question

ahmedfadhil

Lecture_Presentation_15.pptx

Home >Biology homework help >question

Campbell Essential Biology, Seventh Edition, and Campbell Essential Biology with Physiology, Sixth Edition

Chapter 15

The Evolution of Microbial Life

PowerPoint® Lectures created by Edward J. Zalisko, Eric J. Simon, Jean L. Dickey, and Jane B. Reece

This is Not a Hot Tub! Specialized Archaeans are the Only Form of Life that Can Survive in this Water

Biology and Society: Our Invisible Inhabitants (1 of 2)

Your body contains trillions of individual cells.

Microorganisms residing in and on your body

primarily live in your skin, mouth, and nasal passages, and digestive and urogenital tracts and

weigh between 2 and 5 pounds.

Biology and Society: Our Invisible Inhabitants (2 of 2)

Scientists hypothesize that disrupting our microbial communities may

increase our susceptibility to infectious diseases,

predispose us to certain cancers, and

contribute to conditions such as

asthma and other allergies,

irritable bowel syndrome,

Crohn’s disease, and

autism.

Colorized Scanning Electron Micrograph of Bacteria (Red) Nestled Among Ciliated Cells of a Human Small Intestine (7000x)

Major Episodes in the History of Life (1 of 3)

Earth was formed about 4.6 billion years ago.

Prokaryotes, having cells that lack true nuclei,

evolved by about 3.5 billion years ago,

began oxygen production about 2.7 billion years ago as a result of photosynthesis by autotrophic prokaryotes,

lived alone for about 1.7 billion years, and

continue in great abundance today.

Student Misconceptions and Concerns

1. Students often have difficulty grasping the enormity of time. Perhaps surprisingly, many students do not understand that a billion is a thousand times greater than a million! Exercises and examples that help students comprehend such large numbers should be considered, so that students can understand these tremendous periods for evolutionary diversification. Here are just a few examples to consider:

a. If an earthquake or volcano erupts just once every thousand years or so, how often will this event occur in a million years? (One thousand times.) Note that what is rare to us becomes “common” in geologic terms.

b. Have students calculate the age of a human when they reach their 1 billionth second of life. (Starting with birth, the answer is 31.688 years.) 1,000,000,000 (seconds) = 31.688 (years) × 365.25 (days in a year) × 24 (hours in a day) × 60 (minutes) × 60 (seconds).

c. Then have students calculate how long it takes to live 1,000,000 seconds. (About 11.574 days.)

Teaching Tips

1. Consider making some sort of timeline to scale in a hallway, long laboratory, or the side of the lecture hall. Mark these proportional periods: The full length of time is 4.6 billion years. The percentages below were calculated using the textbook’s approximate dates for each of these events.

0.0%—Earth forms.

13%—Earth’s crust solidifies.

24%—The first life appears.

41%—Photosynthetic prokaryotes start producing an oxygen-rich atmosphere.

54%—The first eukaryotes appear.

74%—The first multicellular eukaryotes appear.

89%—Plants first invade land.

0.004%—Our species appears.

2. Students may need to be reminded about the reactive properties of oxygen. Note that rust is the result of oxygen interacting with iron and could be seen in the fossil record. Oxygen is highly reactive and could interfere with life-forming chemical processes today.

Some Major Episodes in the History of Life

Major Episodes in the History of Life (2 of 3)

Eukaryotes

are composed of one or more cells that contain nuclei and many other membrane-bound organelles absent in prokaryotic cells and

first evolved from a prokaryotic community, a host cell containing even smaller prokaryotes.

Mitochondria are descendants of smaller prokaryotes, as are the chloroplasts of plants and algae.

Multicellular eukaryotes first evolved at least 1.2 billion years ago.

Student Misconceptions and Concerns

c. Then have students calculate how long it takes to live 1,000,000 seconds. (About 11.574 days.)

Teaching Tips

0.0%—Earth forms.

13%—Earth’s crust solidifies.

24%—The first life appears.

41%—Photosynthetic prokaryotes start producing an oxygen-rich atmosphere.

54%—The first eukaryotes appear.

74%—The first multicellular eukaryotes appear.

89%—Plants first invade land.

0.004%—Our species appears.

Major Episodes in the History of Life (3 of 3)

The Cambrian explosion, about 541 million years ago, resulted in the evolution of all major animal body plans and all the major groups.

About 500 million years ago plants, fungi, and insects began to colonize the land.

At the end of the Mesozoic, 65 million years ago, flowering plants, birds, and mammals, including primates, began to dominate the landscape.

The origin of modern humans, Homo sapiens, occurred roughly 195,000 years ago.

Student Misconceptions and Concerns

c. Then have students calculate how long it takes to live 1,000,000 seconds. (About 11.574 days.)

Teaching Tips

0.0%—Earth forms.

13%—Earth’s crust solidifies.

24%—The first life appears.

41%—Photosynthetic prokaryotes start producing an oxygen-rich atmosphere.

54%—The first eukaryotes appear.

74%—The first multicellular eukaryotes appear.

89%—Plants first invade land.

0.004%—Our species appears.

The Origin of Life (1 of 2)

For the first several hundred million years of its existence, conditions on the young Earth were so harsh that it’s doubtful life could have originated, or if it did, it could not have survived.

Earth of 4 billion years ago was still violent.

Water vapor had condensed into oceans on the planet’s cooling surface.

Volcanic eruptions belched gases such as carbon dioxide (CO2), methane (CH4), and ammonia (NH3) and other nitrogen compounds into its atmosphere.

Student Misconceptions and Concerns

1. Students might not have considered that cells today are not “created from scratch.” Unlike the way a cake is prepared, or an automobile is constructed, life today is not known to form by the assembly of raw materials in the production of new cells.

2. Students may think that scientists have answers for all of life’s questions. Thus, they may appreciate knowing that many questions are inappropriate for science. Matters of aesthetics, morals, and political issues are often addressed by other methods of thinking. Questions such as “Was Picasso a better artist than Rembrandt?” “How can we help homeless people?” and “Should abortion be illegal?” are examples. This might be a good time to further distinguish between the process of science and other ways of knowing.

Teaching Tips

1. Consider pointing out the logic of spontaneous generation given the knowledge at the time. Piles of manure and rotting flesh left in the open would apparently produce flies. At that time, little was understood about eggs, sperm, and fertilization, making spontaneous generation a logical conclusion.

2. The four-stage hypothesis for the origin of life is a little like building cells “from the bottom up.” If your students do not remember details about biological molecules and basic cell structure, you may need to review these principles before addressing the stages.

