation, baiting people with money. It is possible that genetically modified organs may one day be produced from other organisms, as described in Chapter 5.

Reproduction: an introduction types: sexual and asexual When we think about reproduction as a system, it conjures up images of two people mating; perhaps in a sexy scene from a movie. Reproduction is defined as the making of new organisms from existing ones. It is the final system treated in this unit, and yet, it is not necessary for an individual’s survival.

Dialysis

A treatment for kidney impairment.

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Figure 16.10 How Kidney Dialysis Works: dialysis helps patients to cleanse their blood of nitrogenous and other wastes.

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Chapter 16: Urogenital Functions in Maintaining Continuity 621

An organism may live a long span without reproducing. In fact, studies indicate the greater the number of birds in a clutch (eggs in a nest), the shorter a mother bird’s lifespan. Offspring take energy and sap a parent’s strength in the process. However, reproduction is necessary for the survival of the species.

Therefore, reproduction is a luxury and not a necessity for an individual to sur- vive. Then, why have sex? As discussed in Chapter 6, finding a partner and engaging in sex are costly. It causes battles between males and costs energy to attract females. The answer, biologically speaking, is to improve the genetic quality of the species (how scientific!). Sexual reproduction, during which two individuals contribute genetic mate- rial to their offspring, produces two genetically different organisms (Figure 16.11). This results in genetic diversity among the offspring. Most animals and plants carry out sexual reproduction.

An evolutionary reason for sex is to increase genetic variety in a species, as you may recall from Chapter 6. This is termed genetic variation in a population. If there are more types of organisms (e.g., some resistant to a killer bacteria and others resistant to a killer fungus), some will survive environmental changes and some will die. If all of the organisms were the same, then whole species would be more likely to become extinct when the environment changes.

Organisms benefit by reproducing sexually, adding variety to their genetic make-up. Some organisms, such as earthworms (Figure 16.12), are able to both contain both male and female organs, enabling them to reproduce sexually with more partners. This increases their chances for genetic transfer of materials.

Nonetheless, at their own risks, some organisms simply do not generally engage in sexual reproduction. Many organisms, including all prokaryotes, and some plants, protists, and animals resort mostly to reproduction without using a partner. They carry out asexual reproduction. This is the process by which a single individual produces new offspring, without genetic material contributed from a partner. All offspring reproduced asexually are genetically identical to their parents. The benefit of asexual reproduction is that it is fast and easy. No partner needs to be solicited and large numbers of new offspring are produced. Asexual reproduction would have also prevented Mrs. Eddy’s condition in our story of the stone baby.

There are several forms of asexual reproduction in plants and animals including: (1) budding, whereby a new organism grows directly from the body of its parent. A bud then falls off its parent to develop into a new adult. The Hydra described in Chapter 10 reproduces by budding; (2) fragmentation, in which a piece of a parent breaks off and

Sexual reproduction

The process in which two individuals contribute genetic material to their offspring.

Genetic variation

An evolutionary reason for sex is to increase genetic variety in a species.

Asexual reproduction

The process in which a single individual produces new offspring, without genetic material contributed from a partner.

Budding

A type of asexual reproduction whereby a new, smaller organism grows directly from the body of its parent.

Fragmentation

The process in which a piece of a parent breaks off and forms a new organism.

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Figure 16.11 Two Humans in a Sexy Scene.

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forms a new organism. In willow trees, by cutting a branch off at any point and placing it in water, the branch grows roots ready for planting in new soil. The new willow will grow, genetically identical to its parent, into a new willow tree (both processes are shown in Figure 16.13); and (3) parthenogenesis, or a virgin birth (Figure 16.14) results from a female’s egg developing into a new organism without being fertilized by sperm. In spe- cies of the order hymenoptera, which include ants, bees, and wasps, the queens are capa- ble of giving birth to unfertilized eggs under certain conditions. These eggs develop into males that are haploid. When these haploid males mate with females, their offspring are genetically very similar: 75% identical in gene composition between sisters, to be exact. This makes them the most genetically identical organisms on earth (besides identical twins and asexually produced organisms). The results of parthenogenesis on societal organization of these organisms will be explored in Chapter 20.

External and internal Fertilization The process of forming egg and sperm cells during meiosis was described in Chapter 6. How do these gametes unite, during fertilization, to form a new organism, a zygote? There are two strategies to accomplish fertilization. The first to evolve was exter- nal fertilization, during which sperm and eggs unite outside of the male and female.

Parthenogenesis

A virgin birth.

Fertilization

The process of combining male gametes with female gametes.

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Figure 16.12 Earthworms Are Hermaphroditic, Meaning that They Reproduce Sex- ually and Asexually.

(a) (b) (c)

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Figure 16.13 a. Binary Fission. b. Budding Fission. c. Fragmentation (when a piece of this potato is removed and grown into a new plant).

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Chapter 10 described an example of external fertilization in frogs, which use amplexus. In amplexus, male frogs grab onto females from behind and wait until they release eggs, then releasing their own sperm. This process may go on for days or weeks, leading to female frog deaths in extreme cases of males holding on too long.

During external fertilization, egg and sperm enter a watery world to travel through to unite. This is a major drawback of external fertilization: it must occur in a watery envi- ronment to be successful. Most land animals avoid this strategy because watery areas are often ephemeral and dry out quickly.

Thus, terrestrial animals evolved another strategy: internal fertilization. Internal fertilization instead deposits sperm directly into the female’s reproductive system. The act of placing a male structure into a female’s reproductive tract is called copulation. Copulation solves the problem of dry land and prevents desiccation of sperm and eggs. Internally, a fluid environment protects the gametes. A mammal’s reproductive tract is lined with immune defenses and a stable, wet environment.

Fertilization is more successful internally than externally. Then, why do so many fish, frogs, and toads survive, which reproduce externally? To compensate for the adverse conditions experienced by gametes during external fertilization (Figure 16.15), organisms compensate with large numbers of gametes. This way, at least some will make it to fertilization. Also, these organisms have cues to synchronize their mating strategies: water temperature, courtship rituals, chemicals secreted (pheromones), and even phases of the moon – help dictate the optimal times to mate for external fertilizers.

Male Reproductive system Male structures In humans, reproduction is sexual and internal. Although there are obvious differences between human external male and female anatomy, the inside structures of each are unique to their functions. Let’s study male reproductive anatomy to explore the way a sperm cell travels to a female and becomes a new human being.

Amplexus

Mating behavior seen in frogs and toads.

Copulation

The act of placing a male structure into a female’s reproductive tract.

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Figure 16.14 Parthenogenesis: a queen bee reproduces sexually to create females but gives a “virgin birth” to produce males. This image shows a queen bee surrounded by her workers.

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The external anatomy of the male (Figure 16.16) consists of two structures: a penis and scrotum. The scrotum is a sac beneath the penis, the male reproductive organ. Mus- cles (corpus cavernosum, depicted in figure) within the penis become engorged during sexual arousal to enable copulation. There are three cylinders of muscles within the penis. During arousal, their spongy tissues fill with blood. Viagra, the sexual enhance- ment drug, works by vasodilation of blood vessels in the penis. This causes erection, independent of sexual desires during normal copulation.

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Figure 16.15 Two Frogs Carry Out External Fertilization According to Environmen- tal Cues. A male frog squeezes a female until her eggs are released. His sperm then mix as eggs stream from the female.

Ureter (from kidney) Bladder

Seminal vesicle

Rectum

Ejaculatory duct

Prostate gland

Bulbourethral gland

Corpus spongiosum

Epididymis

Testis

Urethra

Penis

Corpus cavernosum

Ductus deferens

Pubic symphysis

Peritoneum

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Figure 16.16 The Parts of the Male Anatomy. The structures produce and transport sperm and fluids (together called semen) into a woman.

Penis

The male reproductive organ.

Scrotum

A sac beneath the penis.

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Within the scrotum, there are two testes (or testicles), each suspended by a thick spermatic cord. The testes make both sperm and androgen hormones (Chapter 14). Interstitial cells lie in between the tubules in the testes. They produce androgens, which develop the male reproductive system. Hormones of reproduction will be discussed later in this chapter.

Sperm are produced by spermatogonia cells in the testes through a process known as spermatogenesis. Some organisms produce more sperm and deliver it more quickly to females than others.

Spermatogonia undergo meiosis, as described in Chapter 6, producing 100 million sperm each day. Starting at puberty, a male will produce sperm until the end of his life. Spermatogonia line highly coiled structures within the testes (Figure 16.17) called seminiferous tubules. Sperm have a long tail called a flagellum and an acrosome “head” filled with enzymes that digest their way into a female egg cell. Sperm, developed in the seminiferous tubules, are now ready for release.

tracing a sperm’s travel Let’s trace the movement of sperm as it makes its journey through the male reproduc- tive system, using Figure 16.16 and 16.17. Sperm, once produced in the testes, move out of seminiferous tubules. Seminiferous tubules converge together to form the epi- didymis, located mostly on the back side of each testicle. It is an extended and coiled tube, roughly 18-feet long. Sperm mature and become motile in the epididymis, feeding mostly on glycogen along with other macromolecules.

During ejaculation, or release of sperm from males during copulation, sperm enter into the vas deferens. The vas deferens carries sperm from the epididymis through the urethra, a duct passing out of the penis.

Making semen In its trip, other fluids are added to sperm to produce semen. Semen is composed of sperm plus fluids from glands. These fluids help sperm to make their journey through the female reproductive system. There are three glands that add substances to make semen (Figure 16.17). The prostate gland, just below the urinary bladder, secretes a milky and basic fluid to buffer the effects of the acidic female environment sperm will first encounter. Prostate fluids make up about 30% of the volume of the semen. They also contain nutrients and enzymes used by sperm. The bulk of semen volume, about 60% arises from seminal vesicles. Seminal vesicles contribute fructose and amino acids as food sources for sperm. Their secretions also contain prostaglandins (Chapter 11), which stimulate small contractions in females. This enables sperm to more easily travel within a female’s reproductive tract. A small amount of fluid (just a few drops) is donated to the semen at the end of ejaculation by bulbourethral glands. They are located at the base of the penis adding mucous and sugars to aid lubrication.

At the moment of ejaculation, about 280 million sperm are released in the semen. Sperm only comprise 1%–5% of the total volume of semen. The role of semen is to help sperm travel to the female egg by protecting and nourishing it. Sperm donation, used commonly in fertility clinics, assists in reproductive technologies for infertile couples and single women who want to have children (Figure 16.18).

Interstitial cells

Cells that produce androgens.

Spermatogenesis

The process by which sperm are produced by spermatogonia cells in the testes.

Acrosome

A caplike structure covering the top end of the sperm.

Seminiferous tubules

Highly coiled structures within the testes.

Epididymis

An elongated organ that stores sperm and transports them from the testes.

Semen

Male reproductive fluid.

Prostate gland

A gland located just below the urinary bladder that secretes a milky and basic fluid to buffer the effects of the acidic female environment sperm will first encounter.

Seminal vesicle

A gland situated behind the bladder and above the prostate gland in males.

Bulbourethral gland

A small gland located at the base of the male reproductive organ and donates small amount of fluid to the semen at the end of ejaculation.

testes

Organs that produce sperma.

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1a. Rete Testis: responsible for transporting the produced sperm 1b. Testis: the interstitial (Leydig) cells are responsible for the production of sperm and production of testosterone

2. Epididymis: sperm maturation and storage

3. Vas deferens: transport sperm during ejaculation

4. Bulbourethral gland 5. Prostate gland 6. Seminal vesicle

7. Urethra: sperm are transported in seminal fluid through the penis during ejaculation

Meiosis

Spermatogonia

Primary spermatocyte

Secondary spermatocyte

Early spermatids

Late spermatids

Young spermatids Seminiferous tubules

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Figure 16.17 Sperm Formation. Sperm occurs as haploid cells, with a long flagellum and a head containing the haploid nucleus.

Female Reproduction Female structures Females carry out the same process of making sex cells as males – meiosis. Genetically eggs are the same as sperm, as haploid (N) cells. But the reproductive processes and structures in females are so much more complex.

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Gametes form in females by oogenesis, a process which takes place in cells of the ovaries. Ovaries are the female reproductive structures, two of each, which make and release eggs into the reproductive tracts. An ovary is roughly the size of a large almond. Cells of the ovaries, called oogonia carry out meiosis to produce eggs. An egg develops within the follicle of an ovary (Figure 16.19).

The egg develops surrounded by follicle cells. These cells form a protective layer to nourish the egg until it is released. At birth, a female has over 1 million follicles. In adulthood, oogonia occur in each of over 40,000 follicles in the ovaries. Only 400 fol- licles (and their eggs) will ever mature in any woman’s lifetime, one each month. The remaining eggs and their follicles disintegrate with age, but modern technology has made egg donation possible. Eggs when fully developed are ready for release. They are very expensive and donation requires more risks to the donor (Figure 16.20).

Oogenesis

A process which takes place in cells of the ovaries.

Ovary

Female reproductive structure.

Follicle

A small ovarian sac that contains a maturing ovum.

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Figure 16.18 Sperm Donation Advertisements Seek to Recruit Sperm Donors, Paid Significantly Less than Egg Donors.

A scar forms over the empty follicle

Corpus luteum

Ovulation (release of ovum)

Mature (tertiary) follicle

Secondary follicles

Primary follicles (egg nest)

Ovarian ligament

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Figure 16.19 The Event of Ovulation. The stages of development of an egg in the ovary. The final step, ovulation releases the egg for fertilization.

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Figure 16.20 Donor Eggs Are Used to Treat Mitochondrial Diseases. Pronuclear transfer refers to the transfer of a nucleus from one egg to another. Egg donation is paid well but carries risks by invasive proce- dures used to obtain eggs within ovaries.

tracing an Egg’s travel Let’s trace the travels of an egg through the female reproductive system (Figure 16.21). Release of an egg from a follicle is known as ovulation. The follicle becomes a hardened mass known as the corpus luteum. The corpus luteum develops into an endocrine gland, secreting estrogen and progesterone, hormones used during pregnancy (see the corpus luteum in Figure 16.19). As the egg is released, it moves past finger-like projections of the fimbriae and into the oviduct. The oviduct is also known as the fallopian tubes. It is the tube through which an egg passes on its way to the uterus.

The uterus is a thick, muscular organ (also called the womb) with walls well vas- cularized to supply it with nutrients. It is here that a fetus develops. In our story, Mrs. Eddy’s lithopedian developed in the wrong place – the fallopian tubes. Her embryo should have implanted into the uterus and developed there. It should have grown in the part of the wall with a rich blood supply, called the endometrium. A traveling egg is fertilized by a sperm, optimally in the oviduct. As a zygote, it moves along to implant in the endometrium, if pregnancy is successfully started.

Ovulation

The process of producing and discharging eggs from ovary. Corpus luteum

Hardened mass of follicle.

Oviduct (fallopian tube)

Tube through which an ovum passes from an ovary.

Uterus

A thick, muscular organ in which a fetus develops.

Endometrium

A membrane that lines the womb.

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External structures: outside the Cervix On the external side, the female reproductive system consists of tissues arising from the same embryonic layers as the male penis and scrotum. The vulva are external female genital structures: the clitoris and labia surround the opening of the vagina, or birth canal. The cli- toris is a site of external female stimulation. Just inside, the vagina receives semen to begin a sperm’s journey through the female reproductive tract. The lowest portion of the uterus, separating it from the vagina, is the circular opening called the cervix (Figure 16.22).

Vagina

A muscular tube leading from the outside to the cervix of the uterus in female mammals.

Clitoris

A site of external female stimulation.

Suspensory ligament of ovary

Fimbria

Ovary

Ovarian ligament

Round ligament Cervix

Vagina

Uterus

Ovary

Developing follicles

Newly discharged ovum (egg)

EggCorpus luteum

Fallopian tube Fundus of uterus

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Figure 16.21 Female Reproductive Structures. An egg moves from the ovaries through the fallopian tube and when fertilized, it finds a home in the uterus.

Labia minora

Clitoris

Labia majora

Anus

Urethral opening

Vestibule

Vaginal entrance

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Figure 16.22 External Female Anatomy. The external labia surround the vaginal opening. The clitoris is an excitatory center in sexual foreplay.

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hormones of Female Reproduction Hormones dictate the timing and development of eggs within the ovaries (Figure 16.23). Each month, at approximately 28-day intervals, ovulation occurs. This process is known as the ovarian cycle. In order to ready the reproductive system for a pregnancy, a men- strual cycle takes place as well. Hormones also prepare the uterus for an embryo’s

Ovarian cycle

The monthly cycle by which eggs are developed and released from the ovary between puberty and menopause.

1Days 3 5 7 9 11 13 15

OvulationFollicular phase

Levels of reproductive hormones from the anterior pituitary gland

Ovarian hormone levels

Uterine cycle

Menstrual flow

Menstrual phase Proliterative phase Secretory phase

Ovarian cycle

Primary follicle

Secondary follicle

Mature follicle

Ovulation Corpus luteum forms

Regression Corpus albicans

Luteal phase

17 19 21 23 25 27 1

1Days

FSH

Progesterone

Estrogen

3 5 7 9 11 13 15 17 19 21 23 25 27 1

1Days 3 5 7 9 11 13 15 17 19 21 23 25 27 1

1Days

Functional layer

Basal layer

3 5 7 9 11 13 15 17 19 21 23 25 27 1

Ovulation

ycleUterine cy

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Figure 16.23 Hormones and Events of the Ovarian and Menstrual Cycles. Estrogen and progesterone prepare the uterus for egg implantation. LH (luteinizing hormone) and FSH (follicle-stimulating hormone) stimulate the follicles in ovaries to development.

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implantation during the menstrual cycle. In our story, chronicling Mrs. Eddy’s preg- nancy, “the catamenial secretion . . . ” described refers to menses or menstruation. This process takes place in regular intervals, but ceases during pregnancy:

1) Menstruation. When bleeding first appears, the endometrial linings are shed in what has traditionally been called a “period” or menstruation. Menstrua- tion lasts between 3 and 5 days. At the end of menstruation, levels of estrogen decrease. Low amounts of estrogen cause the pituitary gland to release folli- cle-stimulating hormone (FSH). FSH as the name indicates develops eggs in their follicles.

2) Proliferation. Follicles produce estrogen once again, which develops the uterine wall. The uterus grows and develops during the proliferation phase, just before pregnancy occurs. The endometrium thickens and increases in its blood supply. In this phase, the egg travels to the uterus and when fertilized, it is ready to implant.

3) Ovulation. About half way through the menstrual cycle (14 days), high levels of estrogen stimulate the pituitary to release a spike of luteinizing hormone (LH) into the bloodstream. This sharp rise causes the bursting of a follicle and its release of an egg in ovulation. Just after ovulation, the corpus luteum fills with fluid and secretes estrogen and progesterone, both of which thicken the endome- trium. This readies the uterus for another implantation by an embryo.

If pregnancy occurs, a hormone human chorionic gonadotropin (hCG) prevents the breakdown of the corpus luteum. This allows the continued release of estrogen and pro- gesterone. Both hormones maintain the endometrium enabling implantation and preg- nancy. The cycling of menses stops to allow development of an embryo.

However, if pregnancy does not occur, the corpus luteum continues to emit its hor- mones for about 12 days. This prevents another follicle from developing so that two eggs are not moving through the tract at any one time. When the corpus luteum does finally break down, there is a decline in the amount of estrogen. The endometrial lining then sheds and menstruation once again occurs. Also, the pituitary again secretes FSH and LH, stimulating another ovulation, starting the process over.

Menarche and Menopause Reproductive cycling continues from menarche, the age at first menstruation during puberty, until menopause at which time ovulation and menstruation cease. Menopause usually occurs between ages 45 and 55 but there is no exact moment. The onset of menopause is related to the number of viable eggs remaining in the ovaries. Of course, estrogen levels drop in postmenopausal women. Humans are the only species to lose their fertility at a time in their lives. It is likely a result of our longevity that has made this an event – our life expectancy throughout most of human history was well below 40 years of age!

Menarche is taking place at younger ages in our society. In the early 1900s, men- arche was on average at age 15–16, but more recent studies indicate average ages reach- ing 11 and 13 years of age. The graph in Figure 16.24 shows the changing ages at first menarche from the mid-1800s to 2000 in France. U.S. data parallel those found in France. The causes are likely many-fold: changes in diet, easier access to foods, increased intakes of artificial hormones in milk, for example. However, the exact cause is unknown. Additionally, the longer estrogen is in the system, the greater the risks for reproductive cancers and even heart disease. Early menarche may be a health problem in the longer term.

menstrual cycle

The process of ovulation in women and other female primates.

menstruation

Discharge of blood from the uterus.

Proliferation

Rapid growth of cells by producing new parts.

menarche

Beginning of menstruation.

menopause

The time when ovulation and menstruation cease.

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What happens after an Egg Meets sperm? Fertilization

With between 150 and 350 million sperm in the vagina, only about 100 sperm will sur- vive their travels to the oviduct, where eggs are fertilized. It takes about 30 minutes to make it to the site of fertilization. Only one sperm is able to successfully penetrate an egg cell. A layer of proteins called the zona pellucida surrounds and protects the egg.

As the sperm approaches the egg, calcium ions are released from the zona pellucida, which increase sperm speed. They become even more competitive, riled up by the cal- cium in what is termed sperm activation. This ensures that the competition is fierce and that the best or most powerful sperm wins. Sperm compete in several ways, for example by producing a mate plug to prevent other males from penetration of a female after he has had intercourse with her.

The acrosome of the successful sperm’s head fuses with the egg’s protein layers surrounding the egg. When the acrosome’s enzyme contents are released, they digest through the protein layer. This opens a channel pathway through which the sperm travels to enter into the egg. When this occurs, it stimulates changes in the coat surrounding the egg to prevent a second sperm penetration (Figure 16.25).

Once within the egg, a sperm disintegrates except for its nucleus. The sperm’s entrance into the egg causes the final step in meiosis for the egg. The egg divides once again in Meiosis II to become a mature egg, an ovum and releases from it a second polar body. When the haploid sperm nucleus fuses with the egg’s nucleus, a new diploid cell is produced, the zygote.

Embryology A zygote looks as close to a human as a football. How does this spherical ball become a specialized human being? The study of the embryo and the stages it undergoes is known as embryology.

The first step in embryology is mitosis, called cleavage. The more cells a zygote has, the less likely it is to die if something goes wrong in any one of them. Thus, very rapidly after fertilization, in about 30 hours, a zygote undergoes cleavage. As the zygote develops, it divides mitotically, over and over to create a ball of cells as shown in

Zona pellucida

A layer of proteins that surrounds and protects the ovum.

Sperm activation

The process by which sperm are additionally mobilized by calcium and even more able to fertilize the egg.

Ovum

A mature egg.

Zygote

A diploid cell that is produced when the haploid sperm nucleus fuses with the egg’s haploid nucleus.

Embryology

The study of the embryo and the stages it undergoes.

Cleavage

Division of cells in the early embryo stage.

1820 12

A ge

( in

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rs )

1840 1860 1880 1990 1920 19601940 1980 2000

Years

12,6 years

Mean Age at First Menstruation in France 1820–2000

Data used by ducros 1978 ACSJ Survey 1994 Linear ducros model

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Figure 16.24 Graph of Age at First Menarche and Year Since 1820 in France.

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Figure 16.25 Sperm Enters the Female Egg by Burrowing in through Protective Lay- ers. Sperm contacts, penetrates, and fuses its genetic material with an egg’s nucleus. Millions of sperm attempt to fertilize one egg. It is an intense competition.

Figure 16.26. First 2, then 4, then 8 cells divide to become a morula, or a solid ball of cells that resemble a raspberry. During cleavage and the forming of a morula, there is a great increase in the number of cells but not the overall size. Its energy is placed into mitosis and not growth.

After the sixth day of continual mitosis, a morula forms a hollow cavity that con- tains a mass of cells about 1,000 in number. The newly formed structure is called a blastula. The blastula’s inner cells are called its inner cell mass. The inner cell mass

morula

A solid ball of cells formed by cleavage of a fertilized ovum.

Blastula

A hollow ball of cells at the early stage of development. Inner cell mass

Inner cells of the blastula.(a) Zygote

(fertilized egg)

Ovulation

Uterus

Uterine tube

Fertilization

(b) Early cleavage 4-cell stage

many cells, morula

(d) Early blastocyst

Blastocyst cavity

(e) Late blastocyst (implanting)

Endometrium

Secondary oocyte

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Figure 16.26 Cleavage in a Zygote. Cell division forms a ball of cells, the morula after only 4 days from fertilization.

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eventually develops into the embryo and then into a human being. The outer 1,000 cells become structures that support the embryo: the amnion, which is the fluid sac that protects a fetus; a chorion, which nourishes the fetus and becomes a part of its placenta.

In the next phase of development, gastrulation results in the formation of three dis- tinct germ layers (Figure 16.27). When cells of the blastula migrate inward, they form three germ layers. Each layer is specialized to become a different part of the body. The ectoderm is the outer layer of the gastrula, which develops into the skin and nervous system. The mesoderm is the middle layer and develops into the muscles and skeleton. The inner layer, the endoderm, becomes the lining of the digestive and respiratory tracts, along with associated organs: the liver and pancreas. The entire mass of cells, along with their germ layers, is defined as the gastrula.

During the third week, neural tube development occurs, with nerves running along the backside of the embryo. They form a notochord, which is a flexible rod of nerve tissue that develops in all chordates (described in Chapter 10). The ectoderm folds to become our brain and spinal cord in a process known as neurulation.

stages of pregnancy A normal pregnancy lasts 40 weeks and is divided roughly into three parts called trimesters. The process of development in the womb is termed gestation. Each trimes- ter of gestation is characterized by different changes (Figure 16.28). During the first 8 weeks, when the zygote is implanted in the uterus, it is called an embryo. After this point, organs and other major structures form, demarcating a point of higher develop- ment. The embryo after 8 weeks is then called a fetus.

First Trimester

In the first 6–7 days, the embryo still travels to the uterus and implants only on the seventh day. In the second week, gastrulation occurs, forming the three germ layers. Organs begin to form after gastrulation. A heart beats after the third week of gestation, and at the end of the fourth week, pharyngeal arches form in the embryo. These will later become the pharynx, larynx, and features of the face and neck. By the fourth week, all of the major organs, including the eyes and heart, are formed. In the second month, arms and legs develop, along with organs such as the liver, gall bladder, and pancreas. However, very little growth in mass occurs, with the embryo still weighing only about 1 g. In the third month, the embryo’s nervous system develops. This allows it to have reflexes and responses to stimuli, including suckling. A mother’s ability to make milk also begins simultaneously. Her mammary glands are stimulated to ready for milk production.

Second Trimester

During the second trimester, 3 months of growth occur, adding mass to the developing fetus. Muscles and bone enlarge and a fetus may kick in this time. Its size increases from only 1 to 600 g (1.3 pounds). There is less specialization in months 4, 5, and 6 and a focus is increasingly on growth. A fetus still cannot survive outside of the womb in this period.

Amnion

The fluid sac that protects a fetus. Chorion

Fetal membrane that nourishes the fetus and becomes a part of its placenta. Gastrulation

A developmental stage in which three distinct germ layers are formed. Ectoderm

Outer layer of the gastrula, which develops into the skin and nervous system.

Endoderm

Inner layer of gastrula forming the digestive and respiratory tracts.

mesoderm

The middle layer of gastrula that develops into the body’s organs and muscles.

Gastrula

The entire mass of cells in an embryo developing after the blastula stage.

Notochord

A flexible rod of nerve tissue that develops in all chordates. Neurulation

The process by which the ectoderm folds to become the brain and spinal cord. trimester

A normal pregnancy divided roughly into three parts. Gestation

The process of development in the womb.

Embryo

An unborn offspring in the early stages of development.

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(a)

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Figure 16.27 Early Embryo Development. Getting to gastrulation through inward migration of cells and specialization into three germ layers, the ectoderm, mesoderm, and endoderm.

(a) (b)

Figure 16.28 Later Stages of Human Development. a. 6-week-old human embryo (2.5 cm), 1 inch long. b. 16-week-old human fetus (15 cm), 6 inches long. Lennart Nils- son/Bonnier Alba AB./A Child is Born, Dell Publishing Group.

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Third Trimester

Size increases markedly during the third trimester and a fetus’s weight increases from 1.3 pounds to an average of 7.1 pounds at the ninth month. After 24 weeks, modern technology can keep babies alive, but preterm births have risks associated. The earliest preterm baby kept alive was after only 21 weeks gestation, but this is an anomaly. Birth defects and trouble breathing (especially before 34 weeks, when certain lung cells are matured) are at higher risk for premature infants. Premature births should be avoided but do account for about 10% of all live births.

Birth and after Contractions and dilation of the cervix begin normal birth processes, also known as par- turition. Hormones, such as prostaglandins and oxytocin, stimulate uterine contractions. These movements cause the cervix to open and allow the fetus space. The contractions are known as labor. The baby is delivered when the cervix is dilated large enough, usu- ally about 10 cm in width. Widening of the cervix is accompanied by effacement, which is a thinning of the tissues surrounding the cervix.

When contractions increase to every 2 or 3 minutes, birth usually occurs. Delivery happens when the baby’s head passes through the vagina. The umbilical cord is cut and clamped, and the baby is induced to breathe on its own. After the birth, a brief relaxation

Parturition

The contractions and dilation of the cervix during child birth.

Labor

The opening of the cervix and uterus contractions leading to the birth of the baby.

d a

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Figure 16.29 Phases of Birth: Stage 1: Stage 2: Birth, and Stage 3: After-birth.

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Chapter 16: Urogenital Functions in Maintaining Continuity 637

period is followed by smaller contractions that propel the placenta out of the uterus. This is commonly called the after-birth. The phases of birth are shown in Figure 16.29.

When a baby begins suckling on its mother’s breasts, the effect is to stimulate milk production, or lactation. Suckling causes prolactin to be released from the pituitary gland and induces mammary cells to make milk, in the process called lactation. This is one of the few examples when one organism (a baby) causes the production of hormones in another organism (the mother). The positive feedback mechanism for lactation comes from mammary glands shown in Figure 16.30.

In the first few days, a yellowish fluid called colostrum is released. Colostrum is high in proteins and antibodies, which helps develop an infant’s immune system in its early days. Colostrum slowly dissipates over the first week and milk production increases. Milk is high in fat and energy, giving needed nutrients to newborns.

Lactation decreases a woman’s chances at fertility (though not completely) because suckling prevents LH from being released by the pituitary. LH plays a role in ovulation, without which there is no future pregnancy. This period of infertility lasts only about 6 months and is called “lactational amenorrhea.” Nursing is highly recommended by the American Medical Association (AMA) as a natural way to give both immunity and nutrients to newborns during their first year of life. Recent studies report fewer infec- tions and better cognitive skills among children who were nursed compared to bottle-fed at critical points in their development. There is debate on how long and where to breast- feed, but its value is supported by the research.

After-birth

A brief relaxation period followed by smaller contractions that propel the placenta out of the uterus after child birth.

Lactation

Formation of milk by mammary glands.

Suspensory ligament

Lobe

Areola

Nipple

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Figure 16.30 Mammary Gland Milk Production and Suckling. Note that the mecha- nism is an example of positive feedback control. There is hormonal–nerve communica- tion between the hypothalamus, oxytocin, and nerves in the nipples.

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SHOULD GRANDDAD StOP BEING SCREENED FOR PROS- tAtE CANCER?

The AMA now recommends that screening for prostate cancer only prevents one death for every 1,000 men screened over 75 years of age. The AMA based its decision on a meta-analysis (grouping of studies) which shows no statistical significance in survival rates between those screened and those unscreened for prostate cancer after 75 years of age. The medical community cites side effects from false positives and cancer treatments as linked to prostate testing. Therefore, screening men after 75 is no longer recommended.

Thus, the elderly men you may know, some in your own family, are being told by their doctors to stop screening for prostate cancer. However, sup- pose you have prostate cancer and early detection could make you the person whose life the test saves? Is a healthy 75-year-old ready to die, doing nothing about his risks? Foregoing screening after certain ages is still controversial.

The test to screen for prostate cancer is called a prostate-specific antigen (PSA) test. It measures the amount of proteins given off by prostate cancer cells. Consistent levels above 2.5–4.0 generally call for a cancer screening called a biopsy. In a biopsy, cells from the prostate are taken and analyzed under the microscope for cancer. This test should be done along with a digital examina- tion to check if the prostate is rough or smooth in morphology. If it is rough, it is more likely to be cancerous. Many factors such as symptoms – pain – and a person’s family history are considered in determining risks.

Also, perhaps symptoms, patient family history, and other factors should be considered before simply not testing people after 75. Many people are healthy at after age 75. This is probably a reason many men still insist on get- ting tested, regardless of medical advice. Screening catches cancers early and prevents some deaths; but should one go against the doctor’s advice?

Malfunctions of the Reproduction system

Male Cancers Prostate Cancer

Reproductive cancers in men are major killers, with prostate cancer the second leading cause of cancer deaths in men, second only to lung cancer. About 1 in 36 men will die from prostate cancer, but it is a very common disease. If a man lives long enough, his chances of getting prostate cancer is 100%! However, most men die with prostate cancer not because of prostate cancer. This is because most prostate cancers metastasize very slowly. Thus, there is controversy on determining how aggressive prostate cancer treat- ments should be and at what ages screenings should be ceased.

Testicular Cancer

A reproductive cancer of young adults occurs as testicular cancer. It is the most com- mon cancer in young men ages 17–34. It presents as a lump or swelling and may or may not be painful. Many forms are aggressive and travel through the pelvic region to stage

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IV cancer within months. Thus, monthly self-screening is recommended to check for changes occurring on the testicles. Early detection is the key to survival of testicular cancer, like most other cancers.

Penile Cancer

Penile cancer is relatively rare but is associated with not being circumcised. Its incidence is less than 0.01%, but it can be deadly. There is controversy regarding circumcision or the removal of foreskin from the penis. Although uncircumcised males have greater chances of contracting venereal diseases, there are low risks associated with circum- cision as a surgical technique. In one recent case, an infection from instruments used during circumcision, lead to an infant’s death.

inflammations in Male organs A common ailment of athletes is a result of physical trauma to the external male anatomy. In sports, testicles are sometimes twisted, resulting in a swelling. Orchitis is the swelling of the testicles and scrotal sac. Its severity depends upon the damage to the testes. Some- times, the testes are twisted and blood supply is cut off, requiring surgery. Usually, testes can be manipulated to resupply the testes with blood. When the epididymis is inflamed, either due to physical trauma or due to a microbe causing venereal disease such as chla- mydia, it is called epididymitis. It may damage the epididymis to cause infertility in males.

infertility Some of the diseases described result in infertility, or an inability to conceive a child after one year. Infertility affects about 10% of couples. Its causes are evenly split between malfunctions of male and female reproductive systems. There are numerous effective treatments for infertility.

A low amount of semen does not indicate infertility. Fertility is determined by sperm health in males and reproductive health in females. Infertility in males occurs when sperm are abnormal or low in numbers to prevent pregnancy. Male infertility is often a result of physical trauma, hormonal deficiencies, or scarring of tissues along repro- ductive linings. Sometimes damage occurs in males and females as a result of sexually transmitted diseases. Microbes such as the herpes virus or chlamydia bacteria cause damage in reproductive structures.

Assisted reproductive technology to improve fertility is used widely. They include a variety of techniques, but the most common form is in vitro fertilization (IVF) (Figure 16.31). In IVF, female eggs are collected and combined with sperm in a petri dish. The resulting zygote (or fertilized egg, as you recall from other chapters) develops into an eight-cell stage embryo and is then inserted into the female’s uterus. The zygote implants into the uterine wall, allowing development to occur.

Other techniques allow for sex selection by sorting sperm for those containing Y chromosomes and then carrying out in vitro fertilization. This method is called sperm sorting and uses a florescent dye, which latches onto DNA in sperm. Because X chro- mosomes are about 3% larger than Y chromosomes, each sperm type is separated using a small electric shock. The success rate for sperm sorting is about 70%–90%.

To achieve 100% success rates to obtain the desired sex of a child, pre-implanta- tion genetic diagnosis (PGD) is used. In this procedure, females are given hormones to develop their eggs. Their eggs are then surgically removed and used in IVF to produce several embryos. A single cell from each embryo is removed and their chromosomes are analyzed to determine sex. The desired XX or XY embryo is then placed into the

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Figure 16.31 In Vitro Fertilization (IVF) Involves Several Steps, from Egg Removal to Fertilization and Zygotes Growth to Implantation in a Uterus. IVF helps thousands of couples conceive despite infertility.

mother’s uterus. PGD (cost of $12,000) is more invasive and costly than sperm sorting (cost of $1,500), but chances are far greater of obtaining the desired sex of a child.

Contraception Of course, the opposite of infertility is the desire to prevent pregnancy. There are a number of contraception methods, which either prevent ovulation, fertilization, or implantation. Birth control pills work by interfering with ovulation. The pills contain estrogen and pro- gesterone, which prevent FSH and LH from stimulating follicles and ovulation. Because eggs are not released, pregnancy is prevented. Condoms, a diaphragm, and abstinence pre- vent fertilization. Each as varying degrees of success, but abstinence is 100% if used. Con- doms come in at 89-99% when used correctly. Some devices may be implanted into the uterus, preventing implantation. The intrauterine device (IUD) is inserted into the uterus by a doctor and has 99% effectiveness. However, there have been multiple cases of infec- tion and discomfort in IUD use.See Table 16.1 for an overview of birth control methods.

Female Cancers Women’s cancers are very common, in part because of the continual new production of cells during reproductive processes. As shown in previous sections, these cycles require hormones, secretions, and new cells to be produced continually. When mitosis occurs at

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table 16.1 Methods of contraception and their efficacy.

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high rates, its chances for error also increase. In female processes, errors in cell division result in types of cancers.

The most common form of cancer in females is breast cancer. It affects one in nine women and begins as a lump or swelling in the mammary regions. The survival rate from breast cancer, if detected early, is over 90%. However, it requires regular mammograms to screen for abnormal growths. Ovarian cancer is abnormal growth in the ovaries, a deadly cancer because it is often not caught early. It symptoms include bloating and abdominal discomfort, but it is difficult to detect. As a result, ovarian cancer has a sur- vival rate of only 40% after five years.

There is a high genetic link to both breast and ovarian cancer. The BRCA 1 and BRCA 2 genes are strongly associated with these cancers. Angelina Jolie underwent a controversial procedure after finding out that she tested positive for both genes, giving her an 89% chance of getting breast cancer. She elected to have both breasts removed in a double mastectomy. This improves her chances to over 95% of not getting the cancer. It is controversial because surgery has risks and financial costs. Indeed, some health insur- ance companies will not pay for the pre-emptive surgery had by Ms. Jolie (Figure 16.32).

The debate about pre-emptive surgery and early screening for breast and ovarian cancer continues to make headlines. The U.S. Preventive Services Task Force, as well as the American Cancer Society, recently announced that screening for the BRCA genes is not recommended and may lead to false positives and undue stress. It asks doctors to not request screening of women unless the patient has a family history of reproductive cancers.

From our knowledge of genetics and pedigrees, consider that many cancers are recessive in origin and skip generations. Also, pedigrees are quite incomplete for most of us. Do we really know what great aunt Bertha died from in 1936? Because one in three people will die from a cancer-related illness, cancer is probably in everyone’s fam- ily; not just some people’s.

The CA-125 blood test specifically screens for ovarian cancer. Its use has also been placed into question, when in study of over 78,000 women screening was shown not to help survival from the disease. In addition, about 10% had false positives resulting

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Figure 16.32 Angelina Jolie Was Predisposed to Cancer, Harboring the Mutated BRCA Genes. She had a mastectomy to decrease her risks of breast cancer. This pre-emptive surgery is elective and debated.

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in unnecessary ovary removal. However, when used with other methods of screening, fewer errors are likely to be made. A trans-vaginal ultrasound for example detects more ovarian cancer correctly. Thus, I recommend the CA-125 and BRCA gene tests be con- sidered by all women after age 40.

summary The urinary and reproductive systems reside within the same pelvic region in close prox- imity, together referred to as the urogenital system. The two systems separately accom- plish their goals: the reproductive system produces new offspring and the urinary system conserves water and removes wastes. The nephron is the functional unit of the kidney, a human’s main organ of excretion. It concentrates urine as it flows through, removing wastes and selectively bringing back needed solutes and water into the body. Reproduc- tion may be sexual or asexual, externally or internally fertilized, each method with pros and cons. As sperm move through the reproductive tract, fluids are added to form semen, which is injected into females during copulation. Reproductive diseases include cancers, inflammation, sexually transmitted diseases, and infertility.

ChECk oUt

summary: key points

• Medical technology advanced, along with society, to help newborns and pregnancy; but it has also led to ethical challenges when deciding about fetal health.

• Excretion eliminates wastes while conserving water and other needed solutes and cells. • Urinalysis is used to detect disease as well as illegal drugs. • Sexual reproduction and internal fertilization, used by humans, leads to fewer but more genetically

diverse offspring than asexual and external reproduction. • Sperm move from the testes and epididymis through the vas deferens and into the female reproduc-

tive tract during copulation. • Diseases of reproduction include a number of cancers, inflammation, sexually transmitted diseases,

and infertility.

acrosome aldosterone after-birth amnion amplexus angiotensin II antidiuretic hormone (ADH) blastula Bowman’s capsule budding

bulbourethral gland chorion cleavage clitoris collecting duct copulation corpus luteum dialysis, hemo-, peritoneal-, ectoderm embryo

KEy tERmS

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embryology endoderm endometrium epididymis excretion fertilization, -internal, -external, filtration follicle fragmentation gastrula gastrulation genetic variation gestation glomerulus impaired kidney function inner cell mass interstitial cells kidney kidney failure labor lactation Loop of Henle menarche menopause menstrual cycle menstruation mesoderm morula nephron neurulation notochord oogenesis osmoregulation ovarian cycle ovary

oviduct (fallopian tube) ovulation ovum parturition parthenogenesis penis proliferation prostate gland reabsorption renal capsule renal cortex renal medulla renal pelvis reproduction, sexual-, asexual-, reproductive system scrotum semen secretion seminal vesicle seminiferous tubules sperm activation spermatogenesis testes trimester urinalysis urinary bladder urinary system ureter urethra urogenital system uterus vagina zona pellucida zygote

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KMultiple Choice Questions

Reflection questions:

1. Ectopic pregnancies are treated differently today than 150 years ago because: a. new technologies are able to identify ectopic pregnancies b. surgery is now available to remove ectopic pregnancies c. termination of dangerous pregnancies are now acceptable in society d. all of the above

2. Which is NOT a function of the kidneys? a. pH regulation of the blood b. activation of vitamin D by calcium absorption c. removal of nitrogen containing compounds d. body temperature regulation

3. Which process occurs in the glomerulus? a. filtration b. secretion c. reabsorption d. activation

4. Trace the movement of urine from its production to end. Which is correct? a. kidney to bladder to ureter b. ureter to bladder to urethra c. glomerulus to ureter to renal pelvis d. renal pyramid to urethra to bladder

5. Which should NOT be found in normal urine? a. white blood cells b. sodium ions c. potassium ions d. water

6. Which represents a logical order, from production to ejaculation, of a sperm’s move- ment through the male reproductive tract? a. epididymis ➔ vas deferens ➔ testes ➔ urethra b. testes ➔ vas deferens ➔ epididymis ➔ urethra c. testes ➔ epididymis ➔ vas deferens ➔ urethra d. urethra ➔ vas deferens ➔ epididymis ➔ testes

7. A mother gives birth but afterwards another set of contractions occurs, leading to: a. abnormal growth removal b. after birth of the placenta c. umbilical cord severing d. birth of the uterus

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8. In which structure do sperm mature and become motile? a. epididymis b. testes c. vas deferens d. urethra

9. Which correctly MATCHES an organism’s method of reproduction with its characteristic? a. internal fertilization – many offspring b. asexual reproduction – many offspring c. external fertilization – few gametes d. sexual reproduction – few gametes

10. All of the following is true about breast cancer EXCEPT: a. it is the leading cause of female cancer deaths b. it is linked to genetics c. it is treatable best at early stages d. it does not spread past mammary tissues

short answer

1. Pregnancy occurs in three trimesters. Discuss changes in the fetus and mother during these three trimesters. Name one medical technique used today (and unavailable a century ago) that aids pregnancy.

2. Define the following terms: oviduct and vas deferens. List one way each of the terms differ from each other in relation to their (1) function; (2) role in transport of gametes; and (3) relationship with each other in reproductive anatomy.

3. List the three germ layers of an embryo and identify the tissues that they will become. In which phase of embryology are the germ layers found?

4. Draw a sketch of the nephron using arrows to show the role of ions and water in excretion. How does excretion occur in the nephron of kidneys? Be sure to include the three steps of excretion in your discussion.

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5. In kidney impairment, what three processes are measured to determine the extent of kidney disease? What substances might be found in the urine that indicates kidney disease?

6. List the three hormones that control urine formation in the kidneys. Describe how alcohol affects kidney function. Connect kidney function with these hormones in your answer.

7. Explain the role of hormones during the ovarian cycle in females. What is the func- tion of ovulation?

8. For question #7, explain how the menstrual cycle works in tandem with female hormones?

9. Describe the benefits of external fertilization to frogs and other land animals. What are its drawbacks?

10. Describe the symptoms of ovarian cancer. How may the disease be screened? What is the latest research about screening? What are the survival rates for ovarian cancer compared with breast cancer?

Biology and society Corner: Discussion Questions 1. Androgen insensitivity syndrome (AIS) is a disorder in which androgens (male

sex hormones) are dysfunctional in males. Although sufferers are genetically male (XY), they appear as females with external genitalia and undescended testes.

Maria Patino, a former Olympic athlete was found to have AIS. Maria considered herself a woman and the news of having AIS was a shock. She was banned from female competition due to her condition. Research AIS and this case: Was the deci- sion by the Olympics committee justified? Why or why not? Did her condition give her unfair advantage over other women in her competition?

2. Suppose you have a long lost uncle, who has died and will leave you his fortune of 3.5 million dollars. There is one catch – you must have a son within two years. You cannot have a daughter. The uncle was oddly eccentric.

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Would you (and your partner) consider using sex selection techniques described in this chapter to conceive a boy? Defend your answer.

If you answered yes, which technique would you use, sperm selection or PGD (pre-implantation genetic diagnosis)?

3. Would you donate your kidney to your ______ if you had an acceptable MHC match? What factors influenced your decision? a. brother b. father c. mother d. friend e. stranger

4. The 1,500 prenatal tests being developed will soon come to the market. It will tell expecting parents about many aspects of the health of their fetus. Would you con- sider termination of a pregnancy if you find it is likely to be born: a) and suffer from spinal muscular atrophy and die within nine months of birth; b) and have cystic fibrosis, expected to suffer lung problems and die by age 20; c) and have Huntington’s disease, in which the person is healthy until age 40 and

then suffers progressive muscular weakness and dies by age 50.

*Many younger readers draw the line against termination here because they think at 40, one has lived a full life already!

d) will get Alzheimer’s disease at age 60 or suffer manic depression its whole life. e) will have dwarfism f ) no termination is acceptable

5. Workforce screenings use urinalysis to test for drugs in their employees. Should drug testing be allowed under the law or is it a violation of privacy? What about for certain jobs? Which jobs, if any or all, would you suggest for mandatory drug testing?

Figure – Concept Map of Chapter 16 Big Ideas

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649

Unit 5 A Small Hole Sinks a Big Ship –

Our Fragile Ecosystem

CHAptEr 17 population Dynamics and Communities that Form

CHAptEr 18 Ecosystems and Biomes

CHAptEr 19 Biosphere: Life Links to Earth

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population Dynamics and Communities that Form

Cheryl is a model

The cane toad (Bufo marinus) has taken over large parts of Australia’s ecosystems. It is considered an invasive species

Cane toads copylating. Toad sex is external and the male mounts the female

Toads are everywhere, as an invasive species that has a high rate of reproduction because they lack natural predators to keep their population numbers in check

Her prince has arrived!

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the Case of the terrible toads Plop, Plop – into her drink! “What just fell into my drink?!” Cheryl called out. Cheryl, the partier did not like toads or frogs or anything slimy or warty. Cheryl was a model, tall with flowing blonde hair; and as such, she had no use for amphibians. She left the United States last night for a great holiday get away to an island off the coast of Australia.

“How sheik,” Cheryl mused as her plane landed. On her vacation, Cheryl expected a beach hotel with hot days in the sand and hotter parties at night. At the airport, the taxi driver picked her up, quickly asking her, “Do you want to go out with me tonight?” Cheryl replied coldly, “I am sorry. I am here to meet my prince.” The driver was disap- pointed. However, Cheryl had an agenda. She hoped to meet celebrities on the island and start her acting career, now that she finished her days at the university. This trip was her emancipation from school.

As they drove in from the airport, down through the desert, and to the beach, Cheryl noticed a strange sight along the beautiful beachfront – there were warty creatures. They were hanging from the trees, jumping all over the roads, and hopping in unison like dense mats.

The road could no longer be seen and the driver simply ran the animals over, unfazed by their presence. Cheryl was aghast, asking the driver: “Driver, what are these things?” “The cane toad, of course, and they are here to stay.” he replied serenely. Cheryl demanded to him, “Turn back, we are leaving this place!” However, it was too late; the plane had gone and would not be back to the island for one week.

Cheryl did not do her homework about the island or cane toads before booking her trip. The cane toad had been introduced to Australia in 1935, with the hope that it would prey on the destructive cane beetles. About 3,000 cane toads were released into the wild. The experiment was, however, a failure in controlling the beetle populations.

Instead, the cane toad became a much larger problem. Within a few years, millions of cane toads swarmed Australia and continue today to be a pest organism. There are 200 million cane toads in Australia, and the government has identified it as a key threat to the environment and other organisms.

CHECk in

From reading this chapter, you will be able to:

• Explain how invasive species and changes in their populations affect human society and the environment.

• Describe the characteristics of populations, its demographics, and how populations are studied. • Define and describe invasive species, ecology, population ecology, logistic model of growth, expo-

nential model of growth, carrying capacity, fertility rate, age structure diagram, survivorship curve, ecological footprint, density-dependent factor, density-independent factor, niche, habitat, resource partitioning, biotic factor, abiotic factor, predation, herbivory, parasitism, commensalism, mutualism, and competition.

• Apply models of population growth in human and nonhuman populations. • Compare the two types of life histories and apply them to real examples using survivorship curves. • Describe the roles organisms play within their community. • List the types of population interactions within a community and give real examples.

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Cane toads, scientifically named Bufo marinus, appear ugly to many, including Cheryl. They are large, chubby, and have dry, warty skin. They breed easily, having fre- quent copulation. B. marinus is also toxic, affecting the heart muscle of those organisms that consume it, including humans. Cane toads cause the death of many types of native species to Australia. Many pets, cats and dogs especially, eat the toad and die from its venom. Cane toad venom is secreted as a milky liquid from its parotid salivary glands located over its shoulders.

Bufo marinus has no natural predators to keep their population in check. They are native species in South America and the Southern United States, but their natural predators keep their numbers manageable in those areas. Those organisms eaten by cane toads are also being depleted, such as a number of insects. Species consuming those insects are also endangered, with little food remaining after the toads enter into an area. Thus, interactions between the different organisms in Australia have been shifted out of balance. The cane toad is therefore a dangerous invasive species to Australia.

Cheryl saw (and was touched by) things from the sky, from the ground, and from the water. All over, the toad creatures rubbed up against her in ways she had never seen before. The cane toad became, very quickly, Cheryl’s worst nightmare.

That evening, the driver met Cheryl in the local bar. Cheryl sat with her drink, a cane toad and the driver at a table. Cheryl looked at the driver, the toad looked at Cheryl, and the driver looked at the toad. Cheryl looked angry. The driver addressed Cheryl the best way he could: “Here’s your Prince. Pucker up, Cheryl…”

CHECk Up SECtiOn

The cane toad in the story is considered an invasive species, which is any species not native to a region but grows rapidly due to lack of natural predators or parasites to keep them in check.

Over 4,500 invasive species have invaded the United States. Research the types of invasive species impacting the area in which you live or study. Be sure to describe the history of how the invasive species entered into the area and the techniques of eradicating the invasive species.

What changes have occurred in (a) society and (b) in the environment; as a result of the invasive species? How does it differ from organisms native to the region?

Ecology is based on Studying populations Order in a population In our story, invasive cane toads impact the environment and other organisms. They appear as a nuisance and repulse Cheryl on her vacation. However, their biological impacts on the island might be a bit more complex than just a mere bother to Cheryl.

How much land area will B. marinus take over? What can be done to slow its pop- ulation growth? What organisms are eaten by the cane toad? How will the toads impact other species, such as freshwater turtles and crocodiles? All of these questions are answered through ecology, the study of the interactions between organisms and their environments. The term ecology derives from the Greek words “oikos,” which means home and “logos,” which is translated into “the study of.” Together, ecology means the study of our home on this Earth.

Ecology

The study of the interactions between organisms and their environments.

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This unit studies nature and the environment and is divided into three chapters. In this chapter, we will explore how biology occurs within populations. The environment is orga- nized into different groupings (Figure 17.1). A population is a group of organisms of the same species living in an area. A population of organisms, such as B. marinus, for exam- ple, grows and is structured in ways that are studied by ecologists. In the latter part of this chapter, the community (aka biocenoses) is studied. A community is a set of populations interacting with each other.

In Chapter 18, we will study how the environment interacts with those communities, in a grouping called an ecosystem. All of the Earth’s ecosystems are collectively known as the biosphere, which will be the focus of Chapter 19, the last chapter in this unit. The components of the biosphere as well as threats to its health will be explored. Figure 17.1 shows the hierarchy of environmental organization from population, community, and ecosystem to biosphere.

Ecology is based on the dynamics of populations – a population is the basic unit of study in ecology. The ways a group of species grows, shrinks, and breeds, for example, show the dynamics occurring within a population.

Ecosystem

The interaction of the environment with a community of organisms.

Biosphere

All of the Earth’s ecosystems.

Figure 17.1 Hierarchy of environmental organization: individual, population, community, ecosystem, and biosphere of organisms such as the cane toad. The toad’s role within each of these organizations should be studied to help combat its invasiveness.

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Population

Organisms of the same species inhabiting a specific area.

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Population ecology studies a population of organisms and how it interacts with its environment. It explores population patterns of growth and interactions with other spe- cies. B. marinus is treated through this chapter as a unit of study to explore: how its role in biology shapes the environment and other species around it. We will compare cane toad population growth to look at human populations. This chapter especially probes human population growth in its role underlying many ecological issues today.

population Demographics The rate at which a population grows and shrinks is measured in several ways. Trees are tagged to measure their arrangement in a forest and Americans have a census every 10 years. Both of these are methods to quantify and study a population. The data collected by ecologists about the statistics of a population of species is known as its demograph- ics. Population demographics tell us a great deal about how a population is structured in terms of age, size, and density.

Population demographics help scientists predict how populations will change over time and affect other organisms. A population size gives the number of organisms in a population, and a population density reveals the number of organisms per area of land in an ecosystem. For example, the total number of cane toads in Australia is over 200 million, but on the island in our story, there are fewer toads totally but they have a greater population density. Higher population density could have more impacts on the environment than sheer numbers. B. marinus patterns should be studied in greater detail to determine the answers.

A population distribution shows the arrangement of organisms of a population across a particular region. Most cane toads are clumped on the northeastern areas of Australia.

Whether a population grows or shrinks depends on four factors: the number of births (new born additions); the number of deaths (those leaving permanently); the number of immigrants (new organisms from other areas); and the number of emigrants (organ- isms leaving the area). Population growth occurs when more individuals are entering than leaving a population. It can be calculated by the following equation: Growth rate = (Births + Immigrants) – (Deaths + Emigrants). In Mexico, for example, a rapidly growing population is a result of higher birth rates than death rates. Death rates declined much more than birth rates in the 20th century, leading to a need for emigration to stave off even larger population increases.

In the case of finding ways to decrease the cane toad population, natural predators for the cane toad would increase its death rate. So far, this strategy has not shown much success because the cane toad is toxic to many predators, such as the crocodile that swal- lows a cane toad whole, but ingests enough toxin to kill itself. In another approach, by decreasing its birth rate, growth would slow as well.

Some studies look to introduce sterile males into populations to prevent births. This strategy has had limited success. Changing climate would drive populations of cane toads out of areas by making conditions unfavorable. However, limiting immigration and increasing emigration sounds easier than it is – there is difficultly for humans to accomplish desired environmental change, especially without harmful consequences.

population as a Unit of Study A population is the primary focus of ecologists because it is the unit of study of ecology and evolution. An individual is not as important in studying trends associated with changes in gene flow and in the environment. While a single person may respond one way to a changing factor, such as increased sunlight, her or his reaction is not so import- ant to ecologists. If a person moves to Florida and becomes tanned, possibly dying from skin cancer after 30 years of exposure, an ecologist cannot make strong ecological con- clusions. A single data point cannot drive research findings. If, however, offspring of

Population ecology

The study of a population of organisms and how it interacts with its environment.

Population growth

The increase in the number of individuals inhabiting a place.

Population size

A measurement of population that gives the raw number of organisms in a population.

Population density

A measurement of population that reveals the number of organisms per area of land in an ecosystem.

Immigrants

New organisms moving in from other areas.

Emigrants

Organisms leaving an area.

Demographics

The data collected by ecologists about the statistics of a population of species.

Births

New born additions.

Deaths

The end of life; those leaving permanently.

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populations who move to Florida die off more rapidly as a group 30 years after their emi- gration, ecologists can draw stronger conclusions about environmental effects. Groups of organisms (populations) are studied in ecology to make generalizations.

Population demographics are not measurements of an individual: births, deaths, immigration, and emigration are all population terms. They are used to view how whole groups change and form patterns within ecosystems. Ecology requires that ecologists are both inductive and deductive, terms that harken back from Chapter 1. These are each methods of finding the answers to scientific questions. Ecologists make predictions and form models based on information obtained from their measurements of groups. Ecol- ogy forms hypotheses to test about certain questions in deduction: a study introducing sterile males into a population of cane toads, for example. Induction looks at the many factors about cane toads – their toxins, fertility, and relationships with other organisms – to form ideas on how to solve the toad infestation. To illustrate, perhaps a genetically modified hardy reptile could increase B. marinus death rates. Our story would then have a happier ending. There are many ecological approaches that could be taken. Both induc- tion and deduction are vital in studying population ecology.

Individuals were the focus of the previous unit in this text, on anatomy and phys- iology. It studied the individual and its components: the parts of the digestive system, the function of the liver, and the ways the heart works and malfunctions. It studied the organism down. However, ecology is a type of macrobiology, which studies the organism up. It looks at the organization of populations. It shows the movement of genes through a population and not simply the genes of an individual. The ways populations form patterns in their arrangement and the responses to other organisms and nonliving factors are an ecologist’s field. The chapters in this unit represent a shift from micro- to macrobiology.

population Growth As described in Chapter 1, populations tend to increase in size and overreproduce, unless checked by predators. Charles Darwin, in Chapter 1, describes population expansion as a driving force in evolution, as you may recall. Populations grow too large, and competi- tion for scarce resources leads to a survival of those best adapted. Populations grow until they exhaust their available resources.

An exponential model of population growth depicts a population increase that is unlimited. This model assumes that there are no predators, unlimited resources, and no pathogens. A population will grow, under these conditions, to its biotic potential or maximum possible growth under ideal conditions. Population increases for B. marinus in Australia have reached almost its biotic potential. Our story shows, like the cane toad, many invasive species often grow unchecked by predators. They enjoy conditions of full resource availability. Their growth is exponential (Figure 17.2a) and continues until changing conditions limit them.

Populations can never continue to grow unchecked. Even prokaryotes, which grow at the biotic potential most of their lives, become checked with changing environmental con- ditions and competition between themselves. The main limiting factor to population growth in cane toads is one another. When some cane toads are killed by human methods, it stim- ulates even more growth because the competition diminishes between toads themselves.

In natural ecosystems, populations are limited by a scarcity in resources. This results in a logistic model of population growth. In this model, a population first grows slowly, during a lag period, as population gains in size and colonizes an area (Figure 17.2b). Then, a time of rapid and unchecked growth, called the exponential period, occurs when resources are unlimited and the numbers in the population explode exponen- tially. After this phase, growth slows as limiting factors, such as food, spaces, light, and water, become scarcer. These are called density-dependent factors because they become

Logistic model of population growth

A model that depicts the decrease of population growth rate with the increasing number of individuals.

Exponential period

A time of rapid and unchecked growth.

Density-dependent factors

Factors that limit the population size, whose effects are dependent on the number of individuals of a population.

Exponential model of population growth

A model that depicts the increase of population growth at a constant rate.

Biotic potential

Maximum possible growth achieved by organisms under ideal conditions.

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limiting only after populations reach higher densities. This period continues till a popu- lation reaches its carrying capacity or K, defined as the maximum number of individuals an environment is able to sustain in the long term. Most organisms follow this pattern of growth over time. When deer are introduced into a new area, they increase and level off in their rates of growth in a logistic pattern. The logistic model of population growth appears as an S-shape. Figure 17.2b shows this pattern for deer populations in Australia.

Human population Structure Human population has surpassed 7 billion people and is expected to reach 9 billion by 2050. Each year, 80 million new people are added to the total world population, with birth rates higher than death rates (Figure 17.3). During the past 1,000 years, human world population expanded exponentially. Most ecologists predict the emergence of logistic S-shaped growth in the 21st century.

Carrying capacity (K)

The maximum number of individuals an environment is able to sustain in the long term.

Figure 17.2 a. Exponential growth of B. marinus (cane toad). The cane toad population has expanded since 1935 without natural predators. Bacterial growth data, in the chart above, mirror an exponential pattern of growth. b. Logistic model of growth for deer, normally kept in check by limited resources and predators, shows an S-shaped curve of growth. Deer are usually kept in check by many factors including predators. From Biological Perspectives, 3rd ed by BSCS.

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Figure 17.3 Human population growth. World population grew rapidly since the outbreaks of the plague in Europe and Asia. Humans are experiencing exponential population growth today. From Biological Perspec- tives, 3rd ed by BSCS.

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Studying the age structure of a population depicts the number of individuals at dif- ferent age groups. Age structure diagrams are used to predict future patterns of growth or declines, shown in Figure 17.4. The age structure of developing nations is pyramid in shape, showing that there are many more young than old. This indicates that the population is growing. In developing nations, the age structure diagram is rectangular, with individuals evenly distributed at each age level. This indicates that populations in developing nations are stable. Age structure diagrams help us to predict rates of growth for populations.

Of course, number of children actually being born is an important factor in predict- ing population growth. Fertility rate is defined as the average number of children born to females in a population. The world fertility rate declined from 6.5 children per mother in 1950 to 2.5 today. The declines in fertility rate, due to education programs, contra- ception access, and other methods, have slowed the world population growth. However, fertility rate is still above the replacement level of 2.1. Only China, with rates around 1.6, will experience population decreases due to their one child per couple policy.

Age structure diagram

A graphical illustration that are used to predict future patterns of growth or declines of various age groups in a population.

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Figure 17.4 Age structure diagrams: developing and industrialized nations. Devel- oping nations show a greater proportion of younger people and thus are predicted to have higher rates of growth.

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Fertility rate

Is the average number of children born to females in a population.

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The growth curve for past and current world population is shown in Figure 17.3, a result of the effect of high fertility rates in the world.

In 1996, the US population was 235 million. At the time, it was estimated that the carrying capacity of the United States was 250 million people. Today, we have over 310 million people, overshooting carrying-capacity estimates. Were the original estimates wrong? Were ecologists just naysays?

Factors changed, which could not be predicted at the time, which enlarged the United States carrying capacity substantially. There have been significant advances in farming and improvements in production and preservation of foods. The use of genetically mod- ified organisms to increase food supplies, expansion into new habitats to obtain new resources, and new crop methods has increased our carrying capacity to 500 million, according to some estimates.

The US population grows each year by 3.3 million people, making us the fastest growing industrialized nation in the world, according to the US Census Data. The US population, given current rates and density-dependent factors, will reach 500 million in 2050. With new estimates of a carrying capacity, ecologists fear the effects of reaching these levels. Resource limitations are eventually expected to limit population growth. Of course, the wealthiest people consume most of the world’s resources (Figure 17.5).

In every population, starvation, disease, and violence are the results of reaching carry- ing capacity. On the other hand, Often, density-independent factors decrease populations. These are the factors that increase death rate regardless of density. Landslide, earthquakes, and floods destroy life by directly killing organisms or reducing the size of their resources.

Both density-independent and density-dependent factors interact to affect popula- tion size. It is likely that cane toad populations will experience diseases, new predators, and natural disasters such as desertification, given enough time. If the numbers of toads increase, there are more chances for transmission of viruses and parasites. With greater density, disease is shown to spread more quickly. A population’s increase is also seeds of its own destruction – for humans as well as cane toads.

A population’s use of resources determines how quickly it will reach the carrying capacity. The ecological footprint of an organism or a population is defined as the amount of resources used: land, fuel, water, food, and other items. Some nations such as Sweden and New Zealand have small ecological footprints, while the others like the United States, Japan, and England have large ones. The ecological footprint of an American is 24 acres

Density- independent factors

Factors that limit population size, whose effects do not depend on the number of individuals of a population.

Figure 17.5 The wealthiest people in the world use more resources than others. The wealthiest 16% in the world consume 80% of the world’s resources. The cartoon depicts the United States as overusing the world’s energy resources.

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Ecological footprint

A population is defined as the amount of resources used.

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worth of resources, but one from an Egyptian is 4 acres and Bangladesh is 1.5. The map in Figure 17.6 gives a visualization for our resource use on the planet.

The United States, for example, represents only 5% of the world’s population, but consumes 30% of the world’s natural resources. The richest 16% of people consume 80% of the world’s resources. This disparity between nations and the unsustainable lev- els of resource management have dire long-term predictions.

However, some ecologists and economists have a more positive outlook. They surmise that the carrying capacity can forever be increased by human innovation, as done in the past. As cited earlier in this section, this positive argument relies on the power of the human mind to solve the population explosion issue. Possible solutions include harvesting ocean algae, mass producing farm fish, and reducing population on Earth by traveling to Mars and the moon. All of these are plausible, but each possibility is only extrapolation at this time.

Figure 17.6 Our ecological footprint varies for each nation in the world. The eco- logical footprint of an American is 24 acres worth of resources, but an ecological foot- print from an Egyptian is 4 acres and from Bangladeshi 1.5 acres.

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“Once it was necessary that the people should multiply and be fruitful if the race was to survive. But now to preserve the race it is necessary that people hold back the power of propagation,” by Helen Keller, deaf and blind author and lecturer.

Survivorship Curves and Life History Strategies The life history of organisms in a population is the set of inherited characteristics of an individual that tell us how it lives. An organism’s life history, also called its life strategy, includes its fertility rate, breeding patterns, life span, and age at first reproduction.

There are two types of life histories, each representing opposite ends of a spectrum. The first type, used by dandelions and flies, is termed an opportunistic life history. It is also called an r-selected strategy. In this method of living, there are large numbers of young per breeding event, very little or no care of the young, shorter periods of devel- opment, and a higher mortality in early life. Usually, those organisms with opportunistic life histories live a short time and cannot care for their young. Their strategy is to have as many offspring as possible, putting their success in quantity of children and not quality of caring for them. Most flies live only a few weeks. This means that a successful life

Life history

Series of changes an organism undergoes during its lifetime.

Opportunistic life history, r-selected strategy

type of life history when parents have many young and invest very little in each.

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history does not include a long life raising young. It instead focuses on rapid develop- ment of young to adulthood so they do not need care. The cane toads in our story had an opportunistic life history, putting little effort into raising young. Opportunistic organ- isms often exhibit population booms like the one depicted in our opening story.

The second type of life history, called an equilibrial life history, occurs when parents invest in extended care to their young, live a long time, and have few offspring. It is also called a K-selected strategy. Their efforts go into quality of care and not quantity of young. Organisms such as elephants, coconut palm, and humans exhibit an equilibrial life history. They have few offspring and invest heavily in each. A whale and human usually produce only one newborn at a time. A coconut palm waits a long period of time before producing limited numbers of coconuts.

The two life history types are given in Figure 17.7. Each species evolved a particular life history to optimize the survival of its mem-

bers. While there are maximum life spans in every species, not all species will reach this age. In humans, the oldest documented case was Jeanne Calment, who lived up to the age of 122 years, 164 days. Our life history is K-selected and we have longevity, on average long exceeding the time needed to care for our young. However, humans are limited by genetics and may live for only so long.

Equilibrial life history, K-selected strategy

A type of life history that occurs when parents invest in extended care to their young, live a long time and have few offspring.

Figure 17.7 Opportunistic and equilibrial life histories. a. r-selected species such as quinoa produce many tiny seeds in one growing season. b. The coconut palm grows slowly and produces few seeds in its entire lifetime.

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A SuPErCEntEnArIAn LIvES FOr122 YEArS . . .

Jeanne Calment was born in Aries, France, on February 21, 1875. She is the oldest centenarian in history, dying at age 122 in 1997. Longevity ran in her family: her mother died at age 86 and her father died at age 94. These were very old ages in the 1800s, when medical treatments were limited.

She married her cousin but he died of food poisoning in 1942 at age 47. They had only one daughter who died of pneumonia in 1934. She then raised her grandson who died in 1963 from injuries in a car accident. Jeanne never worked a job and attributed her long life to not letting herself get stressed and to eating a diet rich in olives.

Did Jeanne Calment take care of her health? She smoked until age 119 and ate two pounds of chocolate every week. She rode her bicycle until age 100 and although going blind and hard of hearing in her last few years, she remained

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The maximum lifespan in humans is between 100 and 120 years. Jeanne Calment is an extreme example of survivorship. Human life expectancy is the age at which 50% of people in one’s age group have died. To illustrate, life expectancy for men in the United States is 78 years. This means that by age 78 a man has lost half of his cohorts. Life expectancy for women is 82 years. A survivorship curve plots the number of survivors in a population over time.

Ecologists have classified three types of survivorship curves. Type I curves show most individuals surviving until the end of life, when death occurs in high proportions. Humans and large animals, which carry out equilibrial life histories, exhibit this type

Survivorship curve

A graph that gives number of survivors in a population over time.

mentally alert and capable. She appeared humorous: When asked on her 120th birthday what kind of future she expected, she answered, “A very short one.” and on her 110th birthday, she commented, “I’ve waited 110 years to be famous. I count on taking advantage of it. Why did Jeanne Calment live for so long . . .?

Figure 17.8 Three types of survivorship curves show the numbers of individuals surviving throughout their lifespans.

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of survivorship curve. Most individuals live long enough to care for their young. Equal rates of death at every age occur in Type II survivorship curves. This distribution is seen in organisms, such as those in the wild, lizards, birds, and small mammals, which have equal chances at predation and environmental dangers at all ages. Those with Type III curves die off very early in life, depicted by an inward bulge in the graph. Organisms with a Type III curve include frogs and marine animals that give off large numbers of fertilized eggs into the wild. There is a high chance of death due to environmental dan- gers, as the eggs are defenseless and unprotected. Figure 17.8 depicts the three types of survivorship curves.

Characteristics of Communities roles The second part of this chapter explores the features of a community. It examines the interactions of organisms within a community of populations. A forest, with maple trees and white pines, reptiles, amphibians, and humans constitute a community. It is a set of different populations living together. A community may also be something unseen – such as the microbiome of bacteria residing on your skin – which contain millions of species not visible to humans (Figure 17.9).

A biological community therefore includes all of the populations of organisms liv- ing in an area at a particular time, and their relationships with each other. The role an organism plays in the community is it ecological niche. Its niche displays how an organ- ism interacts with all of the features of its environment. The space an organism occupies, including all of the factors with which an organism interacts, is known as its habitat. A habitat is the area in which an organism lives. Some factors in a habitat are nonliving, called abiotic factors. These include soil, sunlight, temperature, and rainfall. Other fac- tors comprise the living things, called biotic factors. These include plants, animals, and microorganisms. Organisms use both biotic and abiotic factors to interact with other members of the community and the environment.

An organism’s ecological niche may be limited by the resources it is actually able to use. An organism’s fundamental niche is the area and resources that it is theoretically able to utilize. Its realized niche is the area and resources actually able to be used by a population. Consider the barnacles on the Scottish seacoast, as an example. They consist

Ecological niche

The role an organism plays in its environment.

Habitat

The space an organism occupies, including all of the factors with which an organism interacts.

Abiotic factors

The non-living factors in a habitat.

Biotic factors

Factors that comprise the living things in a habitat.

Fundamental niche

The area and resources that an organism is theoretically able to utilize.

realized niche

The area and resources that an organism is actually able to use.

Figure 17.9 Communities come in big and small sizes. a. Forest community. b. Microbiome community taken from human skin.

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of two different genera: the Balanus is best adapted to exploit resources at lower portions of the coast and the Chthamalus genus is better suited for upper parts of the shore (Fig- ure 17.10).

interactions within Communities Competition In the example above, the fundamental niche of both genera of barnacles is the entire Scottish coast. Under ideal conditions, with the other genera not around, each are able to use resources in the upper and lower regions of the coast. However, in reality, their real- ized niches matter more. Realized niches are exploited because of competition between the two genera of barnacles.

Competition occurs when organisms strive for the same limited resource. Competi- tion reduces the survival of both organisms. They spend their energy competing with one another. Russian scientist G.F. Gause, in the 1930s developed the competitive exclusion principle, which states that organisms will compete with each other in an area until one goes extinct. He studied two species of paramecium, P. caudatum and P. aurelia. When grown separately in test tubes, each species thrived, using resources. When grown in the same test tube, P. aurelia drove P. caudatum into extinction (Figure 17.11).

Species do evolve to coexist with each other. All birds consume berries, but different species are adapted for different sizes, shapes, and types of berries. Competition does not always need to cause species extinction in an area. When two competitors coexist

Competition

The activity that occurs when organisms strive for the same limited resources.

Competitive exclu- sion principle

A principle, which states that organisms will compete with each other in an area until one goes extinct.

Figure 17.11 Competitive exclusion principle: graph of P. caudatum and P. aurelia

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in the same area, they use resources in different ways, in a process known as resource partitioning. Resources are subdivided into different categories, and each category is separately used by competitors.

Resource partitioning is often accomplished by character displacement. In charac- ter displacement, organisms evolve characteristics to help them to partition resources. Sometimes new traits cause partitioning based on location, as described in our exam- ples of barnacles in Scotland. Sometimes different resource use is temporal, or based on time of the day spent in a habitat. Bats, for example, hunt for prey at night, limiting their competition with birds, as well as predators. Regardless, resource partitioning is a mechanism by which competition is reduced between organisms.

When competition occurs between two different species, it is known as interspecific competition. If B. marinus, the cane toad outcompetes Rana pipiens, the North Ameri- can frog, in obtaining a fly meal, it is an example of interspecific competition. This is the most common form of competition in community ecology. When organisms of the same species compete with each other, it is called intraspecific competition. Mate competi- tions between two deer or when two hemlock trees struggle for limited light and water represent intraspecific competition.

predator–prey relationships Nature can appear cruel to human society. A fast cheetah stalks and kills a cute, little fawn. A California King snake, Lampropeltis getula, swallows a mouse whole, seem- ingly without mercy. We feel sorry for the creature that we like – the one which loses. However, this relationship between species in a community is vital.

The connection between the two organisms is called the predator-prey relationship. Predation is essential for energy flow and the survival of many species in a community. Predation occurs when an organism of one species – the predator – stalks and kills an organism of another species – the prey. Predators obtain required energy from the parts of its prey. When L. getula stalks a mouse, for example, it has adapted, over millions of years of evolution as shown in Chapter 10, strategies and structures to consume small animals. The answer to the problem in our story is to find a predator that is able to withstand the toxin of the cane toad. It kills crocodiles and freshwater turtles when they eat them. There are many species that prey successfully on the cane toad but they

Figure 17.12 A corn snake is a predator that swallows its prey whole. This corn snake is eating a mouse.

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Predator-prey relationship

The connection between two organisms of unlike species.

Predation

When one organism stalks and kills an organism of another species.

Intraspecific competition

The competition between organisms of the same species.

resource partitioning

The condition where two competitors coexist in the same area and use resources in different ways.

Character displacement

The phenomenon where organisms evolve characteristics to help them to partition resources.

Interspecific competition

The competition between two different species.

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are not native to Australia. Ecologists are searching for a suitable predator for the cane toad. However, they should be careful not to introduce a new invasive species. Snakes are an excellent predators to rodents (Figure 17.12), but most snake species cannot eat the cane toad.

The most notable predator–prey relationship takes place between the lynx and the hare. The lynx, a predator in Figure 17.13, stalks and kills its prey, a snowshoe hare. Lynx and hare populations fluctuate, dependent in part on one another. When plot- ting the frequency of individuals of each population over time, Figure 17.13 shows the changes that occur for each species in tandem with one other. As the lynx preys on the hare population, lynx increase because they are exploiting the resource. Then, as they use up the hare (hare population declines) as a food source, they too experience pop- ulation decreases. With fewer lynx, more rabbits survive. Fewer lynx predators allow their numbers to thrive. Afterward, the lynx again have more food available from the increase in hare population. This fluctuation in frequencies make the predator and the prey dependent on each other.

Defenses Evolve However dependent, prey always lose because they are killed and eaten by the predators. The prey’s reproductive success is reduced in its interactions with predators. Therefore over time, many prey species evolved a series of defenses to combat predators. Quills on a porcupine or poisonous glands in a cane toad repel predators and save a prey’s life. There are several defense mechanisms used by prey. They are divided into two types: those that constitute physical prey defenses such as chemicals and structures; and those that are behavioral prey defenses, which comprise the actions a prey takes to ward off predators.

At the same time, predators have evolved counter-measures to prey. They have devel- oped (and continue to evolve) structures and strategies that combat changes in prey. It is a coevolutionary arms race between the two. As discussed in Chapter 9, the ongoing coevolution of the Passiflora flower and the Heliconius butterfly represents an arms race in defenses. In some cases, organisms evolved to help each other to defend against mutual enemies. Several species of ants become attracted to substances on conifers. Ants on coni- fers defend against other insects that eat the tree’s needles. The conifers provide a defense against predators for ants. Together, they evolved strategies to help each other defend against predation. Let’s explore the prey defenses that developed across other species.

Figure 17.13 Predation. The lynx, a predator, stalks and kills its prey, a snowshoe hare; graph of population change of lynx and hare

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physical prey Defenses Mechanical defenses Mechanical defenses are structures, such as quills on porcupines or shells surrounding a turtle, which serve as passive defenses against predators. They require no work and no confrontation to deter predation. A turtle shell is tough and prevents the soft-bodied turtle from many deadly encounters.

Camouflage Armored shells of turtles also usually blend in with the environment. When organisms become less visible in their environments, they are said to use camouflage to avoid being seen. The walking stick, an insect that resembles a branch on a plant, easily blends in with its surroundings. This structure allows a passive defense for walking sticks, as depicted in Figure 17.14.

Warning Coloration Often a bright-colored organism indicates that it is poisonous. The azure poison dart frog, for example, is orange and spotted to warn predators to beware. Warning coloration is called aposematic coloration and serves to deter predators. However, the poison-color

Aposematic coloration

Warning coloration that serves to deter predators.

Figure 17.14 Physical prey defenses. a. Turtle in a shell. b. Aposematic coloration of azure poison dart frog. c. Viceroy and Monarch butterfly. d. A walking sick Diapheromera fermorata.

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The act by which organisms become less visible in their environments to avoid being seen.

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link is not necessarily always present. The cane toad, B. marinus, in our story is drab, but still poisonous. Plants from the noncolorful genus Strychnos produce the toxin strych- nine that kills many vertebrates.

When a palatable species capitalize on aposematic coloration, it mimics the poison- ous organism. This is called mimicry. For example, the Monarch butterfly is poisonous to mammals and bird, containing a toxin that affects heart rate. The Viceroy butterfly resembles the Monarch, both featuring similar orange–black patterns and get protection by appearing similar (Figure 17.14c).

Behavioral prey Defenses Group Behavior The way an organism responds to stimuli or acts comprises their behavioral defenses (Figure 17.15). There are both passive and active forms of behavioral prey defenses. By traveling in groups, prey reduce their individual risks. Usually, when a predator enters the scene, some prey respond, giving warning to the other to flee. In another way, the large numbers of cane toads, for example, satisfy a predator’s appetite and allow oth- ers to go unharmed. Group behavior is a passive adaptation to predation (Figure 17.15 c and d). It saves many by sacrificing the few. In Chapter 20, we will explore how the genetic predisposition to group thinking influences societal behaviors.

Alarm Call Sometimes in a group, there is an alarm call, which is signaled by one member, that a predator has been spotted. An owl may howl or a bird may chirp in an alarm call. This enables the other members of the group to hide and flee or to fight back.

The first is a passive defense, and many animals adapt this strategy when encounter- ing humans, for example. Cattle will travel in herds, fish in schools, and birds in a flock. Often, mainland animals, as opposed to island ones, adapt a passive retreat defense from humans. On the island in our story, hiding and fleeing, in fact any fear from humans is absent in cane toads. These organisms did not evolve the behavior against humans because on islands their species never encountered humans until recently. The second strategy is an active defense. When organisms fight back, they use their defenses to ward off predators. As we discussed in Chapter 10, ostriches are flightless but have strong wings to beat back the predators, when they are unable to run away (Figure 17.15b).

Mimicry

The resemblance of one organism to another

Group behavior

A passive adaptation technique to predation.

Alarm call

A warning signal made by an animal or bird about a predator or when startled.

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Sometimes a behavioral defense will be active to a point of suicide. For example, often an enemy insect group attacks a colony of the Malaysian exploding ant, Campono- tus saundersi. C. saundersi soldiers march up to the enemy. In line and in unison, the C. saundersi ants contract poison glands in their abdomens, squirting formic acid onto the predators.

In the process, C. saundersi soldiers die, with their abdomens exploding. It is an example of devotion to the colony, as suicide ants lose their lives to protect against predators. We will explore the role of genetics in forming social systems in organisms further in Chapter 20.

plants and Herbivory Have you ever looked at the leaves on a tree in early spring compared with the late sum- mer or fall? Early in the growing season, leaves are fresh and undisturbed, but by the end of the season, they change. They become filled with holes, laden with fungus growths, and ultimately appear ugly. The changes are due to herbivory, or the consumption of plants and plant parts by other organisms. In herbivory, the plant may or may not die as a result. Herbivory is commonly thought of as cattle grazing on grasses; but other organisms, such as fungi and bacteria, feed on plants. Herbivory is a form of predation and it kills many plants.

Some plants evolved defenses against herbivory. Humans are unable to eat most forms of grasses because they contain silica, making hardened blades. These plants are too tough

Herbivory

The consumption of plants and plant parts by other organisms.

(a) (b)

Figure 17.15 Behavioral prey defenses. a. Red carpenter ant attacks a gnat. b. Ostrich will use its wings to protect her eggs. c. Cattle in herds. d. A flock of pigeons.

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for humans and many animals to consume. Some organisms, such as the shrub oak, evolved its defense by having most of its mass underground in the form of roots. This way, even if herbivores devour the plant, most of its energy is underground and ready to resprout. The best known evolved defense against herbivory, however is the poison from the poison ivy plant, Toxicodendron radicans. It contains a toxin that binds to T-helper cells. As you may recall from Chapter 14, T-helper cells begin the specific immune response. When the toxins of T. radicans combines with T-helper cells, they initiate an allergic reaction. These manifest as skin rashes commonly seen after contact with poison ivy (Figure 17.16).

Symbiosis Many relationships within communities form close bonds, making them interdepen- dent. Many organisms live in close, intimate association forming a relationship called symbiosis.

There are three types of symbiosis:

1) Commensalism, which occurs when one organism benefits and the other is unharmed by the relationship (Figure 17.17). When epiphytes or vine-like plants grow on trees, they do not harm the supporting plant but do not help it either. Instead, the epiphyte’s motive is to gain height and obtain its limiting resource – sunlight. They are stealing a spot on the tree but not giving anything back. In animals, barnacles are small marine creatures that latch onto skin. When they adhere to a whale’s skin, they are hitchhikers and gain a “free ride” on the whale. The whale receives nothing in return for the trip but is not harmed as the weight of the barnacle is negligible.

2) Mutualism occurs when both organisms benefit in a relationship. Mutualism is commonly found in nature. Both organisms have a stake in the association, making it a stable strategy for survival. In the Alder tree, a special type of bac- teria (which will be discussed in Chapter 19) called nitrogen-fixing bacteria live in the root nodules of the tree. The nodule of the tree provides protection in a “home” for the bacteria. The bacteria provide accessible nitrogen for the Alder tree. Without nitrogen from the bacteria, most of it is unavailable to the tree because it is a gas. Other forms of mutualism are closer to home. The bacteria in our large intestines, described in Chapter 12, provide us with vitamin K and our colons provide a safe and anaerobic home for the enteric bacteria. Mutualism has numerous examples in nature.

(a) (b)

Figure 17.16 a. Toxicodendron radicans. b. A rash on a human from poison ivy.

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Symbiosis

A relationship formed between two different organisms living in a close, intimate association.

Mutualism

A relationship in which both organisms benefit.

Commensalism

The type of symbiosis which occurs when one organism benefits and the other is unharmed by the relationship.

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3) Parasitism is the symbiotic relationship in which one organism benefits and the other is harmed. Parasites kill more people than by predators or by compe- tition. As discussed in Chapter 5, roughly 1 million people die each year from the malaria parasite, Plasmodium alone; and yet only a handful are attacked by sharks. The contrast shows that organisms unseen have more impact on human society that we often realize.

Parasites in the animal phylum Nematode (discussed in Chapter 10), for example, the hookworm, Ancylostoma duodenale, lives in human intestines and survives on blood (Figure 17.18). However, parasitism, as by a hookworm, is different from predation. Parasitism does not seek to kill its host, merely weakening it as it drains away the host’s resources. Predation always seeks to kill its prey. If the parasite kills its host, it too dies, so it pays for the parasite to prevent too much abuse of its host. Many times though, and eventually, parasitism does kill a host organism.

Figure 17.17 Commensalism: Spanish moss on a tree to capture sunlight. While the tree obtains no benefits, the moss species is able to get greater access to sunlight and therefore food.

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Figure 17.18 The hookworm, Ancylostoma duodenale, is a parasite in the intestines of humans.

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Fungi are the ultimate parasites that evolved to lose their own chlorophyll and leaves. They live off the dead, as described in Chapter 8, and cannot make their own food. Fungi evolved a strategy to completely rely, as a parasite, on other organisms.

Other forms of parasitism occur in nature. Brood parasitism takes place when a bird species lays eggs in another bird’s nest (Figure 17.19). The foreign eggs then hatch and are raised by the host mother. The real mother avoids the costs of rearing her young. It is a form of stealing because it saps the energy from the host mother. In cowbirds, females can lay up to 30 eggs a season because they are free of parental care for these newborns. It is a successful parasitic strategy that improves the reproductive success of cowbirds.

Some parasitoids take parasitism to new levels. They lay their eggs within other species. When these eggs hatch, they eat the host organism from the inside out, using it for developmental energy. The braconid wasp, Cotesia congregatus, for example, uses an ovipositor (long tube) to lays its eggs within the body of the tomato horn- worm (Figure 17.20). When wasp eggs hatch within the hornworm, they gnaw at the

Brood parasitism

A form of social parasitism in which a bird species lays eggs in another bird’s nest.

Figure 17.19 Brood parasitism: Chestnut-headed oropendolas (Psarocolius wagleri) suffer brood parasitism by giant cowbirds (Molothrus oryzivorus).

Figure 17.20 The braconid wasp, C. congregatus, uses an ovipositor to lay its eggs within the body of the tomato hornworm. The eggs of the wasp hatch and eat the tomato hornworm (shown in figure above).

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An organism living that spends some period of its development on or in a host organism and later kills its host.

Parasitism

The symbiotic relationship in which one organism benefits and the other is harmed.

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caterpillar hornworm until they reach its exterior. The wasp eggs devour their host completely and emerge as adults from a dead caterpillar carcass.

The many community interactions presented in this section should be understood as complex and sometimes overlapping (Figure 17.21). While mutualism may occur, for example, between species, another interaction is usually taking place simultaneously. A braconid wasp may have within it a parasitoid living in its internal cavities. It is esti- mated that 25% of insect species are parasitoids, forming many interactions within their communities.

Figure 17.21 Multiple relationships in a community: arrows depict relationships between populations within a river community in the waters below these boaters. From Biological Perspectives, 3rd ed by BSCS.

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Summary Invasive species take over regions in which they lack natural predators and have abun- dant resources. There are over 1,500 known invasive species adversely affecting regions around the world. Ecologists study these regions by analyzing population demograph- ics and by looking at how populations interact within a community. Populations grow depending upon the conditions to which they are adapted in their environments. They are limited in growth by scarcity of resources in a given area. We can predict future growth of populations based on their age structure, life history, fertility rates, and sur- vivorship curves. Organisms play differing roles within their community. Many kinds of interactions result from this including competition, predator–prey, and types of symbiosis.

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Summary: key points

• Invasive species, without natural predators, grow logistically and exhaust resources for other species in a community.

• Most populations grow at first exponentially and are then limited by a scarcity in resources at an ecosystem’s carrying capacity.

• An opportunistic life history capitalizes on high numbers of offspring, and an equilibrial life history emphasizes care of the young.

• Organisms in a community have a niche, which may be fundamental or realized. • Interactions within a community include the antagonistic, such as competition and predation and

parasitism; and the cooperative, such a mutualism and, to a lesser extent, commensalism.

abiotic factors age structure diagram alarm call aposematic coloration biosphere biotic factors biotic potential births brood parasitism camouflage carrying capacity, K character displacement commensalism community competition

competitive exclusion principle deaths demographics density-dependent factors density-independent factors ecological footprint ecological niche ecology ecosystem emigrants equilibrial life history, K-selected strategy exponential exponential model of population growth fertility rate

KEY tErMS

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fundamental niche group behavior habitat herbivory immigrants interspecific competition intraspecific competition life history logistic model of population growth mimicry mutualism opportunistic life history, r-selected strategy

parasitism parasitoid population population density population ecology population growth population size predation predator–prey relationship realized niche resource partitioning survivorship curve symbiosis

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Multiple Choice Questions

reflection questions:

1. The cane toad grows: a. inversely b. exponentially c. diversely d. proportionally

2. Populations are: a. groups of communities b. smaller than groups c. larger than ecosystems d. the unit of study in ecology

3 When a population of squirrels hits its _________, it shows a ____ growth curve. a. exponent; exponential b. exponent; logistic c. carrying capacity; exponential d. carrying capacity; logistic

4. A population of field mice has a chance of death equal at all of their ages, with predation a steady possibility. Their survivorship curve would appear as Type: a. I b. II c. III d. IV

5. Before humans hit their carrying capacity, they are likely to experience: a. violence b. disease c. starvation d. growth

6. Which represents a logical order, in the development of new niches for organisms in a high population density and resource scarcity? a. Competition ➔ resource partitioning ➔ character displacement b. Competition ➔ character displacement ➔ resource partitioning c. Character displacement ➔ resource partitioning ➔ competition d. Resource partitioning ➔ character displacement ➔ competition

7. Which is an example of an abiotic factor in a forest community? a. Squirrel droppings b. Sunlight levels c. Competition between wolves d. Competition between wolves and dogs

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8. Which takes place when both organisms benefit in a relationship? a. Mutualism b. Commensalism c. Predation d. Parasitism

9. Which correctly MATCHES terms in community ecology? a. Predator – mutualism b. Herbivory – competition c. Parasite – commensalism d. Predator – prey

10. Herbivory is a form of: a. predation b. mutualism c. commensalism d. all of the above

Short Answers

1. Invasive species are exotic to new areas and growth rapidly. Give two reasons why an invasive species is able to take advantage of a new area.

2. Define the following terms: population size and population density. List one way each of the terms that differ from each other in relation to their: a. importance in predicting competition in a population; b. importance in predicting resource use in an area; and c. relationship with each other.

3. Some ecologists argue that “there is no true form of commensalism.” Define com- mensalism and give an example of it in nature. Do you agree with this statement? Defend your argument.

4. Draw a sketch of an age structure diagram in a growing population. Give an exam- ple of a nation with this type of age structure diagram. What does a high fertility rate tell you about the future of this population?

5. Explain the difference between a fundamental niche and a realized niche.

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6. How does competitive exclusion result in: a. character displacement and b. extinc- tion? Describe the pathway that a community takes to lead to each result.

7. Define aposematic coloration. Give an example of this in nature.

8. For question #7, how does mimicry act as a physical prey defense? Give an example in nature.

9. Describe the predator–prey relationship. Does it pay for the predator to kill its prey? Does it pay for predators to kill off its prey population?

10. Define brood parasitism and parasitoids. How are the two types of parasitism simi- lar? How are they different? Give an example of each.

Biology and Society Corner: Discussion Questions 1. In the past 25 years, China has implemented a One Child Policy, which restricts

couples by placing sanctions on them for having more than one child. However, it is now allowing two children per couple. What changes have taken place societally in China as a result of this policy? What do you recommend for solutions? What do you predict for future generations, as Chinese society favors sons?

2. In the story, the cane toad was introduced into Australia in 1935 to combat beetles. Beetles destroy crops and thus the food supply. The scientists who introduced the cane frog argued that at least their methods were natural, unlike methods of animal control used today. Do you agree or disagree with these scientists? Explain your answer.

3. To reduce our ecological footprint, some scientists argue that the United States would see a reduction in its standard of living. Our resource use is the highest in the world, at this time. Would you be willing to lower your standard of living to reduce our ecological footprint? Why or why not?

4. Unsustainable human population growth is an environmental threat. However, two scholars argue about the effects of human population growth. Julian Simon, an econ- omist, contended that human innovation and technological advance will increase the carrying capacity. Paul Ehrlich argued against Simon, citing limited resources and predicted logistic growth curves for humans. Research these two opposing sets of viewpoints. On the basis of your research, which side do you take? Why?

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5. Jeanne Calment lived for 122 years. Would you like to live for that long? How long would you want to live? What factors play a role in your decision making?

Figure – Concept map of Chapter 17 big ideas

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Ecosystems and Biomes 18

The hitchhiker

He makes his way out west

Through the forests of Pennsylvania

Through the grasslands of Iowa

He meets his destiny in the desert of California

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the Case of the Hitchhiker I woke up excited and ready to start a new life. I packed my bags and had my last break- fast with my mother in our apartment in the upper east side of New York. I was moving to San Francisco, driving across country this morning. My mother was worried about the trip and the long distance, but I could not wait to see the world.

Last night at my graduation party, my old science professor Mike made a great prediction: “The world is your oyster!” . . . and it really was. I accepted a new job in California last week, hired by a small environmental consulting firm. My first project was to study how new road tarring projects affect chaparral in southern California. As I began driving, I was uncomfortable with the thought that enough tar has been placed on roads in the United States in the past 50 years to cover the state of Ohio completely!