3. The inherent property of bipolar molecules such as phospholipids to naturally form double membranes or micelles is worth discussing with your class. Because of these properties, membranes naturally heal as the hydrophobic phospholipid tails and polar heads align.

4. Much of the remaining chapter is descriptive of the traits and habits of single-celled prokaryotes and eukaryotes. Students might benefit from developing a series of charts that allow them to quickly review the properties of various subgroups (for example, the shapes of bacteria, the major modes of nutrition, and the various prokaryote subgroups).

Active Lecture Tips

1. At some point in the presentation of the four-stage hypothesis for the origin of life, students should be challenged to work in pairs or small groups to consider at what point “life” exists. Are self-replicating, RNA-based, membrane-bound structures alive? Discussing the evolution of the first cells helps clarify definitions of life.

An Artist’s Rendition of Conditions on Early Earth

The Origin of Life (2 of 2)

Life is an emergent property that arises from the specific arrangement and interactions of its molecular parts. In this way, life is an example of interactions within systems.

To learn how life originated from nonliving substances, biologists draw on research from the fields of chemistry, geology, and physics.

Student Misconceptions and Concerns

Teaching Tips

Active Lecture Tips

A Four-Stage Hypothesis for the Origin of Life

According to one hypothesis for the origin of life, the first organisms were products of chemical evolution in four stages:

synthesis of small organic molecules, such as amino acids and nucleotide monomers;

joining small molecules into macromolecules, including proteins and nucleic acids;

packaging these molecules into pre-cells; and

origin of self-replicating molecules that eventually made inheritance possible.

Student Misconceptions and Concerns

Teaching Tips

Active Lecture Tips

Stage 1: Synthesis of Organic Compounds (1 of 3)

The chemicals in Earth’s early atmosphere, such as water, methane, and ammonia, are all small, inorganic molecules.

In contrast, the structures and functions of life depend on more complex organic molecules, such as sugars, fatty acids, amino acids, and nucleotides, which are composed of the same elements.

Student Misconceptions and Concerns

Teaching Tips

Active Lecture Tips

Stage 1: Synthesis of Organic Compounds (2 of 3)

The first stage in the origin of life was the first to be extensively studied in the laboratory.

In 1953, Stanley Miller devised an apparatus to simulate conditions of early Earth.

After the apparatus had run for a week, an abundance of organic molecules essential for life, including amino acids, the monomers of proteins, had collected in the “sea.”

Many laboratories have since repeated Miller’s experiment using various atmospheric mixtures and have also produced organic compounds.

Student Misconceptions and Concerns

Teaching Tips

Active Lecture Tips

Apparatus Used to Simulate Early-Earth Chemistry in Urey and Miller’s Experiments

Stage 1: Synthesis of Organic Compounds (3 of 3)

Scientists are testing other hypotheses for the origin of organic molecules on Earth, including

the hypothesis that life may have begun in submerged volcanoes or deep-sea hydrothermal vents and

the hypothesis that meteorites were the source of Earth’s first organic molecules.

Student Misconceptions and Concerns

Teaching Tips

Active Lecture Tips

Stage 2: Abiotic Synthesis of Polymers

Once small organic molecules were present on Earth, how were they linked together to form polymers such as proteins and nucleic acids without the help of enzymes and other cellular equipment?

Researchers have brought about the polymerization of monomers to form polymers, such as proteins and nucleic acids, by dripping solutions of organic monomers onto hot sand, clay, or rock.

Student Misconceptions and Concerns

Teaching Tips

Active Lecture Tips

Stage 3: Formation of Pre-Cells

A key step in the origin of life would have been the isolation of a collection of organic molecules within a membrane.

Researchers have demonstrated that pre-cells could have formed spontaneously from fatty acids.

Student Misconceptions and Concerns

Teaching Tips

Active Lecture Tips

The Synthesis and Structure of a Triglyceride Molecule

Stage 4: Origin of Self-Replicating Molecules

Life is defined partly by the process of inheritance, which is based on self-replicating molecules.

This mechanism of information flow probably emerged gradually through a series of small changes to much simpler processes.

One hypothesis is that the first genes were short strands of RNA that replicated themselves without the assistance of proteins, perhaps using RNAs that can act as enzymes, called ribozymes.

Student Misconceptions and Concerns

Teaching Tips

Active Lecture Tips

A Hypothesis for the First Genes

Identifying Major Themes (1 of 3)

DNA in cells is transcribed into RNA and then translated to produce specific enzymes and other proteins.

Which major theme is illustrated by this action?

The relationship of structure to function

Information flow

Pathways that transform energy and matter

Interactions within biological systems

Evolution

Major Themes Answer—Information flow: Cells store information in DNA, which is used to make RNA, which is used to make proteins.

From Chemical Evolution to Darwinian Evolution

Natural selection would have begun to shape the properties of pre-cells that contained self-replicating RNA.

The pre-cells that contained genetic information that helped them reproduce more efficiently than others would have increased in number, passing their abilities on to later generations.

At some point during millions of years of selection, DNA, a more stable molecule, replaced RNA as the storehouse of genetic information, and protocells passed a fuzzy border to become true cells.

Student Misconceptions and Concerns

Teaching Tips

Active Lecture Tips

Prokaryotes: They’re Everywhere!

Prokaryotes

lived and evolved all alone on Earth for about 2 billion years,

are found wherever there is life,

have a collective biomass that is at least ten times that of all eukaryotes,

thrive in habitats too cold, too hot, too salty, too acidic, or too alkaline for any eukaryote, and

cause about half of all human diseases.

Student Misconceptions and Concerns

1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes more than a billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement.” After all, what eukaryotes can survive in the habitats of extremophiles?

2. Some students might equate the term bacteria with prokaryotes. A discussion of the domains Archaea and Bacteria will help with this distinction.

3. Many students struggle with concepts of size and volume. For example, they may not realize that a cube twice as wide as another has a volume eight times greater. The diameter of eukaryotic cells is about ten times greater than the diameter of prokaryotic cells. Thus, the volume of eukaryotic cells can be nearly 1,000 times greater than prokaryotic cells.

4. Students may think that hand washing and the use of soap, especially antibacterial soap, leaves the washed parts free of bacteria. The tremendous numbers of bacteria that typically remain and routinely reside on and within our bodies are little appreciated.

5. Students may believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination.

Teaching Tips

1. Bacteria and Archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the keywords “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity.