Chaparral is a type of biome, or set of ecosystems that occur across large areas of the world. There are several types of biomes. In chaparral, there are hot and dry summers, and plants are adapted for drought resistance. We were studying the effects of tarring on scrub oak populations in the California chaparral. I was real lucky.

I packed the car, said my goodbyes to the family, and started the drive over the George Washington Bridge from New York City into New Jersey when an accident just missed me. “Whoa, what a sight! A seven car pileup and it looked like people were going to be really hurt or dead. Dude, I am lucky” I thought.

It was there that I saw him for the first time – the hitchhiker – he was an older man, wearing a gray suit much like in the 1930s. He was plain, with a long stark face and almost, non-descript. I ignored him and drove by but as I looked in the mirror, he smiled at me. I hated him.

I tried to forget about the oddness of the hitchhiker; with his strange look and smile. I loved nature, which is why I majored in ecology in college. I looked forward to going through the temperate forest biome of Pennsylvania. I drove through the endless moun- tain range and saw large maples and pines in the temperate forests. These areas have plentiful water (121 cm or 48 inches/yr) and are able to sustain large plants. I stopped and picked my favorite flower, a daisy in a patch of thyme. However, behind a tree, I caught a glimpse of the hitchhiker – the same man in New Jersey! He smiled again and stuck out his thumb. I thought of confronting the man, but I stepped on the gas pedal instead.

Biome

A large community of flora and fauna occupying a major habitat.

CHECk in

From reading this chapter, students will be able to:

• explain how humans benefit from the different biomes but negatively impact their own ecosystems. • define biome, ecosystem, topography, rain shadow desert, tropical rainforests, savannas, deserts,

chaparral, temperate grasslands, temperate deciduous forests, taiga, tundra, polar ice caps, estuary, limnology, producer, herbivore, consumer, omnivore, energy pyramid, biomass, ecological succes- sion, climax community, and colonizer.

• define the term biome and explain how local topography affects biomes. • list and compare each of the nine major biomes of the world. • compare the three types of aquatic biomes. • trace the flow of energy as it moves through an ecosystem. • explain how ecological succession returns an ecosystem to a stable community.

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I was shaken up – was he following me? Why? How? I was panicked. I drove for hours and I enjoyed the beautiful deciduous trees – the foliage colors and its majestic look – I assumed that I must be imagining the hitchhiker. I could not call my mother – she would worry; and maybe think that I was crazy. No, I needed to keep driving and see the sights. I did not stop to get a hotel, as planned.

I drove all the way from Ohio to the Iowa prairies, North America’s temperate grass- lands biome.“Here the open lands will clear my mind and I’ll forget the apparition,” I thought. The thick layers of soil from grasses growing make beautiful crop land. It was open, on I-80 for as far as the eye could see, and only rows and rows of corn fields whisked by me. I loved it. There was a clear and open sky, which you could never get in a city, always surrounded by buildings.

There is not enough precipitation (less than 75 cm or 30 inches/yr) to sustain many large trees in temperate grasslands. The grasslands in the summer are hot, but I know this biome has cold winters. However, again, in between the rows of corn, I saw the hitchhiker popping out, with a smile and a thumb.

As I went to pieces and moved across Colorado, where the farmland gave way to mountains, I thought a change in biome would end this stalker’s persistence. I went up and up hoping to get away from the hitchhiker. High in the Rockies, I felt free from the world. At 5,000 feet, the temperature dropped and with a new biome called taiga. I knew from my studies that the taiga had moderate amounts of rainfall mostly in the summer. I really enjoyed touching the cone-bearing pines and shrubs. They were adapted for the cold winters and low water levels – but not me, I liked it hot in California.

However, the cold did not keep him out – the hitchhiker looked coldly at me this time, impatient and waiting. He stood by a giant Alder tree. I simply wanted to make it to San Francisco and drove without sleeping, after 36 hours of driving. I could not care – I would not care. I would keep going and see this world. I passed the mountains and slowly the region changed to desert, an area where there was almost no precipitation (25 cm or 10 inches/yr). There was little vegetation and little life in the desert. The lower the rainfall a desert has, the fewer plants and animals present.

At this point, I felt a dreadful acceptance. I stopped at a place where there was almost no life – in the Mojave Desert in southern California. I felt the hitchhiker, although I did not see him. I would have it out with that hitchhiker!

I called my mother, and I asked to speak with her. The voice quickly answered at the other end, which I did not recognize, and it said “I am sorry, she is unavailable; there has been a terrible accident – her son died on the George Washington Bridge the day before yesterday.”

I opened my car door and walked to the hitchhiker, standing by a cactus. He smiled and reached out his hand whispering, “I wanted to give you just a little more time to enjoy the beauty that this world has to offer.”

CHECk Up sECtion

In the suspense story above, the main character experiences, among other things, many biomes while driving across the United States. Temperature and rainfall are abiotic factors that help determine the kinds of plants and animals inhabiting an area and comprising a biome.

There are many threats of biome loss throughout the globe. Tarring of surfaces creates many frag- mented ecosystems within biomes, for example. Choose a particular biome and research the effects of tarring roads on biome biology: types of organisms and abiotic factors. (a) Propose a plan for combating the effects of tarred roads. (b) What are the benefits and drawbacks of the solutions you propose?

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– “The Case of the Hitchhiker” is based on a radio play written by Louise Fletcher, first presented on November 17, 1941, broadcast of the Orson Welles Show on CBS Radio.

Major Biomes of the World What are Biomes? The character in our story saw several of the Earth’s biomes as he made his final drive through the United States. As a large nation, the United States encompasses most of the world’s biomes when including Hawaii and Alaska. Let’s travel through the world to experience the biology of the biomes. Each is influenced by abiotic factors that enable growth of different forms of life. Life evolved to inhabit these regions, over long periods of time. Changes in biome biology have historically threaten the existence of many of these species, so well adapted for certain conditions.

As stated in the story, a biome is a set of ecosystems that occur across large areas of the world. Biomes are the largest ecosystems in the world. As you recall from Chapter 17, ecosystems comprise the communities in a region, including how they interact with the environment. Biomes contain innumerable ecosystems that have similarities in types of organisms and abiotic factors.

An ecosystem is an arbitrary unit because it is only a human construct. One eco- system may be a spider web, its relations with prey, and the abiotic factors within its world of a cave. Another ecosystem may include all of the desert area of Death Valley, in California. An ecosystem’s boundaries are determined by how we define them. When an ecosystem is defined, it is by humans in order to study it. When defining large and expansive ecosystems, biomes are created.

Ecologists differ on the number of biomes in the world. We shall accept that there are nine biomes: (1) tropical rainforests, (2) savannas (tropical grasslands), (3) des- erts, (4) chaparral, (5) temperate grasslands, (6) temperate deciduous forests, (7) taiga, (8) tundra, and (9) polar ice caps. Our character in the story drove past and “enjoyed” the sights in four of these biomes (3, 5, 6, and 7). In the next section, we will give the salient features of biomes, each depicted in Figure 18.1.

Biomes are found over large areas and have characteristic plants and species. Each of the biomes has plants, animals, and abiotic factors that are similar. A desert looks like a desert because they all have little water and similar type vegetation such as cac- tuses. As the driver in our story persisted, he noticed the changes in scenery based on the different plants and animals in each biome. He also noticed that abiotic features of each biome – temperature, water, altitude, and sunlight – were similar within a biome. In fact, as the driver went up in altitude as he drove on, the biome changes. Elevation and latitude create similar effects on plant and animal lives in a biome.

These abiotic conditions determine the plant and animal life in an area. The most important abiotic factors to plants are light and water. Organisms adapted for a particular biome are found in that biome. For example, C4 and CAM plants show how organisms adapted to dry conditions are found in deserts. Plant adaptations to hot and arid biomes you may revisit in Chapters 4 and 9.

In another example, in order for angiosperms to grow tall, they must have plentiful water. As our character in the story drove, he saw that trees were found in the wetter, tem- perate forest biome; and grasses on the drier prairies. Trees require more water to persist in a biome. Recall from Chapter 9, transpiration pull requires ample water to allow plants to carry out photosynthesis. Angiosperms are often large in size and require plentiful water to

Ecosystem

A system of interacting organisms and their physical environment.

Tropical rainforest

A type of forest characterized by tall, dense trees in an area that experiences high annual rainfall.

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Figure 18.1 a. The Major Land Biomes of the World. Biomes occupy large regions of the globe and usually extend onto more than one continent.

move all the way up to the top of the tree. Very few angiosperms were seen by our character in the grasslands. There, the precipitation level could no longer support angiosperm growth. Thus, grasslands have few trees, overall except near rivers, lakes, and wetlands, which pro- vide extra water. These are examples of how the biota of a biome reflects abiotic conditions.

topography affects land areas The Earth’s features determine the environmental conditions in each biome: the amount of solar radiation it receives, the circulation of atmospheric winds, and the presence of valleys and land ridges. For example, the direction of the wind determines which spe- cies of birds fly in a region. The angle of the Sun’s rays hitting a biome also plays a vital role in its temperature. Most of us know that the areas closer to the equator of the Earth are warmer than those closer to the poles. These are examples of the Earth’s influences, which have impacts on the weather to determine ecosystems and biomes. These are characteristics of the Earth which will be discussed further in Chapter 19, the biosphere.

Some conditions of the Earth that are regional (not pertaining to the entire Earth) also affect the formation of biomes and ecosystems. Local topography, or the phys- ical features, of the land such as mountains and valleys has dramatic effects on cli- mate in areas. A drive one mile up a steep incline road could change the weather 10°C. As altitude increases, the air pressure in an area decreases because there are fewer air

Topography

The physical features of the land such as mountains and valleys.

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molecules. Lower pressure causes the temperature to go down (recall from Chapter 2 that temperature is a measure of average kinetic energy of molecules, so fewer mole- cules moving translates to lower temperature).

As a result, when the character in our story drove up the Rocky Mountains in Colorado, he noted the biome shift from grassland to taiga. Taiga is a biome usually found in wide regions closer to the poles. His drive up in altitude resembled a movement toward the poles of the Earth, getting colder along the way. The changing topography also shifted the biotic factors found in the areas. On the mountains, he saw Alder and other coniferous trees that were adapted for colder climates and less light.

Large mountains also cause deserts that form when ocean winds cross over them. As moist air from the ocean passes over high mountain ranges, it rises and cools at higher altitudes. Cool air loses moisture and causes precipitation in those areas. Afterward, with little moisture remaining, there is reduced rainfall on the other side of the mountain. This region becomes deserts, called rain shadow deserts (Figure 18.2).

The deserts form in the shadow of the mountains, as a result of those mountains. They always form on the downwind side of a mountain chain. If the wind comes from the west, as in the United States, rain shadow deserts will form on the east side of a mountain. Our final scene in the story takes place in a rain shadow desert, as shown by the hitchhiker and our character walking away together one final time in Figure 18.2d. The Sierra Nevada Mountains create the Mojave Desert in California as a result of this rain shadow effect.

Rain shadow desert

The dry region of land on one side of a mountain; has very little precipitation.

Pacific ocean Pacifific oceaean

Wind direction

Moist

Arid

Rain shadow

(b) (c)

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Figure 18.2 Rain Shadow Desert: a. How it is created? b and c. Soils on the windward side of a mountain receive much more rainfall than on the leeward side. A. B&C From Biology: An Inquiry Approach, 3rd Edition by Anton E. Lawson. d. Photo of the Mojave Desert.

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Smaller topographical changes can also have large effects on climate and create mini-biomes. Characteristics of cities change the local temperatures. On average, cities are 1°C to 6°C hotter than rural areas. Our character in the story landed a job to study the effects of asphalt. The ever-expanding tarring of our nation’s biomes is an ecological threat. The tarring effect increases temperatures, especially in cities. Asphalt absorbs heat as a dark object and raises ground surface temperatures (Figure 18.3). One method of scientists to combat asphalt heat absorption is to use materials that are lighter in color. For example, silver coatings are replacing black tar in roof repair and restoration in buildings in cities. This silver color reflects light and lowers heat absorption on building roofing. In turn, the electric needed to cool top floors of buildings is reduced.

Tall buildings in cities also have the effect of channeling winds into pockets along city sidewalks. This increased surface wind speed changes the dynamic of ecosystems in cities. Birds, for example, have more difficulty flying along certain windy sites, chang- ing their habitat availability. Insect (bird prey) populations are therefore able to thrive,

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Figure 18.2 (continued)

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Figure 18.3 Asphalt on a Series of City Roofs. Asphalt in the city absorbs heat, changing the microclimate of an urban community. Cities are a few degrees warmer than comparative rural areas.

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taking advantage of reduced predation in these city areas. Local changes in topography have large impacts on the ecosystems within these mini-biomes.

a Drive through the Biomes terrestrial Biomes Let’s take a tour of the biomes, like the character in our story, looking at their biotic and abiotic characteristics that make each unique. Figure 18.1 shows photos and geographic regions of the world’s terrestrial biomes from around the globe. Each of the biomes contains life based on the environmental conditions (temperature, light, and rainfall) in which it lives. Rainfall and temperature are the best predictors for where a biome will best develop (Figure 18.4).

1) Tropical rainforests. These occur most along the equator of the Earth. It is the biome richest in biodiversity, containing upward of 50 million species. Tropical rainforests house 50% of all living species but comprise only about 2% of the Earth’s landmass, as seen in Figure 18.1. They occur in Central America, parts of South America, Africa, and southeast Asia.

There is lush plant vegetation because rainforests have abundant precipitation (360 cm or 148 inches per year). Without water as a limiting abiotic factor, the next most import- ant is sunlight. It is estimated that only 2% of sunlight actually reaches the tropical rain- forest floor. Most is filtered through the thick canopy layer, which is made of the animals and leaves and branches of treetops (Figure 18.5).

Canopy layer

Is the upper layer that is made of the leaves of treetops, in forest ecology.

30 20 10 0 −10

Tropical rain

forest

Average temperature (°C)

300

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(cm)

400

Tropical seasonal

forest Temperate deciduous

forest

Woodland Taiga

Tundra

Temperate rain forest

Thorn forest

Desert

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Shrubland Savanna

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Figure 18.4 Using Rainfall and Temperature to Identify Biomes. Temperature and rainfall are the two most important factors determining a biome’s location.

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Competition in rainforest plants is fierce and is particularly directed at limited sun- light. Tropical plants have large, broad leaves adapted to capture low levels of light. Height is important for plants, and many vine species are found in rainforests. Some include epiphytes, shown in Chapter 17 to form commensalistic relationships with trees. Epiphytes climb to great heights to capture sunlight as well as water. They are some- times called “air plants” because they obtain their water from modified leaf structures or from roots suspended in the air. As it rains, epiphyte leaves and roots absorb water.

Logging, mining, and farming have encroached on tropical lands and caused loss of many of its species. Biodiversity loss is a serious threat to the environment and to human society. Some tropical rainforest species are endemic, meaning that they are unique only to those areas. As discussed in Chapter 7, once a species is extinct, it can never be returned to the Earth. Loss of these species also means the loss of the benefits they have to humans. Consider taxol, a cancer therapy, derived from the Pacific Yew tree, Taxus brevifolia. As these trees become increasingly endangered, access to taxol also does.

In deforestation, trees are cut and vegetation is burned (called the slash-and-burn technique) with farmland replacing the forest. However, only a thin layer tropical rain- forest soil is useful to farming. Most of the minerals and organic material are in the vegetation and not in the soils. Soon, rainforest regions become unproductive and this contributes to desertification, forming of new desert biome. As shown in Figure 18.6, dust blowing from the newly formed deserts of the Sahara creates environmental hazards. The increasing desertification process ruins lands and does not become replaced with farmland long term. Local populations point to the need for farmland and the money for its lumber as reasons to remove tropical rainforests. The farmland quickly turns to wasteland and the local population is left with fewer resources. As such, as shown in Figure 18.7, human populations in Borneo are building homes in rainforests cleared by city developers. In the long run, tropical rainforest destruction will have serious negative consequences.

2) Savannas (tropical grasslands). Some regions along the equator experience less rainfall than the rainforests and are called savannas (Figure 18.8). These are tropical grasslands with moderate precipitation (less than 150 cm or 60 inches), more than deserts but less than rainforests. They occur mostly in Sub-Saharan Africa and in pockets across South America and Australia.

Desertification

The process by which fertile lands experience rapid depletion of flora and fauna becoming a desert.

Savanna

Regions along the equator that experience less rainfall than the rainforests.

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Figure 18.5 Many Organisms Live within the Layers of Tropical Rainforests. The canopy is the thickest upper layer of vegetation, containing much of the species diversity. This group of parrots occupy the canopy of a tropical rainforest.

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Figure 18.6 The Expanding Desert. This ship has been left behind after the contraction of the Aral Sea in Asia. Water was used excessively and the sea shrank markedly over the past century. Inhabitants of this area can barely survive the lack of resources and dry conditions.

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Figure 18.7 Deforestation of Tropical Rainforests. This photo shows numerous roads being built in Borneo, Malaysia, directly into the rainforest, making way for human settlement for its growing population.

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Figure 18.8 Savanna of Serengeti, Africa. These wildebeests occupy many areas of this biome.

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Because they contain mostly grasses as plant life, savannas support many animals well adapted for herbivory. Zebras, buffalo, and wildebeests prevail along with smaller plant-eating animals, such as grasshoppers, ants, beetles, and termites.

Savannas are prone to fires because lightening quickly turns into infernos along the dry grasses. Most plants of the savanna have adapted to the frequent fires with a high root-to- shoot ratio. In these plants, most of their mass is underground, located in the root system. When fires blaze through savannas, they may destroy the upper part of the plant but it survives.

3) Deserts. These regions have the lowest rainfall of all the biomes (less than 25 cm or 10 inches per year). Plant life is very sparse in deserts; however, the higher the amount of annual rainfall is, the greater will be the population density of plant species in deserts. Some deserts receive almost zero precipitation, such as the Namib Desert of southeast Africa receiving less than 7 cm or 2.5 inches annually.

When we think of deserts, we often imagine them as hot all through the day and night hours. Deserts are hot only during the day and sometimes their temperatures reach over 58°C (136°F). However, they become very cold at night. They have the most extreme tempera- tures of all the biomes. Temperatures can fluctuate up to 55°C in the course of a day.

Deserts lack water and vegetation, which are able to retain heat at night and prevent surfaces from heating too quickly in the day. A tree will shade the area beneath it but also retain the heat as it is lost. A sandy soil of the desert simply exchanges heat without water’s bonds to make and break. Thus, because of lack of water, deserts lose the ability to moderate temperatures. Most of the heat absorbed in the daytime is radiated very quickly away at night. Recall that water’s properties, and their unique bonding features, were discussed as a stabilizing life force, in Chapter 2 of this text.

The biota of the desert is adapted for water scarcity. Plants either lose their leaves in the very hot seasons or they have hard, thick cuticles to prevent water loss. Cac- tuses are a good example of adapting to this biome (Figure 18.9). They have long roots, which reach deep into the ground to obtain water, and thick cuticles and are adapted to keep photosynthesis (and open stomata) short using their CAM method, as described in Chapter 4. Many desert plants are annuals, which thrive only for one season and produce seeds to avoid the dry conditions.

Desert animals are also adapted for water scarcity. For example, the camel drinks large amounts when water is available and can survive for weeks without a drink. Other animals burrow deeply to avoid the hot temperatures of the day.

Root-to-shoot ratio

The dry weight of the root divided by the dry weight of the shoot.

Desert

A dry, barren area with little or no rainfall.

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Figure 18.9 Desert Biome. The Sonoran Desert of North America. Little rainfall makes many species of cacti, including the treelike saguaro (Carnegiea gigantea) in the photo well adapted for dry conditions.

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4) Chaparral. This ecosystem type is often overlooked as a cross between desert and grassland, but a focus of our story as a desired destination by our character.. However, it has its own unique biome; it is found only on dry coasts. It occurs along the Mediterranean and the southwestern coast of North America. Chapar- ral is seen frequently in movies about the Roman era in Europe, Africa, and Asia Minor. It was probably the climate of the Roman Empire, as it follows along the borders of the old regime.

Chaparral is characterized by mild winters and hot and dry summers. It has more rainfall than desert but less than tropical grasslands. Chaparral is dry and therefore has frequent fires, much like tropical grasslands. Its plant life is fire adapted as well and has high root-to-shoot ratios. Plants appear shrubby with small, leathery leaves (Figure 18.10). Large trees do not grow in chaparral and most of the animals are small rodents.

5) Temperate grasslands. In our story, corn fields predominated in the temperate grasslands of the American Midwest. Before humans cultivated the Midwest, there were no crops and only grasses and small shrubs prevailed. The temper- ate grasslands have moderate levels of rainfall (less than 75 cm or 30 inches), greater than deserts and less than savannas (Figure 18.11). This limited amount of precipitation inhibits the growth of woody shrubs and trees. Temperature grasslands are also called prairies. They occur in the Midwest of the United States, in much of eastern Europe and in scattered portions of Africa, Asia, and Australia (Figure 18.12).

The biome is used throughout the world as farmland. Grasslands are the bread- baskets of the world, feeding the human population. There is a rich layer of topsoil in grasslands. It contains a generous layer of detritus, or dead organic matter that forms as grasses die. This layer, also called sod, contains needed organic matter and minerals to sustain the growth of crops.

As described earlier, grasslands are usually located inland and have warm summers and cold winters. Rodents such as prairie dogs and other small mammals live as burrow- ing organisms to avoid predators on the prairie. Large animals adapted for herbivory are

Chaparral

A type of biome characterized by shrubs and rodents in dry conditions, around the Mediterranean and southern California.

Temperate grassland

Are terrestrial biomes whose main vegetation is grass and shrubs.

Detritus

Dead organic matter that forms as grasses die.

IS IT waRmER In CoaSTal BIomES Than IT IS In InlanD BIomES?

Coastal biomes are surrounded by water and therefore have modified tem- perature changes. Water, held together by many hydrogen bonds, are formed and broken with heat. Hydrogen bonds absorb energy when temperatures warm and release energy when temperatures cool. Water in any biome creates stability in temperature.

When weather warms it is also initially cooler on coastal biomes than in the interior ones. Often the weather shows wide variations in the inland biomes, such as the American Midwest and the plains states, which are both far from large water masses. These biomes experience much wider tempera- ture variations. Highs and lows are unable to be moderated by water’s hydro- gen bonding potential. Inland biomes usually have colder winters and warmer summers.

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Figure 18.10 Chaparral Biome. Chaparral of the Santa Lucia Mountains of California has many drought-resistant shrubs, which occupy most of the plant community.

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Figure 18.11 Temperate Grassland Biome. Tall prairie in eastern Kansas. The hitchhiker followed our story’s character into the grasslands.

Figure 18.12 Bison on a Prairie. They graze to a point where herbivory keeps many plants from growing to full size.

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native to the region, including the North American Bison. Grazing by bison also limits trees and shrubs, keeping the vegetation almost exclusively grasses.

6) Temperate deciduous forests. Our story began with a drive through the north- eastern U.S. temperate forests. They are also located in the western North Amer- ican coast, eastern Asia, eastern Australia, Europe, and New Zealand as well as pockets in South America.

The story depicted abundant plant life in temperate deciduous forests supported by ample rainfall (121 cm or 48 inches). While there are cold winters, there are also warm summers, long enough for a full growing season for most angiosperms. Trees lose their leaves to preserve water during winter months. The trees are called deciduous, from the Latin word “deciduus” meaning “to fall” because plants lose their leaves. When the autumn arrives, the foliage is beautiful as chlorophyll dissipates in leaves, revealing the carotenoids (yellow) and anthocyanin (red) pigments, which are colorful (Figure 18.13).

However, plant life is not nearly as abundant as compared with tropical rainforests. While temperate forests have about only 90 dominating tree species per hectare (2.5 acres), tropical rainforests have over 450 species. A temperate forest comprises an upper canopy of beech, maple, oak, hemlock, and hickory. Its lower layers of shrubs include berry plants, mountain laurel, herbs, ferns, and mosses. Animal life is also diverse, with large animals such as deer and coyotes and smaller ones including porcupines, rabbits, woodchucks, and beavers.

7) Taiga. When our driver reached higher altitudes, he encountered taiga, a biome characterized by long, cold winters and lower levels of rainfall. They dominate in higher latitudes of the globe, including most of Canada, Scandinavia, and Russia.

Taiga contains plants that include mostly cone-bearing (coniferous) evergreen trees, including hemlock, fir, and spruce (Figure 18.14). Evergreens are able to withstand the cold temperatures. They do not need to lose leaves during the long winter months. This way, energy is not lost in leaf abscission (drop) as in deciduous plants. Plants occur in stands across taiga. Some trees thrive, such as Alders, seen in our story. They evolved an advantage over other plants: they contain nitrogen-fixing bacteria in their root nodules. This mutualistic relationship allows Alders to exploit taiga’s nutrient and mineral-poor soils because their bacteria provide it.

Temperate decidu- ous forest

A forest type characterized by leaf- shedding trees.

Taiga

A swampy, subartic forest dominated by conifers.

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Figure 18.13 Autumn in New York. A temperate deciduous forest has many colors as the chlorophyll dissipates from the leaves of trees leaving other pigments to show their colors.

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Taiga has long periods of sunlight in the summers and very short periods (less than 6 hours) in the winters. Thus, during summer months, crops grow rapidly with excess sunlight for photosynthesis. Yields are high in these regions and crops are productive for short seasons.

The animal life found in taiga is also adapted for cold temperatures. All have thick fur coats to survive the long winters. Large animals such as the caribou, elk, and moose predominate. Their predators are wolves and bears, which also migrate to taiga for food.

8) Tundra. Along the top of the globe, tundra encompasses the higher latitudes located only in very cold conditions and minimal sunlight. Northern portions of Canada, Russia, and Alaska are regions with tundra. Tundra covers almost 20% of the Earth’s landmass (Figure 18.15).

Annual precipitation is very low in tundra regions (less than 25 cm or 10 inches per year). Some small trees and shrubs do grow along the sides of lakes and streams because of access to water. Otherwise, rainfall limits plant growth. While vast, its cold tempera- tures are also not favorable to plant growth. A layer of permanently frozen subsoil, called permafrost, extends all through the tundra. Permafrost remains frozen at all times of the year, preventing larger trees and shrubs from rooting into the soil.

Tundra

A tree-less area near the North Pole.

Permafrost

A layer of permanently frozen subsoil.

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Figure 18.14 The Taiga Hills in Canada. Coniferous forests occupy large, colder regions of the northern hemisphere.

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Figure 18.15 Tundra Has Short Growing Seasons, Cold Temperatures, and Permafrost Limits Plant and Animal Lives. Tundra occurs across the northernmost regions of the globe.

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Thus, tundra appears barren, with only small grasses and lichens able to withstand the weather. However, in summer months, life appears. In the summers, herbs grow rap- idly along with small grasses. Migrating birds and large animals such as the caribou and musk ox visit the biome. They find food and isolation away from predators. Perhaps our driver in the story could have escaped his predator, the hitchhiker in this biome as well?

9) Polar ice caps. The ice caps cover the very reaches of the north and south poles, including all of Antarctica. They are almost one mile in thickness and extend across almost 98% of Antarctica. These areas are comprised of not land but almost all ice. It is estimated that more than half of the Antarctic surface does not have actual land beneath it. Almost all of the arctic is merely ocean below (Figure 18.16).

There is very little precipitation (4 cm or 2 inches per year) on the ice caps and extremely cold temperatures, reaching to −89°C (−129°F) at the South Pole. The ice caps are quite barren, but its inhabitants include bacteria, small lichens, and a few mam- mals, such as whales, polar bears, and penguins. There are about 100 species of mosses, 25 species of liverworts, and only 2 flowering plants that are found in Antarctica. Plant growth is accomplished in only a few weeks in the summer. The Antarctic Peninsula has the most moderate climate, home to most of these organisms (Figure 18.17).

Polar ice caps

Dome-shaped ice sheets that slope in all directions from the north and south poles.

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Figure 18.16 Polar Ice Caps. They are composed primarily of ice layers with very little life.

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Figure 18.17 Antarctic Is Comprised of Almost All Ice with Very Few Plants and Animals. Most life in Antarctica exists along the Antarctic (Palmer) Peninsula, shown in the photo above.

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There are human, scientific research stations in different regions at the ice caps at both poles. Some estimates of minerals and oil deposits in the polar ice caps have stimulated political jockeying, claiming rights to mine, and drill in the North Pole. Russia recently announced intentions to extract resources from its northern polar ice caps. In Antarctica, the exploitation of resources has been prohibited by the Protocol on Environmental Pro- tection to the Antarctic Treaty of 1998. Several nations have laid claim to the areas of the continent, but the treaty agrees that it will be used for “peace and science” only. Many resources are expected to be found beneath the ice in Antarctica (Figure 18.18).

Figure 18.18 National Claims for Antarctic Resources. Several nations claim ownership of the regions in Antarctica, sometimes with conflicting boundaries.

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Figure 18.19 Lake Baikal in Russia Contains the Most Freshwater of Any Single Lake on the Earth, with Approximately 20% of the World’s Freshwater.

aquatic Biomes There are many environmental concerns, most a result of scarce resources. Frequently, in history, shortages in resources have stimulated crises in human societies: salt short- ages, energy shortages, lack of food, lack of metals, lack of minerals, to name a few. However, the greatest shortage of the future may become the “water crisis.” Water’s scarcity has limited population growth since the ancients and our society may be headed for a water scarcity crisis. There are three types of water or aquatic biomes: freshwater, estuaries, and marine biomes.

Water is the most important nutrient in every living organism. As discussed in other chapters, organisms cannot survive long without a constant intake of water. It may appear to many readers that water is not scarce nor is very abundant. However, you will see that it is the scarcest of our resources. While roughly three quarters of the Earth’s surface is covered in water, not much is accessible.

Freshwater Biomes Only 2% of that water is freshwater, readily useable to organisms. All the rest is saltwa- ter, which is toxic when ingested by humans. Most of the world’s freshwater is found in only certain regions. For example, the Great Lakes of North America contain over 21% of the Earth’s surface freshwater. The largest amount of freshwater in one region is found in Lake Baikal, Russia (Figure 18.19). It contains about 20% of the world’s freshwater. Many regions of the Earth have little or no available water for their societies. Regions of Africa, Australia, and Asia have very little access to freshwater and experience frequent droughts. The tragedy of droughts occurs in many parts of the world and limits food sup- plies. World hunger problems are linked to water scarcity needs because crops need water.

Limnology is the study of freshwater, and the importance of clean water to human society cannot be overstated. It divides freshwater systems into two types: ponds and lakes; or rivers and streams.

1) Ponds and lakes. These are still or standing bodies of water. Ponds are shal- lower than lakes but both may be classified based on their level of growth, or productivity of aquatic populations within them. Algae, bacteria, and other plant life are measured to determine a lake’s productivity. Oligotrophic lakes, such

oligotrophic

Lakes with low levels of productivity and abundance of dissolved oxygen.

Productivity

The production rate of new biomass by a person or community.

limnology

The study of freshwater systems.

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Cool temperatures and high oxygen

concentrations provide a suitable environment for fish such as trout

and whitefish.

Low availability of nutrients, especially

phosphorus and nitrogen, support low densities of

phytoplankton and vascular aquatic plants.

Warm temperatures and low oxygen

availability provide environments favoring

tolerant fish such as catfish and bowfins.

High availability of nutrients, especially

phosphorous and nitrogen, support high densities of

phytoplankton and vascular aquatic plants.

Invertebrate species requiring high oxygen

concentrations are dominant in the benthic fauna.

Steep shoreline and deep bottom reduce heating during summer and help maintain lower

water temperatures.

Benthic invertebrate biomass is high and dominated by species tolerant of warm

temperatures and low oxygen.

Shallow bottom reduces total water

volume and increases heating in summer.

Oligotrophic lake Eutrophic lake

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Figure 18.20 Oligotrophic and Eutrophic Lakes. Oligotrophic lakes have little productivity and few organisms compared with eutrophic lakes.

as Lake Baikal, have very little growth of organisms in its waters. They are often deep and clear but not very productive. Eutrophic lakes contain many growths of organisms and therefore have a high rate of productivity. They are usually shallow and murky waters. A comparison of the two lake types is given in Figure 18.20.

Lakes and ponds have three layers, each of which has different characteristics (Figure 18.21). The upper layer is called the epilimnion, in which sunlight first hits. Algae known as phytoplankton grow here, often shading out those organisms beneath their layer in eutrophic lakes. The middle portion of lakes is called the metalimnion. Floating organisms feed on phytoplankton in this layer, called zooplankton. Often algal blooms occur in this layer, which can disrupt aquatic ecosystems. The lowest layer is called the hypolimnion, in which there is little productivity because light does not reach so far deep. Temperatures are coldest in this layer during the warm seasons and warmest during the cold season. Aquatic life is able to move to and from the hypolimnion to find the right water temperature.

2) Rivers and Streams. These are moving bodies of water (Figure 18.22). They contain more dissolved oxygen than ponds and lakes because their waters are moving, exchanging gases with the air. It is an open system and it obtains many of its nutrients from drainage from the surrounding land. Rainfall washes in organic materials (as well as pollutants), which increase the productivity of rivers and streams.

Eutrophic

Shallow and productive lakes.

Epilimnion

The top-most layer of lakes and ponds.

metalimnion

The middle portion of lakes.

hypolimnion

The lower-most layer of lakes and ponds.

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Epilimnion

Metalimnion

Hypolimnion

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Figure 18.21 Layers of Lakes: Epilimnion, Metalimnion, and Hypolimnion. Each layer has different characteristics based on light penetration and temperature and dissolved gases.

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Figure 18.22 In Rivers, Water Flows More Slowly than in Narrower Streams. Water flows quickly through this Swiss river.

Estuaries When rivers and streams join saltwater, they are classified as estuaries. The salinity, or concentration of dissolved solutes, of estuaries varies with its distance from the ocean. The ocean is the source of the salinity, as it is saltwater. Estuaries are also the most pro- ductive aquatic biome. Nutrients deposit in estuaries from the many rivers that flow into them before entering the ocean. This also leads to increased pollution, especially in the form of phosphorous as an agricultural waste.

Organisms in estuaries are adapted to different levels of salinity, which determines their locations. Mollusks inhabit estuaries, often embedded in its soils beneath the water. Oysters are commonly found in estuaries, along with other populations that feed on oys- ters – worms, crabs, and snails, for example.

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Some organisms wander the estuaries, including several crustacean species such as lobsters, crabs, and fish. A great deal of fishing occurs in estuaries because these organ- isms are delicacies. Overfishing is a serious concern, disrupting ecosystems and driving some species to extinction in areas.

Marine Biomes All bodies of water that are saltwater are considered marine biomes. As stated earlier, about 98% of the Earth’s water is contained within marine biomes. The study of its biol- ogy is called marine biology. The oceans have an average depth of about 4 kilometers (2.5 miles). The most limiting abiotic factors in marine biomes are light and food. Light penetrates into the water most efficiently to about 100 meters (325 feet). This means that beneath this layer, limited plant life can exist. Therefore, oxygen is present mostly in these upper layers, reaching 200 meters (650 feet) in the ocean.

There are three layers of marine biomes (Figure 18.23). The intertidal zone occurs between the high and low tides along the coasts. It is a harsh environment, with continual change and crashing waves. Nonetheless, the seashore has plenty of living creatures. The next neritic zone extends from the shore to about 100 kilometers (30 miles), reaching a depth of about 200 meters (650 feet). This zone lies above the jutting of land called the continental shelf. Coral reefs are found in this region, the most beautiful and richest ecosystem on the Earth. Once past the continental shelf, the open-sea zone forms the rest of the ocean. Here it reaches its great depths. The top 200 meters of the open-sea zone is called the photic zone. It contains most of the photosynthetic life – namely, phy- toplankton. There is a great diversity of life in the oceans. Beyond this layer, the meso- pelagic zone has little light. Many strange organisms that exhibit bioluminescence have

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Figure 18.23 There Is Great Diversity in the Zones of the Marine Biome. Most life in the open sea occurs within the photic zone, where light drives photosynthesis and plant growth. The slope of the land is exag- gerated in the figure to save space.

marine biology

The study of saltwater organisms. Intertidal zone

The area that is above water level at low tide and below water level at high tide. neritic zone

The zone of ocean where sunlight reaches the ocean floor. open sea zone

The main body of ocean or sea. Photic zone

The part of ocean where sunlight penetrates sufficiently and influences the growth of living organisms. mesopelagic zone

The ocean layer that receives little sunlight.

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evolved in this zone. This region is very dark, and these organisms use bioluminescence to communicate. Below 1500–2000 meters is the abyssal zone, meaning “bottomless.” In this zone, there is tremendous pressure from water above and no light. Here, surprisingly some organisms thrive. Benthic organisms, those feeding at the bottom of the ocean, live off of material that dies and falls to the ocean floor. Others are chemosynthetic bacteria, which obtain energy from sulfur and hydrogen from hot springs and deep sea vents.

Ecosystems Ecosystems Make Up Biomes The biomes presented in this chapter are comprised of numerous smaller environmental areas. These areas are known as ecosystems, comprised of communities interacting with their environment. The mosses growing along the Antarctic Peninsula or the Alder trees of taiga containing roots with bacteria are each a smaller subset of much larger biomes – each is an ecosystem.

As you sit in the backyard of your garden and read this text or open the refrigerator and view a moldy piece of cheese, you should think of the word “ecosystem.” Ecosys- tems are all around us and shape our interactions. As we pass through them in the next section, much in the same way our character drives through the biomes, they become more appreciated.

As stated earlier, an ecosystem is a community of organisms in an area interacting with their abiotic environment. Many ecosystems comprise a biome. However, what happens in an ecosystem? How is energy transferred? What relationships do commu- nities have with their non-living world? Do these relationships follow certain patterns?

Energy Flow through Ecosystems Energy is trapped, transferred, and lost as it moves through organisms in the ecosystem (Figure 18.24). Roughly 1% of sunlight reaching the Earth is transformed by photosyn- thesis into the food’s chemical energy. This process starts the flow of energy through the environment. Organisms that carry out photosynthesis are called producers. Plants and phytoplankton, or marine algae, are the principal producers in natural ecosystems. They possess chloroplasts to carry out photosynthesis and convert sunlight into food, as described in Chapter 4. Over 100 billion metric tons of carbon is made by producers annually.

Producers nourish those organisms that eat them, known as herbivores. Herbivores are also known as primary consumers. Herbivory was discussed in Chapter 17, as a form of predation. Herbivores kill producers and eat them to obtain some of their energy. Cattle, sheep, insects, and humans are examples of herbivores. Some herbivores need the help of other organisms to digest the plant parts. These plant parts evolved against herbivory, such as cellulose plant cell walls. Herbivores contain microorganisms in them live within their guts and digest plant parts. This way, more plant parts provide energy for herbivores.

Organisms that eat herbivores are called secondary consumers or carnivores. Carni- vores are meat eaters – they eat meat by killing herbivores. Spiders, wolves, cats, frogs, and toads are herbivores. They eat their prey to obtain some of the chemical bond energy in those organisms.

Carnivores that eat carnivores are called tertiary consumers. This is generally as high as the pathway of energy flow goes. Humans are unique in the food chain. They are both herbivores and carnivores – we are omnivores, meaning that we eat both meat and

abyssal zone

A deep layer near the bottom of the ocean.

Producer

Organisms that carry out photosynthesis.

herbivore

Organisms that eat plants.

Carnivore (secondary consumer)

Organisms that eat herbivores.

Tertiary consumer

Carnivores that eat carnivores.

omnivore

Organisms that eat both plants and meat.

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Figure 18.24 Flow of Energy in an Ecosystem. Energy is trapped, transferred, and lost as it moves through living organisms in the ecosystem. Note the loss of energy in the associated pyramid of energy. At the bottom, 8000 kcal is reduced to only 8 kcal by the top of the energy pyramid. From Biological Perspectives, 3rd ed by BSCS.

plants. Our diets derive about 1/3 of its energy from animals and animal products and 2/3 from producers.

Each level of eating is called a trophic level. A trophic level is a group of organ- isms with a type of feeding style. For example, grasses are autotrophs because they are all photosynthesizers. Tertiary consumers are the “top” trophic level of all the feeders because they all eat other carnivores.

Movement through trophic levels represent the energy flow from one type of feeder to another. A pathway of energy flow is known as a food chain. The pathway through which energy flows in every system is the same: from producer to herbivore to second- ary consumer to tertiary consumer.

Sometimes food chains overlap within a community, forming a series of pathways called a food web. Food webs better represent a community’s transfer of energy because some organisms, such as humans, are omnivores and may occupy more than one trophic level. As such, complex feeding structures develop, as shown in Figure 18.25. The figure shows the many organisms involved in energy transfer within a forest ecosystem.

Trophic level

A group of organisms with the same feeding style.

Food chain

The pathway through which energy flows in every system: from producer to herbivore to secondary consumer to tertiary consumer.

Food web

A series of pathways formed when food chains overlap within a community.

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Ultimately, energy continues to flow from living systems after they die. Decomposers, such as bacteria or fungi and scavengers, including vultures and worms break down once living organic matter into energy. Decomposers return materials back into the environ- ment, recycling organic material, as will be discussed in another chapter. The start of the transfer of energy is, of course, photosynthesis and the end is bacteria of decay.

Energy pyramids: not Cutting out the Middle Man There are many more grasses in temperate grasslands than there are bison. There are usually more palms in a tropical forest than there are cheetahs. Both bison and chee- tahs are higher on the food chain than palms and grasses. High status on the food chain has drawbacks. Producers, such as grasses, get their energy directly from sunlight. As a Bison grazes on grasses, it uses energy to do this. Energy is lost along the way as heat. There is a net loss of about 90% of energy due to metabolism and is lost in feces. Metabolism loses energy as heat; and feces are undigested matter, which is also unused by organisms. Together, very little of the energy trapped from sunlight moves along an ecosystem, with most dissipated.

We say that there is a net transfer of only 10% of energy per jump in trophic level. Think of each trophic level jump as having a “middle man,” who takes a 90% cut in your profits every time it deals with you. It is a terribly inefficient system but it works the same in every ecosystem. Each time a middle man is involved, energy is taken out of the system. Thus, more energy is concentrated at the bottom of a food chain compared to the top in any ecosystem. The energy pyramid, shown in Figure 18.26, is a pictorial representation showing the net loss of energy as it travels up a food chain.

The losses across trophic levels may also be measured in biomass. Biomass is the total organic matter in an ecosystem. It is the sum total of the weight of all the plants and

Decomposer

Organisms that break down once living organic matter into energy.

Scavenger

Animals that feed on dead or decaying matter.

Energy pyramid

A pictorial representation showing the net loss of energy as it travels up a food chain.

Biomass

Is the total organic matter in an ecosystem.

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Figure 18.25 Food Web of an Eastern Deciduous Forest. The many complex relationships are simplified in comparison with nature’s intricate mechanisms.

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Figure 18.26 Energy Pyramid: The Middle Man Cuts Energy Flow.

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Figure 18.27 Pyramid of Biomass. Higher tropic levels in a tropical forest in Silver Springs, FL show far less biomass than lower levels.

animals in an ecosystem. Suppose that a bison grazes on those grasses. It adds biomass, but not as much as you might think. If a bison eats 100 pounds of grass, it only gains about 10 pounds of weight. Those consuming bison only obtain 10% of the biomass of their prey. With each succeeding level in the food chain, only 10% of biomass is conserved. This is known as the 10-percent rule for calculating net transfer of energy in ecosystems. The pyramid of biomass in Figure 18.27 shows the net loss of biomass along food chains.

Vegetarians Cut out the Middle Man Ecologically, it is more efficient to consume organisms closer to the bottom of the food chain. Vegetarians, who consume primarily producers, do not experience the higher losses in energy seen at higher trophic levels. A more sustainable strategy for eating is to tap lower levels of the food chain. This way, biomass (or food) is more easily conserved, saving food resources. Most of the developing nations rely on this strategy. However, the obesity epidemic expe- rienced in the United States and other developed countries is linked with diets higher in

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the food chain. Eating a large biomass of carrots, for example, does not translate into the same weight gain as eating the same biomass of steak. Eating lower on the food chain may conserve energy resources in the ecosystem and is healthier for us (Figure 18.28).

Ecosystem Disturbance and Ecological succession: Communities Change over time When ecosystems are disturbed, they do not simply die off, never to return. Ecosystems undergo changes when there are natural disasters: volcanoes, floods, earthquakes, fire, and lightening. Humans also create disturbance in building projects and wars. However, nature slowly but surely reclaims the areas, and we see a return to a state of normalcy.

Ecological succession is the process by which nature reclaims an ecosystem after it has been disturbed (Figure 18.29). It occurs slowly over many years of time. Ecolog- ical succession follows certain, predictable stages of change. The first stage, after a

Ecological succession

The process by which nature reclaims an ecosystem after it has been disturbed.

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Figure 18.28 Eating Lower on the Food Chain (such as Fruits and Vegetables of Producers) Conserves Energy and Taps into the More Renewable Resources of an Ecosystem.

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Figure 18.29 The Lichens and Mosses in This Beautiful Ecosystem (Primary Ecological Succession) from a Once-glaciated Area Will Eventually Become a Thriving Forest (and Climax Community).

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disturbance, is colonization of an ecosystem. The area may be bare rock or barren soil with no life. Only organisms such as lichens and bacteria are able to survive. These organisms are able to grow in the harsh conditions found after a major disturbance.

Colonizers are the first stage in primary succession. Primary succession is the series of stages that start succession, in which there is no life and no soil in an ecosystem. Its organisms prepare the soil for future organisms. Lichens for example secrete acids and break down rock into soils and minerals. Continual breaking down of materials forms thicker and richer soils. After lichens and bacteria produce soils rich enough to support higher plants, seeds from those plants germinate. Mosses arrive early on, and then herbs and small shrubs. Trees arrive and eventually those which grow taller and tolerate shade better win out over the others.

Colonizers and small shrubs are eventually replaced. While they were the only organisms able to exploit the ecosystem when it was nutrient poor, it is no longer the best competitor. Larger plants usually win out over smaller plants and longer-lived species tend to persist. The winning organisms endure in a stable and self-sustaining community, known as a climax community. Theoretically, the climax community is the highest level of organization for an ecosystem. Its populations “won” the battle and the payoff is that they remain forever in the climax community.

However, disturbances are a guarantee in nature. Secondary succession occurs when an established ecosystem is disturbed but some life and soil remains behind. While primary succession takes thousands of years, secondary succession usually pro- ceeds quickly, within decades or a century. During secondary succession, a disturbance changes the ecosystem. The changes to an abandoned farm field are an example of secondary succession. When it is no longer farmed, disturbance ends and the natural biota return. First, smaller plants and animals colonize the field and eventually shrubs and bushes take over. Seeds from larger nearby trees land and germinate. Seeds rise to a new population of trees, which outcompete the smaller plants for sunlight and water. Those former plants die away and the trees then crowd and compete with each other. It is an intense fight for survival, except that it is not obvious because it occurs over many decades. White pine and cedar trees are not very shade tolerant, and get overgrown by hemlock, beech, and maple if the old field is in a temperate deciduous forest. Those plants are able to tolerate the shade well and can grow without disadvantage from the bottom of the forest floor.

Disturbance occurs continually in biomes and ecosystems, but each time the com- munities return. Climax communities are only climax when they are undisturbed. Most of the time in nature, this is not the case. Ecosystems follow the predicted stages of eco- logical succession, succeeding pioneer species shown in Figure 18.29.

Some changes are difficult to undo. The massive amount of encroachment into nat- ural areas has led to the formations of pockets of isolated ecosystems. These pockets are called fragmented meta-populations. These populations are cut-off from the rest of their community due to human development. The character is our story begins his trip excited to combat tarring of roads, which are a main cause of fragmented ecosystems. For example, many malls have constructed circular ramps that connect with local roads and highways, as shown in Figure 18.30. They place decorative, small ponds in the center of the circular road. Of course, as you recall from Chapter 10, amphibians breed in ponds. The circular road acts as a death trap for those entering the pond to mate and those born and leaving the pond (Figure 18.30). Amphibian deaths have risen rapidly as an effect of this trend in modern landscaping.

Colonization

A process by which a species spreads to new areas.

Primary succession

The series of stages that begin ecological succession, including lichens and mosses in a disturbed area.

Climax community

The highest level of organization for an ecosystem.

Secondary succession

The process that occurs when an established ecosystem replace organisms and soils of primary succession.

Fragmented meta-population

Pockets of isolated ecosystems due to massive amount of encroachment into natural areas.

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CHECk oUt

summary: key points

• Biomes play a vital role in providing a habitat for organisms but the human exploitation of their resources sometimes threaten their functioning.

• Biomes are discrete sets of ecosystems, which occur across large regions of the Earth. • Topography in local areas has effects on climate in biomes. • The nine major biomes of the world are influenced by three important abiotic factors – light, alti-

tude, and water availability. • The three types of aquatic biomes are freshwater, estuary, and marine systems. • Energy moves from producers to herbivores and finally to consumers in an ecosystem. • Ecological succession, over time, changes soils and organisms within an ecosystem after disturbances.

Figure 18.30 Vanity Ponds in Malls and Surrounding Housing Developments Have High Incidences of Amphibian Deaths due to Their Placement within Roads.

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summary Biomes are ecological regions, which occur over wide areas of the Earth. Humans both derive life’s resources from the biomes of the Earth and enjoy their beauty. Sometimes, human activities, such as overuse of resources, negatively impact biomes. Within biomes, local topography effects smaller changes in abiotic factors to produce regional climates. The nine major biomes of the world are most influenced by light, altitude, and water avail- ability. The aquatic biomes differ in their salinity and locations across the globe. Within all of these biomes are ecosystems, which transfer energy through its organisms. When an ecosystem is disturbed, it undergoes a process of reclamation, returning it back to normal.

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abyssal zone biomass biome canopy layer carnivore (secondary consumer) chaparral climax community colonization decomposer desert desertification detritus ecological succession ecosystem energy pyramid epilimnion estuary eutrophic food chain food web fragmented meta-population herbivore hypolimnion intertidal zone limnology marine biology

mesopelaegic zone metalimnion neritic zone oligotrophic omnivore open sea zone permafrost photic zone polar ice caps primary succession producer productivity savanna scavenger secondary succession taiga tertiary consumer topography trophic level tundra rain shadow desert root-to-shoot ratio temperate deciduous forest temperate grassland tropical rainforest

KEy TERmS

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Multiple Choice Questions

1. How do fragmented meta-populations form? a. through high birth rates b. through human activity c. with community interdependence d. with population interdependence

2. Rain shadow deserts always form on the ________ side of a mountain chain. a. north b. west c. upwind d. downwind

3. Which is NOT a characteristic of deserts? a. hot temperatures b. stable temperatures c. cold temperatures d. all of these are desert characteristics

4. Freshwater biomes represent _____ % of the Earth’s available water. a. 2 b. 10 c. 50 d. 99

5. A layer of permafrost is found in: a. taiga b. tundra c. deserts d. estuaries

6. Which term includes all of the others? a. ecological succession b. climax community c. colonization d. primary succession

7. Which represents a logical order, from start to end, of the flow of energy in an ecosystem? a. producer ➔ herbivore ➔ consumer ➔ bacteria b. consumer ➔ producer ➔ consumer ➔ bacteria c. herbivore ➔ producer ➔ bacteria ➔ consumer d. herbivore ➔ consumer ➔ bacteria ➔ producer

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8. A scientist discovers a tree has fallen in a stand of pines. He notices new organisms now growing in the open space. Which variables determine the direction of this process? a. soil b. populations c. minerals d. all of the above

9. Which of the following biomes is most likely to have a fire? a. chaparral b. temperate deciduous forests c. estuaries d. tropical rainforests

10. Which biome contains the greatest biodiversity? a. chaparral b. temperate deciduous forests c. estuaries d. tropical rainforests

short answer

1. Describe how humans create fragmented populations within ecosystems.

2. List two types of saltwater biomes. Which is likely to provide more protection for its organisms?

3. Define the following terms: producer and herbivore. List one way each of the terms differ from each other in relation to their a. function; b. role in transfer of energy in an ecosystem; and c. relationship with each other in the environment.

4. Explain how a rise in altitude is the same as a rise in latitude on the globe, ecologically.

5. Draw an energy pyramid for a forest ecosystem. Be sure to label each trophic level and give a plausible example for each level.

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6. Describe how 2400 pounds of biomass, when eaten by an elephant, becomes only 240 pounds in her body.

7. Draw a sketch of a food web using arrows to show the flow of energy through the ecosystem. Use the following organisms in your sketch: hawk, dove, cow, corn, grass, bacteria (actinomycota), and human.

8. Explain the process of primary succession from bare rock to beech tress. Use arrows to trace the flow of the animal and plant organism changes.

9. Explain why a high root-to-shoot ratio is important in chaparral.

10. Compare and contrast the characteristics of grasslands and temperate deciduous forest. Be sure to include one way the biomes have similarities and one way they are different.

Biology and society Corner: Discussion Questions 1. Deforestation is a serious environmental hazard. People in economically disadvan-

taged nations claim this is not the case. They feel that exploiting rainforest resources is their only way out of poverty. Research the issue. Form a plan for local farmers, within a developing nation, to implement other methods to improve their situation.

2. Describe how estuaries are easily exploited for its resources? How can safeguards be introduced to prevent this overuse? Research the issue in Chesapeake Bay to make a complete answer.

3. You invite your friend to your home for a meal. Your friend is a vegetarian but offends your father, after declining to eat the steak dinner served. Who is right and who is wrong? What should you do to help? List reasons why a person may be a veg- etarian, in answering this question. List reasons why your father may be offended.

4. The United States built Las Vegas right in the middle of a desert in Nevada. Defend the move to do this. Research those techniques that are able to change desert into arable land. Criticize the location of Las Vegas, ecologically.

5. The Protocol on Environmental Protection to the Antarctic Treaty of 1998 showed cooperation among nations. However, several nations still lay claim to the regions on the continent and have not given those claims up. Suppose that a nation sends troop to occupy the Antarctic Peninsula. Write a plan to diffuse the situation.

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Figure – Concept Map of Chapter 18 Big Ideas

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Biosphere: Life Links to the Earth 19

Comet in the sky

Charred trees in the forest

Villager interviewedA man (Jerry?) looking up at sky through telescope

Meteorite from Tunguska

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the Case of the Big Blast The morning of June 30, 1908, Tunguska, Russia: “It was a visitation by the god, Ogdy!” exclaimed the Siberian villager as he told the story of the great blast. “High in the sky a heavenly body split it into two.” Just say the word “Tunguska” and the people in the area shiver. “The gods hated Siberia and struck them down with their might” continued the man. He was one of the few eyewitnesses to the event. Local people were scared to speak of it for years. The villager continued, “The sky was on fire and stones were fall- ing everywhere from the sky.”

The incident was a mega-blast in the sky over Tunguska. The witness spoke of the event only years afterward, while interviewed by Western scientists. They lived in fear of the gods, who many locals believed sent the blast to punish them. The recount of this event is described by locals as “the day the sky blew apart.” It is now ancient folklore but the ruins are still in the mountains of Tunguska in Siberia. Superstitions and fears of the gods returning with a vengeance led local Siberians to keep quiet about the incident.

The morning of June 30, 2008, Boise, Idaho, the United States: Jerry had gone to the 100-year commemoration of the Tunguska explosion at his local asteroid club. Jerry was an amateur astronomer who studied and followed all of the asteroid sightings. However, the Tunguska event was his favorite.

He read about the asteroid’s impact: The blast happened in the mountains and destroyed over 800 square miles of forest and over 80 million trees. No one was reported killed because the area was so remote but its impact could be felt throughout the Asian continent. All the way in London, seismic waves registered on the Richter scale – earth- quakes from the blast.

It is hypothesized that a large asteroid hit the Earth’s atmosphere at the site of Tun- guska, Russia in the Siberian forests. Scientists believe that the asteroid was about 120 feet across and exploded in the sky above Tunguska. When the space rock exploded, it caused ash and debris to emanate from the site. The asteroid traveled at a speed of 33,500 miles per hour. It is estimated that it weighed 220 million pounds. It must have heated up to 44,500°F. While it flew through the air, it exploded into many fragments, which is what the villagers saw causing the sky to be on fire.

Jerry’s breath was taken away as he read about the event. As an amateur astronomer, he was impressed to learn that it had the strength of 185 Hiroshima bombs. Jerry was waiting for the next time Haley’s comet would visit the Earth, once every 76 years. Its next sighting would be 2062 . . . Jerry hoped that it would not hit the Earth.

ChECk in

From reading this chapter, you will be able to:

• describe extraterrestrial threats to human society. • define the biosphere and describe abiotic conditions affecting its climate. • define and describe terms list. • trace the flow of key chemicals through the ecosystem including water, carbon, nitrogen, and

phosphorous. • describe negative human impacts on the biosphere.

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the Earth, the sun, and atmosphere the Earth’s Boundaries for Life The disturbance in the story shows what could happen when a space body invades the Earth’s thin layer of sky. This layer of global ecosystem, which contains all life on the planet, is called the biosphere. The Earth’s biosphere boundaries are not easily mea- sured. This zone of life on the Earth extends from the polar caps to equatorial zones (Figure 19.1). Boundaries above the Earth’s surface reach over a mile high in the atmo- sphere. Here, birds can reach their highest flight over the tallest mountains. Below the surface soils and in the ocean, single-celled microbes reside miles deep in waters of the

ChECk Up sECtion

In the story, an asteroid created a major ecological disturbance. Threats from extraterrestrial sources are real but the probability of an actual impact is small.

What kinds of global disturbances are caused by such an event in the biosphere? Research the asteroid impact event associated with the hypothesis for why the dinosaurs became extinct 65 million years ago.

Figure 19.1 Life on the Earth Exists in All Regions from Polar to Tropical. The bio- sphere contains life on land, underground, in waters, and in the sky.

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Biosphere

The layer of global ecosystem, which contains all life on the planet.

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Mariana Trench. The biosphere integrates the Earth’s living things and their interactions with water, rock, and air reservoirs – the hydrosphere, lithosphere, and atmosphere. Human activities that disrupt these processes and the life they support will be considered here in this chapter.

atmosphere: a Layer of protection The atmosphere is the gaseous layer surrounding the Earth held in place by gravity. Oxygen (21%) and nitrogen (78%) together make up 99% of gases in the atmosphere, as described in Chapter 2. Organisms that respire aerobically depend on atmospheric oxygen. The remaining 1% of atmospheric gases is made up of a variety of trace gases including argon, carbon dioxide, neon, and helium. Photosynthetic organisms as described in Chapter 4 require these trace components of carbon dioxide to drive the biological food webs. Water vapor is present in the atmosphere in varying amounts across the globe at any given time. Trace amounts of air pollutants including methane, ozone, chlorofluorocarbons (CFCs), dust particles and pollen, and microorganisms are present too. As a whole unit, the atmosphere that envelopes the planet serves to protect and moderate extreme forces acting on the Earth in just the right manner to allow for life to exist.

One essential service provided to the biosphere by the Earth’s atmosphere is the pro- tection from damaging high-energy solar radiation and deadly amounts of cosmic rays from space. Visible light and some infrared radiation do penetrate the atmosphere. The Earth’s surface and lower atmosphere are warmed by this low-energy radiation from the Sun. Energy that reaches the Earth is only a very tiny fraction, less than one billionth, of the Sun’s total energy, as discussed in Chapter 18. Nonetheless, each day, a tremendous amount of energy from the Sun arrives at the Earth’s surface. Of the energy that reaches the Earth, about 30% is rapidly reflected back into space, mainly by surfaces with high albedo or reflectivity such as clouds, snow, and ice (Figure 19.2). The remaining solar energy that is absorbed into the atmosphere is responsible for weather and climate pat- terns, drives water and chemical element cycles, and powers life on the planet beginning with photosynthesis.

Hydrosphere

All of the water on Earth’s surface.

Lithosphere

Earth’s outer part.

Atmosphere

The gaseous layer surrounding a planet.

Albedo

A proportion of solar energy that is reflected from the Earth back to space.

Figure 19.2 A Photo of the Earth from Space. Note the bright white areas of polar ice and cloud systems. Surfaces with high albedo, such as ice and clouds strongly reflect the Sun’s energy.

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solar Radiation: heat from the sun We know that the Earth is generally coldest at its Polar Regions and warmest near the equator. This latitudinal variation in temperature is due to the planet’s spherical shape (Figure 19.3). When sunlight strikes the Earth near the equator, it is nearly perpen- dicular and traveling the shortest possible distance directly through the atmosphere. These rays move into a concentrated surface area, delivering the most intense heating power. Contrast this with sunlight reaching the Earth’s Polar Regions. Here solar energy reaches the Earth at an oblique angle, travels a further distance through the radiation-ab- sorbing atmosphere to the curved surface. These rays are distributed over a larger sur- face area. Energy reaching polar areas is thus more diffuse resulting in lower surface temperatures.

Small alterations in the makeup of the atmosphere can have significant impact on the Earth’s climate by affecting incoming solar radiation. For example, large volcanic eruptions can emit large amounts of gas and ash into the upper atmosphere. Historically, some of these events have lowered global temperatures by a degree or two. Volcanic gases and fine ash can block or reflect portions of solar energy from reaching the Earth’s surface up to a year or more. The 1815 eruption of Mount Tambora in Indonesia contrib- uted to the 1816 “Year Without a Summer” where extreme cooling conditions were noted in the Northern Hemisphere. Reports of late frosts destroying crops and summer snows in New England and Europe were common. As in the chapter’s opening story, destruc- tion from large-scale atmospheric events such as the asteroid impact in Russia creates larger effects such as climate and ecosystem changes in the biosphere.

seasonal Changes in temperature The Earth tilts on its axis of spin at 23.5° from a line perpendicular to its plane of orbit. This tilt remains the same as the Earth orbits the Sun. It is responsible for the seasonal changes we experience here on the planet. The Northern Hemisphere tilts toward the Sun between March 21 and September 22 receiving more concentrated sunlight and longer days (Figure 19.4). For the other half of the year (September 22 to March 21), the Northern Hemisphere is tilted away from the Sun. It receives less concentrated sunlight and shorter days. Northern and Southern Hemisphere orientations are opposite each other in relation to the Sun for the same given time periods. Hence, when the Northern

Figure 19.3 Solar radiation varies with latitude due to Earth’s spherical shape. The sun’s radiation travels the shortest most direct route to the equator providing more intense heating. From Biology: An Inquiry Approach, 3rd ed by Anton E. Lawson.

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Hemisphere is experiencing summer, the Southern Hemisphere is experiencing winter. Seasonal variations in day length and temperature are more pronounced at the Polar Regions because of the Earth’s spherical shape and the tilt of its axis.

Global atmospheric Circulation affects Climate Differences in temperature at the Earth’s surface due to varying amounts of solar radia- tion reaching different locations are the driving force behind circulation patterns in the atmosphere (Figure 19.5). Hot surface temperatures at the equator from intense solar radiation heats surrounding equatorial air.

The hot air mass expands and rises up leaving a low-pressure area at the equator referred to as the intertropical convergence zone (ITCZ) or doldrums. Aloft, the warm air travels away from the equator. The moving air cools as it travels and is unable to hold the same high level of water vapor. Moisture exits the air mass as rain, quenching areas of tropical rain forest.

Intertropical convergence zone

The low pressure area at the equator resulting from the expansion and rising up of hot air mass.

Figure 19.4 Seasonal Variation of Solar Radiation. The tilt of the Earth on its axis remains the same as it orbits the Sun. In June, the Northern Hemisphere receives more intense sunlight and in December, the Southern Hemisphere receives more. These changes account for seasonal variation in temperature and hours of daylight.

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Figure 19.5 Global Atmospheric Circulation. Varying solar radiation by latitude warms equatiorial air masses. Upward flow of these air masses brings about global patterns of air movement idealized in three circulation cells per hemisphere. Air near Earth’s surface is deflected from north-south circulation by the planets rotation cre- ating east or west blowing patterns at different latitudes. Surface winds directions are shown with white arrows.

Polar cell

Descending cool, dry air

Rising warm, moist air

Descending cool, dry air

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Eventually, the air sinks down toward the surface at around 30° latitude north and south. The cool dry area descending around 30° latitudes absorbs moisture from the land below. Desert biomes are often found at these 30° latitudes as a result of these circulation patterns. The bulk of descending air flows back along the surface toward the low-pressure zone at the equator.

Air patterns show a similar upward movement at higher latitudes around 60° nearer to the poles. Cold dry polar air sinks at the polar extremes and flows toward lower lati- tudes generally beneath the warm air aloft flowing in a polar direction. These continually mobile air circulation patterns transfer heat from the equator toward Polar Regions. Air currents return polar air back in an equatorial direction, cooling the surface below as it travels. Air circulation moderates temperatures across the surface of the planet. The nature of global air flow patterns is such that some mixing of the entire atmosphere does take place. Anything held in the atmosphere – dust, ash, pollen, pollutants, and aerosols – can be spread globally as a result.

Winds: Movement Under pressure Differences in atmospheric pressure and the Earth’s rotation are contributors to the intri- cate horizontal movements of the Earth’s atmosphere known as winds. Gases that make up the atmosphere put pressure on the Earth because they have weight. This pressure can vary due to the changes in temperature, altitude, and humidity. Generally, stronger winds result from larger differences in pressure. Winds move from the areas of high pressure to the areas of low pressure.

Wind

The intricate horizontal movements of Earth’s atmosphere caused by differences in atmospheric pressure and Earth’s rotation.

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Figure 19.6 Surface Ocean Currents. Surface ocean currents are primarily wind driven, moving clockwise in the Northern Hemisphere and counter-clockwise in the Southern Hemisphere.

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The Coriolis effect describes deflection based on rotation. The Earth rotates from west to east. Wind patterns are deflected as a result of this spin. The Northern Hemisphere winds swerve slightly to the right of expected flow along pressure gradients and the South- ern Hemisphere wind to the left. These deflections point the winds of atmospheric circu- lation blowing from 30° latitude toward the equator in a western direction (Figure 19.5).

Since winds are named by the direction from which they blow, winds above and below the equator are known as the northeasterly trade winds in the Northern Hemisphere and southeasterly trade winds in the Southern Hemisphere. Similarly, winds moving pole- ward from 30° are deflected by Coriolis forces to blow toward the east. Naming them from their point of origin, they are termed westerlies. The cool dry air returning from the poles is deflected to the west like the trade winds and is termed the polar easterlies.

As described in Chapter 18, local geography combined with winds can affect rainfall and create desert areas. Moisture-rich air masses from wet areas often release water as rain while they rise over mountain ranges. The region past the mountains receives little mois- ture. These rain shadow areas often form deserts downwind of coastal mountain ranges.

hydrosphere: Global transport and Climate Control the Earth’s Waters Water’s moderating effect on weather and climate stems from its chemical property of high heat capacity. Heat capacity describes the amount of energy it takes to raise an amount of substance a given change in temperature. This means that water has a huge

Coriolis Effect

The deflection of a moving object with respect to the Earth’s rotation.

Trade winds

Winds that blow above and below the equator.

Westerlies

Winds that blow from the west.

Polar easterlies

Dry, cold winds that are deflected to the west like the trade winds.

Heat capacity

The amount of heat energy required to raise the temperature of an amount of substance.

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ability to absorb and hold on to heat, about 10,000 times greater than the atmosphere. Because of this, temperature fluctuations in water bodies are much less than those of the air around us. Vast amounts of heat are absorbed from the Sun and held by large water bodies. Temperatures in the areas near large water bodies are moderated by this heat- sink effect of water. Winter air temperatures will be raised as the water slowly releases stored heat to the surrounding air masses. Tropical areas will similarly be cooled by sea breezes from nearby water bodies.

The vast majority, 97%, of the Earth’s water is found in oceans, recall from Chap- ter 18. Ocean water contains an average of 3.5% dissolved salts that add to its density. Freshwater has low concentrations of dissolved salts. Some rivers estuaries such as the Hudson and the Mississippi form a salt wedge at the intersection of the two. Less dense freshwater is sectioned atop the saline ocean water in a wedge shape. This wedge for- mation fades in estuaries where strong tidal forces mix the waters. The remaining 3% of water on the planet is freshwater. A breakdown of freshwater reservoirs finds 69% is locked away in frozen polar icecaps and glaciers and another 30% is held underground (Figure 19.7). Only the remaining 1% or so is easily accessible in rivers, and lakes, as you may recall from Chapter 18.

ocean Circulation Major currents in the oceans affect terrestrial temperatures along coastal regions. Surface ocean currents are driven by winds and temperature. Masses of water flowing at the ocean surface are affected by trade winds and temperate westerlies. Water flows generally in the direction of prevailing winds forming major surface currents. Rotation of the Earth, grav- ity from the moon, location of landmasses, and topography or shape of the ocean basins also impact the movements of ocean currents. Generally, oceanic circulation moves clock- wise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere (Fig- ure 19.6). Notable spills of ship cargos, such as Nike sneakers and Yellow duck bathtub toys in the 1990s, have been used to study the flow of surface ocean currents in the North Pacific. Beachcombers on shore picked up and logged location and dates for such items found thousands of miles away from the spills from Oregon to Vancouver. Data entered into computers provided a model for seasonal flows in the North Pacific.

In addition to ocean surface currents, the circulation of global deep ocean water also has an influence on the Earth’s climate. This vast underwater current is driven by density differences in addition to temperature. Dense salty waters cooled by arctic air in

Freshwater

Water with low concentrations of dissolved salts.

Salt wedge

A wedge-shaped intrusion of sea water into a fresh-water estuary.

Figure 19.7 Freshwater Distribution on the Earth.

Earth’s freshwater distribution

Frozen in polar ice caps and glaciers Underground Readily available for use from rivers, lakes, and the atmosphere

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the North Atlantic sink deep into the ocean (Figure 19.8). This water flows south in deep under-ocean currents like a submarine river to the Indian and Pacific Oceans where it then rises to the surface. Surface currents of warmer water are wind driven to replace the sinking waters. This moves warmer water from the South Atlantic to the North Atlantic. These warm surface currents moving northward as the Gulf Stream flow keeps Europe and the eastern US waters warmer than expected. Without this warming flow, the United States would experience a cooler climate more like that of Canada. Global distribution throughout the oceans takes place as part of this massive conveyer belt-like flow. Heat and nutrients, along with pollutants, are moved in this way.

ocean–atmospheric interactions: El nino El Nino refers to a band of unusually warm ocean water that develops off the western coast of South America (Figure 19.9). The name El Nino refers to the “boy child” recall- ing Jesus the Christ child. It is in December around the Christmas season that these periodic warming effects in the southern Pacific were first noted. The pattern creates a disruption in ocean currents and causes dramatic changes in weather resulting in floods and droughts in far-reaching regions. The event is characterized by a 0.5°C (0.9°F) fluc- tuation in ocean temperature over the tropical central Pacific Ocean. The duration of the warming anomaly ranges approximately 1–2 years. El Nino events occur at intervals between two and seven years.

The initial forces that drive El Nino events are not fully understood by scientists but a series of notable changes are associated with event cycles. During the event, trade winds blowing west in the south Pacific weaken and may even reverse direction. Upwelling of normally cold nutrient-rich waters along the western coast of South Amer- ica (Figure 19.6) is blocked by warm Pacific surface waters being pushed eastward to

El Nino

A band of unusually warm ocean water that develops off the western coast of South America.

Figure 19.8 Global Ocean Circulation. Warm water from the South Atlantic Ocean moves to the North Atlantic as the Gulf Stream flow. As these waters are cooled by arctic air, the dense salty waters of the North Atlantic sink down into a global submarine river. Heat, nutrients, and pollutants are moved oceanwide by these deep ocean currents.

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the coast by strong surface currents. These warmer waters are usually held back from the South American coast by the western blowing trade winds. The lack of nutrient-rich waters limits plankton growth and can dramatically reduce local fish populations. The air along South America’s western coast is usually cool and dry but the warm waters of El Nino add moisture to air masses. Storms and floods result in the usually arid areas. Areas at the western reaches of the Pacific, Indonesia, and India experience extreme drought. Such changes in weather and fish populations have dramatic effects on the lives of people in countries that border the Pacific. Many rely heavily on fishing and agriculture to live (Figure 19.10).

In the case of La Nina “girl child” events, nearly reverse events occur (Figure 19.9). Increased upwelling of deep ocean waters occur along the western South American coast. Nutrient loading and fish populations boom during La Nina events. Increasing droughts occur along west coastal South America and stormy wet weather toward Indonesia. Cli- mate effects from the El Nino/La Nina events extend globally and social impacts are felt by changes in incidences of epidemic diseases. The cycle is linked to increased risks in mosquito-borne diseases such as malaria, dengue fever, forms of encephalitis, and fun- gal diseases in the areas that prone to flooding from these events.

Biogeochemical Cycles Biogeochemistry encompasses the chemical, physical, geological, and biological pro- cesses and reactions that govern the workings of the natural environment. Vital chem- icals cycle through the Earth and affect the availability of environmental resources.

La Nina

Cooling of the ocean surface off the western South American coast.

Biogeochemistry

A scientific discipline that encompasses chemical, physical, geological, and biological processes and reactions that govern the workings of the natural environment.

Figure 19.9 A Strong Warming Band across the Pacific Ocean Reaches the Western Coat of South America during El Nino Events.

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Environmental resources determine where organism will live. If an area has limited nitrogen in the soil, for example, many plants will not grow there.

Biogeochemical cycles move life’s necessities into and out of storage reservoirs for availability and usage. Let’s take a closer look at how water, carbon, nitrogen, and phos- phorous move between land water and air in the biosphere. In each biogeochemical cycle, materials are circulated and stored within the ecosystem.

Each chemical – H2O, C, N, and P – has varying time it spends stored in any given reservoir. Residence time tells us how long something is retained in a given storage reservoir in the biogeochemical system. Matter stored in rock in the Earth’s crust may have long residence periods of millions of years, for example. Ocean waters can have residence times for carbon on the order of hundreds of years. Shorter residence times occur in food webs and the atmosphere.

Water Cycle Water is necessary for life and its functions. In fact, recall from Chapter 2 that humans are made up of over 65% water. We are very much a part of the water and other biogeo- chemical cycles. All life continually requires inputs of water to keep us alive. Osmoreg- ulation in Chapter 16 demonstrates the difficulty in maintaining life on land, given our links to water needs.

Residence time

The average length of time that tells how long something is retained in a given storage reservoir in the biogeochemical system.

(a) (b)

Figure 19.10 Devastating Impacts of El Nino Events Include: a. stormy weather and flooding in Peru b. drought in Indonesia, c. increase in mosquito-borne disease in flooded areas, and d. decline in fish population off the coast of Peru.

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The Earth’s water is in constant motion, allowing water to become available for living systems. The water cycle moves water through various terrestrial, aquatic, and atmospheric regions as seen in Figure 19.11. The Sun’s energy is the main driver of the water or hydrologic cycle.

When heat from the Sun reaches wet surfaces (oceans, rivers, and lakes), water is converted from liquid to gas through evaporation. On very humid days, the atmosphere holds more water in gas form – water vapor. You can feel the “stickiness” from this water vapor in the air. Water vapor moves through the atmosphere where it condenses to small water droplets on particles, ice, or dust. Water droplets form clouds and eventually water falls back to the Earth as precipitation in the form of rain, snow, sleet, or hail. Rain may fall directly onto water bodies or land.

On land, gravity leads water to flow downhill via overland flow or surface runoff. Eventually, water reaches rivers or lakes and continues on toward oceans. A fraction of this runoff may infiltrate or soak into soils and move into groundwater flow. Ground- water can be stored below ground in aquifers (the saturated areas of bedrock) or con- tinue moving toward lakes or oceans. Cold regions may accumulate snow into ice caps or glaciers where water may reside for thousands of years. Temperate regions release snowmelt to surface runoff as they warm. Runoff finds its way into streams or ground- water for flow toward oceans and aquifers. Groundwater can also stay near the surface and seep into nearby rivers and lakes, or emerge upward from a land opening such as a freshwater spring.

Biogeochemical cycles work together to distribute the chemicals necessary for life functions on the Earth. The water cycle is the essential driver of other biogeochemical cycles including carbon, nitrogen, and phosphorous. Water moves these elements out of

Water cycle

The process by which water continuously moves on, above, and below Earth’s surface.

Surface runoff

The flow of water over the land surface.

Aquifer

Saturated areas of bedrock.

Figure 19.11 The Water Cycle. Energy from the Sun drives water’s movement across air, land, and ocean reservoirs. Most of the Earth’s water is held in the oceans. From Biological Perspectives, 3rd ed by BSCS.

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long-term storage in the Earth through weathering or breaking them down. Rivers then serve as a major form of transport, moving available elements to locations where living organisms can utilize them.

Carbon Cycle Carbon serves as a backbone for biological molecules including carbohydrates, proteins, and lipids. Terrestrial and marine food webs will cycle carbon in the atmosphere and oceans. Photosynthesis and respiration, described in Chapter 4, move these chemicals with relatively short residence periods.

Carbon fixation during photosynthesis moves carbon dioxide out of the atmosphere and into plants for availability in the food web (Figure19.12). Respiration returns carbon to the atmosphere as CO2. Atmospheric carbon exists largely as carbon dioxide (CO2). Carbon in the atmosphere is only a tiny fraction of the Earth’s total carbon storage. Impact on the biological world due to photosynthesis from this small quantity, however, is massive. The structure of living things is made mostly of this carbon.

Ocean waters are the second largest carbon reservoir on the Earth. Ocean waters hold carbon largely in the form of dissolved bicarbonate ions (HCO3−). Diffusion takes place between the ocean surface and atmosphere. Carbon in the ocean is available for biological uptake by marine organisms. Some organisms incorporate carbon into shells or coral reefs in the form of calcium carbonate (CaCO3). As these shelled organisms die and sink to the bottom of the ocean, they are buried with sediments. Ocean sediments

Figure 19.12 The Carbon Cycle. The vast majority of carbon is stored for long times in sedimentary rock. Only small amounts of carbon are found in the atmosphere as carbon dioxide, but changes in atmospheric carbon can have wide-ranging effects. From Biological Perspectives, 3rd ed by BSCS.

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are compacted with massive pressure from weight of the ocean water above. Over time, they become the sedimentary rock we know as limestone.

Carbon-rich sediments from decomposition of organic waste compressed into layers of the Earth form fossil fuel deposits of coal, oil, and natural gas. These resources are mined by humans for use as electricity from coal-burning power plants and fuel for auto- mobiles. Combustion of fossil fuels or burning of wood releases and returns a portion of stored carbon back to the atmosphere as CO2.

Sedimentary rock of the Earth’s crust is the planet’s largest carbon reservoir. Car- bon stored here can be locked away from use for millions of years. It is later released through either volcanic emissions or geological uplifting events. Uplifting events push the Earth’s crustal plates toward one another leading to upward movement of rocks or mountain building.

Greenhouse Effect and Global Climate Change The greenhouse effect is the process of trapping heat energy in the atmosphere (Figure 19.13). Without any greenhouse effect, the Earth would be diminished to a frozen rock, too cold for living organisms. Greenhouse gases are gases in the atmosphere that slow the release of heat from the planet to space by absorbing and re-emitting long-wave radiation heat back to the surface. Greenhouse gases in the Earth’s atmosphere include carbon dioxide, methane, nitrous oxide, ozone, water vapor, and CFCs. Water vapor and carbon dioxide (CO2) are the largest contributors to the Earth’s greenhouse effect.

Greenhouse effect

The process of trapping heat energy in the atmosphere.

Greenhouse gases

The gases in the atmosphere that slow the release of heat from the planet to space by absorbing and re-emitting long wave radiation heat back to the surface.

Figure 19.13 The Greenhouse Effect. Greenhouse gases including water vapor and carbon dioxide absorb and trap some of the Sun’s heat and reflect it back to the Earth’s surface with a warming effect. Greenhouse gases in the Earth’s atmosphere trap warmth from the Sun necessary for our survival. Changes in global greenhouse gas concentrations have effects on climate.

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Figure 19.14 Greenhouse Gases From Fossil Fuel Burning. Carbon dioxide emis- sions to the atmosphere have increased since the Industrial Revolution.

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Atmospheric concentrations of both water vapor and carbon dioxide have natural variations based on temperature and vegetation. Over geologic time, there have been ice ages and warming periods on the Earth. Long-term climate variations are part of the planet’s natural cycles. Solar cycles, changes in ocean currents, volcanic eruptions, and even asteroid collisions such as the Tunguska event in our story have altered climate in geologic history.

Carbon dioxide is released to the atmosphere when fossil fuels and wood are burned. Human activities producing CO2 emissions from burning fossil fuels have soared in the past 150 years since the Industrial Revolution (Figure 19.14). Levels of CO2 in the atmosphere have risen in tandem with average global temperatures over this time period.

Clearly, human activities such as fossil fuel combustion are adding to the atmospheric levels of CO2. Another contributor to this effect is deforestation. Deforestation across the globe results in tree loss. Fewer trees mean less plant biomass is available to uptake atmo- spheric CO2. The many possible changes to the Earth’s climates due to rises in greenhouse gases in the atmosphere are referred to by scientists as global climate change.

Scientists see these possible changes as the cause for concern if current warm- ing trends continue rising. Many populations cannot adapt evolutionarily when climate shifts occur rapidly or at extremes. Climate change outside of the Earth’s normal pat- terns might not allow ecosystems time to adjust. Possibilities include melting polar ice caps and glaciers. Rapid sea level rise could theoretically alter huge coastal areas. These massive ecosystem changes could result in species loss if organisms are unable to adapt.

nitrogen Cycle Biological organisms rely on the element nitrogen to form necessary nitrogenous bases that make up DNA, proteins, and enzymes critical to life functions. Our atmosphere is abundant in nitrogen. In fact, about 78% of the air we breathe is nitrogen. Nitrogen

Global climate change

The many possible changes to Earth’s climates due to rises in greenhouse gases in the atmosphere.

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found in the atmosphere is in molecular form (N2). Atmospheric nitrogen is bonded so tightly that plants and animals are unable to metabolize it directly. The nitrogen cycle incorporates soil microbes that transform nitrogen from the atmosphere into a form usable by plants and animals.

Nitrogen fixation is the process of converting molecular nitrogen (N2) into ammonia (NH3) and ammonium ions (NH4+). These forms are more readily available to plants for biological uptake. Some nitrogen fixation takes place in the atmosphere from volcanic action and lightning. Most nitrogen is biologically fixed by bacteria and archae in soils (Figure 19.15). These microbes are abundant and widely available to do the work of nitrogen fixation. Some microbes form symbiotic relationships with specific plant spe- cies including peas, beans, clover, and alders as discussed in Chapter 17. These plants have special protective nodules on their roots. Root nodules provide a secure holding place for nutrients and safe housing for the microbes in exchange for the nitrogen they fix. Nitrogen-enriched plants later return nutrients to the soils as they decompose.

Organic decomposition occurs as bacteria and fungi break down nitrogen from living organisms, which have died. This process of ammonification converts organic nitrogen into NH3 and dissolved NH4+ forms ready for uptake. Some ammonia (NH3) escapes back to the atmosphere as a gas. During nitrification, bacteria in soils produce nitrites (NO2−), which are then converted by other bacteria into plant-usable nitrates (NO3−). Some soil bacteria can also denitrify or return nitrates back to molecular nitrogen (N2) gas. Soil gas can readily escape back to the atmosphere. These nitrogen forms found in soils are water soluble. They can be lost or leached away into groundwater and river systems. Nitrogen runoff that reaches coastal waters is available for uptake in marine food webs.

Nitrogen fixation

The process of converting molecular nitrogen (N2) into ammonia (NH3) and ammonium ions (NH4+).

Ammonification

The process in which organic nitrogen is converted into ammonia and dissolved NH4+ forms ready for uptake.

Figure 19.15 Nitrogen Cycle. Most of Earth’s nitrogen is found in the atmosphere. Nitrogen fixing microbes in the soil move nitrogen from its atmospheric form to one available for uptake by plants. After plant uptake it can enter terrestrial food webs. The many different soil microbes can convert nitrogen between many forms. From Biological Perspectives, 3rd ed by BSCS.

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Nitrification

The process by which bacteria in soils produce nitrites.

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Eutrophication Movement of nitrogen in the global system can take place mechanically through pro- cesses of weathering and runoff. Widespread use of lawn and agricultural fertilizers in recent decades, runoff of agricultural waste, sewage discharges, and burning fossil fuels are all human activities that have altered the natural nitrogen cycle. Runoff and point source discharges of such wastes to rivers have increased the amount of nitrogen and another limiting nutrient, phosphorous, in waters.

Extra nutrient loading left unchecked can lead to massive algal growth, known as eutrophication (Figure 19.16). As large colonies of algae die, bacterial decomposition of their remains occurs. Available oxygen levels in the waters may become severely depleted. Low oxygen levels can result in the death of fish and loss of marine life as observed in the Mississippi River Delta’s so-called Dead Zone.

phosphorous Cycle Phosphorous, like nitrogen, is a limiting nutrient for plant growth. Phosphorous is bio- logically required for energy transfers as a functional component of ATP. Phosphorous is also found in nucleic acids, as the sugar–phosphate backbone of DNA, and in phos- pholipids, as a component of cell membranes. Thus, phosphorous is vital for the growth of producers. Fertilizers for large agricultural operations contain added phosphorous to promote vigorous plant growth needed for high-yield crops.

Since phosphorous compounds do not commonly exist in a gaseous phase in the Earth’s atmosphere, there is no atmospheric reservoir. The Earth’s crust is the primary reservoir for phosphorous found in sedimentary rocks in the form of phosphates (PO43−).

Eutrophication

The massive algal growth resulting from unchecked extra loading of nutrients.

Figure 19.16 Eutrophication. Nitrogen and phosphorous are needed for healthy functioning of aquatic systems. Excess inputs of these nutrients due to human activities can create unhealthy habitats. Massive algal growth can take place. When large num- bers of algae die, oxygen is limited and can result in significant loss of aquatic life. From Biological Perspectives, 3rd ed by BSCS.

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Small amounts of phosphates are gradually released into the environment over time. This occurs as rocks are weathered into small particles and moved by erosion into soils and streams for biological availability (Figure 19.17). Plants absorb the nutrient through their roots in terrestrial food webs. Excretion, death, and decomposition return phospho- rous from the food web back to the land. Runoff carries some terrestrial phosphorous to oceans. Phosphates in oceans may enter the marine food web, but eventually deposit as sediments on the marine floor. Millions of years will pass before these marine sediments from sedimentary rock can be moved upward to the Earth’s surface for recycling again.

human influences on the Biosphere Deforestation Removal of forested areas or deforestation can result in drastic changes to the individual ecosystems. In our story, massive deforestation of 800 miles was caused by the explo- sion of the Tunguska asteroid in 1908. However, more significantly in present times, humans have been removing forest lands in many biomes across the globe, in ways described in Chapter 18.

As human populations grow, lands are cleared for agricultural use and cities are built. Loss of tropical rain forest is believed to contribute significant amounts of car- bon dioxide to the atmosphere, contributing to the greenhouse effect described earlier. Deforestation affects the biosphere – climate, water, soil, and biodiversity.

When forest areas are cut, the plant transpiration process stops adding moisture to the air. Exposed soils tend to dry out. Best practices for forestry harvesting can limit devastating effects. Avoiding clear cutting can preserve forest pathways utilized by local wildlife populations rather than cutting them off, in isolation. Erosion problems and landslides of forest soils can be limited if some plants and trees are left in a cut

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Figure 19.17 Phosphorous Cycle. Rocks and marine sediments are Earth’s largest reservoir of phosphorous. Most phosphorous moves through the cycle bonded to oxygen as inorganic phosphate (PO43-) until it enters a food web. From Biological Perspectives, 3rd ed by BSCS.

Deforestation

Removal of forested areas.

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area. Studies conducted at the Hubbard Brook Experimental Forest in New Hampshire demonstrated the damaging ecological effects of forest clear cutting. Soil composition and mineral cycles in forests are severely affected. Forests farmed for lumber are often replanted, but lose their biodiversity in the process of being farmed.

Engineering of Waterways Mississippi and Atchafalaya Rivers

Engineering of natural waterways is an obvious human interference with natural water eco- systems. Changes that result from these alterations can be problematic. Still, there is much to be gained in the way of flood control and power generation through engineering solutions.

The Mississippi watershed drains surface water from a large area in the interior United States. A watershed is an area that collects flow, runoff, and precipitation from a region into a specific body of water. For example, the Mississippi River in the United States flows south to the Gulf of Mexico primarily due to the flow from high to low elevation – there are mountains bordering the river’s watershed. The Mississippi River changes its course into the Gulf of Mexico around every thousand years. Each new course adds to the Mississippi Delta complex that makes up the state of Louisiana’s unique coastline (Figure 19.18).

Delta lobes shift when the river is captured by a tributary, with a steeper and shorter route to the gulf waters. Abandoned lobes compact and make up the bayous we know today. In the mid-twentieth century, migration of the Mississippi River from its current channel to the Atchafalaya River appeared likely. Flood concerns, navigation interests, and economic structure led the Army Corps of Engineers to build a control structure in 1963 to maintain the balance of water flow. Confinement of the river to human-built canals in the lower Mississippi is changing the ecology of the natural river. Muddy waters of the Mississippi are now shunted out to sea. Soils are no longer deposited in land areas downstream. Wetland or saturated areas are no longer being created. Wetlands require slow, meandering rivers that allow sediments and vegetation to build up over time.

Wetlands serve as natural buffers from heavy flows and hurricanes. Our attempts at engineered flood control are eliminating the river’s natural flood regulation systems. The

Watershed

An area that collects flow, runoff, and precipitation from a region into a specific body of water.

Wetland

A land that consists of swamps or marshes.

Figure 19.18 A. The Mississippi River Delta. The Mississippi River changes its course into the Gulf of Mexico about every thousand years. These changes are responsible for Louisiana’s uniquely shaped coastline today.

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natural waters of the Mississippi have been greatly altered in terms of salinity balances, erosion, and ecological effects.

Three Gorges Dam

The recently completed Three Gorges Dam Project in Hubei Province, China is the larg- est hydropower station the world (Figure 19.19a). Over 10 trillion gallons of water are held behind a massive cement wall. Annual energy output is rated at nearly 100 billion kilowatt-hours, enough to supply 10% of China’s electricity needs. The dam is 1.3 miles (2.3 km) wide across the Yangtze River and 610 ft (186 m) high. The Project is designed to prevent flooding in the middle and lower reaches of the Yangtze River.

Floods in the river system have killed hundreds of thousands of people in the past century alone. The vast reservoir of water held behind the dam allows for controlled releases to regulate floodwaters. Water from the reservoir is also available for irriga- tion of farmlands. Widened shipping lanes and a system of locks allow for improved navigation. This should bring more commerce and ease of transportation to the interior of China. Tens of millions of people living in interior China are expected to experience economic benefits, added jobs and better quality of life.

In the wake of the power, flood control, and economic benefits offered by the dam, some social and ecological problems remain. Large tracts of productive farmlands, scenic gorges, and historical sites were forever flooded for the project. Over 1000 villages were submerged (Figure 19.19b) and 1.3 million people permanently displaced from their homes. Rare and endangered populations of river dolphin, sturgeon, and cranes are further threat- ened by ecological changes due to construction. Sewage and pollution normally washed out to sea are held up by the dam. Soil runoff combined with water retention creates excess silt that clogs power generation equipment. Furthermore, the project overlies seismic zones. There is concern that the excess weight of water could trigger earthquake events.

Figure 19.19 a. China’s Three Gorges Dam Project Is the Largest Hydropower Station in the World. b. Over a Thousand Villages Were Submerged and More than a Million People Relocated for the Project.

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CAN HumANS CAuSE EARTHquAkES?

The Earth’s crust is made up of moveable tectonic plates that do shift naturally. A release of energy from movement in the Earth’s crust is called an earthquake. Geological research shows that human-induced seismicity or vibrations in the Earth’s crust do take place.

Earthquake

A release of energy from movement in Earth’s crust.

Seismicity

Vibrations in Earth’s crust.

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pollution The introduction of any contaminant introduced into the environment that causes a harmful change is considered to be pollution. A pollutant can take a natural form such as noise, light, smell, or heat. Pollutants also take form as garbage, sewage, nuclear radiation, and chemi- cals. Human activities produce vast amounts of waste. Our waste takes up so much space that we sometimes find ourselves unsure where to dispose of it (Figure 19.20). Landfills are overflowing with trash. Mining operations and industries discharge liquid wastes into rivers and oceans. Smokestacks from industry and electric plants release air pollution into

Pollution

The introduction of any contaminant into the environment that causes a harmful change.

Figure 19.20 Pollution Takes Many Forms in Our World. a. Household wastes crowd a landfill. b. Pollution to rivers, lakes, and oceans damage our waters. c. Smokestack emissions from energy and industry add to air pollution.

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Small seismic events from surface loading – like water pressure from tons of water behind a dam – are documented. These mini earthquakes might hold potential to stimulate larger ones. A large 2008 earthquake – magnitude of 7.9 – in China’s Sichuan Province is suspected to be linked to filling of the nearby Zipingpu Dam.

Mining activities also link to seismic events. The US Geological Survey (USGS) reports a number of small earthquakes – magnitudes up to 2.8 – linked to hydraulic fracturing or fracking activities. Hydraulic fracturing involves injec- tion of high pressure water and chemicals into the ground. The process breaks through shale rock formations to allow for extraction of trapped natural gas.

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our atmosphere. Acid rain formed from polluting gases in the atmosphere is slowly changing the chemistry of global soils and waters. In some areas, acid rain has killed vegetation or corroded bridges and statues. Its effects on the environment are far reaching and varied.

Ideally, waste should be limited to the highest degree possible. We can do our part to limit waste production by reducing the amount of materials we consume, reusing items that still have useful life, and recycling unusable items or materials for repeat use. Industries are being restricted by government regulations to limit pollution to regulated levels for certain listed pollutants from discharge points into water ways and the atmo- sphere. Coal-burning facilities have added “scrubbers” to smoke stacks to filter out and limit some of their pollution. Natural gas collected by hydraulic fracturing methods is marketed as a cleaner burning fuel with less greenhouse emissions.

Plenty of pollution still abounds, but new technologies are helping to limit some of its harmful effects. Renewable energy solutions focus on expanding solar, wind, and hydro- power to release us from our dependence on fossil fuels (Figure 19.21). Each of these renewable solutions comes with limitations for where they can be used and unique chal- lenges for large-scale energy production. Ethanol is replacing some of the traditional petro- leum-derived fuel being put in our cars. It is important to note that all new solutions to our energy and waste problems come with their own set of downfalls and environmental setbacks that should be carefully weighed out to produce the most sustainable technologies.

Bioaccumulation/Biomagnification Some chemical pollutants are particularly toxic. They can lead to negative neurological or reproductive effects in biological populations. Lipid- or fat-soluble substances can

Figure 19.21 Renewable Energy Solutions of Wind, Solar, and Hydropower Offer Freedom from Depen- dence on a Limited Supply of Fossil Fuels but Their Own Challenges As Well.