2. Some modeling clay (oil-based resists drying out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity.

3. The exponential growth of bacteria is like the growth represented in the correct answer to the classic math question “Would you rather be paid a million dollars for one month’s work or start out with just a penny for the first day of the month, but have your pay doubled every remaining day of that month?” Choosing the doubling amount pays off at about $10 million after just one month!

4. The ecological impact of prokaryotes is directly relevant to students' lives and can be of great interest to them. Consider a short Internet assignment in which each student must locate a recent article or website that addresses one aspect of this topic. (For example, exotoxins, endotoxins, bioremediation, and so on.) They can then write a short summary or e-mail the website address to you for your inspection.

5. Students might enjoy an assignment to determine where and to what extent bioremediation is being used to help address the devastating results of the 2010 BP oil spill in the Gulf of Mexico.

6. The website https://pubs.usgs.gov/fs/1995/0054/report.pdf is a good source for information on bioremediation.

7. The relatively new distinction between the prokaryote groups Bacteria and Archaea helps to illustrate the tentative nature of science. You might wish to point out to your students that science textbooks and our understanding of biological diversity are subject to change.

8. Students interested in global warming might research the estimated impact of methanogens in the digestive tract of herbivores raised by humans.

Active Lecture Tips

1. Some aspects of the complex structure and organization of biofilms are similar to eukaryotic tissues and organs. Challenge students to work in pairs to identify analogous components of biofilms and eukaryotic tissues and organs.

2. Students often have difficulty grasping geological timescales. Many students (and politicians) do not intuitively understand that a billion is a thousand times greater than a million. Consider having students work in pairs in your class to quickly calculate:

a. If an earthquake occurs once every 1,000 years, how often will it take place over a million years? (Answer: 1,000 times.) Note that what is rare to us becomes common in geological terms.

b. What is the age of a human when he or she reaches the one-billionth second of life (if we begin counting at birth, the answer is 31.688 years). Then have them calculate how long it takes to live 1,000,000 seconds. (Answer: about 11.6 days.)

A Window to Early Life?

They’re Everywhere!

However, prokaryotes also form our microbiota, the community of microorganisms that live in and on our bodies, which help to

supply essential vitamins,

allow us to extract nutrition from food molecules that we cannot otherwise digest,

decompose dead skin cells, and

guard against disease-causing intruders.

Prokaryotes also help decompose dead organisms and other waste materials, returning vital chemical elements such as nitrogen to the environment.

Student Misconceptions and Concerns

2. Some students might equate the term bacteria with prokaryotes. A discussion of the domains Archaea and Bacteria will help with this distinction.

Teaching Tips

5. Students might enjoy an assignment to determine where and to what extent bioremediation is being used to help address the devastating results of the 2010 BP oil spill in the Gulf of Mexico.

6. The website https://pubs.usgs.gov/fs/1995/0054/report.pdf is a good source for information on bioremediation.

8. Students interested in global warming might research the estimated impact of methanogens in the digestive tract of herbivores raised by humans.

Active Lecture Tips

a. If an earthquake occurs once every 1,000 years, how often will it take place over a million years? (Answer: 1,000 times.) Note that what is rare to us becomes common in geological terms.

Bacteria on the Point of a Pin

The Structure and Function of Prokaryotes

Prokaryotic cells

lack a membrane-enclosed nucleus,

lack other membrane-enclosed organelles,

typically have cell walls exterior to their plasma membranes, and

display a remarkable range of diversity.

Student Misconceptions and Concerns

2. Some students might equate the term bacteria with prokaryotes. A discussion of the domains Archaea and Bacteria will help with this distinction.

Teaching Tips

5. Students might enjoy an assignment to determine where and to what extent bioremediation is being used to help address the devastating results of the 2010 BP oil spill in the Gulf of Mexico.

6. The website https://pubs.usgs.gov/fs/1995/0054/report.pdf is a good source for information on bioremediation.

8. Students interested in global warming might research the estimated impact of methanogens in the digestive tract of herbivores raised by humans.

Active Lecture Tips

a. If an earthquake occurs once every 1,000 years, how often will it take place over a million years? (Answer: 1,000 times.) Note that what is rare to us becomes common in geological terms.

Comparing Prokaryotic and Eukaryotic Cells

A Prokaryotic Cell

An Idealized Animal Cell and Plant Cell

Prokaryotic Forms (1 of 2)

The three most common shapes of prokaryotes are

spherical, called cocci (singular, coccus),

rod-shaped, called bacilli (singular, bacillus), and

spiral or curved, including spirochetes.

Although all prokaryotes are unicellular, the cells of some species usually exist as groups of two or more cells.

About half of all prokaryotic species are mobile. Many of those that travel have one or more flagella.

Student Misconceptions and Concerns

2. Some students might equate the term bacteria with prokaryotes. A discussion of the domains Archaea and Bacteria will help with this distinction.

Teaching Tips

5. Students might enjoy an assignment to determine where and to what extent bioremediation is being used to help address the devastating results of the 2010 BP oil spill in the Gulf of Mexico.

6. The website https://pubs.usgs.gov/fs/1995/0054/report.pdf is a good source for information on bioremediation.

8. Students interested in global warming might research the estimated impact of methanogens in the digestive tract of herbivores raised by humans.

Active Lecture Tips

a. If an earthquake occurs once every 1,000 years, how often will it take place over a million years? (Answer: 1,000 times.) Note that what is rare to us becomes common in geological terms.

Three Common Shapes of Prokaryotic Cells

A Diversity of Prokaryotic Shapes and Sizes

Prokaryotic Forms (2 of 2)

In many natural environments, prokaryotes attach to surfaces in a highly organized colony called a biofilm, which may consist of one or several species of prokaryotes.

Biofilms can form on almost any type of surface, such as rocks, organic material (including living tissue), metal, and plastic.

A biofilm known as dental plaque (Figure 15.9) can cause tooth decay.

Biofilms are common among bacteria that cause disease in humans.

Student Misconceptions and Concerns

2. Some students might equate the term bacteria with prokaryotes. A discussion of the domains Archaea and Bacteria will help with this distinction.

Teaching Tips

5. Students might enjoy an assignment to determine where and to what extent bioremediation is being used to help address the devastating results of the 2010 BP oil spill in the Gulf of Mexico.

6. The website https://pubs.usgs.gov/fs/1995/0054/report.pdf is a good source for information on bioremediation.

8. Students interested in global warming might research the estimated impact of methanogens in the digestive tract of herbivores raised by humans.

Active Lecture Tips

a. If an earthquake occurs once every 1,000 years, how often will it take place over a million years? (Answer: 1,000 times.) Note that what is rare to us becomes common in geological terms.