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bioaccumulate. They stay in organisms because they are not metabolized or excreted. Over time, this leads to higher and higher concentrations of the substance held inside the organism’s tissues.

As an example of bioaccumulation, follow methylmercury through an aquatic sys- tem. Methylmercury is a toxic form of mercury available for biological uptake. Low levels of methylmercury, 0.001 ppb (parts per billion), are taken in from seawater by zooplankton. Methylmercury is stored in the zooplankton rather than excreted. Small fish then eat the zooplankton. These small fish have their own burden of methylmercury from surrounding waters. They add to their own levels of methylmercury over time by eating the zooplankton. As they grow and eat more and more zooplankton, they store more and more methylmercury in their own tissues. Methylmercury is being accumu- lated and concentrated in tissues of the small fish (Figure 19.22).

Big fish consume the small fish and the process is magnified. The methylmercury levels grow larger with each move to a higher trophic level in the food chain. As the toxin moves up successive trophic levels of a food chain, the increase in concentration is known as biomagnification. A shark eating the big fish may be found to have high levels of methylmercury nearing 500 ppb. Biomagnification demonstrates that even in waters with low pollution levels, toxic levels of chemicals can be retained in fish.

A shark is the top carnivore in the example food chain. However, it is important to note that all at the top trophic levels of the food web are at risk from biomagnification of toxic chemicals including eagles, polar bears, and humans. Methylmercury discharged to bay waters from a chemical factory in Minamata, Japan during 1956 lead to severe mercury poisoning of thousands of people, cats, and other wildlife. Locals consumed fish from the polluted waters as a primary staple of their diet. An outbreak of neurolog- ical effects in the local populations, some resulting in death, proved later to result from toxic levels of methylmercury.

Bioaccumulate

Accumulation of substances in an organism.

Biomagnification

The increasing concentration of a particular substance in organisms at the top of the food chain.

Figure 19.22 Bioaccumulation and Biomagnification of Methylmercury in an Aquatic System. Methylmer- cury levels in small fish tissue increase over time or bioaccumulate as the fish live and eat in the aquatic system (left). Methylmercury levels increase or biomagnify with each move to a higher trophic level in the food chain (right).

Bioaccumulation Biomagnification

T I M E

Contaminant levels

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As a result of events such as the Minamata disaster, the US FDA makes fish con- sumption recommendations for pregnant or nursing mothers as well as young children who are most susceptible to the neurological effects of mercury poisoning. Suggestions restrict consumption of top-level predators such as sharks and swordfish. They advise consumption limited to two meals per week of low-mercury seafood such as salmon, light tuna, catfish, or shrimp. For fish with a higher likelihood of increased mercury levels such as albacore, one meal per week is the recommendation. Check advisories in your own area for recommendations on locally caught fish. Other chemicals subject to biomagnification include heavy metals such as arsenic and lead; the insecticide DDT; PCBs, used widely as coolants and insulating fluids for electrical transformers; and PCDD/Fs or dioxins, formed during low-temperature burning.

ozone Ozone (O3) is a pollutant affecting the Earth in two atmospheric zones. Ozone in the atmosphere near the Earth’s surface is a form of air pollution. It is formed by reactions between air pollutants released from fossil fuel combustion and sunlight. Ozone found in the lower atmosphere or troposphere in urban areas is referred to as smog. This can lead to respiratory problems for humans.

Ozone higher up in the Earth’s stratosphere or upper atmosphere serves as a protective barrier for the planet. The ozone layer in the stratosphere protects the Earth from dam- aging UV solar radiation. The whole ozone layer that wraps the Earth has shown some overall thinning over recent decades. Polar Regions, however, show a significant seasonal decrease in ozone levels, particularly over Antarctica (Figure 19.23). This depletion in ozone concentration is sometimes referred to as a hole in the ozone layer.

Concern here is that without this protective layer, damaging effects from enhanced UV radiation can occur. Resulting effects include a rise in skin cancer rates caused by increased UV exposure, as described in Chapter 15, and damage to plants. CFCs (chlorofluorocarbons) are chemicals used in older Styrofoam, aerosol sprays, and cool- ants. CFCs have been shown to react in a way that lowers ozone amounts in the upper atmosphere. Attempts to reduce the use of CFCs have been made in recent decades with hopes to limit further deterioration of the planet’s valuable ozone layer.

Ozone

A gas that is a pollutant in Earth’s lower atmosphere, but acts as a protector from UV radiation in the upper atmosphere.

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summary Many biotic and abiotic systems interact in the Earth’s biosphere. The Earth, solar energy, and biogeochemical distribution of planetary resources make life on the Earth possible and sustain ecosystems. Winds, weather, and ocean circulation are driven by the Sun. Biogeochemical cycles continually move the elements necessary for life to the regions where they are available for biological uptake. Many factors, some of them are human induced, can disrupt these environmental cycles resulting in damage to living communities and ecosystems. We can take steps to help by limiting waste and pollution, using best practices, striving for sustainable solutions, and being environmentally con- scious of impacts on the biosphere.

Figure 19.23 The Ozone Layer in the Earth’s Upper Atmosphere Shields the Planet from Damaging UV Light. Ozone concentrations over Antarctica have decreased in recent decades. Purple and dark blue areas represent the ozone hole. From Biology: An Inquiry Approach, 3rd ed by Anton E. Lawson.

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summary: key points

• The biosphere is made up of all areas on the Earth that contain life. • Climate is affected by solar radiation, the tilt and orbit of the Earth, atmospheric make up, and air

and ocean circulation patterns. • Energy from the Sun powers the water cycle. • Water drives biogeochemical cycles and transport for carbon, nitrogen, and phosphorous. • Carbon dioxide, a greenhouse gas, results from burning fossil fuels. • Nitrogen and phosphorous are limiting nutrients for biological growth. • Human influences on the biosphere can have negative effects on the biosphere – pollution, defor-

estation, engineering waterways, ozone depletion, and climate change.

albedo ammonification atmosphere aquifer bioaccumulate biogeochemistry biomagnification biosphere Coriolis effect deforestation earthquake El Nino eutrophication global climate change greenhouse effect greenhouse gases freshwater heat capacity hydrosphere

La Nina intertropical convergence zone lithosphere nitrification nitrogen fixation ozone polar easterlies pollution residence time salt wedge seismicity surface runoff trade winds water cycle watershed wetland wind westerlies

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Multiple Choice Questions

Reflection questions:

1. Where is the majority of the Earth’s carbon stored? a. plants b. atmosphere c. sedimentary rock d. oceans

2. Depletion of the Earth’s ozone layer has resulted in human health risks by: a. increased effects from solar radiation. b. increased effects by asteroid impacts. c. decreased effects from solar radiation. d. decreased effects by asteroid impacts.

3. Which has the LEAST albedo effect in the Earth’s biosphere? a. plants b. snow c. ice d. cloud

4. Which region of the biosphere receives the most direct sunlight? a. 30° latitude b. 60° latitude c. Polar Regions d. equator

5. In 1816, the year without a summer was caused by: a. volcano ash b. asteroid dust c. ozone depletion d. dust bowls

6. Which represents a logical order, in biogeochemical cycling, in the movement of nitrogen through the biosphere? a. atmosphere ➔ soil bacteria ➔ animal ➔ plant b atmosphere ➔ soil bacteria ➔ plant ➔ animal c. soil bacteria ➔ atmosphere ➔ plant ➔ animal d. animal ➔ atmosphere ➔ plant ➔ soil bacteria

7. Which transports chemicals through their cycles on the Earth? a. water b. air c. soil d. all of the above

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8. Which is NOT a contributor to the greenhouse effect? a. nitrogen gas b. carbon dioxide gas c. water vapor d. methane gas

9. Which correctly MATCHES pollutant with its effect? a. ozone – thyroid disease b. nitrogen gas – greenhouse effect c. phosphorous – eutrophication d. carbon dioxide – biomagnification

10. Which is an effect on the western South American coast, caused by El Nino? a. poor fishing b. nutrient upwelling c. droughts d. plankton growth

short answer

1. List three dangers from extraterrestrial sources that could threaten the life on the Earth. Which threat is most likely?

2. Define the following terms: albedo and greenhouse effect. List one way each of the terms differ from each other in relation to their a. role in the biosphere; b. relation- ship with each other.

3. What is the function of the ozone layer in protecting life on the Earth?

4. Draw a sketch of the nitrogen cycle, using arrows to show four key organisms trans- ferring nitrogen through the biosphere. Which organism makes nitrogen available to living organisms?

5. List and discuss three negative effects that a dam construction has on its surround- ing ecosystems?

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6. Pretend that you are a molecule of carbon dioxide, recently placed into a plant. Describe three pathways you might take from the plant to the rest of the biosphere. What process placed you into the plant in the first place? Where will you spend most of your time in the biosphere?

7. Define biomagnification in living organisms. Choose a chemical that biomagnifies and trace it through a food chain.

8. For question #7, how can you change your diet to reduce the effects on biomagnifi- cation in your own life? Explain why?

9. Describe the contributing abiotic factors to wind movements in the biosphere. Be sure to use the following terms in your explanation: air pressure, temperature, Cori- olis effect, and rotation.

10. Describe three methods that limit the negative ecological effects of deforestation. How are they different? Which would you advise as least costly?

Biology and society Corner: Discussion Questions 1. In China, over 1000 villages were flooded, their population relocated due to dam-

ming of rivers. This massive resettlement was not well received by the local popu- lation. Form a four talking point argument explaining the benefits of damming the rivers to the citizens of the flooded towns. What are ecological drawbacks to your argument?

2. Diets high in fish, including swordfish and albacore, have heart healthy benefits. Fish contain a good proportion of unsaturated fats, omega 3 fatty acids, and vita- mins. However, they also contain higher levels of biomagnified mercury in their tissues. Develop a plan to limit the negative effects of toxic mercury with the health benefits of eating fish in your diet.

3. Recently, an asteroid traveled within miles of hitting the Earth. Some scientists suggest that such a collision will occur, as in Tunguska, within the next few years. Should you be concerned? Why or why not? Also research the chances predicted for types of extraterrestrial impacts. Name two ways to prepare for or prevent such an impact, if any.

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4. On October 31, 2012, a hurricane flooded of the Greater New York seacoast destroyed thousands of homes and whole neighborhoods. Its costs for rebuilding are in the billions of dollars. Some insurance companies refuse to insure homes along the coast. Do you think that insurance companies should have the right to refuse insurance on people’s homes along the coast? Why or Why not?

5. Hydraulic fracturing, also known as “hydrofracking,” drills into the Earth to obtain natural gas from shale rock layers. It is controversial because the chemicals used to dissolve rock may leak into layers of the lithosphere and pollute. Proponents of hydrofracking cite increasing energy needs and less greenhouse gases as benefits. Research the pros and cons of hydrofracking. Which side do you agree with more? Why?

Figure – Concept Map of Chapter 19 Big Ideas

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747

Unit 6 Biology and Society

Chapter 20 the evolution of Social Behavior: Sociobiology

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the evolution of Social Behavior: Sociobiology

An ant hill is a vibrant, social organization of organisms

Ants move in a line using pheromones to direct their often-complex activities

A party is enjoyable until someone gets hurtHumans can be violent as well as destructive to other organisms. The ant’s perspective – humans can be cruel

Do we destroy ourselves?

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the Case of the nuclear ant hill I was glued to the news on the TV in my backyard. While I was never into politics, this time there were events going on. North Korea has threatened to launch a nuclear strike against the United States. How could they bother us? We always heard about nuclear war but no one really took it seriously. It was only a worry from the 1950s; from our grandparents’ days, when there were communists and an “enemy” behind the Iron Curtain.

However, I had better things to do than think about boring politics. This afternoon, I am hosting a clam bake in my backyard. I invited my coworkers from the office. While I did not like most of them, I thought it would be good politics. I would have them over and maybe bond a bit. We’ll see . . .

I started barbequing in the backyard and noticed a new, large ant hill right in front of my grill. It was blocking the way but I could manage around it for now, but it had to go. The ants must have constructed this monstrosity overnight. It was two feet high and a couple of feet across. I had heard that ants were industrious but they were a problem.

I took a shovel from the garage to remove the ant hill. As I placed the spade into the dirt bordering the colony, I noticed something strange: these ants were lined up, single file, working on some project. They looked serious as they moved a large piece of meat that I must have dropped while barbequing.

I decided to take a closer look at the ants. I brought my magnifying glass up to the line of ants on the ant hill. I examined the ants and noticed, “The meat was way bigger than any of the ants – maybe by 100 times – but seriously, those ants moved the piece with ease.” The ants were very orderly, as they swiftly brought the food back into their hole. I was amazed at how they cooperated with each other. Their workplace was great – the ants were helping each other. I did not see the usual complaining or disrespect or underhandedness that I suffer through every day in the office.

It was at that point that I decided to let the ant colony live – I would show it mercy, one of my fellow living creatures. This may sound crazy, but I guess at that moment, I yearned to be an ant.

My coworkers came to the yard, boisterous as always. We exchanged the usual pleasantries and I offered them a drink or two. One of my “friends” noticed the ant hill, remarking “What’s, this?” Before I could respond, he kicked it across the yard.

A loud beep on the TV interrupted the party. Then, after a few minutes, an announce- ment was made, “This is an emergency . . .”

CheCk in

From reading this chapter, students will be able to:

• explain how social structure in animals compares with human society. • define sociobiology, animal behavior, innate behavior, learned behavior, behaviorism, cognitivism,

imprinting, habituation, classical conditioning, operant conditioning, insight, dominance hierarchy, aggression, self-gene hypothesis, altruism, selfishness, reciprocal altruism, and kin selection.

• list the two types of animal behaviors. • compare the types of learned behaviors. • use examples of selfishness and altruism to examine animal social structures.

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Defining Sociobiology A theme threading through this text explores society’s relationship with biology. Stories in each chapter touch on biological matters facing humans: life, death, struggles for survival, and community relations. Medical advances, the human encroachment on eco- systems, and the importance of healthy soil chemicals to human survival all represent the ways biology and society intertwine.

Understanding our society can be complex to study. In this chapter, we tease out the factors underlying human and animal behaviors within societies. There are many ques- tions with complex answers. To start off with, what features of human society make us similar to and different from other organisms? Why do we enjoy other living creatures and yet harm their biosphere, where we all live? Our social structure defines how our species lives and interacts with its environment.

The answer to these questions lies in our behaviors – how humans act toward each other, for example. Any action taken by an organism is defined as its behavior. Behav- iors evolved and are subject to natural selection pressure, just like any other trait in an organism. Behaviors evolved in human society to help our survival, and they also adapted to suit members within animal social systems. An animal social system is the social unit of any animal, its organization, and workings. We will explore the biology of animal social systems and compare them with human society.

The evolution of behavior may be studied in the same way we look to adaptations in studying evolution in Chapter 7. Biologists look at how a behavior improves survival in organisms. By doing this, we attempt to answer the questions: How hostile are humans to each other compared with other organisms? Are they more like ants or like warriors? Do other organisms, such as the ants in our story, really get along better than humans? The story posits that this is the case, but should a biology text make such an assertion? The basis of the claim is that both human and ant social structure are dependent on the same biological principles.

Humans, as animals, are driven by the same rules underlying all biological sys- tems. This text has explored these characteristics of life all through the chapters. Human behavior and its resulting social order are no exceptions to the tenets. The themes of survival, evolution, and the importance of genetics, for example, are vital in establishing social organization.

animal Behavior Biological principles help us to understand how organisms behave in a society. They help us predict social behaviors – in animals and in humans – by applying their param- eters. This study is termed animal behavior. Animal behavior is the branch of biology that studies the ways in which animals act within their environment. Ethology, before the 1950s, was the precursor to the modern study of animal behavior. It looked at how

Animal behavior

The branch of biology that studies the ways in which animals act within their environment.

CheCk Up SeCtion

The juxtaposition of the ant hill’s cooperation with human society is a point of the story. Animal social systems have differing characteristics to compare with human society. Research the ecology of ants. What are the benefits and drawbacks of living in their colony? Do you think the character in our was story right “to yearn to be an ant”?

Behaviors

Any action taken by an organism.

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organisms behave based on their physical processes. Dissection of nervous system and endocrine glands helped ethologists study patterns in behaviors.

The father of ethology Konrad Lorenz was one of the first scientists to argue that behaviors, just like biological structures, evolved to benefit organisms. Thus, behaviors are “tools” that organisms use to survive. Fleeing or fighting, cooperating or acting self- ishly – these are all behaviors that have adapted through evolution.

Lorenz focused on geese and their behaviors within social groups. In Figure 20.1, he is shown, famous for the geese he raised. He has a flock following him after their birth. They imitated Lorenz as if he were their own mother. He was the first organism they saw after their birth, so they followed his movements.

The study of the physical and physiological adaptations of behavior advanced to become the study of modern animal behavior. The study of the ways that groups of ani- mals act is called sociobiology (or behavioral ecology). Sociobiology is the focus of this chapter. We close the book with sociobiology because it brings the application of biol- ogy back to the society. We can better understand biology and our place in the biosphere by understanding how our social structure evolved.

Sociobiology answers the mystery questions to why humans and other animals behave the way they do. In our story, the ant hill is portrayed as a group with good sets of behaviors, defined here as “helping one another.” Humans are contrasted as a group that has bad sets of behaviors, defined here as “a selfish or harmful act.” Behaviors change in a species over time – or evolve – to benefit an organism’s reproductive success (RS), defined as the number of live young it produces. The RS of an organism depends on the choices it makes to survive. Ants cooperate on their hill in our story to help them to survive. Humans also make choices that impact their survival. If a behavior helps an organism’s RS, it is likely to persist in a population and become established. These behaviors are called adaptive behaviors because they have evolved to help organisms adapt to their environments and improve their RS.

The story ends with the possibility that a nuclear war is breaking out. Do other organisms kill their own species en masse? It is rare to find other organisms kill their own species, except by accident. Our ultimate destruction may be implied at the end of the story – intraspecific competition and killing. This makes humanity bad. But then,

Sociobiology

The study of the ways that groups of animals act.

Reproductive suc- cess (RS)

Is the number of live young ones an organism produces.

Adaptive behaviors

The behavior that helps an organism’s reproductive success by helping it to persist in a population and become established.

Figure 20.1 Konrad Lorenz: Father of Ethology. After imprinting on Lorenz, his geese followed him into the water, imitating him while swimming.

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what is a “good” or “bad” behavior? Are human behaviors following the “rules” of RS? We should first define the types of behaviors organisms display.

types of Behaviors Behaviors encompass movements, sounds, mating, and communication – all of the acts an organism performs. Some behaviors are genetically determined, called innate behav- iors. Organisms are born with innate behaviors, compelling them to act in certain ways. A bird migrates from taiga to warmer climates during the winter. This innate behavior was established the day the bird was born. It did not need to be told to migrate and did not do it because its parents taught it. When raised in isolation, a bird will still migrate. Other examples of innate behaviors include single-celled organisms. A Euglena will travel toward light, a behavior called phototaxis, also found in plants as described in Chapter 9. Innate behaviors, such as butterfly migration are shown in Figure 20.2.

learning Not all behaviors are innate. Are we born knowing how to solve an algebra equation? Do we know how to cook an omelet, without ever having been shown? Some behaviors are developed as we experience the world. These are learned behaviors, which result when experience alters an organism’s response. Learning is the process of taking in informa- tion and using it to perform tasks and “think” about situations. Learning in animals is a controversial area of study because there is debate on whether animals have self-aware- ness and a capacity to think so deeply.

Learning is defined as a change in behavior as a result of a stimulus. You touch a hot iron and it hurts; in the future, you avoid hot items. This example shows a change in behavior based on an unpleasant stimulus (the burning of the iron). This is a simple example of learning.

Learned behaviors are beneficial to organisms because they help them adapt to changes in surroundings. Learning evolved to help organisms survive better. Learning tailors an organism’s responses to unique circumstances in its environment. By adapting

Innate behaviors

Behaviors that are genetically determined.

Figure 20.2 Monarch Butterfly Migration Is an Example of Innate Behaviors. They are not taught to go south for the winter but still form groups and travel each year away from the cold weather. From Biological Perspectives, 3rd ed by BSCS.

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Behavior that develops through experience.

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to changing conditions, an organism is more likely to improve its RS. Thus, learning, by altering responses based on experience, is itself an adaptive behavior. Both innate behav- iors and learned behaviors influence an organism’s actions. Learning occurs as soon as an animal is born (Figure 20.3).

Behaviorism Behaviorism looks at the responses organisms make to stimuli. It studies the way in which organisms, particularly people, learn from their experiences. When an organism is presented with a stimulus, it responds in predicted ways. There are five classifications of learned behavior, according to behaviorism: imprinting, habituation, classical condi- tioning, operant conditioning, and insight.

Imprinting

During imprinting, the learning that occurs is just after an organism’s birth. Timing is of the essence, because at first a newborn is most impressionable to imprint. The stimuli must be presented in the very early developmental stages of an organism’s life. When a bird is born, for example, it forms an attachment with its mother upon seeing her for the first time. They bond, in part, through feeding, and the baby chicks imitate their mother’s behaviors.

Konrad Lorenz, depicted in Figure 20.1, grew gosling eggs in an incubator, which hatched and began imprinting Lorenz’s habits and behaviors. The behavior is adaptive because baby goslings know nothing about their world. They are vulnerable and their survival increases as they learn the “dos and don’ts” from their mothers. The photo shows Konrad Lorenz with his baby goslings learning from him, imitating his movements.

There is evidence that psychological and physiological responses are also imprinted early in human life. From Chapter 14, we know that immune system imprinting occurs when T-cells recognize “self ” from “non-self ” antigens. However, behaviors are also imprinted. Most behaviorists agree that human infants use imprinting to form psycho- logical bonds. Infants begin imitation of those around them, mimicking their behaviors early on. Movements of lips, making noise, and imitating sounds are all example of imprinting in humans. Children learn from imitating older children and adults, as shown in Figure 20.4. Learning at early ages begins the complex pathway to adult behavior in humans.

Behaviorism

The theory that human and animal responses are measured to determine an organism’s learning.

Classical conditioning

An association between a new stimulus and a natural stimulus.

Figure 20.3 This Chihuahua Puppy Is Learning Good Behavior.

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Habituation

The process of “getting used to” stimuli is called habituation. Habituation happens when stimuli become familiar, over a period of time, after which organisms no longer respond to them. In humans, we habituate to many changes in the course of our lives. After moving to a city from the country, the sounds of car alarms and street noise slowly extin- guish. Habituation allows us, almost unconsciously, to adapt to changing environments.

Birds that are raised in a town, with people around, habituate to their coexistence. They are not “wild” and afraid of humans as in nature. The process of habituation is gradual and often unnoticed by an organism. Figure 20.5 gives an odd example of habit- uation in the Serengeti Grasslands of Africa.

Classical Conditioning

An association between a new stimulus and a natural stimulus is called classical con- ditioning. It is the classic example of how organisms connect new information and

Habituation

The process of “getting used to” stimuli.

(a) (b)

Figure 20.4 a. Imitation by Children. Imprinting occurs when babies and children learn to imitate others. It is a way of learning about and assimilating to the world. b. Sometimes higher level learning, as in a game of chess, is taught by parents. Courtesy Peter Daempfle.

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Figure 20.5 Habitation in the Serengeti Grasslands of Africa. These elephants are used to the appearance of vans and no longer run and hide from them. This photo shows a unique elephant traffic jam.

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experiences with their innate behaviors. For example, if a person gets food poisoning, they are likely to associate that food with the pain and suffering of the new experience. Pain is a natural stimulus and the food is the cause. If someone loves pizza but becomes violently ill after eating a slice, he or she is likely to stay away from pizza for a long time. The connection between food and illness is particularly strong.

In an example of classical conditioning, Ivan Pavlov trained dogs to salivate when- ever a bell rang. He would bring a juicy steak into the room and allow them to eat it. Their innate response was to salivate with the presentation of steak (and its odor). Pavlov then coupled the steak with the ring of a bell (the new stimulus). Repeated coupling of the new stimulus (the bell) with the steak caused the dogs to salivate whenever they heard the bell even without a steak present. The example in Figure 20.6 shows how learning is also coupled with our innate behaviors.

Operant Conditioning

A more complex set of behaviors occurs during operant conditioning, in which an organ- ism learns to respond to stimuli to produce a desired effect. It is trial-and-error learn- ing, whereby organisms use their natural associations to obtain a positive stimulus. The “operant” is the stimulus that produces an effect.

In an experiment by B.F. Skinner, a famous behaviorist, rats were placed in a box with a series of levers. This box is now called the Skinner box, which contained rats in a box with levels. Rats learned to press levers that enabled them to obtain food. The oper- ant was the lever that gave the desired food. The behavior (pressing the right level) led to a desired positive stimulus (the desired food). The lever and the food were associated together to produce the learned response of pressing the right levers.

Of course, animals also learn by operant conditioning in nature. In Figure 20.7, the pelican chick pecks his mother’s beak to beg for food. His mother gives him food each time, positively reinforcing this behavior. Quickly, the chick learns to be more accurate in his begging for food from his parent.

In nature, operant conditioning also avoids negative responses. When a crocodile, for example, eats a cane toad, it becomes violently ill. The crocodile will learn to avoid

Operant conditioning

A complex set of behaviors during which an organism learns to respond to stimuli to produce a desired effect.

Figure 20.6 Pavlov’s Experiment Is an Example of Classical Conditioning. His dog salivates at the sound of a bell even though this stimulus does not include food.

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cane toads in the future and start eating other animals to get the desired food. Figure 20.8 shows the learning process. This is the basis for aposematic coloration in Chapter 17, which associates negative outcomes eating organisms with bright coloration.

Insight

The most complex and poorly understood form of learning occurs during insight. Insight is the recognition and mental solving of a problem before attempting it. The complex- ity of forethought and planning is obvious when the solution happens. However, what occurs within the mind remains a black box. Reasoning or the process of figuring out novel problems is the highest level of human thought. There are levels of reasoning and the highest forms use analysis and evaluation of information.

No other mammal, except chimpanzees, demonstrates insight besides humans (Figure 20.9b). In experiments observing chimpanzees, they are noted for being able to solve problems. In a classic experiment by Wolfgang Kohler in the 1920s, he placed a box and some poles in a room with bananas suspended in the air. On their own, the chimpanzees figured out how to construct a structure to reach up to the bananas.

Figure 20.7 Operant Conditioning. A pelican chick learns to peck his mother more efficiently through operant conditioning.

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Figure 20.8 a. This Cane Toad Is Not Attacked by a Crocodile. The crocodile learns that the toads are toxic and avoids them as a source for food. b. Instead, crocodiles find birds tasty.

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Cognitivism Another approach to learning explores its mental processing. Cognitivism studies the ways individuals use information to learn. It has become popular in educational research to apply learning in schools. Cognitivism describes organisms as able to process infor- mation, store it in their brains, and then retrieve it at a later time. Applying knowledge and using it in novel situations is the focus of cognitive science.

The development of language is an enormous undertaking in humans and a focus of cognitivism. Language requires many of the behaviors described in this section. Humans must remember and apply numerous words to create thought, make associa- tions, and learn numerous words. The development of the alphabet allows this to occur (Figure 20.9). The average human has automaticity with 13,000 words. These con- struct all of the ideas to help humans communicate with each other and pass down their thoughts. Cognitive psychology is a branch of cognitivism that studies how this happens.

Sociobiology and Society Sociobiology explores the social behaviors organisms demonstrate in their groups. Forming societies has advantages and disadvantages. Ants in our story helped each other to gather food. Chimpanzees groom each other to remove debris, dirt, and insects from their fur. In Chapter 17, the benefits of group behavior showed better defense against predators. Alarm calls in prairie dogs, for example, tell others in the group that preda- tors are present. This helps a group to defend against them. The use of language, espe- cially in human societies, further enhances cooperation and benefits of living together. Social organisms seek each other out and desire to form bonds. Group behavior can help members, as shown in Figure 20.10.

Living in groups has its drawbacks for its members, depending upon the type of spe- cies and the social construction of the society. For example, in most groups, population density increases as compared with living singularly. This leads to greater competition for mates, food, and territories. Sex is also a resource in an animal society, influencing

Cognitivism

The theory that studies the ways individuals use mental abilities to learn.

Language

A method of communication.

Figure 20.9 a. Language Use. The Egyptian alphabet has been used for over 3000 years. This ancient alphabet required massive amounts of memory storage and information to be utilized by human brains. It was the start of higher order communication among humans. b. Chimpanzees also show cognitive processes, as shown in the figure in which a chimpanzee (Pan troglogytes) uses tools to get fruit from a box.

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social systems. Sexual selection drives many social behaviors. Recall that sexual selec- tion was introduced in Chapter 7.

When groups form, behaviors occur that set up a social structure. A battle for terri- tory and mates sometimes leads to a dominance hierarchy or rank order within a society. High-ranking organisms dominate over lower-ranking organisms. In Corvus monedula, a type of jackdaw bird the dominance hierarchy leads to behaviors in which the highest jackdaws support the lowest. Complex systems emerge, which foster discontent between several lower groups by the higher group. This is done to keep the lower levels fighting so that the highest jackdaws may keep their coveted positions. A jackdaw social group is shown in Figure 20.11.

We will explore some of these societies in the next section, evaluating them as they occur in nature. We will look at how they compare with human society. Ultimately, was our character in the story right to yearn to be another organism?

Dominance hierarchy

A rank order within a society.

Figure 20.10 Social Behavior in Zebras. The stripes on zebras together in a herd confuse their predators, saving some from attack.

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Figure 20.11 Jackdaws in a Group. Dominance hierarchy can be vicious at times, but maintains order in the society.

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aggression There is often aggression, or hostility, between organisms. Humans experience it in groups but it is also intrinsic to animal social systems. However, most sociobiologists agree that intraspecific aggression (between members of the same species) usually chases off and does not kill rivals. Some organisms show intimidation displays with other members of the same species to chase them away, as seen in Figure 20.12. Others, when a battle appears to be lost, avoid further fighting by submissive behavior. Examples of submissive behavior include hiding fangs or concealing claws. With these strategies, animals of the same species almost never fight to the death. It would destroy their own related genes, as species share almost 99% of their DNA among members.

In our story, human conflict reaches a climax with the threat of nuclear war. Human population is threatened by the members of our own species. These situations are unfamiliar in other species. Perhaps because we have evolved complex thoughts to pre- meditate and invent devices, we are different from other species? Perhaps we are different innately – more aggressive? Alternatively, maybe our society corrupts us, lead- ing to such behaviors? Regardless, humans are 99.9% identical genetically, so killing each other is akin to killing oneself. It violates biological principles that dictate self- preservation and genetic survival.

Then, why do murder and warfare occur in human society, and not intentionally, as in most other animal societies? Lorenz argues that society makes humans excessively aggressive. Others argue that the selfish behaviors are inherent within. Richard Daw- kins developed a selfish-gene hypothesis that states that we are merely vessels holding our genes. The genes are selfish and want to reproduce to increase its own RS (Figure 20.13).This hypothesis contends that selfish genes drive all human behavior. In this next section, we will explore these two opposing sets of viewpoints.

human and animal kindness Let’s revisit the character’s contention in the story: Animals really are kinder than humans. This is true, surficially. It pays for many animal species to cooperate with each other, forming social groups. Many animals cannot survive long without being in a soci- ety. Ants in our story, when taken out of the colony, die very quickly with no purpose and no society.

Cooperation is the cornerstone factor in the success of any animal society. However, what drives organisms to help one another? Recall our biological principle – each mem- ber behaves to improve its RS. The same principles apply to the ants in the colony.

Aggression

Hostility between organisms.

Intimidation displays

Threat display that makes an organism look large and intimidating.

Submissive behavior

Willing to submit to avoid further fighting, when a battle appears to be lost.

Selfish-gene hypothesis

The hypothesis that states that organisms are merely vessels holding their genes.

Figure 20.12 A Cat often Engages in Intimidation Displays to Prevent Further Aggression.

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In our story, then why did all of these ants help carry the food, without even one ant taking a quick bite for itself? It is a form of altruism, when one organism helps without receiving an individual benefit. The opposite is selfishness, when one organism harms the other for its own benefit. However, ants are not really altruistic. They work together to improve their RS. The goal of any organism is to increase its RS, as discussed earlier. Ants are no exception. If a behavior increases an organism’s RS, then it will be favored in an ecosystem. If not, it will be eliminated.

Then, how can altruism be favored? Altruism gains nothing for an individual giving to another, such as an ant giving food to her queen. Is there true altruism or are all ani- mals, including humans, selfish? Ecologists contend that humans and animals are both very selfish. They cooperate based only on principles to benefit their own genes. It may be that our character in the story is naive to the ways of nature.

kin Selection Let’s look at kin selection to better understand the ants in our story. When helping is observed in nature, it is often between kin or family members. Kin selection occurs when individuals help each other because they share genes in common – they are related. For example, your mother, father, brother, sister, and children are related to you so you are more likely to help them, according to kin selection. (Figure 20.14).

As described earlier, our selfishness drives us to help our own genes get to the next generation – to have increased RS. Our immediate kin are 50% identical to us, which means that by helping them we are actually helping ourselves by the amount we are related.

According to kin selection, the amount of help we give depends upon the degree to which we are related to our kin. One’s aunt, uncle, nephew, and niece share 25% of the same genes in common. Thus, one might help each of them, but only half as much as our immediate kin. These predictions are not without flaws. Perhaps you dislike your cousin – this complicates matters. You may be inclined not to help them out. Humans are complex but still, the drive of biological principles is present. We are always obli- gated to help based on our selfish genes. This hypothesis contends that the closer the relatedness is, the stronger will be the helping behavior between kin. Do you think that this is so?

The selfish gene hypothesis is a cold and calculating view of human and animal kindness. It is suspicious and looks for the genetic payoff to helping. Let’s take a look at family that has helping as a cornerstone behavior.

Altruism

A type of behavior in which one organism helps without receiving an individual benefit.

Selfishness

A behavior in which one organism harms the other for its own benefit.

Kin selection

Natural selection in which individuals help each other because they share genes in common.

Figure 20.13 Are We Selfish in Our Inner Core?

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Family is an important factor in all human society. We take our girlfriend or boy- friend to “meet the parents” because kin are important. Family is set up, according to the selfish-gene hypothesis, to help each other’s genes. Because the members of the unit are more related, it evolved, much like an ant colony, into a helping system. By helping family members, we are helping our own genes that are shared in common. Family is a social construct to act as a vehicle to accomplish this, according to Dawkins.

Even human laws are based on family importance. Inheritance of assets moves down family lines to preserve wealth in tandem with genetic relatedness. Interesting, in a recent study of genetics, after 14 generations removed from our ancestors, we are no more related to them than a stranger. The advice: spend the money and do not save for generations down the road to preserve you wealth genetically!

What about helping in Unrelated organisms? Some animals help each other who are not related. It is pleasant to imagine that ants are kind and considerate of each other because they are “just nice.” Self-sacrificing organ- isms often have a reason behind their behaviors. To illustrate, vampire bats, Desmodus rotundus, appear to help one another in an altruistic way. They are small creatures, each weighing between 15 and 50 grams (0.5–1.7 ounces). Vampire bats are native to South America and the areas of Central America. D. rotundus are flying mammals with a bad reputation – they suck blood. (Figure 20.15).

Upon closer evaluation of their society, however, they help each other when one of their members misses a meal. They are communal roosters, meaning that they leave their nests as a group to feed. Usually, they make their journeys in the night to forage for food. When vampire bats bite, they make a quick and painless insertion into their victim. D. rotundus feed for up to half an hour (about 20 milliliters of blood) at any one time on its victim. They have a voracious appetite and want to latch on for extended time. To do this, they evolved an anticoagulant in their saliva to keep the victim’s blood flowing.

After they return to their nests, they are frequently observed regurgitating blood to each another. By regurgitating blood, they give away some of their own food to benefit

Figure 20.14 Kim Selection. Does a mother only help her children because she helps herself? Sociobiology asks the question.

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the other bat. It is an example of altruism. The most surprising part is that vampire bats do not discriminate – whether kin or not, they help their fellow bat.

It appears to be altruism but upon an even closer analysis, helping behavior is linked to something more selfish: It is a “You scratch my back, I’ll scratch yours” mentality. Because these bats are so small, missing a meal is deadly, with a steady proportion of bats always missing a meal at any one night’s feeding. Eventually, every bat will be in the same position and need some regurgitated blood. Thus, by regurgitating blood, such a strategy will pay off in the future. Therefore, the next time a bat needs a blood meal, it will be saved by what is called reciprocal altruism, in which all members of a group cooperate altruistically so that each survive better. This system of reciprocal altruism depends upon members not cheating and mechanisms to detect cheaters; otherwise, the whole set up would fall apart.

Debate on the nature of animal Society OK, so bats are not really all that loving to each other. What about human kindness to each other? Don’t strangers help each other, despite being unrelated? What about human acts of kindness in the world? Dogs may show love to their master but is there an ulterior motive? There is debate on the nature of goodness and badness in animal and human society.

Konrad Lorenz (1903–1989) and the current Richard Dawkins, both introduced earlier in this chapter, offer opposing viewpoints. In the selfish gene hypothesis, Daw- kins argues that all life is extremely selfish by nature. He claims that our genes puppet our behavior and that it is their selfish desire to reach the next generation that forms human society. He adds the caveat that society should “. . . try to teach generosity and altruism, because we are born selfish.” Dawkins sees social structure in all organisms, including ants in our story, driven by this selfishness. He would view the line of ants in the story as a set of selfish vessels doing the will of genes. They help each other to benefit the colony and the colony is only an extension of the selfish genes within (Figure 20.16).

Lorenz argues that behaviors are adaptive and that they benefit the organism. How- ever, his view looks at animals are more caring about each other. He views behaviors such as grief in geese and love of music as beyond mere benefits to the individual – these

Reciprocal altruism

A behavior in which an organism helps another and the second organism returns the favor either to the benefactor or his/her progeny.

Figure 20.15 Vampire Bats, Desmodus rotundus. While appearing altruistic, they actu- ally only help each other to get something back in return – blood when they need it.

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behaviors do not benefit an individual. It shows that we are more complex than mere selfishness.

It is not humans but society that leads to animal selfishness, in Lorenz’s view. His approach depicts humans and animals as basically good. Aspects of society, such as high density and crowding, he views as corrupting humans. He points to examples of other animal social systems that restrain their aggression except when crowded. Lorenz cites fish in a tank, which become aggressive but in nature, given free space, they are passive. Lorenz blames, in several of his books, the crowded capitalist system as unnatural to animals, as the reason for our excessive aggression (Figure 20.17).

Group Cooperation vs. Selfish Genes Lorenz points out kindness in various animal social systems, much as the character in our story notices cooperation on the ant hill. Insect members of the order Hymenoptera (ants, bees, and termites) all exhibit cooperative systems. These societies have traditionally

Figure 20.16 Are Humans Inherently Good or Evil? A debate about our inner depths. Richard Dawkins

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Figure 20.17 People Crowded in a City May Not Be Living in a Natural Situation. A busy street in New York City is shown in this image.

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Is the highest level of social organization, in which organisms cooperate and their members have sterile castes.

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been looked upon as a role model of good group behavior. However, how altruistic are the ants in the colony? Finally, let’s look at how the ant society is constructed.

Hymenoptera species all have similar characteristics: they exhibit eusocial behav- ior. Eusociality is defined as the highest level of social organization, in which organisms cooperate and their members have sterile castes (Figure 20.18). These castes do not reproduce and instead give their life for the colony. It is the ultimate in altruism – or is it?

An ant soldier will attack its enemy to save the group in a seemingly selfless act, rip- ping itself apart, as described in Chapter 17. This act occurs despite the fact that the ant will die within a few hours. As stated, worker ants are sterile and instead serve a queen master. All of this points to the kind of selflessness missing in humans.

However, Dawkins argues that this selflessness is actually selfish. Dawkins posits that the behaviors of these ants are solely based on their desire to pass their own genes onto the next generation.

Dawkins cites the haplodiploidy of the hymenopterans: the queen gives birth by par- thenogenesis, which recall from Chapter 16 is a virgin birth (Figure 20.19). She pro- duces all of the males in the colony in this way. The males are thus haploid (contain half of the full set of DNA) and are all identical to one another. After some basic genetic cal- culations, it is determined that females in the colony are 75% related to each other. Their father contributes all of his genes to his children. This makes the offspring identical on the paternal side. Gene differences only arise from the mother.

Hymenopteran, such as the ants in the story, are therefore more likely to help one another because of their high degree of genetic relatedness. It pays to help each other out – ants are actually helping 75% of themselves, since eusocial insect females are 75% identical to each other. They are like one large family, more related to each other than any other family. In humans, immediate family members (non-twins) are at a maximum 50% related, as shown earlier in the chapter. It would be expected that human helping would be less than in ants. The more related organisms are, the more they tend to help one another. This is a selfish reason why ants are so cooperative – they are really helping themselves by helping each other.

The motivation behind a behavior is important in determining whether it is a truly helping or based on selfishness. If someone walks a stranger across the street, only to steal a wallet, was the behavior a true act of kindness? Natural laws of genetics and ecology may have more influence on human society than expected. Should the character

Haplodiploidy

Sex-determining method in which females are developed from fertilized eggs (diploid) and males are developed from unfertilized eggs (haploid).

Figure 20.18 Eusociality. The order of animals, Hymenoptera (ants, bees, and wasps) exists in highly organized colonies.

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in our story really envy the citizens on the ant hill colony – the polite and helpful Hymenopterans? Are humans able to overcome their genes through acts of kindness? Will humans eventually destroy themselves? . . .

Summary Social structure in humans and in animals mirrors the principles of biology discussed in this text. Animal social systems include innate and learned behaviors. Learned behaviors help animals to adjust to changing environments. Some animals organize into social systems that have both positive and negative consequences for its members. Ultimately, social systems seek to benefit more than harm the RS of its members, taken as a whole unit. Social systems are set up based on a drive to improve RS among its members. Organisms and social systems operate to accomplish this task.

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Summary: key points

• Human society often follows the same principles of survival, competition, and aggression as animal social systems.

• Animals behave either innately or through learning by interacting with others. • Learned behaviors include imprinting at early ages, habituation or getting used to stimuli, classical

conditioning, operant conditioning, and insight. • The selfish-gene hypothesis claims that all organisms act selfishly to extend their genes to new

generations.

Figure 20.19 Ants Help Each Other. From BSCS Biology: An Ecological Approach, 9th Edition by BSCS.

(a) A foraging honeybee returns to the hive after finding a nectar source. Other bees soon leave the hive and fly to the same source. How does the first bee inform the other bees about the food source?

(b) The returning bee gives nectar to the other bees, then begins a dance on the vertical face of the hive.

(d) If the dance is a figure 8 with wagging of the abdomen, bees search at a distance.

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adaptive behaviors aggression altruism animal behavior behaviorism behaviors classical conditioning cognitivism dominance hierarchy eusociality habituation haplodiploidy

innate behaviors intimidation displays kin selection language learned behaviors operant conditioning reciprocal altruism reproductive success (RS) selfish-gene hypothesis selfishness sociobiology submissive behavior

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Multiple Choice Questions

1. Both human and animal social systems seek to improve: a. selfishness b. altruism c. parasitism d. reproductive success

2. A pigeon gets accustomed to people in an urban area. It no longer is afraid of them. This is an example of which type of learned behavior? a. adaptation b. habituation c. imprinting d. operant conditioning

3. In question #2 above, the same pigeon gets attacked by cats whenever it enters Mr. McGreeley’s backyard. This is an example of: a. adaptation b. habituation c. imprinting d. operant conditioning

4. Sisters in ant colonies are _____ % related genetically. a. 1 b. 50 c. 75 d. 99

5. The statement, “Humans are basically good but society is the problem” is a state- ment from: a. Dawkins b. Lorenz c. Skinner d. Pavlov

6. Which term includes all of the others? a. social organization b. dominance hierarchy c. reciprocal altruism d. cooperation

7. A whale, born knowing how to defend itself is an example of ____ behavior. a. imprinted b. innate c. learned d. habituated

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8. Social organization in vampire bats was shown to be: a. selfish b. altruistic c. uncooperative d. individualistic

9. Cognitivism studies: a. mental processes b. responses c. negative stimuli d. positive stimuli

10. A change in behavior as a result of stimuli is: a. learning b. non-social c. innate d. all of the above

Short answer

1. Describe one way human society is the same and one way it is different when com- pared with animal social systems.

2. List three ways learning occurs in animal social systems.

3. How does association play a role in classical conditioning?

4. List and define the two types of animal behaviors. How do they both work to help organisms?

5. Explain how reciprocal altruism is demonstrated in vampire bats.

6. Explain how altruism differs from selfishness, using the term reproductive success.

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7. Give one example of psychological imprinting and one example physiological imprinting.

8. What dangers exist in habituation? Do you think that this plays a role in car acci- dents? Explain.

9. Explain why insight is so difficult to measure, as compared with other behaviors.

10. Compare and contrast the goals of submissive displays and intimidation displays. Be sure to include one way the behaviors have goals in common and one way the behaviors are different.

Biology and Society Corner: Discussion Questions 1. How are dominance hierarchies seen in the work place? Compare it to the jackdaw

social system described in this chapter. Are human employment systems very dif- ferent from those found in animal social systems? Explain your answer.

2. The selfish gene hypothesis and Lorenz’s views oppose each other. After reading this chapter, form an argument supporting or refuting the following statement: “Humans are selfish to the core.” By the end of the chapter, did you agree with the character in the story, that you too wish you were an ant? Why or why not?

3. A controversial statement was made by a scientist in the news recently: “Nations that are more homogeneous have better cooperation.” Based on the readings in this chapter, do you agree or disagree with this assertion? Why or why not?

4. The use of behaviorism in schools often looks only at the test results (an expressed behavior) and not at the total person, according to many education groups. In Amer- ica today, testing in schools evaluates the scores and makes decisions. Educators argue that scores on tests do not look deeper into the whole person. Do you agree or disagree? Why?

5. What if ants in the hill in our story were only related by 10%? Predict how its soci- ety would change. Explain your answer.

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Figure – Concept Map of Chapter 20 Big Ideas

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Abiotic factors The non-living factors in an environment.

Abscess Collection of pus that is walled-off and builds within the tissues of the body.

Abyssal zone A deep layer near the bottom of the ocean.

Accessory organs Association of organs that produce, store and/or release chemicals to carry out the processes of the breakdown of food.

Acid The resulting solution in which water yields more hydrogen into its surroundings.

Acrosome A caplike structure covering the top end of the sperm, containing enzymes that digest layers surrounding the egg.

Actinomycetes A type of bacteria having filament strands and resembles fungi. They are decomposers, recycling dead organic matter.

Action The direction in which muscles move when they contract.

Action potential A change in the electric potential across the plasma membrane that occurs when a cell is stimulated.

Activation energy The minimum amount of energy that must be possessed by the reacting species to undergo a specific reaction.

Active artificial The condition that occurs when a vaccine activates the immune system to produce antibodies in a response to.

Active natural A type of immunization that occurs when the immune system defends itself and enables future defense against pathogens.

Active site Special shapes on enzymes that allow for binding to other chemicals.

Active transport Is the movement of substances against a concentration gradient, from a lower concentration to a higher concentration, which requires cellular energy.

Adaptation Populations of living things change a result of their surroundings and evolve or change as a group.

Adaptive behavior The behavior that helps an organism’s reproductive success by helping it to persist in a population and become established.

Adaptive radiation The changes that occur in a group of organisms to fill different ecological niches.

Adenine A purine base that is a base, a component of RNA and DNA.

Glossary

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Adenosine triphosphate (ATP) A special nucleotide that holds readily available energy for cell functions.

Adipose A body tissue used for fat storage.

Adrenal cortex The exterior portion of the adrenal gland that secretes steroid hormones.

Adrenal glands Glands that sit atop both kidneys and control a variety of body functions.

Adrenal medulla The inner part of the adrenal gland.

Adult Fully grown or developed.

Aerobic Occurring in the presence of oxygen or require oxygen to live.

After-birth A brief relaxation period followed by smaller contractions that propel the placenta out of the uterus after child birth.

Age structure diagram A graphical illustration that is used to predict future patterns of growth or declines of various age groups in a population.

Aggression Hostility between organisms.

Air sacs (alveoli) Tiny sacs within the lungs where exchange of oxygen and carbon dioxide gases takes place.

Alarm call A warning signal made by an animals or birds about a predator or when startled.

Albedo A proportion of solar energy that is reflected from the Earth back to space.

Albinism Is a noncontagious disease that is genetically inherited and results in a lack of pigmentation.

Aldosterone A hormone produced by the cortex of adrenal gland.

Algae Are multicellular organisms that are photosynthetic, and they contain a variety of pigments such as chlorophyll a and b (green), carotenoids (yellow-orange), phycobillins (red and blue), and xanthophyll (brown).

Alimentary canal The tube and associated organs of digestion, which includes all of the parts of the digestive system that contribute to the breakdown of food.

All-or-none response All sarcomeres contract in a muscle fiber or none at all.

Alleles An alternative form of the same trait.

Allergen Antigens that cause allergies.

Allergy An inappropriate immune reaction to antigens that are otherwise not harmful.

Allopatric speciation The process of development of new species when there is a physical barrier separating members of a group of organisms.

Alpha cells of pancreas Cluster of cells found in the pancreas, which make glucagon.

Alternation of generations The life cycle of plants in which haploid and diploid phases of their lives exist for survival and reproduction.

Altitude sickness The condition in which the altitude affects a person’s ability to breath.

Altruism A type of behavior in which one organism helps without receiving an individual benefit.

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Alzheimer’s disease Progressive mental deterioration brought on by aging. The disease is associated with protein masses or tangles that form plaques along the nerves in the brains of the victims.

Amino acid The building blocks of proteins.

Ammonification The process in which organic nitrogen is converted into ammonia and dissolved NH4+ forms ready for uptake.

Amnion The fluid sac that protects a fetus.

Amniotes Terrestrial animals that develop their eggs encapsulated within an amniotic sac.

Amoebocytes A type of sponge cell that transports food through the sponge body.

Amphibians Vertebrates that live a portion of their lives in water and another portion on land.

Amplexus Mating behavior seen in frogs and toads.

Amygdala A section of brain associated with fear, panic, and aggression.

Anabolism A series of reactions that build up complex molecules, using stored energy.

Anaerobic respiration A series of reactions that form alcohol from sugar.

Anal canal Terminal part of the large intestine.

Anaphase A cell division stage in which chromosomes split into two identical groups and move toward the opposite poles of cells.

Anaphase I The stage of cell division in meiosis in which homologous chromosomes separate.

Anatomical position The position that describes a specific way of positioning for a human body.

Anatomy The study of the structure of body parts.

Anemia The condition in which blood lacks normal oxygen carrying capacity.

Angioplasty A surgical procedure to widen obstructed arteries or veins.

Angiosperm Are flowering plants with seeds developed in an ovary.

Angiotensin A hormone that promotes aldosterone secretion in blood and causes blood pressure to rise.

Animal behavior The branch of biology that studies the ways in which animals act within their environment.

Animalcules The dated term for a microscopic animal, we now know of as microorganisms.

Animals Living organisms that feed on organic matter (other living creatures) for survival. Animals are multicellular eukaryotes and motile in nature.

Anion Negatively charged ion.

Anorexia nervosa An eating disorder characterized by a loss of appetite for food and a fear or refusal to maintain normal body weight.

ANOVA (Analysis of Variance) Is a powerful statistical method that compares the means of three or more groups.

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Anterior At the front of or situated before.

Anther A reproductive structure that holds pollen grains.

Anthropoids A higher primate, including monkeys.

Anti-codon A sequence of three nucleotides in transfer RNA molecules.

Antibiotic Any chemical that stops the growth of microorganisms.

Antidiuretic hormone (ADH) A hormone released by the pituitary gland that helps in water retention in the body.

Antigens Any molecule or cell part that initiates an immune response.

Antioxidants The substances that eliminate molecules with extra electrons, thus preventing damage to body structures.

Anvil A tiny bone in the middle ear.

Aortic arches The simple hearts of segmented worms.

Apical meristem Meristems that are found at the tips of roots and in shoot buds to begin primary growth.

Apical surface The free side of all epithelial tissues.

Apoptosis Cell death that occurs as a part of an organism’s growth.

Aposematic coloration Warning coloration that serves to deter predators.

Appendicular skeleton The portion of skeleton that consists of bones of the limbs, the pelvic girdle, and the pectoral girdle.

Apple shape A body shape that is characterized by excess body fat in the abdominal region.

Aqueous humor The clear fluid present between the cornea and lens of the eyes.

Aquifer Saturated areas of water within bedrock.

Arachnids An arthropod characterized by having eight legs.

Arachnoid The middle layer of meninges.

Archaea Microorganisms that are similar to bacteria in size and structure but different in molecular organization.

Archaebacteria Ancient forms of bacteria, with only a few surviving branches.

Areolar Packaging type tissue.

Arrector pili muscle Small muscles attached to hair follicles in skin.

Arrhythmia A condition in which the heart beats in an abnormal rhythm.

Arteriole A small branch of artery leading to a capillary.

Arteriosclerosis A chronic condition characterized by abnormal thickening of vessel walls.

Artery A vessel that carries oxygenated blood away from the heart to cells, tissues, and organs.

Arthropods Invertebrates with a specialized segmented body and a protective external skeleton, or exoskeleton, and jointed appendages.

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Articulation The area of connection between two bones.

Asexual reproduction The process in which a single individual produces new offspring, without genetic material contributed from a partner.

Asexuality The lack of sex drive.

Asthma A respiratory condition characterized by inflammation of the respiratory passageways.

Atherosclerosis Condition in which saturated fats are linked to heart disease and hardening of the arteries occurs.

Atmosphere The gaseous layer surrounding a planet.

Atom The smallest component of any element that retains the unique properties of that element.

Atomic mass The mass of an atom is the combined weights of the subatomic parts that have weight.

Atomic number The number of protons in the nucleus of an atom.

Atoms Are the smallest units of matter that can exist and maintain the properties of the larger sample.

Atrioventricular (AV) node Small mass of neuromuscular fibers located at the base of the interatrial septum.

Atrium An entry chamber of the heart from which blood is passed to the ventricles.

Auscultation Listening to sounds produced within the body.

Autogenous model The model that states that eukaryotes developed directly from a prokaryote by compartmentalization of functions of the prokaryote plasma membrane.

Autoimmune disease A disease in which the immune system overreacts to its own cells.

Autonomic nervous system System of involuntary nerves.

Autorythmic Cardiac muscle cells that beat independent of the nervous system.

Autosomal dominant The patterns of inheritance of single-gene traits in which the dominant allele gets expressed.

Autosomal recessive The patterns of inheritance of single-gene traits in which both recessive alleles are present for a person to get the recessive trait.

Axial skeleton The portion of skeleton that consists of the skull bones, ribs, sternum, and vertebrae.

Axon A long thread-like structure of the nerve cell that transmits information to other cells away from the cell body.

B-cell A type of white blood cell that produces antibodies.

Bacillus Rod-shaped bacteria.

Backbone Set of nervous tissue surrounded by bones for protection.

Bacteria Single-celled microorganisms that are found everywhere.

Bacteria Single-celled organisms that have cell walls but lack an enclosed nucleus and organelles.

Basal cell carcinoma A type of skin cancer, which is relatively common, but very rarely kills its victims.

Basal layer The lowest layer of epithelial layers.

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Basal metabolic rate (BMR) The minimal rate of energy used by an organism at complete rest.

Base The resulting liquid in which water absorbs more hydrogen from its surroundings.

Basement membrane A thin extracellular membrane underlying the epithelium of many organs.

Basophil A type of white blood cell associated with allergies.

Behaviorism The theory that human and animal responses are measured to determine an organism’s learning.

Behaviors Any action taken by an organism.

Beta cells of pancreas Cluster of cells found in the pancreas, which make insulin.

Bicarbonate (HCO3-) A buffer; within the digestive system it neutralizes the acidic chyme entering the intestines.

Bilateral symmetry The property of being roughly identical upon surface observation when a line is drawn down their middle.

Bilirubin A substance produced by the digestive system during the breakdown of RBCs.

Binary fission The process by which a cell divides directly in half.

Binomial nomenclature Naming convention for living creatures, in which organisms are a given unique scientific name, composed of two parts. The first indicates the genus and the second the species.

Bioaccumulate Accumulation of generally harmful substances in an organism.

Biodiversity Variety of life forms in a particular habitat.

Biogeochemistry A scientific discipline that encompasses chemical, physical, geological, and biological processes and reactions that govern the workings of the natural environment.

Biogeography The way species are distributed.

Biological literacy Is the ability to interpret, negotiate, and make meaning from the many aspects of knowing about life to make decisions and use biology and its technology.

Biology Study of living creatures.

Biomagnification The increasing concentration of a particular substance in organisms at the top of the food chain.

Biomass Is the total organic matter in an ecosystem.

Biome A large community of flora and fauna occupying a major habitat.

Biophilia The affinity human beings share with other living creatures.

Bioprocessing The process of building up (anabolism) and breaking down (catabolism) of macromolecules.

Biosphere All of the different ecosystems of the Earth interacting with their environment make up the biosphere.

Biotechnology The branch of science that uses biological knowledge and procedures to produce goods and services for human use and financial profit.

Biotic factors Factors that comprise the living things in a habitat.

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Biotic potential Maximum possible growth achieved by organisms under ideal conditions.

Bipolar cells A neuron that has two processes.

Birds Warm-blooded vertebrates characterised by feathers, wings, beak with no teeth, scaly legs, and typically by being able to fly.

Births New born additions.

Bivalves The property of having two shells hinged together.

Blastula A hollow ball of cells at the early stage of development.

Blood A red fluid that connects different parts of the body by providing nourishment and removing wastes.

Body landmarks (surface regions) Terms for the specific location of the lesions on the human body to give detail to their descriptions.

Bolus A rounded mass of food with the digestive tract.

Bone Is the substance that has a solid form, with calcium salts embedded within fibers of its extracellular matrix.

Bone marrow A compartment within bones that stores stem cells.

Bony fishes Type of fishes that have skeletons composed of bone.

Bowman’s capsule A cup-like sac surrounding the glomerulus within the nephron.

Brain A part of central nervous system that functions as the command center of the body.

Brainstem The portion of brain that consists of pons, midbrain, and medulla oblongata.

Bronchial tubes Tubes that let air in and out of the lungs.

Brood parasitism A form of social parasitism in which a bird species lays eggs in another bird’s nest.

Budding A form of asexual reproduction in which new organisms develop from a bud as a result of cell division at one specific site.

Bulbourethral gland A small gland located at the base of the male reproductive organ and donates small amounts of fluid to the semen at the end of ejaculation.

Bulimia An eating disorder characterized by abnormal and constant craving for food alongside purging.

Bulk transport Is the movement of large amounts of material across the plasma membrane.

Bundle of His A collection of heart muscle cells that transmit electrical impulses from the AV node to the interventricular septum and ventricles.

C3 pathway The most common form of photosynthesis that uses a 3-carbon molecule in the Calvin cycle.

C4 pathway A method used by plants to pull carbon dioxide into the Calvin Cycle more easily.

Calcitonin A hormone made by the thyroid directs calcium ion uptake by the bones.

Calcium carbonate A naturally occurring chemical compound , making up by coral skeletons.

Calories The amount of energy required to raise 1 gram of water by o1 Celsius.

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Calvin cycle A set of chemical reactions absorbing carbon dioxide and making glucose, taking place in chloroplasts during photosynthesis.

CAM pathway A type of photosynthesis working at night and exhibited by plants that inhabit warm and dry areas.

Cambrian explosion A evolutionary event during which rapid diversification of multicellular animal life occurred.

Camouflage The act by which organisms become less visible in their environments to avoid being seen.

Cancer A tumor caused by an uncontrolled division of cells.

Canines The front teeth on the side, long and narrow, evolved to tear and pull foods.

Canopy layer Is the upper layer that is made of the leaves of treetops, in forest ecology.

Capillary A tiny blood vessel that connects arteries and veins.

Capillary bed The whole system of capillaries of the body.

Capsid The protein coat that surrounds structure of a typical virus.

Carbaminohemoglobin One of the forms in which carbon dioxide exists in blood.

Carbohydrate Organic compounds providing “instant energy” for living tissues.

Carbon fixation The conversion process of carbon dioxide to organic compounds by living organisms.

Carbon monoxide poisoning A potentially fatal condition that occurs when carbon monoxide binds to hemoglobin, replacing oxygen.

Carbonic acid-bicarbonate buffering system A set of reactions that regulate the pH of blood.

Cardiac muscle The muscle found only in the heart and beats spontaneously to pump blood throughout the body.

Cardiac sphincter The muscle surrounding the opening between the stomach and esophagus.

Cardiovascular system The system comprising the heart and blood vessels

Carnivore -(secondary consumer) Organisms that eat herbivores.

Carpals Any bones of the wrist.

Carpel An organ found at the center of a flower and bears one or more ovules.

Carrying capacity (K) The maximum number of individuals an environment is able to sustain in the long term.

Cartilage A dense connective tissue that provides cushioning support in vertebrates.

Cartilaginous fishes Are fishes that have a skeleton composed of the flexible but solid connective tissue, cartilage.

Catabolism A series of reactions that break down complex molecules to yield energy.

Catastrophism The theory that explained that new species formed after sudden and violent catastrophes.

Cation Positively charged ion.

Cell The structural and functional unit of an organism.

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Cell body The central part of the neuron that contains the machinery of the cell, with organelles and a nucleus that directs nerve functions.

Cell cycle The life span phases a cell goes through.

Cell respiration A series of energy-producing reactions that convert food energy into ATP.

Cell-mediated immunity An immune response that is based on on antigen-specific T lymphocytes.

Cellular respiration The process through which most organisms break down food sources into useable energy.

Cementum A glue-like substance holds the tooth’s ligament that connects the dentin to the underlying bones of the face.

Central canal A central tube through which water enters the arms of a starfish.

Central core The foundational part of an organism that helps regulate basic life processes.

Central Dogma A theory that explains how inherited material gives rise to all our unique structures, functions, assets, and liabilities.

Central nervous system (CNS) The part of the nervous system consisting of the brain and the spinal cord.

Centriole Minute cylindrical organelles found in animal cells, which serve in cell division.

Cephalopods A group of mollusks characterised by a large head, eyes, and a ring for sucker-bearing tentacles.

Cerebellum The posterior part of the brain, involved in coordination.

Cerebrum The largest region of the brain.

Cervical vertebrae The top seven vertebrae of the spinal column that form the neck.

Chaparral A type of biome characterized by shrubs and rodents in dry conditions, around the Mediterranean and southern California.

Character displacement The phenomenon in which organisms evolve characteristics to help them to partition resources.

Characteristics of life The features (adaptation, order, response to stimuli, growth development, and use of energy, homeostasis, reproduction, metabolism, diversity) that differentiate between life and nonlife.

Chemical bond Relationship between atoms, involving the exchange of electrons.

Chemistry Study of matter, its properties and its interactions.

Chemoautotroph Bacteria that use inorganic chemicals as energy.

Chemoreceptor A sensory cell that is stimulated by chemicals.

Chlorophyll a A special pigment molecule in a photosystem that does not move its electrons back to the ground state.

Chloroplast A part of plant that contains chlorophyll and conducts photosynthesis.

Cholecystokinin (CCK) A hormone that slows peristalsis.

Chondrocyte A cell within cartilage.

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Chordates Are animals with a spinal cord or spinal cord-like structure.

Chorion Fetal membrane that nourishes the fetus and becomes a part of its placenta.

Chromatin Is a complex of macromolecules found in cells and consist of protein, RNA, and DNA.

Chromoplast An organelle that contains any plant pigment other than chlorophyll.

Chromosome A thread-like structure formed when a cell divides and its DNA coils more tightly to histones.

Chyme Acidic ball of food within the digestive tract.

Cilia Are short extensions that help cells move.

Ciliary body A part of the eye located between the choroid and iris.

Circular genome Genetic material in a circular form found in prokaryotes.

Class A group of related orders.

Classical conditioning An association between a new stimulus and a natural stimulus.

Cleavage Division of cells in the early embryo stage.

Climax community The highest level of organization for an ecosystem.

Clitoris A site of external female stimulation.

Clonal selection The process by which T-cells or B-cells divide rapidly to produce large numbers of their own type of immune cells on encountering an antigen.

Clotting factors Are proteins that undergo a series of chemical reactions that halt bleeding.

Cnidarian An aquatic invertebrate that comprises coelenterates.

Cnidocysts Stinging cells present in Cnidarians.

CNS (central nervous system) The part of the nervous system that consists of the brain and spinal cord.

Coccus Round-shaped bacteria.

Coccyx A small triangular-shaped bone located at the base of the spine.

Cochlea A spiral-shaped cavity of inner ear.

Codon (triplet) Normal genetic code in which a sequence of three nucleotides codes for a specific amino acid.

Coelenterons The open body cavity present in Cnidarians and opens to the outside environment, in which digestion occurs.

Coelom An open body cavity that separates the organs of the annelid.

Cognitivism The theory that studies the ways individuals use mental abilities to learn.

Cohesion (or cohesive forces) The force that is formed when water molecules stick together due to hydrogen bonding.

Collar cells A type of sponge cell that has beating flagella move water through the internal cavity of the sponge.

Collecting duct A collecting tube that receives urine from several nephrons.

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Colonization A process by which a species spreads to new areas.

Commensalism The type of symbiosis which occurs when one organism benefits and the other is unharmed by the relationship but does not benefit.

Community A group of living organisms living in the same area or having a particular characteristic in common.

Compact bone A portion of bone that is dense and contains very little open space.

Companion cells Are specialized parenchyma cells found in the phloem of flowering plants.

Compartmentalization The formation of cellular spaces, each separate from one another.

Competition The activity that occurs when organisms strive for the same limited resources.

Competitive exclusion principle A principle, which states that organisms will compete with each other in an area until one goes extinct.

Complementarity The specific coupling of bases.

Compound light microscope Microscope that uses two sets of lenses (an ocular and an objective lens).

Concentration, higher and lower The presence of a certain amount of a specific substance in a solution or mixture in a certain concentration. Any solution containing fewer dissolved particles is lower concentration.

Cones A form of photopigment that sends impulses to the brain that give color perception.

Conjugation The process of exchange of genetic material through pili in bacteria.

Connective tissue Tissue that binds and supports different parts of the body.

Contact inhibition Cell’s normal ability to come into contact with its neighbors while dividing and this inhibits its growth based on the limited spacing around it.

Control center An operational center for a group of related activities.

Control group A group in a study or experiment not receiving treatment by researchers and used as a benchmark to measure how other tested subjects do.

Copulation The act of placing a male structure into a female’s reproductive tract.

Coral bleaching The loss of algae from corals, and resulting coral death.

Corals Marine invertebrates that live in large colonies composed of limestone skeletons.

Coriolis Effect The deflection of a moving object with respect to the Earth ‘s rotation.

Cork cambium A tissue found in a plant’s stem and is responsible for thickening stems and roots.

Cornea Transparent part of the eye.

Coronary artery An artery supplying blood to the heart.

Coronary artery bypass graft (CABG) A type of surgery that improves blood flow in the heart.

Coronary circuit The system in which some vessels branch off and resend blood toward the heart.

Corpus callosum An attachment area that connects the two hemispheres of the cerebrum.

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Corpus luteum Hardened mass of an ovarian follicle.

Correlation Relationship between two variables.

Cotyledon The first leaf formed during the initial development of embryos in a seed.

Covalent bond Bonds that result from the equal sharing of electrons between atoms.

Cranial bones The bone that enclose the brain.

Cristae A fold in the inner membrane of the mitochondria.

Critical thinking The analysis and evaluation of an issue to form a judgment

Critical threshold potential The critical level (-55mV) at which the entire neuron fires a nerve impulse across its membrane.

Crossing over The exchange of genes between chromosomes.

Crustaceans An arthropod characterized by having five sets of appendages.

CT scan Computerized axial tomography that produces detailed images of internal organs.

CTP (connective tissue proper) A set of tissue types that act as package materials in the body.

Cuboidal A type of epithelial cell appearing square in shape.

Cyanobacteria Are photosynthetic bacteria that contains bacteriochlorophyll.

Cytochrome Heme proteins that contain heme groups and are responsible for ATP generation through electron transport.

Cytokinesis The division of cell cytoplasm following mitosis or meiosis.

Cytology The study of cell parts.

Cytoplasm A semisolid liquid that holds organelles suspended within it.

Cytosine A type of base found in DNA.

Cytotoxic T-cells Killer T-cells stimulated by T-helper cells to kill specific invaders.

Data analysis (Qualitative and Quantitative) The process of evaluating information that is obtained by investigation. The reporting and use of non-numerical data is qualitative data analysis while reporting and use of numerical data is quantitative data analysis.

Deaths The end of life; those leaving permanently.

Decomposer Organisms that break down once living organic matter into energy.

Dedifferentiation Is the loss of the specialized functions that normal cells perform.

Deep A surface marking that is considered the opposite of superficial and away from a surface.

Deep vein thrombosis (DVT) The condition that occurs when a blood clot forms in one of body’s large veins, most commonly in legs.

Deforestation Removal of forested areas.

Dehydration synthesis A process in which hydroxyl and hydrogen atoms are removed from two organic compounds that merges them into one (covalent) bond.

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Demographics The data collected by ecologists about the statistics of a population of species.

Dendrite A thread-like structure of the nerve cell that receives signals from other cells

Dense irregular Connective tissue composed of irregularly arranged fibers, such as the dermis of the skin.

Dense regular Connective tissue composed mostly of collagen fibers such as ligaments and tendons.

Density-dependent factors Factors that limit the population size, whose effects are dependent on the number of individuals of a population.

Density-independent factors Factors that limit population size, whose effects do not depend on the number of individuals of a population.

Dentin The bony tissue of a tooth.

Deoxygenated blood Blood that lacks oxygen.

Deoxyribonucleic acid (DNA) A long macromolecule containing the information code that directs cellular activities in living organisms.

Deoxyribose The sugar backbone found in DNA.

Dependent variable The results of an experiment.

Depression Blood or nerve openings in human bones.

Dermal papillae A wavy layer of the skin which is also responsible for human fingerprints.

Dermis The middle layer of the skin, containing most of its organs and sense receptors.

Desert A dry, barren area with little or no rainfall.

Desertification The process by which fertile lands experience rapid depletion of flora and fauna becoming a desert.

Desmosome One of the three types of connections between cells, is a cell structure specialized for cell-to-cell adhesion.

Detritus Dead organic matter that forms as grasses die.

Deuterostomes Animals belonging to the group Deuterostomia, in which the body cavity first forms from the back, or anus region.

Developmental anatomy The study of changes in structures of an organism since its birth.

Diabetes Type I An autoimmune disease resulting from an attack on the pancreatic cells making insulin.

Diabetes Type II A medical condition as a result of resistance to insulin by cells.

Dialysis A treatment for kidney impairment.

Diatoms A single-celled algae that are a major producer of oxygen via photosynthesis.

Dicot Angiosperms which produce seeds that contain an embryo with two seed leaves.

Diffraction The random scattering of light.

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Diffusion The net movement of molecules from higher concentration to a lower concentration.

Digestion The process in which food breaks down mechanically and chemically. Mechanical digestion changes only the size of food particles, making them smaller and easier to digest, while chemical digestion changes the structure of the substances being digested.

Dioecious Flowers that have only a male or a female part, with stamen and carpals on separate plants.

Diploid (2N) The full complement of chromosomes in all body cells (except sex cells).

Directional selection The process that occurs when individuals at one extreme of the range of variation in a population have a higher degree of fitness.

Directional terms Are words that describe a location or position on the human body.

Disaccharide A class of sugars formed when two monosaccharaides combine.

Disease An imbalance in the proper working of a tissue, organ, or organ system.

Disruptive selection The process in which individuals at extremes of the variation spectrum experience higher fitness than at the middle.

Distal Situated away from the point of attachment.

Diversity The adaptation and evolving of organisms showing a great deal of variety.

DNA A long macromolecule containing the information code that directs cellular activities in living organisms; see deoxyribonucleic acid.

DNA ligase A type of enzyme that joins DNA strands together.

DNA polymerase Special enzymes that add new bases onto the exposed DNA strands.

Domain A division of organisms ranking above a kingdom in the systems of classification based on similarities in DNA and not based on structural similarities.

Dominance hierarchy A rank order system developed within an animal society.

Dominant The trait that covers up other forms of the characteristic.

Dopamine A neurotransmitter type that plays an important role in a number of different brain functions.

Down regulation Decrease in the number of effective receptors on cell surfaces.

Duodenum The top portion of the small intestine.

Dura mater The outer layer of meninges.

Ear drum The membrane separating the outer ear from the middle ear.

Earthquake A release of energy from movement in Earth’s crust.

Echinoderms A group of marine animals with a spiny skin and an endoskeleton.

Ecological footprint The amount of resources used by a specified group.

Ecological niche The role an organism plays in its environment.

Ecological succession The process by which nature reclaims an ecosystem after it has been disturbed.

Ecology The study of the interactions between organisms and their environments.

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Ecosystem The interaction of organisms with their physical environment.

Ectoderm Outer layer of the gastrula, which develops into the skin and nervous system.

Ectotherm Organisms that rely on their environment to set their internal temperature.

Effector A muscle that moves or a gland that sends out chemicals to carry out a response.

Egg The female reproductive cell in plants and animals.

El Nino A band of unusually warm ocean water that develops off the western coast of South America.

Elastic cartilage A type of cartilage that is composed of large amounts of elastin fiber, which is able withstand pulling forces.

Elasticity The ability of a muscle cell to resume its original length after a contraction.

Electromagnetic energy A type of energy released into space by stars (sun).

Electron A negatively charged subatomic particle found in the orbit.

Electron transport chain (ETC) A chemical reaction in which electrons are transferred from a high- energy molecule to lower-energy molecule.

Electronegativity The ability of an atom to attract electrons to itself.

Element Substances that cannot be broken down by ordinary chemical means.

Elongation One of the three phases of transcription in which nucleotides are added to the growing RNA chain.

Embolus A floating thrombus.

Embryo An unborn offspring in the early stages of development; before 12 weeks gestation in humans.

Embryology The study of anatomy before birth; looks at structures of developing embryos and fetuses

Emigrants Organisms leaving an area.

Emphysema A condition in which lungs lose their elasticity and air sacs are hardened, unable to properly exchange gases.

Enamel The strong covering protecting the teeth.

Endocrine cell Any cell that secretes a hormone.

Endocrine system Glands and parts of glands that produce internal chemicals called hormones that cause a response in another organ or tissue.

Endocytosis The process of moving materials into the cell.

Endoderm Inner layer of gastrula forming the digestive and respiratory tracts.

Endometrium A membrane that lines the womb.

Endoplasmic reticulum (ER) Is a system of interconnected membranes that form canals or channels throughout the cytoplasm of a cell.

Endorphins A type of neurotransmitter that improves mood and inhibits pain and depressive feelings.

Endoskeleton A living, internal but hard structure found in animals and humans.

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788 Glossary

Endosperm The nutritive tissue found inside the seeds of flowering plants.

Endospore-forming bacteria Are Gram-positive, flagellated rods that form endospores to endure harsh, dry conditions.

Endosymbionts Any organism living in the body or cells of another organism.

Endosymbiotic theory The theory that states that some organelles in eukaryotes were descendants of ancient bacteria that were absorbed by larger cells.

Endothelium The squamous epithelial tissue lining the chambers of heart and blood vessels.

Endotherm Organisms that generate heat produced internally by cell respiration to maintain a stable internal body temperature.

Energy pyramid A pictorial representation showing the net loss of energy as it travels up a food chain.

Entropy Randomness or any increase in disorder.

Enzyme Specialized protein that speeds up chemical reactions.

Epidermal cells A type of sponge cell that covers and protects sponges.

Epidermis The outer layer of the skin.

Epididymis An elongated organ that stores sperm and transports them from the testes.

Epiglottis The flap of elastic cartilage covering the trachea.

Epilimnion The top-most layer of lakes and ponds.

Epinephrine A hormone secreted by adrenal medulla.

Epithelial tissue Tissue made of cells that either covers other tissues or cells that produce hormones or other materials for export.

Equilibrial life history, K-selected strategy A type of life history that occurs when parents invest in extended care to their young, live a long time and have few offspring.

Equilibrium The even level of dispersion of substances.

Esophagus Food tube which connects the mouth with the stomach.

Essential amino acids Amino acids that are not synthesized by the body.

Estuary An area where rivers and streams join saltwater.

Euglena A green single-celled, motile freshwater organism.

Eukarya One of the three domains of the biological classification system.

Eukaryote Organisms that contain organelles and a distinct, true nucleus with genetic material contained therein.

Euler’s Buckling equation An engineering formula to show where a cylinder is most likely to fail. When applied to a femur, equation shows a thicker area in the region predicted to break.

Eusociality Is the highest level of social organization, in which organisms cooperate and their members have sterile castes.

Eutherians Mammals that develop their embryos internally and nourish them using a placenta.

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Eutrophic Shallow and productive lakes.

Eutrophication The massive algal growth resulting from unchecked extra loading of nutrients.

Evolution The change in gene frequencies in a population, over time.

Excited state A state of a physical system that is higher in energy than in its normal state.

Excretion The process of eliminating wastes from organisms.

Exocytosis The process of moving materials outside the cell.

Exon A segment of RNA or DNA that contains information coding for a protein.

Exoskeleton A rigid outer covering of an animal.

Experiment A planned intervention that analyzes the effects of a particular variable.

Experimental group A group in a study or experiment that receives the test variable.

Expiration The process of expelling air to the outside world.

Exponential model of population growth A model that depicts the increase of population growth at a constant rate.

Exponential period A time of rapid and unchecked growth.

Extant Are organisms that exist today.

External fertilization The fertilization process that occurs outside the bodies of animals.

Extinct Are organisms that have died off.

Extinction The state in which a species is lost forever, with no remaining organisms to maintain its population reproductively.

Extracellular matrix Is a collection of proteins and carbohydrates found in every connective tissue type.

Facial bones The bones that attach to the muscles of the face.

Facilitated diffusion A type of passive transport requiring a carrier protein.

Family A group of genera consisting of organisms related to each other.

Fascicle Bundle of muscle fibers.

Fat-soluble vitamins Includes D, A, E, and K, which accumulate in fatty tissues in the body.

Fermentation A special kind of anaerobic respiration yielding low amounts of energy from sugars, when oxygen is not present.

Fertility rate Is the average number of children born to females in a population.

Fertilization Is the process in which male and female sex cells unite.

Fibers Threadlike structure embedded in connective tissue, giving strength and support.

Fibroblast Specialized cells that produce and maintain connective tissue.

Fibrocartilage Cartilage that contains many elastic and collagen fibers in its extracellular matrix.

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Fibrosis The scarring or thickening of connective tissue.

Fibrous protein Structural compound that does not dissolve in water but remains solid support in parts of organisms.

Fibrous root A root system made up of numerous branching roots and gives increased exposure to water in soils.

Filament Thread-like structure supports the anther.

Filtration The process by which substances in blood are separated out by pressure through kidneys.

First law of thermodynamics A law that states that energy can be changed from one form to another but cannot be created or destroyed.

Flagella Are long, whip-like extensions on a cell’s surface that help in the movement of cells.

Flame cells Specialized excretory cells found in certain invertebrates.

Flatworms Any worm belonging to the phylum Platyhelminthes.

Fluid mosaic model A model that describes the structure of cell membranes.

Folic acid A water-soluble vitamin and a very important nutrient in a fetus’s brain and spinal cord development.

Follicle A small ovarian sac that contains a maturing ovum.

Food chain Interactions of organisms with each other through the transfer of nutrients and energy.

Food Plate (MyPlate guided diet) A nutrition guide modeled for healthy eating in the United States.

Food pyramid A pyramid-shaped graphic representation that represents the optimal number of servings to be taken each day.

Food web A network of interdependent and interlocking food chains.

Formed elements The cells and cell fragments formed within the blood and have a definite shape.

Fossil record One of the four sources of evidence for evolution, which shows organisms of the past in rock layers.

Fragmentation The process in which a piece of a parent breaks off and forms a new organism.

Fragmented meta-population Pockets of isolated ecosystems due to massive amounts of encroachment into natural areas.

Free radicals Molecules with extra electrons that cause damage to body structures.

Freshwater Water with low concentrations of dissolved salts.

Frontal lobe The anterior part of the brain that is responsible for much of human personality, intelligence, and skeletal movements.

Frontal plane The plane that divides the front (anterior) and back (posterior) regions of the body.

Functional group A group of atoms that are involved in reactions.

Fundamental niche The area and resources that an organism is theoretically able to utilize.

Fungi Eukaryotic organisms that secrete chemicals to break down other living or once-living materials.

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Glossary 791

G1 phase A period in the cell cycle in which a cell grows rapidly in size, forming new organelles and proteins for future daughter cells.

G2 phase A period in the cell cycle in which growth of the cell’s cytoplasm and organelles is completed and final preparations for mitosis takes place.

G3P Also known as glyceraldehyde 3-phosphate, is a chemical substance occurring as a product of the Calvin Cycle.

Gall bladder A small organ on the underside of the liver, which stores bile.

Gametes Reproductive cells which include eggs and sperm.

Gametophytes Haploid organisms that produce the gametes.

Gap (communicating) junction Are channels that run from one cell into another to allow rapid transport helping cells communicate with other cells.

Gastro-esophageal reflux disease (GERD) A chronic condition caused when acids repeatedly escape into the esophagus.

Gastropods Mollusks with an enlarged foot.

Gastrovascular cavity The primary organ of digestion found in Cnidaria and Platyhelminthes.

Gastrula The entire mass of cells of an embryo developing after the blastula stage.

Gastrulation A developmental stage in which three distinct germ layers are formed.

Gene A portion DNA sequence serving as the basic unit of heredity, coding for a polypeptide (protein).

Gene expression The ability of a gene to carry its information to the rest of a cell and perform its directives.

Gene regulation The ability to shut certain genes off and turn some genes on.

Gene technology The technology that modifies plants, bacteria and animals to create products for society.

Gene therapy The process in which genes are inserted into an organism to treat its disease.

Genetic engineering The process in which an organism’s genes are manipulated in a way other than is natural.

Genetic variation The sum total of gene differences in a population. An evolutionary reason for sex is to increase genetic variety in a species.

Genetically -modified organism Are organisms in which DNA is genetically altered via genetic engineering techniques.

Genotype The genetic makeup of a cell.

Genus A group of individuals of the same species.

Geotropism The growth of shoots upward and roots downward in response to gravity, results also from plant chemicals.

Germ theory The theory that places a focus on sterile techniques to prevent microbial disease spread, led to important improvements in medicine.

Germinate To begin to grow.

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792 Glossary

Gestation The process of development in the womb.

Giant cells Enlarged macrophages.

Glands Collections of epithelial cells that secrete a product such as hormones.

Global climate change The many possible changes to Earth’s climates due to rises in greenhouse gases in the atmosphere.

Globular protein A type of protein that is water soluble.

Glomerulus A ball of blood vessels at the start of a nephron.

Glucagon A hormone produced by pancreas, which causes the liver to convert stored glycogen into glucose, sent into the blood and thus available for cells to use.

Glycolysis Is a sequence of chemical steps in which glucose is rearranged to form two molecules of pyruvic acid, or pyruvate.

Gold Foil experiment Also called Rutherford’s gold foil experiment, is a series of experiments that showed an atom’s structure.

Golgi apparatus Is the processing plant of the cell city that refines the materials passing through it.

Gradient The difference between higher and lower concentration areas.

Gram stain A dying technique that identifies bacteria as being one of two categories.

Gram-negative bacteria A group bacteria that lose the crystal violet dye in Gram staining method of bacterial differentiation.

Gram-positive bacteria A group of bacteria that retains the dye in Gram staining method of bacterial differentiation.

Greenhouse effect The process of trapping heat energy in the atmosphere.

Greenhouse gases The gases in the atmosphere that slow the release of heat from the planet to space by absorbing and re-emitting long wave radiation heat back to the surface.

Gross anatomy The study of body parts that can be seen without use of microscopy.

Ground state The lowest state of energy of a particle.

Ground tissue Tissues that are neither vascular nor dermal and support a plant’s structure and store and produce food.

Group behavior A passive adaptation technique to minimize the effects of predation.

Guanine A purine base that functions as a fundamental constituent of RNA and DNA.

Gymnosperm Plants with seeds that do not develop in an ovary, usually cone producing.

Habitat The space an organism occupies, including all of the factors with which an organism interacts.

Habituation The process of “getting used to” stimuli.

Hair follicle A structure from which hair grows.

Hair root Part of hair embedded in a hair follicle.

Halophiles Are organisms that grow or live in very salty conditions.

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Hammer A bone that is the outermost of the three small bones in the middle ear.

Haplodiploidy Sex-determining method in which females are developed from fertilized eggs (diploid) and males are developed from unfertilized eggs (haploid).

Haploid (N) The half number of chromosomes of the parent.

Heart A specialized muscular organ that propels blood through the body of vertebrates.

Heart attack (myocardial infarction) The condition in which heart muscle is damaged from the sudden blockade of coronary artery by blood clot.

Heat capacity The amount of heat energy required to raise the temperature of an amount of substance.

Helicase The enzyme that untwists the double helix so that replication can occur.

Hemagglutinin A type of protein that enables Myxovirus to bind with its host.

Hemophilia A condition of uncontrolled bleeding in which blood clots occur too slowly.

Herbivore Organisms that eat plants.

Herbivory The consumption of plants and plant parts by other organisms.

Heredity The passing of characteristics from parent to offspring.

Hermaphrodite A person or animal having both male and female reproductive parts.

Herpes simplex I An inflammatory skin disease characterized by the formation sores around the lips.

Herpes simplex II A sexually transmitted virus and disease that is characterized by genital sores.

Heterotrophs Also called consumers, these organisms acquire energy by eating other organisms.

Heterozygous The condition in which alleles a pair are different from each other.

High blood pressure A chronic elevation of pressure above the normal 120/80, for a consistent period of time.

Hippocampus Part of the brain involved in short term memory inputs, acting as a conduit to long term memory storage in the cerebrum.

Histamines Chemicals that bring more blood to a site of infection by vasodilation of the vessels surrounding the area.

Histology The study of tissues.

Histone Group of basic proteins in chromatin, around which DNA coils.

Homeostasis Maintaining a steady set of environmental conditions.

Homeotherm Organisms that maintain a stable internal body temperature.

Hominids A primate belonging to the family Hominidae.

Homologous structures Similar structures found in different species.

Homologous The chromosome partners in a diploid cell.

Homology Common ancestry.

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Homozygous The condition in which a pair of alleles is the same.

Hormones Chemical messengers that cause change or direct activity in another area of the body.

Humerus Upper arm bone.

Humoral immunity A form of immunity in which plasma cells and B lymphocytes produce antibodies.

Hyaline cartilage A type of cartilage that is composed of large amounts of collagen fibers, giving it strength.

Hydra Freshwater organisms with a set of tentacles on the outside of their coelenterate opening.

Hydrochloric acid (HCl) An aqueous solution of hydrogen chloride.

Hydrogen bond Are fleeting bonds that form between hydrogen atoms and atoms of different structures. These bonds are based on attraction between positive and negative charges.

Hydrolysis The breakdown of a compound due to its reaction with water.

Hydrophilic Compounds that have the tendency to dissolve in or mix with water.

Hydrophobic Compounds that do not dissolve in water (also called, water fearing).

Hydrosphere All of the water on Earth’s surface.

Hydrostatic skeleton A type of skeleton found in earthworms and jellyfish, which use water and muscles for support and movement.

Hydroxyapatite An essential component and major ingredient of normal bone.

Hyper-disease theory The theory that states that a microbe evolved rapidly to kill off other living creatures during the time period.

Hypersexuality The condition in which one has many sex partners.

Hyperthyroidism An overactive thyroid, which results in too much thyroxine, causing nervousness, excess energy, sometimes enlarged eyes and irregular heart rates.

Hypertonic A cell having a higher concentration of solutes as compared with its surrounding environment.

Hypha Each of individual threads that make up the fungal mycelium.

Hypodermis The deepest layer of skin, composed mostly of fat.

Hypolimnion The lower-most layer of lakes and ponds.

Hypothalamus The region below the thalamus.

Hypothesis A possible or proposed explanation based on limited evidence for a natural phenomenon.

Hypothyroidism An underactive thyroid, which results in weight gain, intolerance to cold and higher cholesterol.

Hypotonic A cell having a lower concentration of solute as compared with its surrounding environment.

Ileum The third and final portion of the small intestine.

Imbibition The process in which germination starts with the massive influx of water into the seed.

Immigrants New organisms moving in from other areas.

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Immune system A system that includes the set of disease-fighting factors that protect against pathogens.

Immunization The technique that uses weakened or dead pieces of disease-causing agents to strengthen immunity against a disease.

Immunodeficiency The most serious malfunction of the immune system; occurs when it does not work efficiently.

Impaired kidney function The failure of kidneys to function properly.

Incisors The four front teeth evolved and adapted for cutting and tearing.

Incomplete dominance A genetic situation in which one allele does not completely dominate another allele.

Independent variable A variable that is altered by the experimenter.

Inflammation A series of events which identify, recruit and attack invading cells, causing swelling.

Ingestion Consumption of a substance by living organisms.

Initiation sequence A sequence of bases that starts the unwinding of DNA during replication.

Innate behaviors Behaviors that are genetically determined.

Inner cell mass A central set of cells of the blastula, which develop to become a new, whole organism.

Innervation The distribution of nerves to a muscle.

Inquiry Critical thinking used behind science to arrive at the truth.

Insects Small invertebrates with a head, thorax, abdomen, six legs, and one or two pairs of wings.

Insertion Movable end of a muscle; the bone or part that moves when a muscle contracts.

Insoluble fiber Fibers that do not dissolve in water and serve as roughage to cleanse the intestines.

Inspiration The process of taking of air into the lungs.

Insulin A hormone produced in the pancreas that regulates the amount of glucose in blood.

Integral protein (transmembrane or carrier protein) A type of membrane protein permanently embedded within the biological membrane.

Interdisciplinary Involves two or more areas of knowledge.

Interferon Small proteins which bind with receptors on neighboring cells.

Intermediate fiber The smallest fibers of the cytoskeleton, which circulate materials within a cell.

Intermembrane space The area of a mitochondrion found outside of cristae.

Internal fertilization The fertilization process that occurs inside the bodies of animals.

Interneuron A neuron that transmits impulses between other neurons.

Interphase The stage in cell development in between two successive mitotic or meiotic divisions

Interspecific competition The competition between two different species.

Interstitial cells Cells that produce androgens, sex hormones.

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Intertidal zone The area that is above water level at low tide and below water level at high tide.

Intertropical -convergence zone The low pressure area at the equator resulting from the expansion and rising up of hot air mass.

Intervertebral disc Pads of fibrocartilage that separate individual vertebrae.

Intestinal cells Cells lining the GI tract.

Intimidation displays Threat display that makes an organism look large and intimidating.

Intracellular digestion The process of breakdown of substances within the cytoplasm of a cell.

Intracellular parasite Living organisms that invade host cells and live within them.

Intracellular transport A process in which microfilaments circulate materials within cells.

Intraspecific competition The competition between organisms of the same species.

Intron A nucleotide sequence removed by RNA splicing.

Invagination The process of being folded back on itself to form a pouch (not given in bold in text).

Invertebrates Animals that lack a backbone.

Ionic bond Bonds that result from complete transfer of electrons from one atom to another.

Iris The colored part found around the pupil of the eye.

Iron deficiency anemia A condition characterized by lack of healthy RBCs in blood.

Isotonic Even concentration of solute and water on either side of the plasma membrane.

Isotope Are atoms of the same element having different atomic masses.

Jaundice A disease characterized by yellow coloration of the skin.

Jejunum The second part of the small intestine.

Jellyfish Free-swimming marine creatures that have a central cavity making them appear as cup-like.

Keratin A protein that is the principal constituent of nails, hair, and skin tissues.

Keratinocyte An epidermal cell that produces keratin granules.

Kidney failure A medical condition in which the filtration rate falls to 50 percent or below.

Kidney Organ that filters blood, removes wastes, and at the same time conserves needed materials including water.

Kin selection Natural selection in which individuals help each other because they share genes in common.

Kin selection The theory that evolution favors helping between family members or kin to augment the transmission of their related genes.

Kingdom The highest grouping under which living organisms are classified.

Krause’s corpuscle A bulbous cell that senses cold.

Krebs cycle A series of enzyme-catalyzed reactions forming an important part of aerobic respiration in cells.

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Glossary 797

La Nina Cooling of the ocean surface off the western South American coast.

Labor The opening of the cervix and uterus contractions leading to the birth of the baby.

Lactation Formation of milk by mammary glands.

Lacteal A lymphatic vessel of the small intestine that absorbs digested fats.

Lacuna An open space containing a chondrocyte in cartilage.

Langerhans cell Special white blood cells that reside within the skin.

Language A method of communication.

Larvae The active immature form of an insect.

Larynx The part of throat containing the vocal cords.

Larynx Voice box.

Lateral meristem A type of meristem that is found along the sides of stems and roots which gives rise to secondary growth.

Lateral Of or relating to the side.

Law of dominance The idea that a dominant trait covers up another.

Law of independent assortment The idea which tells that each pair of alleles is sorted independently when sperm and egg are formed.

Law of segregation The hypothesis that states that there are two separate, discrete alleles that could be inherited separately.

Leaf abscission Loss of leaves.

Learned behaviors Behavior that develops through experience.

Lens A very hard structure of the eye but flattens to focus the rays of light passing through it.

Lichens Green algae or cyanobacteria living in association with fungi.

Life history Series of changes an organism undergoes during its lifetime.

Ligament Band of tissue that anchor bones to bones.

Light reactions A reaction that traps energy from sunlight using special pigments.

Light-independent reactions Chemical reactions that convert carbon dioxide into glucose.

Limbic system A group of brain structures found on both sides of the thalamus, along the inner core of the brain.

Limbs An arm or a leg of a person or animal.

Limnology The study of freshwater systems.

Lipid Neutral fats, phospholipids, and steroids found in food and in living systems.

Lithosphere Earth’s outer part.

Liver A large glandular organ found in the abdomen of vertebrates.

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Lobe-finned fishes A smaller group of fishes having a developed pelvis, primitive lungs and muscular fins — precursors to life on land.

Logistic model of population growth A model that depicts the decrease of population growth rate with the increasing number of individuals as they reach a certain point.

Loop of Henle A large tube in the nephron that descends and then ascends.

Lumbar vertebrae The five vertebrae that make up the lower back

Lungs A pair of breathing organs.

Lymph The fluid of the body that carries excess liquids and cells not normally transported by the circulatory system.

Lymphatic system The series of vessels, nodes and their organs carrying lymph.

Lymphocyte White blood cells that work to specifically target invaders.

Lyse Breakdown of cell membrane.

Lysogenic life cycle A reproduction cycle during which a virus inserts its genes into a host and waits for a time in the future to destroy the host.