Dental Plaque, a Biofilm that Forms on Teeth

Household Sponge Contaminated with Bacteria (Red, Green, Yellow, and Blue Objects in this Colorized Micrograph)

Prokaryotic Reproduction

Many prokaryotes can reproduce by dividing in half by binary fission and at very high rates if conditions are favorable. But few prokaryotic populations can sustain exponential growth.

Environments are usually limiting in resources such as food and space. Prokaryotes also produce metabolic waste products that may eventually pollute the colony’s environment.

Some prokaryotes can survive very harsh conditions by forming endospores, thick-coated, protective cells produced within the prokaryotic cell that can survive trauma and extreme temperatures.

Student Misconceptions and Concerns

2. Some students might equate the term bacteria with prokaryotes. A discussion of the domains Archaea and Bacteria will help with this distinction.

Teaching Tips

5. Students might enjoy an assignment to determine where and to what extent bioremediation is being used to help address the devastating results of the 2010 BP oil spill in the Gulf of Mexico.

6. The website https://pubs.usgs.gov/fs/1995/0054/report.pdf is a good source for information on bioremediation.

8. Students interested in global warming might research the estimated impact of methanogens in the digestive tract of herbivores raised by humans.

Active Lecture Tips

a. If an earthquake occurs once every 1,000 years, how often will it take place over a million years? (Answer: 1,000 times.) Note that what is rare to us becomes common in geological terms.

Prokaryotic Nutrition (1 of 3)

The prokaryotic pathways that transform energy and matter are far more diverse than those of eukaryotes.

Some species harvest energy from inorganic substances such as ammonia (NH3) and hydrogen sulfide (H2S).

The metabolic talents of prokaryotes make them excellent symbiotic partners with animals, plants, and fungi.

Student Misconceptions and Concerns

2. Some students might equate the term bacteria with prokaryotes. A discussion of the domains Archaea and Bacteria will help with this distinction.

Teaching Tips

5. Students might enjoy an assignment to determine where and to what extent bioremediation is being used to help address the devastating results of the 2010 BP oil spill in the Gulf of Mexico.

6. The website https://pubs.usgs.gov/fs/1995/0054/report.pdf is a good source for information on bioremediation.

8. Students interested in global warming might research the estimated impact of methanogens in the digestive tract of herbivores raised by humans.

Active Lecture Tips

a. If an earthquake occurs once every 1,000 years, how often will it take place over a million years? (Answer: 1,000 times.) Note that what is rare to us becomes common in geological terms.

Two Methods of Obtaining Energy and Carbon

Identifying Major Themes (2 of 3)

Prokaryotic metabolic processes are far more diverse than those of eukaryotes.

Which major theme is illustrated by this action?

The relationship of structure to function

Information flow

Pathways that transform energy and matter

Interactions within biological systems

Evolution

Major Themes Answer—Pathways that transform energy and matter: When prokaryotes break down complex molecules to simpler ones, they transform energy and matter.

Prokaryotic Nutrition (2 of 3)

Symbiosis (“living together”) is a close association between organisms of two or more species. For example, many of the animals that inhabit hydrothermal vent communities, such as the giant tube worm shown in Figure 15.12, harbor sulfur bacteria within their bodies.

The animals absorb sulfur compounds from the water. The bacteria use the compounds as an energy source to convert CO2from seawater into organic molecules that, in turn, provide food for their hosts.

Student Misconceptions and Concerns

2. Some students might equate the term bacteria with prokaryotes. A discussion of the domains Archaea and Bacteria will help with this distinction.

Teaching Tips

5. Students might enjoy an assignment to determine where and to what extent bioremediation is being used to help address the devastating results of the 2010 BP oil spill in the Gulf of Mexico.

6. The website https://pubs.usgs.gov/fs/1995/0054/report.pdf is a good source for information on bioremediation.

8. Students interested in global warming might research the estimated impact of methanogens in the digestive tract of herbivores raised by humans.

Active Lecture Tips

a. If an earthquake occurs once every 1,000 years, how often will it take place over a million years? (Answer: 1,000 times.) Note that what is rare to us becomes common in geological terms.

Giant Tube Worm

Prokaryotic Nutrition (3 of 3)

In addition to photosynthesis, many cyanobacteria are also capable of nitrogen fixation, the process of converting atmospheric nitrogen (N2) into a form usable by plants.

Symbiosis with cyanobacteria gives plants such as the water fern Azolla an advantage in nitrogen-poor environments.

This tiny, floating plant has been used to boost rice production for more than a thousand years.

Student Misconceptions and Concerns

2. Some students might equate the term bacteria with prokaryotes. A discussion of the domains Archaea and Bacteria will help with this distinction.

Teaching Tips

5. Students might enjoy an assignment to determine where and to what extent bioremediation is being used to help address the devastating results of the 2010 BP oil spill in the Gulf of Mexico.

6. The website https://pubs.usgs.gov/fs/1995/0054/report.pdf is a good source for information on bioremediation.

8. Students interested in global warming might research the estimated impact of methanogens in the digestive tract of herbivores raised by humans.

Active Lecture Tips

a. If an earthquake occurs once every 1,000 years, how often will it take place over a million years? (Answer: 1,000 times.) Note that what is rare to us becomes common in geological terms.

Azolla (Water Fern, Inset) Floating in Rice Paddy

The Ecological Impact of Prokaryotes: Prokaryotes and Chemical Recycling

As a result of their nutritional diversity, prokaryotes perform a variety of ecological services that are essential to our well-being.

Life depends on the recycling of chemical elements between the biological and physical components of ecosystems, an example of interactions within biological systems.

Prokaryotes play essential roles in these chemical cycles.

Prokaryotes also promote the breakdown of organic wastes and dead organisms.

Student Misconceptions and Concerns

2. Some students might equate the term bacteria with prokaryotes. A discussion of the domains Archaea and Bacteria will help with this distinction.

Teaching Tips

5. Students might enjoy an assignment to determine where and to what extent bioremediation is being used to help address the devastating results of the 2010 BP oil spill in the Gulf of Mexico.

6. The website https://pubs.usgs.gov/fs/1995/0054/report.pdf is a good source for information on bioremediation.

8. Students interested in global warming might research the estimated impact of methanogens in the digestive tract of herbivores raised by humans.

Active Lecture Tips

a. If an earthquake occurs once every 1,000 years, how often will it take place over a million years? (Answer: 1,000 times.) Note that what is rare to us becomes common in geological terms.