Lysosome storage disease A group of 30 known inherited human diseases associated with the abnormal functioning of lysosomes.

Lysosome A small sac filled with digestive, hydrolytic enzymes enclosed in a membrane.

Lytic life cycle A reproduction cycle which results in a virus’s immediate destruction of a host cell.

Macrobiology The study of how organisms interact with each other and within the environment

Macromolecules Molecules containing large number of atoms, which are the building blocks of living things.

Macronutrients Macromolecules that possess energy within their bonds.

Macrophage The largest of the white blood cells.

Macrophage--presentation The display of antigens by a white blood cell.

Magnification Is the amount by which an image size is larger than the object’s size.

Malaria An infectious disease spread by mosquitos carrying a parasite that invades red blood cells and reproduces in them.

Malignant The ability of a cancerous cell to spread.

Mammals Are homeotherms that produce milk to feed their young.

Mandible Jawbone.

Manipulation Manual movement of anatomical parts to either help treat symptoms or diagnose the cause of a disease or injury.

Mantle One of the three-point body plans of mollusks that secretes the outer shell.

Marine biology The study of saltwater organisms.

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Marsupials A type of mammal in which young ones are born immature and continue to develop in a pouch.

Mast cell A type of immune cell.

Matrix The inside space within the cristae.

Matter Anything that has mass and occupies space.

Mechanical breathing The process of moving air into and out of the lungs

Mechanoreceptors A sense organ responding to physical changes.

Medial Situated in the middle.

Medulla oblongata The inner part of the brain.

Medusa stage Cnidarians in their free swimming stage.

Meiosis A special form of cell division in which the newly produced daughter cells contain only half the number of chromosomes of the parent.

Meiosis I The process of cell division by which homologous chromosomes separate and new cells are haploid.

Meiosis II The stages in which sister chromosomes are separated.

Meissner’s corpuscle A receptor that senses light touch.

Melanin The pigment that gives color to human eyes, hair, and skin

Melanocyte Cells that make the skin pigment, melanin.

Melanoma The most dangerous form of skin cancer.

Melatonin A hormone produced by the pineal gland that makes a person sleepy.

Membrane A sheet-like structure that acts as a boundary in an cell.

Memory cell Type of lymphocytes that continue to defend against pathogens long after they are gone.

Menarche Beginning of menstruation.

Mendelian characteristic (single-gene trait) Traits that are determined by instructions on a single gene.

Meninges A series of protective membranes that surround the spinal cord nerves.

Menopause The time when ovulation and menstruation cease.

Menstrual cycle The process of ovulation in women and other female primates.

Menstruation Discharge of blood from the uterus.

Meristem A formative plant tissue responsible for growth whose cells divide to form plant tissues and organs.

Mesenchyme Embryonic connective tissue that gives rise to all the connective tissues.

Mesoderm The middle layer of gastrula that develops into the body’s organs and muscles.

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Mesoglea The gelatinous filling found in between the two cell layers in the bodies of Cnidarians and sponges.

Mesopelagic zone The ocean layer that receives little sunlight.

Metabolism Chemical processes occurring in a living organism that are necessary for life maintenance.

Metalimnion The middle portion of lakes.

Metamorphosis A complete change of physical form.

Metaphase A phase in which homologous chromosomes line up at the middle of the nucleus, the equator, attaching to the spindle fibers.

Metaphase II The stage of meiosis in which chromosomes line up singly and then the two sister chromatids separate and move to opposite poles of the cell.

Metastasize The process in which cancer cells spread to other parts of the body.

Methanogens Organisms that react to oxygen as a poisonous substance.

Microfilament A cytoskeletal fiber used for muscle movement.

Micronutrients Chemical substance required in small quantities, namely vitamins and minerals.

Microscopic anatomy The study of structures too small to be seen with the naked eye

Microtubule Is a larger filament structure that helps whole cells move.

Microvilli Smaller villi; used to increase surface area for absorption within intestines.

Midbrain The short part of the brainstem above the pons.

Middle ear Middle ear bones found inside the eardrum.

Mimicry The resemblance of one organism to another.

Minerals Are inorganic substances that form ions in the body, which help to perform many functions.

Mitochondria Is the organelle that makes energy for a cell.

Mitral (bicuspid) valve A heart valve located between the left atrium and left ventricle.

Molars A grinding tooth found at the back of the mouth and suited for grinding and chewing foods.

Molecular genetics A new field that united biology, chemistry and genetics, to study inheritance at the chemical level.

Molecules Atoms bonded together.

Mollusk Invertebrates, chiefly marine, characterized by a soft unsegmented body and an external hard shell.

Molt To shed the outer covering.

Monocot Angiosperms-produced seeds that contain embryo with one seed leaf.

Monoecious Flowers that have both male and female parts.

Monohybrid cross The mating between two organisms, each having both characteristics for a particular trait.

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Monosaccharide Ring-shaped structures that are the building blocks of carbohydrates.

Monotremes Primitive mammals that lay eggs.

Morphology A particular structure or shape.

Morula A solid ball of cells formed by cleavage of a fertilized ovum.

Motor neuron A nerve cell that brings nerve impulses from the brain and spinal cord to a muscle.

Mouth An opening in the lower part of the face.

MRI A technique that uses radio waves and magnetic field to generate detailed images of tissues and organs.

Multiple alleles A series of three or more alternative forms of a gene, out of which only two can exist in a normal, diploid individual.

Murmur An abnormal sound made by blood during the heartbeat cycle.

Muscle fibers The functional muscle cell.

Muscle tissue A type of tissue that is composed of cells that are able to contract.

Muscular foot One of the three-point body plans of mollusks, used for movement.

Muscular pump A collection of skeletal muscles that aid the heart in blood circulation.

Mutualism A relationship in which both organisms benefit.

Mycelium The mass of filaments that form the vegetative part of a fungus.

Mycoplasma The smallest known bacterium.

Myelin sheath Pads of insulation that prevent the action potential from weakening.

Myofibrils A rod-like protein structure in a muscle cell.

Myxovirus Any group of RNA-containing viruses.

NADH Nicotinamide adenine dinucleotide is a naturally occurring biological compound, which is converted to energy (not given in bold in text).

NADPH Nicotinamide adenine dinucleotide phosphate is used as reducing agent in reactions.

Natural selection The process whereby organisms better adapted to their environment survive and produce more off spring.

Necrosis Death of tissue.

Negative feedback A key mechanism that regulates the physiological functions in living organisms.

Nematocysts Barbed threads found in tentacles of Cnidarians.

Neolithic diet The prehistoric nutrition system.

Nephridia Excretory organs found in many invertebrates.

Nephron The functional unit of the kidney.

Neritic zone The zone of ocean where sunlight reaches the ocean floor.

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Nerve cord A dorsal tubular cord of nervous tissue present in chordates.

Nerve impulse Neuron message signals that are actually a flow of charged ions.

Nerve network Set of nerve cells that help Cnidarians respond to stimuli.

Nervous system Network of nerve cells that transmits messages from one part of the body to another.

Nervous tissue An excitable tissue specialized to send, store, and receive ionic impulses

Neuraminidase A protein found in Myxovirus that digests through mucous membranes.

Neuroglia Helper nerve cells present in the nerve tissue.

Neuron A nerve cell.

Neurotransmitter Special chemicals that carry a nerve impulse to new cells.

Neurulation The process by which the ectoderm folds to become the brain and spinal cord.

Neutral fat A fat that is composed of three large fatty acids joined together by a short-chained glycerol molecule.

Neutron Particles with zero charge found in the nucleus.

Neutrophils A type of WBC that are the most abundant in mammals and are first to arrive at an invasion.

Nitrification The process by which bacteria in soils produce nitrites.

Nitrogen fixation The process of converting molecular nitrogen (N2) into ammonia (NH3) and ammonium ions (NH4+).

Nitrogenous base A nitrogen containing molecule having the same chemical properties as a base.

Nociceptors A sense organ responding to pain.

Non-amniotes Terrestrial animals that develop their eggs in the absence of an amniotic sac.

Nonessential amino acids Amino acids made by the human body and thus are not required in a diet to survive.

Notochord A flexible rod of nerve tissue that develops in all chordates.

Nuclear envelop The double membrane that protects the nucleus.

Nucleic acid The genetic material of a cell.

Nucleoli A small, dense round structure found in the nucleus of a cell.

Nucleoside triphosphate A molecule that contains a nucleoside bound to three phosphates.

Nucleotide The basic functional unit of a DNA molecule.

Nucleus The central and the most important part of a cell and contains the genetic material.

Null hypothesis The hypothesis that asserts that there is no effect or change due to a potential treatment.

Nutrients The substances that the body uses to obtain energy and to maintain the body’s activities, such as growth, repair, and reproduction

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Glossary 803

Obesity The state of being overweight with a BMI greater than 30.

Obligatory parasite Organisms that are unable to live outside of a host cell.

Oblique plane A plane running at an angle to the organ or organisms.

Observation The act of obtaining information from a primary source.

Occipital lobe The posterior lobe of the brain.

Octet rule A chemical rule that reflects how atoms react to attain eight electrons in their valence shell.

Olfaction The sense of smell.

Oligochaetes Aquatic and terrestrial worms.

Oligotrophic Lakes with low levels of productivity and abundance of dissolved oxygen.

Omnivore Organisms that eat both plants and meat.

Oncogene A normal gene that under certain circumstances can cause cancer.

Oncovirus Any virus that carries a gene associated with cancer.

Oogenesis A process which takes place in cells of the ovaries.

Open sea zone The main body of ocean or sea.

Operant conditioning A complex set of behaviors during which an organism learns to respond to stimuli to produce a desired effect.

Opportunistic life history, r-selected strategy Type of life history when parents have many young and invest very little in each.

Opsonization The process by which antibodies often coat the invading pathogen to enable macrophages to attach more easily.

Order Used in classification as a group of families.

Organ System A group of organs working together performing a united function.

Organelle (subcellular structure) Structures that function within cells in a discrete manner

Organelles Structures that carry out specific functions within cells.

Organism Living creature formed as a whole by organ systems.

Organs Specialized body parts that carry out specific functions for organisms.

Origin The location (bone) at which muscles attach.

Osmoregulation The process by which organisms control their fluid intake along with dissolved solute balances.

Osmosis The process of diffusion of water through a semipermeable membrane that allows the transfer of only some substances.

Osteoarthritis A disease in which bones and their joints deteriorate, usually because the cushioning cartilage in between these bones wears out.

Osteoblast Special bone building cells.

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804 Glossary

Osteoclast Bone destroying type cell.

Osteoporosis Thinning and weakening of bones.

Outer ear Pinna and eardrum.

Oval window An oval-shaped opening that is the start of the inner ear.

Ovarian cycle The monthly cycle by which eggs are developed and released from the ovary between puberty and menopause.

Ovary A female reproductive organ containing ovules in which eggs develop.

Oviduct (fallopian tube) Tube through which an ovum passes from an ovary.

Ovulation The process of producing and discharging eggs from ovary.

Ovule The female gametophyte.

Ovum A mature egg.

Oxygen revolution The biologically induced appearance of dioxygen in Earth’s atmosphere 2.5 billion years ago.

Oxyhemoglobin A bright red complex of oxygen and hemoglobin present in oxygenated blood.

Oxytocin A hormone released by the pituitary gland that enhances the stimulation of muscle contraction in the uterus.

Ozone A gas that is a pollutant in Earth’s lower atmosphere, but acts as a protector from UV radiation in the upper atmosphere.

Pacinian corpuscle A receptor that senses deep pressure.

Palpation The act of feeling with one’s hand.

Pancreas A diffuse gland located near the stomach.

Pancreatic juice A secretion of the pancreas that contains enzymes that digest all of the macromolecules.

Papillomavirus A group of viruses that cause papillomas or warts.

Paracrine regulators Chemicals that bind to receptors on neighboring cells to elicit a response.

Parasitism The symbiotic relationship in which one organism benefits and the other is harmed.

Parasitoid An organism living that spends some period of its development on or in a host organism and later kills its host.

Parasympathetic nervous system Opposing set of nerves that are stimulated when the body calms down, under relaxing conditions.

Parathyroid hormone (PTH) Hormone produced by the parathyroid glands help in regulating the amount of phosphorous and calcium in the body.

Parenchyma cells The typical plant cells that carry out most of the metabolism in plants.

Parietal lobe One of the four major lobes of the brain that contains an area concerned with higher levels of thought (speech, sensation, and sensory integration).

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Glossary 805

Parthenogenesis A virgin birth.

Parturition The contractions and dilation of the cervix during child birth; the act of giving birth.

Passive artificial The condition that occurs when a medicine gives immunity to a patient without stimulating their immune system.

Passive natural The condition that occurs when immunity is obtained naturally but without the work of the immune system.

Passive transport The movement of substances across cell membranes without the need of energy expenditure by the cell.

Pathogen Any disease causing organism.

Pear shape A body shape characterized by extra weight around the hips.

Pedigree Are diagrams of genetic relationships among family members through different generations; they are used to trace gene flow through a family.

Penicillin An antibiotic obtained from the molds of the Penicillium genus.

Penis The male reproductive organ.

Pepsin An enzyme produced in the stomach which breaks down protein.

Pepsinogen The inactive precursor to pepsin.

Peptidoglycan Are a type of protein found in bacterial cell walls.

Peripheral nervous system (PNS) The portion of the CNS that is outside the brain and the spinal cord.

Peripheral protein Is a protein that adheres only temporarily to the biological membrane with which it is associated.

Peristalsis The involuntary muscular contractions of the digestive tract by which contents are forced onward.

Permafrost A layer of permanently frozen subsoil.

pH scale A numeric scale that specifies the acidity or alkalinity of an aqueous solution.

Phagocytosis The movement of solid particles into a cell.

Pharyngeal slits Openings in the pharynx that develop into gills in some chordates.

Pharynx A tube that starts behind the nose and mouth connecting to the esophagus.

Phenotype The observable traits of an organism.

Pheromone A chemical that travels between different organisms to interconnect them.

Phloem A series of tubes that carry sugars and dissolved organic materials down a plant.

Phospholipid A lipid composed of both a charged phosphate group and fatty acid chains.

Photic zone The part of ocean where sunlight penetrates sufficiently and influences the growth of living organisms.

Photo pigments Special pigments found in the retinal rods and cones.

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Photolysis The process in which water is split to yield free electrons and hydrogen ions to replace electrons lost from a photosystem.

Photon Discrete unit of light energy that when hits a pigment in chlorophyll transfers its energy to electrons in the pigment

Photosynthesis The process by which green plants (plus some algae and bacteria) use sunlight to synthesize nutrients from water and carbon dioxide.

Photosystems A light capturing bundle of pigments which absorbs light for photosynthesis.

Phototrophic anaerobic bacteria A group of bacteria that do not release oxygen in their photosynthetic-like processes because the photolysis of water does not occur.

Phototropism A tropism in which the growth of a plant is toward sunlight.

Phylum Number of similar classes grouped together.

Physiology The study of the function of body parts.

Phytoplankton All the aquatic organisms that absorb carbon dioxide and release oxygen into the atmosphere.

Pia mater The inner layer of meninges.

Pigment A naturally occurring special chemical that absorbs and reflect light.

Pili Surface hairs that allow bacteria to bind with each other.

Pineal gland A small gland located deep within the brain.

Pinna Projecting part of the external ear.

Pinocytosis The mechanism by which cells ingest extracellular fluid and its contents.

Pituitary gland The master gland of the endocrine system that sends messages to stimulate all of the other glands.

Placenta An organ inside the mother’s body that provides food and removes the waste of a developing organism.

Plants Living organisms that are able to obtain food by converting sunlight’s energy to chemical energy through the process of photosynthesis.

Plasma The straw-colored liquid that makes up 55 percent of the blood.

Plasma (cell) membrane A biological membrane that separates the cell’s interior from the outside environment.

Plasma cell A type of lymphocyte produces antibodies.

Plastid Organelle, found only in plants and algae, which store special substances.

Platelets Are chips of cells that form clots within vessels to prevent blood loss.

Pleiotropy The condition in which one gene affects more than one trait.

PNS (peripheral nervous system) The portion of the nervous system situated outside the brain and spinal cord.

Polar covalent bond The unequal sharing of electrons between atoms.

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Polar easterlies Dry, cold winds that are deflected to the west like the trade winds.

Polar ice caps Dome-shaped ice sheets that slope in all directions from the north and south poles.

Pollen grains The male gametophyte.

Pollination Movement of pollen from one plant to another.

Pollution The introduction of any contaminant into the environment that causes a harmful change.

Polyatomic ion A special kind of ion, composed of more than one atom, forming a charge.

Polychaetes A marine annelid worm.

Polygenic traits Are traits with patterns of inheritance determined by more than one gene and influenced by the environment.

Polyp stage The stage in which Cnidarians are sessile.

Polypeptide A long string of amino acids formed as molecules of protein adds amino acids.

Polysaccharide The combination of three or more monosaccharides.

Pons Part of the brainstem that helps relay impulses from cortex to cerebellum.

Population A group of organisms of the same species living in a given area.

Population density A measurement of population that reveals the number of organisms per area of land in an ecosystem.

Population ecology The study of a population of organisms and how it interacts with its environment.

Population genetics The study of patterns of gene flow from one group to another and within groups.

Population growth The increase in the number of individuals inhabiting a place.

Population Organisms of the same species inhabiting a specific area.

Population size A measurement of population that gives the number of organisms in a population.

Porifera A phylum of aquatic invertebrates that is comprise of sponges.

Porphyria An inherited disease which is characterized by abnormal metabolism of the blood hemoglobin.

Positive feedback A key regulatory mechanism that enhances the original stimulus.

Post-anal tail An extension of the spinal cord that extends beyond an animal’s normal digestive tract at some point in development.

Posterior Backside.

Powerstroke Movement of muscle filaments using ATP during the contraction of muscle.

Pre-molars Teeth situated between canine and molar teeth and suited for grinding and chewing foods.

Prebiont A sphere of organic material that led to first living cells.

Predation When one organism stalks and kills an organism of another species.

Predator-prey relationship The connection between two organisms of unlike species.

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Primary electron acceptor An electron acceptor in a substance that can be reduced by gaining an electron from some other particle

Primary succession The series of stages that begin ecological succession, including lichens and mosses as first organisms in a disturbed area.

Prions A small, infectious particle believed to be the smallest disease-causing agent.

Producer Organisms that carry out photosynthesis.

Productivity The production rate of new biomass by a person or community.

Projection Sites for muscle attachment or joint connections.

Prokaryote Organisms that lack a distinct nucleus and organelles.

Proliferation Rapid growth of cells by producing new parts.

Prophase A stage that is characterized by chromatin being packaged into chromosomes in a cell’s nucleus.

Prophase I Also called the first stage of meiosis I, in which homologous chromosomes in proximity to each other exchange genetic material through a process called crossing over.

Prophase II The first stage of meiosis II.

Prostate gland A gland located just below the urinary bladder that secretes a milky and basic fluid to buffer the effects of the acidic female environment sperm will first encounter.

Protein The most common macromolecule in living systems.

Prothallus The gametophyte generation of ferns.

Protime A blood test that measures the rate at which blood clots.

Protista A diverse group composed of both single-celled and multi-celled organisms.

Proton A subatomic particle found in the nucleus, which is positively charged.

Protostomes Organisms that form their mouth first.

Protozoan A group of single-celled protists that resemble animals.

Proximal Situated close to a point of attachment.

Pulmonary artery The artery that carries blood from the right ventricle to the lungs.

Pulmonary circuit The connection between the heart and lungs.

Pulmonary embolism The condition in which an embolus lodges in the lungs.

Pulmonary vein A vein that carries oxygenated blood from lungs to the heart’s left atrium.

Pulp cavity A cavity within the dentin containing blood vessels and nerves.

Pupa The stage between the larval and adult stage, in a cocoon.

Pupil The opening in the center of iris.

Purkinje fibers Specialized heart muscle fibers that carry electrical impulses controlling the contraction of ventricles.

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Glossary 809

Pus A yellow fluid emerging from a site of infection.

Pyloric sphincter Muscle fibers around the stomach opening between it and the duodenum.

Pyrogene A chemical that causes fever.

Radial symmetry Symmetry that describes any organism that is structured so that when a line is drawn down the middle of it, at any orientation, both sides are identical.

Radiant energy A type of energy travelling by waves or particles.

Rain shadow desert The dry region of land on one side of a mountain; has very little precipitation.

Ray-finned fishes Fishes characterized by skeletal rays emanating from their central backbones.

Reabsorption The process by which some materials that were filtered out by the kidneys are returned back into the blood.

Realized niche The area and resources that an organism is actually able to use.

Receptor A special protein that monitors or receives information from the environment.

Receptor-mediated endocytosis A form of endocytosis that requires a specific binding of a receptor protein to cell membrane.

Receptor-hormone match Match making between the receptors of target cells and their respective hormones.

Recessive The trait that is covered up by a dominant trait.

Reciprocal altruism A behavior in which an organism helps another and the second organism returns the favor either to the benefactor or his/her progeny.

Recognition protein A protein type functioning as binding site for hormones.

Recombinant DNA technology The process by which DNA is extracted from nuclei of organisms and treated with restriction enzymes.

Rectum The final part of the large intestine.

Red blood cells Blood cells that contain hemoglobin and carry oxygen to and from the tissues.

Referred pain Pain that is not at the site of its cause.

Regeneration Replacement of damaged tissues with an original tissue type.

Regulation Control over functions of the body.

Regurgitation The most common valve problem; a backflow of blood from a valve.

Relaxation A state of freedom from skeletal muscle tension and anxiety.

Renal capsule A fibrous layer surrounding the kidney, affording it some protection.

Renal cortex The outer portion of the kidney.

Renal medulla The inner portion of the kidney.

Renal pelvis A hollow funnel that removes liquid from the kidney and into the ureters.

Replication fork Molecules of DNA with both its sides exposed for adding bases.

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Reproduction The process of making new offspring.

Reproductive isolation The inability to mate.

Reproductive success (RS) Is the number of live young an organism produces.

Reproductive system The system that includes all of the pelvic structures and it products related to forming new organisms.

Reptiles Cold-blooded vertebrates that crawl or creep.

Residence time The average length of time that tells how long something is retained in a given storage reservoir in the biogeochemical system.

Resilience The ability of the lungs to inflate and deflate continuously to function properly.

Resolution Is the ability to see two close objects as separate.

Resource partitioning The condition where two competitors coexist in the same area and use resources in different ways.

Respiration The process of taking up of oxygen gas from the environment and the release of the waste gas, carbon dioxide.

Respiratory acidosis A condition that occurs when the lungs and heart do not sufficiently transport needed gases within the body, leading to the development of acidic blood.

Respiratory burst: The rapid release of hydrogen peroxide and superoxide radical from neutrophils.

Respiratory pump The movement of blood when muscles contract in the chest and abdominal cavity during normal breathing.

Respiratory system The system by which oxygen is taken into the body from the environment and carbon dioxide is eliminated.

Response to stimuli Ability to react to the various changes of the environment.

Resting potential The potential of a cell that does not exhibit the activity resulting from a stimulus; -70mV.

Reticular A connective tissue that traps foreign invaders such as bacteria; found in lymph nodes and the spleen.

Retrovirus A virus containing RNA and the enzyme reverse transcriptase.

Reverse transcriptase An enzyme that generates complementary DNA from an RNA template.

Rhabdovirus A bullet- or rod-shaped RNA virus found in plants and animals.

Rhinovirus The most common viral infectious agent that causes the common cold in humans.

Rhodopsin One type of photo-pigment found in rods that responds to light by changing shape and generating a nerve impulse and sending it to the brain.

Ribonucleic acid (RNA) A nucleic acid present in living cells, used in ribosomes and in the processes of transcription and translation of proteins.

Ribose The sugar backbone found in RNA.

Ribosome Small, spherical organelle that is the site protein synthesis.

Rigor mortis Stiffening of the body that happens a few hours after death.

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Glossary 811

RNA processing The process in which cap and tail is added to mRNA before it leaves the nucleus (for protection).

Rods One form of photopigment that sends impulses to the brain that give black-and-white perception.

Root cap A section of tissue at the tip of a plant root.

Root system The parts of plants below the surface.

Root-to-shoot ratio The dry weight of the root divided by the dry weight of the shoot.

Round worms A nematode worm infesting the intestine of mammals.

rRNA RNA component of ribosome.

RUBISCO An enzyme present in chloroplast of plants that helps absorption of carbon dioxide.

RuBP The first chemical in the Calvin Cycle, which combines with carbon dioxide.

Ruffini’s corpuscle A receptor that senses heat.

Rugae Series of folds produced by folding the wall of an organ.

S phase A period in the cell cycle in which DNA is replicated.

Sacrum A large, wedge-shaped bone located between the two hip bones of the pelvis.

Sagittal plane A vertical plane that divides the left and right side of an organism.

Salivary amylase An enzyme present in the saliva that chemically breaks down starch into smaller polysaccharides.

Salivary glands The gland that secretes saliva.

Salt wedge A wedge-shaped intrusion of sea water into a fresh-water estuary.

Sarcolemma A nerve’s cell membrane.

Sarcomere A series of contractile units that make up the myofibrils.

Saturated fat Neutral fats that are literally saturated with as many hydrogen atoms as is possible in the carbon skeleton.

Savanna Regions along the equator that are warm but experience less rainfall than the rainforests.

Scales Dermal or epidermal structures that form the external covering of reptiles, fishes, and certain mammals.

Scanning -electron -microscope (SEM) An electron microscope that looks at the surfaces of objects in detail by focusing a beam of electrons on the surface of the object.

Scavenger Animals that feed on dead or decaying matter.

Science literacy The comprehension of scientific concepts, processes, values, and ethics, and their relation to technology and society.

Scientific method A procedure that has characterized natural science for centuries.

Sclerenchyma Stringy and elongated cells with thick cell walls.

Scrotum A sac beneath the penis, holding the testes.

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Sea anemone Water-dwelling animals that are brightly colored and fix themselves onto rocks.

Second law of thermodynamics A law that states that all reactions within a closed system lose potential energy and tend toward entropy.

Secondary active transport The movement of substances using stored energy.

Secondary growth Growth in vascular plants emanating from two lateral meristems resulting in wider branches and stems.

Secondary succession The process that occurs when established ecosystems replace organisms and soils of primary succession.

Secretin A digestive hormone secreted by the duodenum.

Secretion The removal of unwanted or unneeded substances from the blood.

Seed An embryonic plant with its own internal and protected supply of water and nutrients, which led to another division of plants: seedless and seeded.

Segmented worms Worms characterized by cylindrical bodies segmented both externally and internally.

Segments The repeating chambers or units found in annelids.

Seismicity Vibrations in Earth’s crust.

Selectively permeable A condition in which the membrane allows some materials to pass through cells but not others.

Selfish-gene hypothesis The hypothesis that states that organisms are merely vessels holding their genes.

Selfishness A behavior in which one organism harms the other for its own benefit.

Semen Male reproductive fluid.

Semi-conservative model A mode by which DNA replicates as half-new and half-old DNA.

Semicircular canals Part of the inner ear filled with a fluid substance.

Semilunar valves A valve of the heart that prevents backflow into vessels.

Seminal vesicle A gland situated behind the bladder and above the prostate gland in males.

Seminiferous tubules Highly coiled structures within the testes.

Senescence The process of aging.

Sensation Information received by the neurons.

Sensory neuron Neurons that bring information from the external environment, toward the brain and spinal cord.

Septum A partition that separates two chambers of tissue in an organism.

Serotonin A type of neurotransmitter that improves mood and inhibits pain and depressive feelings.

Sessile Immobile.

Set point The normal value at which a variable physiological state stabilizes.

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Glossary 813

Sex chromosome The final smallest pair of the 23 pairs of chromosomes in humans.

Sex-linked One of the three possible patterns of inheritance of single-gene traits in which the X chromosome determines the characteristic.

Sexual reproduction The process in which two individuals contribute genetic material to their offspring.

Sexual selection Is the natural selection not based on a struggle for survival but instead based on a struggle for the opposite sex.

Shoot system The system that consists of stem, leaves, lateral buds, flowering stems, and flowering bud.

Sickle cell anemia A disease that leads to abnormally shaped red blood cells, poor oxygen carrying capacity, and a host of complications such as blood clots and organ damage.

Sieve-tube members Cells that transport sap through phloem vessels, are alive at maturity, unlike xylem cells.

Significance level The percentage chance that the results of a study are wrong.

Simple An epithelial tissue that is only one cell layer in thickness.

Sinoatrial (SA) node The center that controls the heart beats.

Skeletal muscle Long muscles that are found attached to bones of the skeleton and move the bones.

Skin cancer A condition characterized by the abnormal growth of cells of the skin.

Sliding filament theory The theory that explains muscle contraction.

Slime molds Organisms that live freely as single cells but form multicellular reproductive structures upon reaching a certain size.

Small intestine The portion of digestive tract that lies between the colon and stomach.

Smooth muscle Muscle tissue that provides support and propels movement of food through the organs in which it is found.

Sociobiology The study of the ways that groups of animals act.

Sodium–-potassium pump An integral protein that uses ATP energy to move sodium ions out of the cell and brings potassium ions into the cell.

Soluble fiber Fibers that dissolve in water.

Solute The component in a solution that is dissolved in the solvent.

Solvent Substance that does the dissolving.

Somatic cells The body cells other than gametes (or sex cells).

Somatic nervous system Part of the PNS that controls the voluntary movements in the body.

Special connective tissue A unique connective tissue that has either a rigid or a liquid extracellular matrix.

Specialized cells Cells that carry out a particular function.

Speciation The process by which natural selection drives one species to split into two or more species.

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Species A group of individuals similar enough to be able to reproduce with one another to produce live, fertile young.

Species-specific Limited to or found in one species.

Specific-immunity The third line of defense in the human immune system; involves targeting of antigens by immune system.

Sperm activation The process by which sperm are additionally mobilized by calcium and even more able to fertilize the egg.

Spermatogenesis The process by which sperm are produced by spermatogonia cells in the testes.

Spinal cord A long cord of nerve tissues that connect the brain to the other parts of the body.

Spirillum Spiral-shaped bacteria.

Spongy bone Tissue found inside the bones that resemble a sponge; it contains many open spaces.

Spontaneous generation The idea that states that life appeared from nowhere.

Sporophyte The diploid organism in plants, producing spores.

Squamous cell carcinoma A type of skin cancer characterized by a flaky, reddened area.

Squamous Flat-shaped epithelial cells.

Stabilizing selection Occurs when individuals at mean or average range of variation in a population have higher fitness.

Stamen Male reproductive structure in flowering plants.

Staph The prefix given to bacteria that are found in clusters.

Statistics The study of the collection, organization, analysis and interpretation of data.

Stem cells (Pleuripotential) Are specialized cells that are able to develop into many types of cells, given particular conditions.

Steroid A type of fat that stabilizes the structure of cell membranes.

Stigma A sticky flat surface on which pollen grains land in flowering plants.

Stimulus Something that causes an organ or cell to react.

Stirrup The innermost bone of the middle ear.

Stomach An internal organ sac that holds and digests food before entering the small intestines.

Stomata A minute pore found in the epidermis of a plant’s leaf or stem through which gas and water pass.

Stratified An epithelial tissue that is two or more layers thick.

Stratum basale The deepest layer of the epidermis, mitotic.

Stratum corneum The outermost layer of the epidermis; it is thickest and is composed of dead cells.

Stratum granulosum A thin layer of granular cells in the epidermis located between stratum lucidum and stratum spinosum.

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Stratum lucidum A clear layer of dead skin cells in the epidermis located between stratum corneum and stratum granulosum.

Stratum spinosum A layer in the epidermis located between stratum granulosum and stratum basale.

Strep The prefix given to bacteria that are found in chains.

Striations Alternating patterns of proteins in the skeletal muscle.

Stroke The sudden diminution of brain cells due to lack of oxygen caused by obstruction or rupture of a blood vessel of brain.

Style The part of carpel that extends to ovules in which eggs develop in flowering plants.

Submissive behavior Willing to submit to avoid further fighting, when a battle appears to be lost.

Substrate A compound on which an enzyme acts.

Superficial An anatomical term referring to a surface region or area of the body.

Surface markings The distinctive features found on human bones.

Surface runoff The flow of water over the land surface.

Surfactant A special chemical that helps to keep the alveoli open by reducing the surface tension of fluid within the lungs.

Survivorship curve A graph that gives number of survivors in a population over time.

Sweat glands A tubular gland that secretes sweat.

Swim bladder Organ that is present in many bony fishes and helps them maintain buoyancy.

Symbiosis A relationship formed between two different organisms living in a close, intimate association.

Sympathetic nervous system A part of the nervous system that increases heart rate, stimulates muscles, and raises blood pressure.

Sympatric speciation The emergence of new species while living within the same geographical areas.

Synapse The gap or region separating neurons from other cells or each other.

Systemic circuit The vessel connection between the heart and body cells.

T-cell A type of lymphocyte that matures in the thymus.

T-helper cell A specific type of T-cell that attaches to the macrophage to start specific-immunity.

T-suppressor cell Type of immune cells “demilitarize” an immune response when an immune response ends.

Taiga A swampy, subartic forest dominated by conifers.

Tape worms Parasitic flatworms that live in the intestines of people and animals.

Taproot Large vertical root that burrows downward, anchoring the plant.

Target cell Any cell having a specific receptor for an antibody, hormone, or antigen.

Taxonomy The science of classifying the vast biodiversity.

Telomerase An enzyme that rebuilds the DNA ends of cancer cells.

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816 Glossary

Telomere A compound structure found at the end of a chromosome.

Telophase A phase during which time there is a reversal of the events occurring during prophase.

Telophase I The stage meiosis resulting in the forming of a set of new cells.

Telophase II The last stage in the second meiotic division of meiosis resulting in a new set of haploid cells.

Temperate deciduous forest A forest type characterized by leaf-shedding trees.

Temperate grassland Are terrestrial biomes whose main vegetation is grass and shrubs.

Temporal lobe One of the four major lobes of the brain that contains an area concerned with hearing and visual sensing as well as language comprehension.

Tendon Strong fibrous tissue that anchors muscles to bones.

Termination The phase in which RNA polymerase will reach a sequence of DNA that tells it to stop.

Tertiary consumer Carnivores that eat carnivores.

Testcross A known homozygous recessive organism is mated with a dominant organism.

Testes Organs that produce sperm.

Thalamus The rounded area underneath the corpus callosum.

Thalassemia The condition in which a faulty or absent hemoglobin chain makes the molecule fragile and less able to carry oxygen.

The bends The condition in which nitrogen gas accumulates in a diver’s blood.

Thermacidophiles Organisms that thrive in strongly acidic environments at high temperatures.

Thermodynamics The science of energy transformations that explains the flow of energy through environment and in cells.

Thermoreceptors A sense organ responding to temperature.

Thigmotropism Any plant growth response to touch.

Thoracic vertebrae The 12 vertebrae along the thorax along the center of the vertebral column.

Thrombin An important enzyme in blood that facilitates clotting of blood by converting fibrinogen to fibrin.

Thrombosis Clots forming in the wrong places (an unbroken vessel).

Thymine A pyrimidine base that is found in DNA but not RNA.

Thyroid stimulating hormone (TSH) Hormone produced by the pituitary gland and stimulates the thyroid gland.

Thyroxin A hormone that increases metabolism throughout the human body.

Tight junction A specialized cell junction that fuses areas together to prevent leaking and acts as a sealant.

Tissues Groups of cells having similar structure and performing similar functions.

Topography The physical features of the land such as mountains and valleys.

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Glossary 817

Trabeculae Small spindles that make up the spongy bone.

Trachea A tube-like portion of the respiratory tract that connects to the lungs.

Tracheids Elongated cells found in the xylem of vascular plants that conduct the transport of water and mineral salts.

Tracheophyte Vascular plant; plants having a well developed vessel system.

Trade winds Winds that blow above and below the equator.

Transcription The first step of gene expression in which information in a DNA strand is copied into mRNA by RNA polymerase.

Transduction The process that occurs when a virus invades a prokaryote, inserting its genes into the host.

Transformation The process in which a newly inserted DNA from the environment changes or transforms a bacterial cell into a new genotype.

Transitional epithelium A type of tissue that consists of multiple layers of epithelial cells, which looks at times cuboidal and at other times squamous in shape; responds to pressure as in the bladder.

Translation The synthesis of protein from the information contained in a molecule of mRNA.

Transmission electron -microscope (TEM) A type of electron microscope that magnifies structures within a cell.

Transpiration Loss of water from leaves by evaporation through stomata.

Transpirational pull The process in which water and minerals are transported upwards through xylem from roots because of an upward force or pull.

Tricuspid valve A heart valve between the right atrium and ventricle and keeps blood from flowing back into the atrium.

Trimester A normal pregnancy divided roughly into three parts.

tRNA Small RNA molecules that carry amino acids to ribosomes for protein synthesis.

Trophic level A group of organisms with the same feeding style.

Tropical rainforest A type of forest characterized by tall, dense trees in an area that experiences high annual rainfall.

Tropomyosin A protein rope that plays an important role in muscle contraction.

Troponin A protein found in all muscle.

Tube feet Small suction cup-shaped feet that are used for holding prey.

Tundra A tree-less area near the North Pole.

Turgor pressure The pressure exerted against the walls of a plant cell when water enters the water vacuoles of plant cell.

Twitch The time period comprising a contraction and relaxation.

Ultrasound A technique that emits high frequency sound waves and creates images based on the echos received back from the body part.

Universal donor A person of blood type O who may donate blood to any other blood group because the blood group contains no antigens on its red blood cells.

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818 Glossary

Universal recipient A person of blood type AB who may receive blood from any other blood group because the blood group contains all antigens on its red blood cells.

Uracil A pyrimidine base that is one of the fundamental components of RNA.

Ureter A tube connected to each kidney responsible for transporting urine from the renal pelvis to the urinary bladder.

Urethra The duct by which urine is removed from the body.

Urinalysis An analysis that tests urine for normal and abnormal substances.

Urinary bladder An organ that holds the urine.

Urinary system The system that is responsible for eliminating wastes.

Urogenital system The system comprising the reproductive organs and the urinary system.

Uterus A thick, muscular organ in which a fetus develops.

Vacuole Single membrane structures that hold materials in a cell.

Vagina A muscular tube leading from the outside to the cervix of the uterus in female mammals.

Valence electrons Electrons present in the outermost shell of an atom; these electrons are responsible for the chemical reactivity of atoms.

Variable region Regions that vary from antibody type to antibody type.

Variation Differences that are inherited from generation to generation.

Varicose veins The condition in which valves are incompetent within the legs leading to the formation of blood pools.

Vascular cambium One of the lateral meristems that produces xylem and phloem.

Vascular tissue Tissues that transports water, minerals and food throughout a plant.

Vasoconstrict Narrowing of blood vessels.

Vasodilate Widening of blood vessels.

Vein A blood vessel that carries deoxygenated blood back to the heart after it has picked up wastes and carbon dioxide from body cells.

Vena cava A large vein that carries deoxygenated blood into the heart.

Ventricle A chamber of heart that receives blood from the atrium.

Venules Small veins connecting capillaries with larger systemic veins.

Vertebrates Animals having a backbone.

Vessel element A cell type found in xylem.

Vestigial organs Structures that once had a purpose but no longer appear to be functional.

Villi Small folds or projections lining the walls of the small intestine.

Visceral mass One of three-point body plans of mollusks that contain the internal organs.

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Glossary 819

Vitamin D A fat-soluble vitamin that promotes that is essential for the absorption of calcium.

Vitreous humor Posterior chamber of the eyes.

Vocal cords Two elastic cords stretching across the upper end in the larynx.

Vomer A small bone found inside the nose.

Water An essential nutrient, comprising between 60% and 80% of the volume of cells, and is the medium in which all cell reactions take place.

Water cycle The process by which water continuously moves on, above, and below Earth’s surface.

Water-soluble vitamins Includes B-vitamins and vitamins C and K, can be taken in large doses and do not become toxic because they are eliminated through the urine.

Water-vascular system A set of internal channels that circulate water through echinoderm bodies, enabling gas exchange and waste removal.

Watershed An area that collects flow, runoff, and precipitation from a region into a specific body of water.

Westerlies Winds that blow from the west.

Wetland A land that consists of swamps or marshes.

White blood cells Blood cells that help body fight infections.

Wind The intricate horizontal movements of Earth’s atmosphere caused by differences in atmospheric pressure and Earth’s rotation.

Wolff ’s law The phenomenon which states that bones grow and remodel according to the forces placed upon them.

X chromosome A sex chromosome that is found twice in females and singly in males (not given in bold in text).

X-rays A form of EM radiation that visualizes dense structures within the body.

Xylem A series of tubes conducting water and dissolved minerals up a plant.

Y chromosome A sex chromosome that is found only in males (not given in bold in text).

Yellow marrow Hollow cavities within bones filled with fat.

Zona pellucida A layer of proteins that surround and protect the ovum.

Zone of cell division One of the zones of development in which mitosis occurs in a slow but protected manner.

Zone of differentiation One of the zones of development in which cells become one of the three types of plant tissues.

Zone of elongation One of the zones of development in which cells elongate.

Zoology The branch of biology that is dedicated to the study of animals and their characteristics.

Zygomatic bone Bone that forms an important part of the cheeks.

Zygote A diploid cell that is produced when the haploid sperm nucleus fuses with the egg’s haploid nucleus.