Putting Prokaryotes to Work

Bioremediation is the use of organisms to remove pollutants from water, air, or soil.

One example of bioremediation is the use of prokaryotic decomposers to treat our sewage (Figure 15.14).

Bioremediation has also become an important tool for cleaning up toxic chemicals released into the soil and water by industrial processes. In Figure 15.15, an airplane is spraying chemical dispersants on oil from the disastrous 2010 Deepwater Horizon spill in the Gulf of Mexico.

Checkpoint: How do bacteria help restore the atmospheric CO2 required by plants for photosynthesis?

Checkpoint response: By decomposing the organic molecules of dead organisms and organic refuse such as leaf litter, bacteria release carbon from the organic matter in the form of CO2.

Student Misconceptions and Concerns

2. Some students might equate the term bacteria with prokaryotes. A discussion of the domains Archaea and Bacteria will help with this distinction.

Teaching Tips

5. Students might enjoy an assignment to determine where and to what extent bioremediation is being used to help address the devastating results of the 2010 BP oil spill in the Gulf of Mexico.

6. The website https://pubs.usgs.gov/fs/1995/0054/report.pdf is a good source for information on bioremediation.

8. Students interested in global warming might research the estimated impact of methanogens in the digestive tract of herbivores raised by humans.

Active Lecture Tips

a. If an earthquake occurs once every 1,000 years, how often will it take place over a million years? (Answer: 1,000 times.) Note that what is rare to us becomes common in geological terms.

Putting Microbes to Work in Sewage Treatment Facilities

Spraying Chemical Dispersants on an Oil Spill in the Gulf of Mexico

The Two Main Branches of Prokaryotic Evolution: Bacteria and Archaea (1 of 2)

By comparing diverse prokaryotes at the molecular level, biologists have identified two major branches of prokaryotic evolution:

Bacteria and

Archaea.

Thus, life is organized into three domains:

Bacteria,

Archaea, and

Eukarya.

Student Misconceptions and Concerns

2. Some students might equate the term bacteria with prokaryotes. A discussion of the domains Archaea and Bacteria will help with this distinction.

Teaching Tips

5. Students might enjoy an assignment to determine where and to what extent bioremediation is being used to help address the devastating results of the 2010 BP oil spill in the Gulf of Mexico.

6. The website https://pubs.usgs.gov/fs/1995/0054/report.pdf is a good source for information on bioremediation.

8. Students interested in global warming might research the estimated impact of methanogens in the digestive tract of herbivores raised by humans.

Active Lecture Tips

a. If an earthquake occurs once every 1,000 years, how often will it take place over a million years? (Answer: 1,000 times.) Note that what is rare to us becomes common in geological terms.

The Two Main Branches of Prokaryotic Evolution: Bacteria and Archaea (2 of 2)

Archaea are abundant in many habitats, including places where few other organisms can survive.

One group of Archaea, the extreme thermophiles (“heat lovers”), live in very hot water.

Another group is the extreme halophiles (“salt lovers”), Archaea that thrive in salty environments.

A third group of Archaea are methanogens, which live in anaerobic (oxygen-free) environments and give off methane as a waste product.

They are abundant in the mud at the bottom of lakes.

Great numbers inhabit the digestive tracts of animals.

Student Misconceptions and Concerns

2. Some students might equate the term bacteria with prokaryotes. A discussion of the domains Archaea and Bacteria will help with this distinction.

Teaching Tips

5. Students might enjoy an assignment to determine where and to what extent bioremediation is being used to help address the devastating results of the 2010 BP oil spill in the Gulf of Mexico.

6. The website https://pubs.usgs.gov/fs/1995/0054/report.pdf is a good source for information on bioremediation.

8. Students interested in global warming might research the estimated impact of methanogens in the digestive tract of herbivores raised by humans.

Active Lecture Tips

a. If an earthquake occurs once every 1,000 years, how often will it take place over a million years? (Answer: 1,000 times.) Note that what is rare to us becomes common in geological terms.

Heat-loving Archaea

Pipes for Collecting Gas Generated by Methanogenic Archaea from a Landfill

Bacteria that Cause Disease (1 of 3)

Bacteria and other organisms that cause disease are called pathogens. Most pathogenic bacteria cause disease by producing a poison.

Exotoxins are proteins that bacterial cells secrete into their environment.

Endotoxins are chemical components of the outer membrane of certain bacteria. All endotoxins induce the same general symptoms: fever, aches, and sometimes a dangerous drop in blood pressure (septic shock).

Checkpoint: How can an exotoxin be harmful even after bacteria are killed?

Checkpoint response: Exotoxins are secreted poisons that can remain harmful even when the bacteria that secrete them are gone.

Student Misconceptions and Concerns

2. Some students might equate the term bacteria with prokaryotes. A discussion of the domains Archaea and Bacteria will help with this distinction.

Teaching Tips

5. Students might enjoy an assignment to determine where and to what extent bioremediation is being used to help address the devastating results of the 2010 BP oil spill in the Gulf of Mexico.

6. The website https://pubs.usgs.gov/fs/1995/0054/report.pdf is a good source for information on bioremediation.

8. Students interested in global warming might research the estimated impact of methanogens in the digestive tract of herbivores raised by humans.

Active Lecture Tips

a. If an earthquake occurs once every 1,000 years, how often will it take place over a million years? (Answer: 1,000 times.) Note that what is rare to us becomes common in geological terms.

Bacteria that Cause Meningitis

Bacteria that Cause Disease (2 of 3)

Sanitation is generally the most effective way to prevent bacterial disease. The installation of water treatment and sewage systems continues to be a public health priority throughout the world.

Antibiotics have been discovered that can cure most bacterial diseases. However, resistance to widely used antibiotics has evolved in many of these pathogens.

A third defense against bacterial disease is education. For example, Lyme disease is caused by a spirochete bacterium carried by ticks.

Student Misconceptions and Concerns

2. Some students might equate the term bacteria with prokaryotes. A discussion of the domains Archaea and Bacteria will help with this distinction.

Teaching Tips

5. Students might enjoy an assignment to determine where and to what extent bioremediation is being used to help address the devastating results of the 2010 BP oil spill in the Gulf of Mexico.

6. The website https://pubs.usgs.gov/fs/1995/0054/report.pdf is a good source for information on bioremediation.

8. Students interested in global warming might research the estimated impact of methanogens in the digestive tract of herbivores raised by humans.

Active Lecture Tips

a. If an earthquake occurs once every 1,000 years, how often will it take place over a million years? (Answer: 1,000 times.) Note that what is rare to us becomes common in geological terms.

Lyme Disease, a Bacterial Disease Transmitted by Ticks

Bacteria that Cause Disease (3 of 3)

The potential of some pathogens to cause serious harm has led to their use as biological weapons.

One of the greatest threats is from endospores of the bacterium that causes anthrax. When anthrax endospores enter the lungs, they germinate, and the bacteria multiply, producing an exotoxin that eventually accumulates to lethal levels in the blood.

Another bacterium considered to have dangerous potential as a weapon is Clostridium botulinum. Unlike other biological agents, the weapon form of C. botulinum is the exotoxin it produces, botulinum, rather than the living microbes.

Student Misconceptions and Concerns

2. Some students might equate the term bacteria with prokaryotes. A discussion of the domains Archaea and Bacteria will help with this distinction.

Teaching Tips

5. Students might enjoy an assignment to determine where and to what extent bioremediation is being used to help address the devastating results of the 2010 BP oil spill in the Gulf of Mexico.

6. The website https://pubs.usgs.gov/fs/1995/0054/report.pdf is a good source for information on bioremediation.

8. Students interested in global warming might research the estimated impact of methanogens in the digestive tract of herbivores raised by humans.

Active Lecture Tips

a. If an earthquake occurs once every 1,000 years, how often will it take place over a million years? (Answer: 1,000 times.) Note that what is rare to us becomes common in geological terms.

The Process of Science: Are Intestinal Microbiota to Blame for Obesity? (1 of 3)

Background:

Our bodies are home to trillions of bacteria that cause no harm or are even beneficial to our health. Because our intestinal microbes are known to be involved in some aspects of food processing, researchers speculate that they might be involved in obesity.

Researchers routinely test hypotheses in animal models before using human subjects. Mice that have been raised in germ-free conditions have no microbiota.

Student Misconceptions and Concerns

2. Some students might equate the term bacteria with prokaryotes. A discussion of the domains Archaea and Bacteria will help with this distinction.

Teaching Tips

5. Students might enjoy an assignment to determine where and to what extent bioremediation is being used to help address the devastating results of the 2010 BP oil spill in the Gulf of Mexico.

6. The website https://pubs.usgs.gov/fs/1995/0054/report.pdf is a good source for information on bioremediation.

8. Students interested in global warming might research the estimated impact of methanogens in the digestive tract of herbivores raised by humans.

Active Lecture Tips

a. If an earthquake occurs once every 1,000 years, how often will it take place over a million years? (Answer: 1,000 times.) Note that what is rare to us becomes common in geological terms.

The Process of Science: Are Intestinal Microbiota to Blame for Obesity? (2 of 3)

Method:

Researchers recruited four pairs of human female twins to donate their microbiota for the experiment. In each pair of twins, one was obese and the other was lean.

Researchers extracted the microbes from the feces of each individual and then transplanted these microbiota into separate groups of lean, germ-free mice.

Student Misconceptions and Concerns

2. Some students might equate the term bacteria with prokaryotes. A discussion of the domains Archaea and Bacteria will help with this distinction.

Teaching Tips

5. Students might enjoy an assignment to determine where and to what extent bioremediation is being used to help address the devastating results of the 2010 BP oil spill in the Gulf of Mexico.

6. The website https://pubs.usgs.gov/fs/1995/0054/report.pdf is a good source for information on bioremediation.

8. Students interested in global warming might research the estimated impact of methanogens in the digestive tract of herbivores raised by humans.

Active Lecture Tips

a. If an earthquake occurs once every 1,000 years, how often will it take place over a million years? (Answer: 1,000 times.) Note that what is rare to us becomes common in geological terms.

The Process of Science: Are Intestinal Microbiota to Blame for Obesity? (3 of 3)

Results:

Mice that received microbiota from an obese donor became more obese.

Mice that received microbiota from a lean donor remained lean.

Is a microbe-based cure for obesity just around the corner? It’s not likely. The experiment described here—and many similar experiments—represents an early stage of scientific investigation. A great deal more research is needed to determine whether our microbial residents are responsible for obesity.

Student Misconceptions and Concerns

2. Some students might equate the term bacteria with prokaryotes. A discussion of the domains Archaea and Bacteria will help with this distinction.

Teaching Tips

5. Students might enjoy an assignment to determine where and to what extent bioremediation is being used to help address the devastating results of the 2010 BP oil spill in the Gulf of Mexico.

6. The website https://pubs.usgs.gov/fs/1995/0054/report.pdf is a good source for information on bioremediation.

8. Students interested in global warming might research the estimated impact of methanogens in the digestive tract of herbivores raised by humans.

Active Lecture Tips

a. If an earthquake occurs once every 1,000 years, how often will it take place over a million years? (Answer: 1,000 times.) Note that what is rare to us becomes common in geological terms.

Experiment to Investigate the Effect of Microbiota on Body Composition

Protists (1 of 3)

The fossil record indicates that eukaryotes evolved from prokaryotes around 2 billion years ago.

These primal eukaryotes were the predecessors of the great variety of modern protists and ancestral to all other eukaryotes, plants, fungi, and animals.

The term protists is not a taxonomic category.

Hypotheses about protist phylogeny (and thus, classification) are changing rapidly as new information causes scientists to revise their ideas.

Thus, protist is a catch-all category that includes all eukaryotes that are not fungi, animals, or plants. Most, but not all, protists are unicellular.

Student Misconceptions and Concerns

1. Students may need to be reminded that most prokaryotes are about a tenth the diameter of eukaryotic cells. Thus, by the process of endosymbiosis, symbiotic bacteria could easily fit within larger eukaryotic cells.

2. Students might think of protists as “simple” organisms in comparison to our own complex multicellular bodies. However, within a single cell, protists must carry out all the basic functions performed by the set of specialized cells that collectively form the bodies of plants and animals.

3. Students might immediately expect that all symbiotic relationships benefit both members. Consider noting that parasitism is a type of symbiotic relationship in which one member is harmed.

4. Students often mistakenly think that chloroplasts are a substitute for mitochondria in plant cells. They might think that cells either have mitochondria or they have chloroplasts. You might challenge this thinking by asking how plant cells generate ATP at night.

Teaching Tips

1. The reconsideration of the classification of protists further illustrates the tentative nature of science, in which no information is considered final. You may point out that new molecular tools have allowed us to understand new levels of diversity and required reconsiderations of classification schemes.