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821

A accessory organs, 442 Acer rubrum, 14 acid-base buffering system in blood, 54 acids, 52–55 acquired immunity

active artificial, 593 active natural, 593 passive artificial, 593 passive natural, 593 vaccine effects, Rubella incidence, 592

action potential, 518–520 activation energy, 63 active transport, 107 acute intermittent porphyria (AIP), 196 adaptation, 7–8 adaptive behaviors, 752 adenosine diphosphate (ADP), 64 adenosine triphosphate (ATP), 64, 65, 122 aerobic cells, 87 aerobic respiration, 133 afferent neuron. see sensory neuron age-related dementia, 3 aggression, 760 air sacs (alveoli), 488 albinism, 154 alleles, 195–196 allergens, 598 allergies, 598 altitude sickness, 497, 498 altruism, 761 Alzheimer’s disease, 3, 28 amino acid, 61 amniotes, 365 Amoeba, 15, 85, 98, 99 Amorphophallus titanum, 4 amygdala, 533

anaerobic respiration, 141 Analysis of Variance (ANOVA), 27 anaphase I, 205 anaphase II, 207 anemia, 471 angiosperms, 318–319 animal behavior, 752 animal classification

body cavity formation, 345 molting, 344–345 radial symmetry, 344, 345 specialized cells, 344

animalcules, 156 animal diversity

arachnids, 356–357 Cambrian explosion, 342 Cambrian period, 342 characteristics, 342, 343 chordates (see chordates) classification (see animal classification) Cnidarians (see Cnidarians) crustaceans, 355, 357–358 echinoderms, 360–361 extant organism, 342 flatworms, 351–352 insects, 355, 358–359 invertebrates, 341 mollusks, 353–355 phyla, 345, 346 roundworms, 352 scattered sponges, 345–347 segmented worms, 353, 354 vertebrates, 341

animal organization, 406–407 anorexia nervosa, 423–424 Antarctic resources, national claims, 697 antioxidants, 427

INDEX

ch22_idx.indd 821 11/12/15 6:02 pm

C R O O M , D O N A V A N 4 6 4 5 T S

822 Index

apoptosis, 534 appendicular skeleton, 543, 548 aquaporins, 92 aquatic biomes, 698 arachnids, 356–357 arachnoid layer, 530 archaebacteria, 289–290 areolar connective tissue, 401 arrhythmia, 479 arthropods

arachnids, 356–357 crustaceans, 355, 357–358 insects, 355, 358–359

asbestos fibers, 490 asexuality, 212 asexual reproduction

animals and plants, 621 binary fission, 622 budding fission, 622 earthworms, hermaphroditic, 621 fragmentation, 621–622 parthenogenesis, 622, 623

asthma, 499 atherosclerosis, 59 atomic mass, 43 atomic number, 42 atoms, 9, 39–41 atrioventricular (AV) node, 479 autogenous model, 294 autoimmune disease, 597–598 autonomic nervous system, 516 autosomal chromosomes, 210 autosomal dominant, 213 autosomal recessive, 213, 214 axial skeleton, 543, 544

B bacillariophyta, 294, 295 bacterial reproduction, 288–289 Barrett’s esophagus, 54 basal metabolic rate (BMR), 441–442 bases, 52–55 behavioral ecology, 752 behavioral prey defenses

alarm call, 668–669 community interactions, 673 C. saundersi, 669

group behavior, 668 hiding and fleeing, 668 plants and herbivory, 669–670 symbiosis, 670–673

behaviorism classical conditioning, 755–756 habituation, 755 imitation, children, 754, 755 imprinting, 754 insight, 757 operant conditioning, 756–757 Serengeti Grasslands of Africa, habitation, 755

Big Bang Theory, 256, 257 bilateral symmetry, 344, 345 binary fission, 288, 622 bioaccumulation

lipid/fat-soluble substances, 737–738 of methylmercury, aquatic system, 738

biodiversity, 8 biofuels, 287–288 biogeochemistry

aquifers, 727 carbon cycle, 728–729 environmental resources, 725 eutrophication, 732 global climate change, 729–730 greenhouse effect, 729–730 nitrogen cycle, 730–731 phosphorous cycle, 732–733 residence time, 726 surface runoff, 727 water cycle, 726–728

biology biophilia, 4 cell, 4 characteristics of life (see characteristics of life) definition of, 3 ecosystem, 5 interdisciplinary, 5 literacy, 4 microbiology, 5 size, 77

biomagnification, 738–739 biomes

abiotic factors, 684 aquatic biomes, 698 chaparral, 682, 684

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Index 823

deciduous forests, temperate, 684 deserts, 684 estuaries, 700–701 freshwater (see freshwater biomes) grasslands, temperate, 684 innumerable ecosystems, 684 marine biomes, 701–702 polar ice caps, 684 savannas (tropical grasslands), 684 taiga, 684 temperate forest, 682 terrestrial (see terrestrial biomes) tundra, 684 types, 682

biophilia, 4 bioprocessing

alcohol and cellular respiration, 142–143 anabolism, 139 anaerobic respiration, 141 catabolism, 139 deamination, 139, 140 definition, 139 fermentation, 141–142 lipogenesis, 140 lipolysis, 140 metabolism, 139

biosphere, 11 atmosphere, protection layer, 718 biogeochemistry (see biogeochemistry) biotic and abiotic systems, 740 earth’s boundaries for life, 717 global atmospheric circulation, 720, 721 global transport and climate control (see

hydrosphere) hemisphere, 720 human influences (see human influences,

biosphere) hydrosphere, 718 lithosphere, 718 seasonal changes, temperature, 719–720 solar radiation, 719 surface ocean currents, 722 winds, movement under pressure, 721–722

biotechnology, 222, 224–225 bipolar cells, 527 Bistonbetularia f. carbonaria, 8 Bistonbetularia f. typical, 8

bivalves, 353 blood

acid-base balance, 476 defense, 475 definition, 470 Mayan Indian sacrifices, 469 plasma, 470 platelets, 472–475 red blood cells, 470–472 temperature regulation,

475–476 transport, 473, 475 white blood cells, 470

blood doping, 497, 498 blood pressure

definition, 484 high, 485–486 muscular pump, 487 respiratory pump, 487

blood vessels arteries, 483–484 capillaries, 484 veins, 484

body art, 76 body cavity formation, 345 body mass index (BMI), 424, 425 bone

functions of, 542 morphology of, 542–544 remodeling and disease, 549–551

brain anatomy, 530–531 limbic system, 532, 533 regions, 531, 532 specialized hemispheres, 533, 535 structure of, 533, 534

brood parasitism, 672 brown algae, 294 bryophytes

gametophytes, 315 haploid and diploid phases, 315 life cycle, 315 sporophytes, 315

budding fission, 622 bulimia, 423–424 bulk transport, 107–109 bundle of his, 479

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824 Index

C calcium homeostasis, 554, 555 calories (cal), 440–441 Calvin cycle, 124, 130–131 Cambrian explosion, 342 Cambrian period, 342 CAM pathway, 132 Camponotus saundersi (C. saundersi), 669 carbaminohemoglobin, 495 carbon, 55–56 carbon cycle, 728–729 carbon fixation, 131 carbonic acid-bicarbonate buffering system, 476 carbon monoxide (CO) poisoning, 496–497 cardiovascular system

heart (see heart) vessels, 483–484

carnivores (secondary consumers), 702 carpal tunnel syndrome, 548, 549 cartilaginous fishes, 362 catastrophism, 20 cell

architecture, 90–91 biological differences, 75 cell theory, 80–81 culture, 75 endosymbiosis, 75 eukaryotes (see eukaryotes) inheritance role, 86–87 microscope (see microscope) mitochondria, 74–75 plasma membranes (see plasma membranes) prokaryotes, 81–82

cell diversity, 77 cell energetics, 121 cell junctions, 100–101 cell-mediated immunity

clonal selection, 586 cytotoxic T cells, 585 T-helper cells, 584–585

cell theory, 80–81 cellular respiration, 88

energy exchange, 120–122 ETC, 135–139 glycolysis, 133–134 Krebs Cycle, 134–135

cementum, 446

Central Dogma of Biology, 174 central nervous system (CNS), 405, 406, 516 centrioles, 84 cephalopods, 353–354 chaparral biome, 692, 693 characteristics of life

adaptation, 7–8 diatom cell wall structure, 5, 6 diversity, 8 homeostasis, 6 human fetus growths, 7 metabolism, 6 ordered, 9–11 reproduction, 8–9 response to stimuli, 7

chemical warfare anti-inflammatory medicines, 584 aspirin, 584 hydrogen peroxide (H2O2), 583, 584 interferons, 583 pyrogenes, 584 respiratory burst, 583

chemoautotrophs, 288 chemotaxis, 287 child birth process, 392–393 chlorophyll a, 128 chlorophyta, 294 chloroplasts, 88–89, 124–125 cholecystokinin (CCK), 454 chondrocyte, 403 chordates

amphibians, 364–365 birds, 367–368 fish, 362–364 human evolution, 369–371 lancelets, 361 mammals, 368–369 notochord, 361 reptiles, 365–366 spinal cord/spinal cord-like structure, 361 tunicates, 361–362

chromatin, 95, 96 chromoplasts, 100 chromosome, 95 chronic obstructive pulmonary disease (COPD), 499 chrysophyta, 295 cigarettes, 481–482

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Index 825

cilia, 94 classical conditioning, 755–756 clotting factors, 472 cnidarians

bodyplan, 348 cnidocysts, 348 coelenteron, 347 corals, 350–351 ectoderm, 349 endoderm, 349 hydras, 350 jellyfish, 349 life cycle, 349 medusa stage, 349 mesoglea, 349 nerve network, 349 polyp stage, 349 sea anemones, 350

coastal biomes, 692 coconuts, 323 codon (triplet), 175 coelenteron, 347 coenzyme A, 134 cognitivism, 758 cohesion, 50, 51 commensalism, 670, 671 communities

abiotic factors, 663 Balanus and Chthamalus genera, 664 behavioral prey defenses, 666 biotic factors, 663 character displacement, 665 competitive exclusion principle, 664 ecological niche, 663 fundamental niche, 663 habitat, 663 interspecific competition, 665 intraspecific competition, 665 physical prey defenses, 666 predator-prey relationships, 665–666 realized niche, 663 resource partitioning, 664–665

compact bone, 542 compartmentalization cell, 91 competitive exclusion principle, 664 complementarity

auscultation, 388

CT, 388 definition, 386 knee joint, 386, 387 MRI, 388 observation, 387 palpation, 388 physical manipulation, 387 ultrasound, 388 X-rays, 388

compound light microscope, 78, 80 compounds, 46 concentration, higher and lower, 103 conjugation, 287 connective tissue

adipose tissue cells, 402 areolar, 401 blood, 402–403 bone, 403 cartilage, 403 chondrocyte, 403 CTP, 401 dense regular and irregular, 402 extracellular matrix, 400 fibers, 400 fibrocartilage, 403 function, 395 mesenchyme, 401 reticular, 401 special connective tissue, 402 starfish anatomy, 397

connective tissue proper (CTP), 401 contractile vacuole, 99 corals, 8, 350–351 Coriolis effect, 722 coronary artery bypass graft (CABG), 481 coronary circuit, 477 corpse flower. see Amorphophallus titanum correlation, 27 covalent bonds, 49 C3 pathway, 131–132 C4 pathway, 132 cranial bones, 543 cristae, 135 critical threshold potential, 518 crossing over, 205 crustaceans, 355, 357–358 cyanide, 138–139

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826 Index

cyanobacteria, 290, 291 cytochromes, 128–129 cytokinesis, 207 cytoplasm, 90–91, 101 cytoskeleton, 93–95

D Darwin’s theory of evolution, 21–22 data analysis, 26 deamination, 139, 140 Death Cap Mushroom, 16 deep vein thrombosis (DVT), 473 deforestation, 733–734 dehydration synthesis, 56, 57 dentin, 446 deoxygenated blood, 477 deoxyribonucleic acid (DNA)

adenine, 160 complementarity, 160–161 cytosine, 160 deoxyribose, 160 electrophoresis, 171 gene, 161 genetic code, 160 guanine, 160 histone proteins, 164 malaria, 171 melanin mutation, genetic code, 160, 161 mutation, 160 nucleotide, 160 Plasmodium, 172 ribose, 160 sickle-cell anemia, 171, 172 structure, 159, 161 supercoiling genes, 164 thymine, 160 uncoiled, 159

deoxyribonucleic acid (DNA ), 9, 64 desert biome, 691 desertification, 689 desmosomes, 100 dialysis, kidney impairment treatment, 620 diatom cell wall structure, 5, 6 diatoms, 294, 295 digestion

chemical, 444 definition, 443

esophagus, 446–448 large intestines, 456–457 mechanical, 444 mouth, 445–447 small intestine (see small intestine) stomach, 449–451

digestive system alimentary canal, 442–443 colon cancer, 459 digestion (see digestion) GERD, 458 heartburn, 458 stomach cancer, 458 ulcers, 458

dihybrid cross, 196 dinosaur extinction, 249, 250 dinosaurs, 366–367 diploid (2N), 201, 203 disaccharides, 57, 58 diversity

archaebacteria, 289–290 cyanobacteria, 290, 291 endospore-forming bacteria, 292 enteric bacteria, 293 phototrophic anaerobic bacteria, 292–293

divisions, plants bryophytes (nonvascular plants) (see bryophytes) tracheophytes (vascular plants) (see

tracheophytes) docking, 273, 274 dollar bill, 515–516 dominance hierarchy, 759 double fertilization, 320 down regulation, 555 Drosophila’s fruit flies mating, 14 drug testing, 616, 617

E earthquake, 735–736 eating disorders

anorexia nervosa, 423–424 bulimia, 423–424 obesity epidemic, 425–427

ecosystems, 5 abiotic factors, 707 carnivores (secondary consumers), 702 climax community, 707

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Index 827

colonization, 706–707 decomposers, 704 disturbance and ecological succession, 706–708 estuary, 682 flow of energy, 702, 703 food chain, 703 food web, 703, 704 fragmented meta-populations, 707 herbivores, 702 housing developments, 707, 708 omnivores, 702–703 primary succession, 707 producers, 702 scavengers, 704 secondary succession, 707 tertiary consumers, 702 topography, 685–688 trophic level, 703 vanity ponds, malls, 707, 708

efferent neurons. see motor neurons elastic cartilage, 403 elasticity, 535 electroencephalography (EEG), 533 electromagnetic energy, 124–125 electronegativity, 48 electron microscope, 79, 80 electron transport chain (ETC), 129, 135–139 elements, 40 El Nino, 724–725, 726 embolus, 473 embryology

amnion, 634 blastula, 633 chorion, 634 cleavage, zygote, 632, 633 ectoderm, 634 endoderm, 634 gastrulation, 634 inner cell mass, 633–634 mesoderm, 634 mitosis, cleavage, 632 morula, 633

enamel, 446 endocrine system

adrenal glands and actions, 557, 558 blood sugar and diabetes, 554–555 calcium and bones, 554, 555

hormone communication process, 551, 552 metabolism, 555–557 pain and paracrine glands, 559 pheromones, 558, 559 pineal gland, 557–559 receptor-hormone match, 551 reproduction, 558

endocytosis, 107, 109 endoplasmic reticulum (ER), 96–97 endorphins, 519 endoskeleton, 542 endospore-forming bacteria, 292 endosymbionts

definition, 87 mitochondria and chloroplasts, 88–89

endosymbiotic theory, 88 endothelium, 477 energy exchange

ATP molecule, 122 cellular respiration, 120–122 first law of thermodynamics, 121–122 photosynthesis (see photosynthesis) plants and animals, 123 Priestly’s experiment, 120 second law of thermodynamics, 122 thermodynamics, 121

energy-investment phase, 133 energy pyramids

biomass, 704–705 losses, trophic levels, 704

energy-yielding phase, 133 engineering of waterways

Mississippi and Atchafalaya Rivers, 734–735 Three Gorges Dam Project, China, 735

English peppered moths, 8 enteric bacteria, 293 entropy, 122 enzymes, 63, 92 epithelial tissue

apical surface, 396 basement membrane, 396 cuboidal, 396 function, 395 protection, 396–397 secretion, 399 simple columnar, 396, 399 squamous, 396, 399

ch22_idx.indd 827 11/12/15 6:03 pm

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828 Index

epithelial tissue (continued) starfish anatomy, 397 stratified, 396, 399–400 structure of, 396, 398 transport, 397, 399

equilibrium, 103 errors, gene regulation

cancer, 182 contact inhibition, 182 dedifferentiation, 182 immortality, 183 loss of cellular affinity, 182 malignant cells, 182 telomerase, 183 telomeres, 183

esophagus epiglottis, 446 Heimlich Maneuver, 447, 448

Euglena, 15, 295 euglenophyta, 295 eukaryotes

animal cells, 82–86 endosymbionts (see endosymbionts) fungi, 84–86 introns and exons, 176 mitosis (see mitosis) plant cell, 82, 84–86 protists, 85, 86

eusociality, 764, 765 eutrophication, 732 evolution

Big Bang Theory, 256, 257 catastrophism, 20 Darwin’s Voyage, natural selection, 21–23 diabetes, 258–259 and economic systems, 22–23 fossil record, 19–20 inheriting acquired traits, 20–21 negative feedback, sugar levels, 258, 260 peacock’s large tails, 257, 258 Pima Indians, Sierra Madre Mountains, 259, 260 of social behavior (see sociobiology)

exocytosis, 107, 109 exoskeleton, 542 expiration, 488–489 external fertilization, 365 extinction

and biodiversity, 250 butterfly species, England, 248 definition, 246 ecosystem of island, 249 environmental changes, 248 natural selection, 249 record, geologic history, 246, 247

F facial bones, 543 facilitated diffusion, 106 fascicles, 536 fat emulsification, 454 fat-soluble vitamins, 427, 429 female reproduction

clitoris, 629 corpus luteum, 628 donor eggs, mitochondrial diseases, 627, 628 endometrium, 628 external structures, 629 follicle, 627 hormones, 630 meiosis., 626 menarche, 631, 632 menopause, 631 menstrual cycle, 630–631 oogenesis, 627 ovarian cycle, 630 ovaries, 627 oviduct (fallopian tube), 628 ovulation, 627, 628 ovum, 632 sperm activation, 632 structures., 626–627, 629 uterus, 628 vagina, 629 zona pellucida, 632 zygote, 632

fermentation, 141–142 fertilization, 201, 622–623 fibrocartilage, 403 fibrous/globular protein, 62 finch beak anatomy, 21, 22 first law of thermodynamics, 121–122 flagella, 94 flowers, fruit and plant reproduction

animal pollination, 322

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Index 829

anther, 319 asexual reproduction, 322 carpel, 319 dioecious, 319 double fertilization, 320 endosperm, 320 filament, 319 gemmae, 322 genetic diversity, 322 insect pollination, 322 male and female structures, 319, 321–322 monoecious, 319 ovules, 319 pollen grains, 319 stamen, 319 stigma, 319 style, 319 wind pollination, 322

fluid mosaic model, 91–93 food chain, 10–12, 703 food tube. see esophagus food vacuoles, 99 food webs, 10, 12, 703, 704 fossil fuel burning, 730 fossil record, 252–253 fragmentation, 300, 707 free radicals, 56, 427 freshwater biomes

limnology, 698 ponds and lakes, 698–700 rivers and streams, 699, 700

functional groups, 55–56 fungi

fragmentation, 300 hypha, 299 mycelium, 299 in nature, 299 reproductive cycle, 300 septum, 299

G gametes, 201 gas transport, 494–495 gastroesophageal reflux disease (GERD),

54, 458 gastropods, 353 gene expression

codon, 175 definition, 173 genotype, 173 phenotype, 173 transcription, 174 translation, 174 triplet sequence, DNA, 174

gene regulation errors, 182–183 histone protein, 182 primary mechanisms, 182

gene technology, 222 gene therapy, 224 genetically modified organism (GMO), 222, 225 genetic code (for amino acids) table, 175 genetic diversity, 322 genetic engineering, 222 global climate change, 729–730 glucagon, 390, 554 glyceraldehyde 3-phosphate (G3P), 131 glycolysis, 133–134 golden-brown algae, 295 Gold Foil experiment, 42 golgi apparatus, 97, 98 gram-negative bacteria, 286 gram-positive bacteria, 286 green algae ancestry, 294, 311–312 greenhouse effect, 729–730 Grey, Jennifer, 512–513 Griffith’s experiement, 158 group cooperation vs. selfish genes

ant hill colony, 765–766 eusociality, 764, 765 haplodiploidy, 765 hymenopteran, 765

gustation, 521–523 gymnosperms

conifers, 317, 318 cycads, 317, 318 ginko plants, 317 gnetophytes, 317, 318

H habituation, 755 halophiles, 290 haplodiploidy, 765 haploid (N) condition, 201

ch22_idx.indd 829 11/12/15 6:03 pm

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830 Index

Hardy–Weinberg equation, 220 heart

arteriosclerosis, 481 atherosclerosis, 483 blood movement, 477–479 controls of, 499–501 definition, 476 electricity activity, 479–480 heart valve disease, 482 MI, 480

heart attack, 473, 480 hemophilia, 472 herbivores, 702 heredity, 194 herpes virus, 277–278 heterocysts, 290 heterotrophs/consumers, 15 heterozygous/hybrids, 198 HGH, 225–226 high fructose corn syrup (HFCS), 426 hippocampus, 533 histone proteins, 95 HIV infection rates, 599 homeostasis, 6

control center, 389 definition, 388 discovery of, 393, 395 effector, 389 endocrine system, 393, 394 negative feedback, 389–391 nervous system, 393, 394 positive feedback, 390–393 receptor, 389 set point, 389

homeotherms, 341 hominid timeline, 371 homologous chromosomes, 201–203 homozygous, 198 Hooke’s microscope, 78, 79 hormones, kidney

aldosterone, 619 angiotensin II, 619 antidiuretic hormone (ADH), 619

human body abdominopelvic regions, 410, 411 anatomy, 384, 385, 408 body planes, 410, 411

cytology, 384 developmental anatomy, 386 directional terms, 408–410 disease, 386 embryology, 386 gross anatomy, 384 histology, 384 microscopic anatomy, 384 organ systems, 411–414 physiology, 386 senescence, 386 surface regions/body landmarks, 406–408 urinary system, 383–384

human influences, biosphere bioaccumulation/biomagnification, 737–739 deforestation, 733–734 earthquake, 735–736 engineering of waterways, 734–735 ozone (O3), 739, 740 pollution, 736–737 renewable energy solutions, 737 seismicity, 735–736

human laws, 762 human population structure

age structure diagrams, 658 density-independent factors, 659 ecological footprint, 659, 660 farming and production, 659 fertility rate, 658 food preservation, 659 logistic S-shaped growth, 657

human skeleton bones (206), 543, 544 Carpal tunnel syndrome, 548, 549 intervertebral discs, 548 skull bones, 544, 546–547 vertebral bones, 545, 547

humerus, 548 humoral immunity

antibodies, 586, 587 B-cell lymphocytes, 586 and cell-mediated immunity, interactions, 589,

590 constant regions, 587 memory cells, 586 opsonization, 587 plasma cells, 586

ch22_idx.indd 830 11/12/15 6:03 pm

C R O O M , D O N A V A N 4 6 4 5 T S

Index 831

T-suppressor cells, 589 variable regions, 587

hyaline cartilage, 403 hydras, 350 hydrochloric acid (HCl), 449 hydrogen bonds, 50 hydrolysis, 56, 57 hydrophilic, 58 hydrophobic, 58 hydrosphere

earth’s waters, 722–723 El Nino, 724–725 freshwater, 723 heat capacity, 722 ocean circulation, 723–724 salt wedge, 723

hydrostatic skeleton, 542 hydroxyapatite, 550 hymenopteran, 765 hyperbaric chamber, 497 hyper-disease theory, 243 hypersexuality, 212 hyperthyroidism, 556 hypertonic, 104, 105 hypha, 299 hypothalamus, 532 hypothesis testing, 25 hypothyroidism, 556 hypotonic, 104, 105

I immune system

antibodies, 570 chemical warfare, 583–584 herpes, 569 infection agents, 569 lymphocytes, 583 macrophages, 581–583 neutrophils, 581 nonspecific immunity, 570 physical barriers, body, 570 specific immunity, 570

immunization, 271 immunodeficiency, 598 inbreeding, 220–221 incomplete dominance, 215 induction/deduction, 25

inflammation heparin, 580 histamines, 580 mast cell, 580

inheriting genes biotechnology, 222, 224–225 gene technology, 222 gene therapy, 224 GMO, 222 HGH, 225–226 incomplete dominance, 215 meiosis (see meiosis) Mendelian characteristics/single-gene traits,

212–215 Mendel’s experiment, 194–195 Mendel’s Laws (see Mendel’s Laws) multiple alleles, 215–216 pedigree analysis, 218–219 pleiotropy, 218 polygenic traits, 216–218 population genetics, 219–220

inland biomes, 692 innate behavior, 753 insect pollination, 322 insects, 355, 358–359 insoluble fiber, 457 inspiration, 488–489 insulin, 390, 554 integral proteins, 91–92 intermediate fiber, 93, 94 internal fertilization, 365 intertropical convergence zone (ITCZ), 720 intervertebral discs, 548 intimidation displays, 760 intracellular digestion, 98 intracellular transport, 94 invagination, plasma membrane, 108 invertebrates, 341 ionic bonds, 50 ions, 43 iron deficiency anemia, 471 isotonic, 105 isotopes, 43–45

J jellyfish, 349 joint/articulation, 542

ch22_idx.indd 831 11/12/15 6:03 pm

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832 Index

K kidneys

alcohol, 619 dialysis, 620 drug testing, 616, 617 excretion, 617, 618 filtration, 615 fish, birds and cats, excretory product types, 618 functions, 612–613 hormones, function control, 619 impaired kidney function, 619–620 kidney failure, 619 nephrons, 613–614 pregnancy, 612 reabsorption, 615 renal capsule, 611 renal medulla, 611 renal pelvis, 612 secretion, 615 ureter, 612 urethra, 612 uric acids, 618–619 urinalysis, 616 urinary bladder, 612 water conservation, 616

kin selection, 761–762 “King Phillip Came Over From German Shores,”

14 kin selection, 212

L La Nina, 725 law of dominance, 195 law of independent assortment, 196, 198 law of segregation, 195–197 learning

behaviorism, 754–757 cognitivism, 758 language use, 758

leukocytes, 470 life history strategies

K-selected strategy, 661 opportunistic and equilibrial life histories, 661 opportunistic life history, 660 r-selected strategy, 660 survivorship curve types, 662, 663

light, 124–125 light-independent reactions, 130 light reactions

definition, 126, 127 excited electron, 126, 127 NADPH-producing photosystem, 129 photons, 126 water-splitting photosystem, 128–129

limnology, 698 Linnaeus’ binomial nomenclature, 14 lipids

hydrophilic, 58 hydrophobic, 58–59 phospholipids, 60 steroids, 60–61 triglycerides, 59, 60

lipogenesis, 140 lipolysis, 140 living systems, 46, 47 lobe-finned fishes, 363 lumbar vertebrae, 546 lungs

cancer, 497–498 compliance, 494 controls of, 499–501 exchange, 491, 493–494

lymphatic system breast cancer stages, 596 fluid and nutrient transport, 595 immunity and lymph, 595 lacteals, 596 lymphedema patient, 596 organs, 594, 595

lymphocytes, types, 583 lyse, 104 lysogenic life cycle, 275, 277 lysosome storage diseases, 99 lytic life cycle, 275–276

M macromolecules, 10

carbohydrates, 56–58 definition, 56 dehydration synthesis, 56, 57 enzymes, 63 hydrolysis, 56, 57

ch22_idx.indd 832 11/12/15 6:03 pm

C R O O M , D O N A V A N 4 6 4 5 T S

Index 833

lipids (see lipids) nucleic acids, 64–65 phospholipids, 59, 60 proteins, 61–62

macronutrients carbohydrates, 437–438 food pyramid, 434–435 lipids, 435–436 MyPlate guided diet, 434 proteins, 435

macrophages antigens, 581 phagocytosis, neutrophil, 582 skin abscess, 582

magnification, 78 major histocompatibility (MHC) proteins, 586 male reproductive system

acrosome, 625 anatomy, 623–625 bulbourethral gland, 625 epididymis, 625 external anatomy, 624 flagellum, 625 interstitial cells, 625 penis, 624 prostate gland, 625 scrotum, 624 semen, 625 seminal vesicle, 625 seminiferous tubules, 625 spermatogenesis, 625 sperm formation, 625, 626 sperm movement, tracing, 625 testes, 625

marine biology, 701 marine biomes

abyssal zone, 702 diversity, zones, 701 intertidal zone, 701 mesopelagic zone, 701 neritic zone, 701 open-sea zone, 701 photic zone, 701

marsupials, 369 mechanical breathing, 488 mechanoreceptors, 530 medial preoptic area of the brain (MPOA), 211

medulla oblongata, 499 meiosis

chromosomes, 201–203 determining sex, 210–211 fertilization, 201 haploid or N condition, 201 male and female gametes, 207–209 meiosis II, 207 phases of, 203–207 sex, cost-benefit analysis, 209–210 somatic cells, 201 zygote, 201

Mendelian characteristics/single-gene traits, 212– 215

Mendel’s laws law of dominance, 195 law of independent assortment, 196, 198 law of segregation, 195–197 testcross, 200–201

meninges, 516 menstrual cycle

menstruation, 631 ovulation, 631 proliferation, 631

mesenchyme, 401 messenger RNA (mRNA), 174 metaphase I, 205 metaphase II, 207 methanogens, 290 microbiology, 5 microfilaments, 93, 94 microscope

biological size and cell diversity, 77 compound light microscope, 78, 80 diffraction, 79 magnification, 78 measurements, 78, 79 resolution, 79 TEM and SEM, 80 Van Leeuwenhoek’s microscope, 78, 79

microtubules, 93, 94 Mississippi and Atchafalaya Rivers, 734–735 mitochondria, 74–75, 135 mitochondrial Eve, 109 mitosis, 203, 205

anaphase, 167 cell cycle, 165

ch22_idx.indd 833 11/12/15 6:03 pm

C R O O M , D O N A V A N 4 6 4 5 T S

834 Index

mitosis (continued) cytokinesis, 167 definition, 166 G1 phase, 165 G2 phase, 165 interphase, 165 metaphase, 167 molecular processes, 168–170 MPF, 165–166 prophase, 167 S phase, 165 stages, 166 telophase, 167

modern day evolution, 251–252 molecular genetics

albinism, 154 animalcules, 156 chromosomes, 157 DNA uncoiled, 159 Griffith’s experiement, 158 sperm’s composition, 156 spontaneous generation, 155 Watson and Crick’s model, 158

molecular processes, mitosis albinism, 169 DNA ligases, 169 DNA polymerases, 168 helicase, 168 initiation sequence, 168 light variation, Biston betularia, 170 nucleoside triphosphate, 168 rebuilding phase, 168 replication fork, 168, 169 semi-conservative model, 168 S (synthesis) phase, 168 unwinding phase, 168

molecules, 9, 46 mollusks, 353–354 monohybrid cross, 195 monosaccharides, 57 monounsaturated fat, 59 motor neurons, 514, 515 mouth

bolus, 445 incisors and canines, 446 ingestion, 445 peristalsis, 445

premolars and molars, 446 pulp cavity, 446 salivary amylase, 445 salivary glands, 445, 446 tooth anatomy and types, 446, 447

multiple alleles, 215–216 muscle fibers, 536 muscle tissue

cardiac, 404 function, 395 skeletal, 403–404 smooth, 404 starfish anatomy, 397

muscular pump, 487 muscular system

characteristics, 535–536 fast vs. slow twitch fibers, 537, 539–541 organization, 536 rigor mortis, 537, 539 sliding filament theory, 536–538

mutualism, 670 myelin sheath, 518 myocardial infarction (MI), 480 MyPlate guided diet, 434 myxovirus, 278–279

N National Institutes for Health (NIH), 424 natural selection and biodiversity

behavioral genetics, 242 directional selection, 242 disruptive selection, 243–244 evolution, 241 extinction (see extinction) eyed hawk-moth, 244 light and dark trees, 241, 242 phenotypic traits, 241 RS, 240–241 speciation, 245–246 stabilizing selection, 243 types, 242–244 Ursus americanus, 241

nature of animal society, 763–764 neolithic diet, 438–440 nerves

impulses, 514, 517–518, 526–527 interneurons, 514, 515

ch22_idx.indd 834 11/12/15 6:03 pm

C R O O M , D O N A V A N 4 6 4 5 T S

Index 835

motor neurons, 514, 515 nerve impulses, 514 perception, 513–514 sensation, 513 sense receptors, 514 sensory neuron, 514, 515 stimulus, 514

nervous system brain (see brain) electricity, 517 gustation, 521–523 hearing, 527–529 nerve impulses, 517–518, 526–527 nerves, 513–515 neurotransmitters, 518–520, 522 olfaction, 524 organization, 516–517 pain, 511–513 regulation, 511 senses, 520–521 touch, 529–530 vision, 525–526

nervous tissue CNS, 405, 406 function, 395 nerve cells/neurons, 404–405 neuroglia, 405 PNS, 405, 406 starfish anatomy, 397

neuron, 513 neurotransmitter, 212 neutral fats/triglycerides, 59, 60 nicotinamide adenine dinucleotide phosphate

(NADPH), 128, 129, 131, 133 nitrates (NO3), 47, 65, 66 nitrogen cycle

ammonification, 731 nitrification, 731 nitrogen fixation, 731 organic decomposition, 731

nitrogenous base, 64 noble gases, 49 nociceptors, 530 nonspecific immunity

cells, immune system (see immune system) inflammation, 580–581 necrosis, 579

tissue injury, 579 white blood cells, 579

nuclear ant hill, 750 nuclear envelop, 95 nucleoli, 95 null hypothesis, 26–27 nutrients

classes of, 427, 428 macronutrients (see macronutrients) micronutrients, 427, 429–430 minerals, 431–433 water, 433–434

O obesity, 424–425 ocean circulation, 723–724 octet rule, 48 omnivores, 702–703 oncogene, 280 oncovirus, 280–281 operant conditioning, 756–757 organelles, 10, 74 organ system, 10 origins of life

germ theory of biology, 239 Miller and Urey’s experiment design, 239, 240 Pouchet’s experiment, 238–239 prebionts, 240 Redi’s experiment, 238 spontaneous generation, 237 sterile techniques, 239

osmosis, 104–106 osteoarthritis, 550 osteoblast, 550 osteoporosis, 550, 551 oxygen revolution, 87 oxyhemoglobin, 495 oxytocin, 392 ozone (O3), 739, 740

P papillomavirus, 279 paracrine regulators, 559 Paramecium, 15, 99, 100, 105 parasitism, 671 parasitoids, 672 parasympathetic nervous system, 517

ch22_idx.indd 835 11/12/15 6:03 pm

C R O O M , D O N A V A N 4 6 4 5 T S

836 Index

parenchyma cells, 325 parthenogenesis, 622, 623 passive transport, 103–104, 106–107 Pasteur–Pouchet debate, 239 pathogens, 269–272 pea plants, 196, 198 pedigree analysis, 218–219 penicillin, 272 pepsin, 449 periodic table of elements, 40, 41 peripheral nervous system (PNS), 405, 406, 516 peripheral proteins, 91 peristalsis, 442 phaeophyta, 294 phagocytosis, 107 pheromones, 558, 559 phosphoenolpyruvate (PEP), 132 phospholipids, 59, 91 phosphorous cycle, 732–733 photolysis, 129 photo-pigments, 525 photoreceptors, 527 photosynthesis

Calvin cycle, 124, 130–131 CAM pathway, 132 carbon dioxide and water, 120 chloroplasts, 124–125 C3 pathway, 131–132 C4 pathway, 132 glucose, 122 light reactions (see light reactions) pigments, 126

photosystems I and II, 128 phototaxis, 287 phototrophic anaerobic bacteria, 292–293 pH scale, 52–53 physical barriers, skin

and mucous membranes, 570–571 structure and function, 572–573 (see also skin)

physical prey defenses aposematic coloration, 667 camouflage, 667 mechanical defenses, 667 warning coloration, 667–668

phytoplankton, 294, 295 pia mater, 530 pinocytosis, 108 pituitary gland, 551

plant growth apical meristems, 326 cork cambium, 327 germination, 326 imbibition, 326 lateral meristems, 326 meristems, 326 root cap, 326 root tip structure, 326, 327 secondary growth, 327 vascular cambium, 327 zone of cell division, 326 zone of differentiation, 326 zone of elongation, 326

plant responses, environment hormones and tropisms, 330–331 mechanical defenses, 332 plant’s defense, 332

plant tissues dermal, 324 ground tissue, 325 guard cells, 324 leaf structure, 324 parenchyma cells, 325 sclerenchyma cells, 325 stem, cross section, 325, 328 tracheids, 325 vascular, 324–325 vessel elements, 325

plasma membranes active transport, 107 bulk transport, 107–109 carbohydrate chains, 92, 93 cell junctions, 100–101 cell shape and size, 101–103 chromoplasts, 100 cytoplasm, 90–91 cytoskeleton, 93–95 endoplasmic reticulum, 96–97 energy requirement, 102 golgi apparatus, 97, 98 lysosomes, 98–99 membrane proteins, 91 mosaic, 92–93 nucleus, City Hall, 95, 96 osmosis, 104–106 passive transport, 103–104, 106–107 phospholipid bilayer, 91

ch22_idx.indd 836 11/12/15 6:03 pm

C R O O M , D O N A V A N 4 6 4 5 T S

Index 837

plant cell wall, 93, 94 plastids, 100 ribosomes, 95, 97 selective permeability, 90 vacuoles, 99, 100

plastids, 100 platelets, 391, 392, 472–474 pleiotropy, 218 pleuripotential stem cells, 473 polar covalent bonding, 49 polar easterlies, 722 polar ice caps, 696–697 pollination

animal, 322 insect, 322 wind, 322

pollution, 736–737 polyatomic ion, 48–49 polycyclic aromatic hydrocarbons (PAHs), 459–460 polygenic traits, 216–218 polypeptide, 61 polysaccharide, 57, 58 polyunsaturated fats, 59 ponds and lakes

epilimnion, 699, 700 eutrophic, 699 hypolimnion, 699, 700 Lake Baikal in Russia, 698 metalimnion, 699, 700 oligotrophic, 698, 699 zooplankton, 699

population demographics density, 655 emigrants, 655 gene flow and environment, 655 immigrants, 655 number of births, 655 number of deaths, 655 size, 655

population dynamics characteristics, communities (see communities) ecology (see population ecology) survivorship curves, 660–663

population ecology growth, 655 hierarchy, environmental organization, 654

population genetics, 219–220 population growth

biotic potential, 656 carrying capacity (K), 657 density-dependent factors, 656–657 exponential model of, 656 exponential period, 656, 657 logistic model of, 656, 657

porphyria, 193, 196, 197 potato spindle-tuber disease (PSTV), 272 powerstroke, 537 praying mantis sex, 210 predation, 665, 666 predator-prey relationships, 665–666 Priestly’s experiment, 120 primary electron acceptor, 128 primary protein structure, 61, 62 producers, 702 prokaryotes, 81–82

bacterial reproduction, 288–289 binary fission, 170 circular genome, 170 classification, 283 decomposition and recycling, 284, 285 diversity (see diversity) vs. eukaryotes, 283 genetic variation, 171 gram-positive and gram-negative bacteria, 286 nutrition, 287–288 shapes and arrangements, 285 testing methods, 283

prophase I, 205 prophase II, 207 prostaglandins, 392 proteins

in living systems, 172, 173 melanin, 172

Proteus mirabilis, 94 protime, 472 protists

algae, 294–296 autogenous model, 294 classification, 294 diverse kingdom, 293 images of, 293 molecular evidence, 293 protozoans, 296–297 slime molds, 297

protists/protista, 15 protostomes, 345

ch22_idx.indd 837 11/12/15 6:03 pm

C R O O M , D O N A V A N 4 6 4 5 T S

838 Index

pulmonary capillaries, 491 pulmonary circuit, 477 pulmonary embolism, 473 Punnett square, porphyria, 196, 197

Q quaternary proteins, 62

R radial symmetry, 344, 345 radiant energy, 124 radiation, 45 Rana pipiens, 7 receptor-mediated endocytosis, 108 recessive trait, 195 reciprocal altruism, 763 recognition proteins, 92 recombinant DNA technology, 222, 223 red algae, 294 red blood cells (RBC), 470–472 Redi’s experiment, 238 red maples, 14, 15 referred pain, 512 regurgitation, 482 relaxation, 537 reproduction

definition, 620 external and internal fertilization, 622–623 genetic quality, species, 621 sexual and asexual, 620–622

reproductive success (RS), 240–241, 752 reptile egg, 365 resilience, 494 resource partitioning, 664–665 respiration

air sacs (alveoli), 488 definition, 487–488 expiration, 488–489 inspiration, 488–489 mechanical breathing, 488

respiratory acidosis, 495–496 respiratory system

altitude sickness, 497, 498 anatomy, 489–492 the bends, 496 controls of, 499–501 COPD, 499

CO poisoning, 496–497 gas transport, 494–495 lung cancer, 497–498 lung compliance, 494 lungs exchange, 491, 493–494 respiration, 487–489 respiratory acidosis, 495–496

resting membrane potential, 517–518 reticular connective tissue, 401 retrovirus, 281–282 reversible reactions, 54 rhabdovirus, 278 rhinovirus, 278, 279 rhodophyta, 294 rhodopsin, 526 Rhogam, 221 ribonucleic acid (RNA), 64 ribosomal RNA (rRNA)., 177 ribosomes, 95, 97 ribulose (RuBP), 131 rigor mortis, 537, 539 root beer, 300–301 RUBISCO, 130 Rutherford’s Gold Foil Experiment, 42

S sarcolemma, 536 sarcomeres, 536 saturated fats, 59 Savannas (tropical grasslands)

root-to-shoot ratio, 691 Savanna of Serengeti, Africa, 689, 690

scala naturae, 11, 13 scanning electron microscope (SEM), 79, 80 scattered sponges

hermaphrodite, 347 sessile, 345 sponge body cells, 346, 347

science literacy, 24 scientific investigation, 25–26 scientific method, 24 sclerenchyma cells, 325 sea anemones, 350 secondary active transport, 107 second law of thermodynamics, 122 seedless plants, 316 seed plants, 316–317

ch22_idx.indd 838 11/12/15 6:03 pm

C R O O M , D O N A V A N 4 6 4 5 T S

Index 839

selectively permeable, 90, 104 selfish-gene hypothesis, 760, 761 sensory neuron, 514, 515 septum, 299 serotonin, 519 sex chromosomes, 210 sex-linked, 213–215 sexual reproduction

animals and plants, 621 earthworms, hermaphroditic, 621 genetic variation, 621

sexual selection, 261 sickle-cell anemia, 471 sinoatrial (SA) node, 479 skeletal system

bone remodeling and disease, 549–551 functions of, bones, 542 human skeleton (see human skeleton) morphology of, bones, 542–543

skin basal cell carcinoma, 576 blood regulation, 577 body temperature regulation, 577 keratinocytes, 574 Krause’s corpuscle, 574 Langerhans cells, 574 melanocytes, 574 melanoma, 576 and mucous membranes, 570–571 protection, 576 Ruffini’s corpuscle, 574 sensation of stimuli, 577 skin cancer, 576 squamous cell carcinoma, 576 sweat glands, 574 vitamin D synthesis, 577 wastes excretion, 577

skin and disease bilirubin, 578–579 jaundice, 578

skin’s defenses and immune attack barriers, physical (see physical barriers, skin) chemistry nightmare, 568–569 immune system’s war (see immune system)

skin structure and function arrector pili muscle, 573 dermal papillae, 573

dermis, 572–574 epidermis, 572, 573 hair root and follicle, 573 hypodermis, 572–574 Krause’s corpuscle, 574 Langerhans cells, 574 Meissner’s corpuscle, 573 Pacinian corpuscle, 573 Ruffini’s corpuscle, 574 sebaceous oil glands, 574 sweat glands, 574

slash-and-burn technique, 689 sliding filament theory, 536–538 slime molds, 294, 297 small intestine

Celiac disease, 453 chyme, 451 duodenum, 453 gall bladder, 455 ileum, 453 intestinal cells, 453 jejunum, 453 macronutrients, 453 major accessory organs, 453–454 microvilli, 452 principal digestive enzymes, 455 smaller and smaller folds, 452

smoked/grilled meats, 459–460 sociobiology

aggression, 760 animal behavior (see animal behavior) definition, 751 dominance hierarchy, 759 group cooperation vs. selfish genes, 764–766 human and animal kindness, 760–761 intimidation displays, 760 kin selection, 761–762 learning (see learning) nature of animal society, 763–764 nuclear ant hill, 750 reciprocal altruism, 763 selfish-gene hypothesis, 760 submissive behavior, 760 types, behaviors, 751, 753 Vampire bats, Desmodus rotundus, 762, 763 in zebras, 758, 759

sodium-potassium pump, 107

ch22_idx.indd 839 11/12/15 6:03 pm

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840 Index

soluble fiber, 457 somatic cells, 201 somatic nervous system, 516 speciation

adaptive radiation, 246 allopatric, 245 biogeography, 255–256 embryos, vertebrates, 254 geographical arrangement, organisms, 255 homologous structures, 253, 254 molecular DNA comparisons, 255 reproductive isolation, 245 sympatric, 245, 246 vestigial organs, 253

specific-immunity methods, 570 cell-mediated immunity (see cell-mediated

immunity) humoral immunity (see humoral immunity) macrophage presentation, 584, 585

sperm donation advertisements, 625, 627 spies and corruption, immune defenses, 598–599 spinal cord, 516 “splitting (-lysis) of sugar (-glyco)”, 133 spongy bone, 542 statistics, 26 Stentor roeseli, 6 steroids, 59 stomach

anatomy, 449–450 cardiac/gastro-esophageal sphincter, 449 pepsin, 449 pepsinogen and HC1, 449, 451 pH, 449 pyloric sphincter, 449 rugae, 449

stomach and respiratory tract defenses, 579 stomata, 131 stroke, 473 submissive behavior, 760 sugar, 130–131 surface markings, 542, 544 surface-to-volume hypothesis, 102 surfactant, 494 sweat odor molecules, 103 symbiosis

commensalism, 670, 671 mutualism, 670

parasitism, 671 sympathetic nervous system, 517 synapse, 518, 520–521 systemic circuit, 477

T Taiga Hills in Canada, 694–695 tapeworms, 352 taxis, 287 taxonomy

animals, 16–18 Bacteria-Archaea, 14–15, 18–20 binomial nomenclature, 11, 14 biological classification of red maples, 14, 15 definition, 11, 12 Eukarya, 15–16, 18–19 kingdom, 14 plants, 16, 18 predicting sex behaviors, 12 scala naturae, 11, 13

Tay–Sachs disease, 99 telophase I, II, 207 temperate grasslands biome

Bison on a Prairie, 692, 693 detritus, 692 Tall prairie in eastern Kansas, 692, 693

terrestrial biomes Autumn in New York, 694 chaparral, 692, 693 deserts, 691 polar ice caps, 696–697 rainfall and temperature, 688 Savannas (see Savannas (tropical grasslands)) taiga, 694–695 temperate deciduous forests, 694 temperate grasslands, 692–694 tropical rainforests (see tropical rainforests) tundra regions, 695–696

tertiary consumers, 702 testcross, 200–201 thalamus, 531 thalassemia, 471 T-helper cells, 281 thermacidophiles, 290 thermodynamics, 121 thermoreceptors, 530 thoracic vertebrae, 546

ch22_idx.indd 840 11/12/15 6:03 pm

C R O O M , D O N A V A N 4 6 4 5 T S

Index 841

Three Gorges Dam Project, China, 735 thrombin, 472 thrombosis, 472–473 thrombus, 472–473 thylakoid membranes, 124, 128 thyroid-stimulating hormone (TSH), 556 thyroxine production, 556, 557 tight junctions, 100 tissue regeneration

fibroblasts, 589 fibrosis, 589 hierarchy, 591 scar tissue, 590

topography Asphalt, City Roofs, 687 mini-biomes, 687 mountains and valleys, 685 rain shadow deserts, 686–687

tracheophytes angiosperms, 317 Coast Redwood, 318, 319 evolution, seed, 316 fertilization, prothallus, 316, 317 gymnosperms, 317 Methuselah tree, 318, 319 ovary, 317 prothallus, 316 seedless plants, 316 seed plants, 316–317 vascular system, 316

trade winds, 722 transcription

DNA to mRNA, 174 elongation, 176 exons, 176 initiation, 176 introns, 176 RNA polymerase, 174 RNA processing, 176 termination, 176

transduction, 288 transfer RNA (tRNA), 176, 177 transformation, 289 transgenic tobacco plants, 222 transition of plants

advantages, 310 alternation of generations, 311

cotyledon, 323 fibrous root system, 323 green-algae ancestry, 311–312 life cycle, 314 monocots and dicots, 323–324 mutations, green algae, 309 phloem, 312 protection from predators, 313 root systems, 312 shoot system, 313 structure refinements, 312–314 taller trees and human pollution, 310 taproot, 323 transition, 309 xylem, 312

translation anti-codon, 178 dehydration synthesis, 178 elongation, 176, 180 exons, 176 folic acid depletion, 179 hemoglobin molecule, 179, 181 initiation, 176, 180 methionine tRNA, 177 mRNA to peptides, 178–179 rRNA, 177 start codons, 178 stop codons, 178–179 termination, 176, 180 vitamin D, 179

transmembrane proteins, 91 transmission electron microscope (TEM), 79, 80 transpirational pull, tree, 327, 329 transport proteins, 92 traveling nerve impulse, 518, 520–521 trichinosis, 352 trimethylamine N-oxide (TMAO), 437 tropical rainforests

biodiversity loss, 689 canopy layer, 688 deforestation, 689, 690 desertification, 689 destruction, 689 environmental hazards, Sahara, 689 epiphytes, 689 Expanding Desert, 689, 690 logging, mining and farming, 689

ch22_idx.indd 841 11/12/15 6:03 pm

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842 Index

tropical rainforests (continued) lush plant vegetation, 688 rainfall and temperature, 688 taxol, cancer therapy, 689

tropisms and hormones abscisic acid, 330 auxins, 331 cell division and growth, 331 cytokinins, 331 ethylene, 331 geotropism, 330 gibberellins, 331 leaf abscission, 330 phototropism, 330 red cabbage, Brassica oleracea, 331 thigmotropism, 330

turgor pressure, 106 twitch, 537 type I diabetes, 555 type II diabetes, 555

U universal donor, 216 universal recipient, 216 uric acids, 618–619 urinalysis, 616, 617 urinary system

excretion, 610 kidneys (see kidneys) osmoregulation, 610 water balance regulation, 610, 611

urogenital functions embryology (see embryology) female reproduction (see female reproduction) male reproductive system (see male reproductive

system) reproduction (see reproduction) stone baby, 608–609 urinary system (see urinary system)

US Geological Survey (USGS), 736

V vacuoles, 99 valence electrons, 47–48 Van Leeuwenhoek’s microscope, 78, 79 vascular system, 316 vegetarians, 705–706 vertebrates, 341

amphibians, 364–365 birds, 367–368 fish, 362–364 human evolution, 369–371 mammals, 368–369 reptiles, 365–366

viruses capsid, 273 docking, 273, 274 herpes virus, 277–278 intracellular parasite, 272 lysogenic life cycle, 275, 277 lytic life cycle, 275–276 myxovirus, 278–279 oncovirus, 280–281 papillomavirus, 279 retrovirus, 281–282 rhabdovirus, 278 rhinovirus, 278, 279 size of, 273, 275 species-specific, 273 typical, 273, 274

visible light, 125 vitamin A (retinol), 527 vitamin C, 431 vitreous humor, 525 vocal cords, 490

W waste vacuoles, 99 water cycle, 726–728 water-soluble vitamins, 427, 429–430 water-splitting photosystem, 128–129

ch22_idx.indd 842 11/12/15 6:03 pm

C R O O M , D O N A V A N 4 6 4 5 T S

Index 843

water transport and nutrients, plants cell respiration, 329 photosynthesis, 329 transpirational pull, tree, 327, 329 water potential, 328

Watson and Crick’s model, 158, 160, 162–164 westerlies, 722 white blood cells (WBC), 470 wind pollination, 322 worms

flatworms, 351–352 roundworms, 352 segmented worms, 353

X X chromosome, 213

Y Y chromosome, 210

Z zone of cell division, 326 zone of differentiation, 326 zone of elongation, 326 zygomatic bones, 544 zygote, 201

ch22_idx.indd 843 11/12/15 6:03 pm

C R O O M , D O N A V A N 4 6 4 5 T S

Ch 7.pdf
Ch 8.pdf
Ch 9.pdf
Ch 10.pdf

Unit 3: We Are Not Alone!��

Chapter 10: Moving on Land and in the Sea: Animal Diversity��

Ch 11.pdf
Ch 12.pdf

Chapter 12: Nutrition and Digestion��

Ch 13.pdf

Chapter 13: The Heart Lung Machine: Circulation and Respiration��

Ch 14.pdf

Chapter 14: Regulation: Nervous, Musculoskeletal, and Endocrine Systems��

Ch 15.pdf

Chapter 15: A War against the Enemy - Skin's Defenses and the Immune Attack��

Ch 16.pdf

Chapter 16: Urogenital Functions in Maintaining Continuity��

Ch 17.pdf
Ch 18.pdf
Ch 19.pdf

Unit 5: A Small Hole Sinks a Big Ship - Our Fragile Ecosystem��

Chapter 19: Biosphere: Life Links to Earth��

Ch 20.pdf

Unit 6: Biology and Society��

Chapter 20: The Evolution of Social Behavior: Sociobiology��

Ch 21_glossary.pdf

Glossary

Ch 22_index.pdf

Index