2. The evidence that mitochondria and chloroplasts evolved from free-living prokaryotes is further supported by the small prokaryote size of these organelles in eukaryotes. Mitochondria and chloroplasts are therefore helpful in comparing the general size of eukaryotic and prokaryotic cells. You might think of these organelles as built-in comparisons.

3. The extensive diversity of protists permits endless opportunities for students to select an example of a protist and report on it in some way. For example, students can sketch “their protist,” find web resources, and/or plot its position in a classification of protists. These short exercises in content “ownership” enable students to develop a greater depth of understanding and increase interaction with the subject.

4. Mitochondrial DNA is widely used to analyze evolutionary relationships. Challenge students to explain why mitochondrial DNA might be better than nuclear DNA to trace these relationships. (Nuclear DNA in sexually reproducing organisms reflects a mixture of the parents’ genetic material. Mitochondrial DNA is typically inherited just from the mother, and therefore only changes by the accumulation of mutations.)

5. This is a very exciting time for new scientists entering the field of renewable fuels. You may wish to share with your students how they can still get in on the “ground floor” of these emerging energy fields. Sometimes instructors need to help students imagine a place for them in the future of science.

6. The evolution of multicellularity requires the subdivision of labor in ways similar to modern human societies. Providing structure, acquiring and processing food, and facilitating movement are specialized functions of cells as well as members of society.

Active Lecture Tips

1. See the Activity A Chance Discovery of Endosymbiosis? A Case Study on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

Protists (2 of 3)

One mark of protist diversity is the variety of ways they obtain their nutrition.

Photosynthetic protists belong to an informal category called algae (singular, alga), which also includes cyanobacteria.

Other protists are heterotrophs, acquiring their food from other organisms. Some are fungus-like and obtain organic molecules by absorption. Still others are parasitic. A parasite derives its nutrition from a living host, which is harmed by the interaction.

Other protists are mixotrophs, capable of photosynthesis and heterotrophy.

Student Misconceptions and Concerns

3. Students might immediately expect that all symbiotic relationships benefit both members. Consider noting that parasitism is a type of symbiotic relationship in which one member is harmed.

Teaching Tips

Active Lecture Tips

Protist Modes of Nutrition

Protists (3 of 3)

Protist habitats are also diverse.

Most protists are aquatic, living in oceans, lakes, and ponds.

Some are found almost anywhere there is moisture, including terrestrial habitats such as damp soil and leaf litter.

Others are symbionts that reside in the bodies of various host organisms.

Because the classification of protists remains a work in progress, our brief survey of protists is not organized to correspond with any hypothesis about phylogeny.

Student Misconceptions and Concerns

3. Students might immediately expect that all symbiotic relationships benefit both members. Consider noting that parasitism is a type of symbiotic relationship in which one member is harmed.

Teaching Tips

Active Lecture Tips

Video: Euglena Motion

https://mediaplayer.pearsoncmg.com/assets/secs-euglena

Protozoans (1 of 5)

Protists that live primarily by ingesting food are called protozoans.

Protozoans thrive in all types of aquatic environments. Most species eat bacteria or other protozoans, but some can absorb nutrients dissolved in the water.

Protozoans that live as parasites in animals, though in the minority, cause some of the world’s most harmful diseases.

Checkpoint: How might symbiosis with an oxygen-using prokaryote benefit the prokaryotic host cell?

Checkpoint response: The host would benefit if its symbiont used oxygen to release large amounts of energy in the form of ATP from organic molecules (the role of mitochondria in eukaryotic cells).

Student Misconceptions and Concerns

3. Students might immediately expect that all symbiotic relationships benefit both members. Consider noting that parasitism is a type of symbiotic relationship in which one member is harmed.

Teaching Tips

Active Lecture Tips

A Diversity of Protozoans

Protozoans (2 of 5)

Flagellates are protozoans that move by means of one or more flagella.

Most species are free-living (nonparasitic).

However, this group also includes some nasty parasites that make people sick. An example is Giardia, a common waterborne parasite that causes severe diarrhea.

Other flagellates live symbiotically in a relationship that benefits both partners. Flagellates that reside in the termite’s digestive tract break down the cellulose into simpler molecules, sharing the bounty with their hosts.

Student Misconceptions and Concerns

3. Students might immediately expect that all symbiotic relationships benefit both members. Consider noting that parasitism is a type of symbiotic relationship in which one member is harmed.

Teaching Tips

Active Lecture Tips

Protozoans (3 of 5)

Amoebas are characterized by great flexibility in their body shape and the absence of permanent organelles for locomotion.

Most species move and feed by means of pseudopodia (singular, pseudopodium), temporary extensions of the cell.

Other protozoans with pseudopodia include the forams, which have shells.

Student Misconceptions and Concerns

3. Students might immediately expect that all symbiotic relationships benefit both members. Consider noting that parasitism is a type of symbiotic relationship in which one member is harmed.

Teaching Tips

Active Lecture Tips

Video: Amoeba

https://mediaplayer.pearsoncmg.com/assets/secs-amoeba

Video: Amoeba Pseudopodia

https://mediaplayer.pearsoncmg.com/assets/secs-amoeba-pseudopodia

Protozoans (4 of 5)

Apicomplexans are all parasitic and some cause serious human diseases.

Plasmodium is the parasite that causes malaria.

Toxoplasma requires a feline host to complete its complex life cycle.

People can become infected by handling cat litter of outdoor cats, but they don’t become sick because the immune system keeps the parasite in check.

But a woman who is newly infected with Toxoplasma during pregnancy can pass the parasite to her unborn child, who may suffer damage to the nervous system as a result.

Student Misconceptions and Concerns

3. Students might immediately expect that all symbiotic relationships benefit both members. Consider noting that parasitism is a type of symbiotic relationship in which one member is harmed.

Teaching Tips

Active Lecture Tips

Protozoans (5 of 5)

Ciliates are protozoans that

are named for their hairlike structures called cilia, which provide movement of the protist and sweep food into the protist’s “mouth,”

are mostly free-living (nonparasitic), such as the freshwater ciliate Paramecium, and

include heterotrophs and mixotrophs.

Student Misconceptions and Concerns

3. Students might immediately expect that all symbiotic relationships benefit both members. Consider noting that parasitism is a type of symbiotic relationship in which one member is harmed.

Teaching Tips

Active Lecture Tips

Video: Paramecium Cilia

https://mediaplayer.pearsoncmg.com/assets/secs-paramecium-cilia

Slime Molds (1 of 3)

Slime molds are multicellular protists related to amoebas and feed on dead plant material.

Although slime molds were once classified as fungi, DNA analysis showed that they arose from different evolutionary lineages.

Two distinct types of slime molds have been identified:

plasmodial slime molds and

cellular slime molds.

Student Misconceptions and Concerns

3. Students might immediately expect that all symbiotic relationships benefit both members. Consider noting that parasitism is a type of symbiotic relationship in which one member is harmed.

Teaching Tips

Active Lecture Tips

Slime Molds (2 of 3)

Plasmodial slime molds have a feeding body that is an amoeboid mass called a plasmodium that extends pseudopodia among the leaf litter and other decaying material on a forest floor.

The weblike form of the plasmodium enlarges the organism’s surface area, increasing its contact with food, water, and oxygen—an example of structure and function.

Student Misconceptions and Concerns

3. Students might immediately expect that all symbiotic relationships benefit both members. Consider noting that parasitism is a type of symbiotic relationship in which one member is harmed.

Teaching Tips

Active Lecture Tips

Plasmodial Slime Mold

Identifying Major Themes (3 of 3)

The weblike form of the plasmodium enlarges the organism’s surface area, increasing its contact with food, water, and oxygen.

Which major theme is illustrated by this action?

The relationship of structure to function

Information flow

Pathways that transform energy and matter

Interactions within biological systems

Evolution

Major Themes Answer—Relationship of structure to function: The web form increases the surface area, which facilitates absorption of necessary resources.

Slime Molds (3 of 3)

In cellular slime molds, the feeding stage consists of solitary amoeboid cells that function independently of each other rather than a plasmodium.

But when food is in short supply, the amoeboid cells swarm together to form a slug-like colony that moves and functions as a single unit.

Some of the cells then dry up and form a stalk supporting a reproductive structure in which other cells develop into spores.

Student Misconceptions and Concerns

3. Students might immediately expect that all symbiotic relationships benefit both members. Consider noting that parasitism is a type of symbiotic relationship in which one member is harmed.

Teaching Tips

Active Lecture Tips

Unicellular and Colonial Algae (1 of 3)

Algae are protists and cyanobacteria whose photosynthesis supports food chains in freshwater and marine ecosystems.

Researchers are currently trying to harness their ability to convert light energy to chemical energy for another purpose—to produce biofuels.

Student Misconceptions and Concerns

3. Students might immediately expect that all symbiotic relationships benefit both members. Consider noting that parasitism is a type of symbiotic relationship in which one member is harmed.

Teaching Tips

Active Lecture Tips

Unicellular and Colonial Algae (2 of 3)

Many unicellular algae are components of phytoplankton, the mostly microscopic photosynthetic organisms that drift near the surfaces of ponds, lakes, and oceans.

Each dinoflagellate species has a characteristic shape reinforced by external plates made of cellulose.

Diatoms have glassy cell walls containing silica, the mineral used to make glass.

Green algae are named for their grass-green chloroplasts.

Student Misconceptions and Concerns

3. Students might immediately expect that all symbiotic relationships benefit both members. Consider noting that parasitism is a type of symbiotic relationship in which one member is harmed.

Teaching Tips

Active Lecture Tips

Unicellular and Colonial Algae (3 of 3)

Video: Dinoflagellate

https://mediaplayer.pearsoncmg.com/assets/secs-dinoflagellate

Video: Volvox Flagella

https://mediaplayer.pearsoncmg.com/assets/secs-volvox-flagella

Seaweeds

Seaweeds are large, multicellular marine algae, that grow on rocky shores, are only similar to plants because of convergent evolution, and are most closely related to unicellular algae.

Seaweeds are classified into three different groups, based partly on the types of pigments present in their chloroplasts:

green algae,

red algae, and

brown algae (some of which are known as kelp).

Student Misconceptions and Concerns

3. Students might immediately expect that all symbiotic relationships benefit both members. Consider noting that parasitism is a type of symbiotic relationship in which one member is harmed.

Teaching Tips

Active Lecture Tips

The Three Major Groups of Seaweeds

Evolution Connection: The Sweet Life of Streptococcus Mutans (1 of 3)

A biofilm-forming species of bacteria called Streptococcus mutans thrives in the anaerobic environment found in tiny crevices in tooth enamel.

The bacteria use sucrose (table sugar) to make a sticky polysaccharide, glue themselves in place, and build up thick deposits of plaque.

Within this fortress, S. mutans ferments sugars to obtain energy, releasing lactic acid as a by-product. The acid attacks tooth enamel and eventually eats through it. Other bacteria then use the entrance and infect the soft tissue in the interior of the tooth.

Student Misconceptions and Concerns

3. Students might immediately expect that all symbiotic relationships benefit both members. Consider noting that parasitism is a type of symbiotic relationship in which one member is harmed.

Teaching Tips

Active Lecture Tips

Checking the effects of Streptococcus mutans

Evolution Connection: The Sweet Life of Streptococcus Mutans (2 of 3)

Studies of prehistoric human remains have correlated dental disease with changes in diet.

Recent research links S. mutans directly to these rises in tooth decay.

Diversity of the oral microbiota dropped dramatically about 400 years ago, around the time sugar was introduced into the diet and S. mutans became the overwhelmingly dominant species.

Student Misconceptions and Concerns

3. Students might immediately expect that all symbiotic relationships benefit both members. Consider noting that parasitism is a type of symbiotic relationship in which one member is harmed.

Teaching Tips

Active Lecture Tips

Evolution Connection: The Sweet Life of Streptococcus Mutans (3 of 3)

What adaptations gave S. mutans an advantage over other species? Researchers discovered

more than a dozen genes that improved the ability of S. mutans to metabolize sugars and survive increased acidity and

chemical weapons produced by S. mutans that kill harmless bacteria, their competitors for space in the limited terrain of the human oral cavity.

Student Misconceptions and Concerns

3. Students might immediately expect that all symbiotic relationships benefit both members. Consider noting that parasitism is a type of symbiotic relationship in which one member is harmed.

Teaching Tips

Active Lecture Tips

This work is protected by United States copyright laws and is provided solely for the use of instructors in teaching their courses and assessing student learning. Dissemination or sale of any part of this work (including on the World Wide Web) will destroy the integrity of the work and is not permitted. The work and materials from it should never be made available to students except by instructors using the accompanying text in their classes. All recipients of this work are expected to abide by these restrictions and to honor the intended pedagogical purposes and the needs of other instructors who rely on these materials.

.MsftOfcThm_Text1_Fill { fill:#000000; } .MsftOfcThm_MainDark1_Stroke { stroke:#000000; }