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2.1b
Scientists Are Curious and Skeptical and Demand Evidence
Good scientists are curious about how nature works (Individuals Matter 2.1), but also skeptical about new data and hypotheses. They say, “Show me your evidence. Explain the reasoning behind the scientific ideas or hypotheses that you propose to explain your data.”
Individuals Matter 2.1
Jane Goodall: Chimpanzee Researcher and Protector
A photo shows Jane Goodall expressing her love to a chimpanzee.
JENS SCHLUETER/AFP/Getty Images
Jane Goodall is a scientist who studies animal behavior. She has a PhD from England’s Cambridge University and is a National Geographic Explorer. At age 26, she began a decades-long career of studying chimpanzee social and family life in the Gombe Stream Game Reserve in Tanzania, Africa.
One of her major scientific discoveries was that chimpanzees make and use tools. She watched chimpanzees modifying twigs or blades of grass and then poking them into termite mounds. When the termites latched on to these primitive tools, the chimpanzees pulled them out and ate the termites. Goodall and several other scientists have also observed that chimpanzees, including captive chimpanzees, can learn simple sign language, do simple arithmetic, play computer games, develop relationships, and worry about and protect one another.
In 1977, she established the Jane Goodall Institute, an organization that works to preserve great ape populations and their habitats. In 1991, Goodall started Roots & Shoots, an environmental education program for youth with chapters in more than 130 countries. She has received many awards and prizes for her scientific contributions and conservation efforts. She has written 30 books for adults and children and has been involved with more than 40 films about the lives and importance of chimpanzees.
Over the years Goodall has spent as many as 300 days a year traveling and educating people throughout the world about chimpanzees, which are an endangered species, and the need to protect the environment. She says, “I can’t slow down … If we’re not raising new generations to be better stewards of the environment, what’s the point?”
An important part of the scientific process is peer review, in which scientists publish details of the methods they used, the results of their experiments, and the reasoning behind their hypotheses for other scientists working in the same field (their peers) to evaluate. Scientific knowledge advances in this self-correcting way, with scientists questioning and confirming the data and hypotheses of their peers. Sometimes new data and analysis can lead to revised hypotheses (Science Focus 2.1).
Science Focus 2.1
Revisions in a Popular Scientific Hypothesis
For years, the story of Easter Island has been used in textbooks as an example of how humans can seriously degrade their own life-support system and as a warning about what we are doing to our life-support system.
What happened on this small island in the South Pacific is a story about environmental degradation and the collapse of an ancient civilization of Polynesians living there. Over the years, John Fenley, his colleagues, and other researchers have studied the island and its remains, including hundreds of huge statues (Figure 2.A).
Figure 2.A
These and several hundred other statues were created by an ancient civilization of Polynesians on Easter Island. Some of them are as tall as a five-story building and weigh as much as 89 metric tons (98 tons).
A photo shows several statues of human head with upper body made of rock, arranged in a sequence.
shin/ Shutterstock.com
Some of these scientists drilled cores of sediment from lakebeds and studied grains of pollen from palm trees and other plants in sediment layers to reconstruct the history of plant life on the island. Based on these data, they hypothesized that as their population grew, the Polynesians began living unsustainably by using the island’s palm forest trees faster than they could be renewed.
By studying charcoal remains in the island’s layers of soil, scientists hypothesized that when the forests were depleted, there was no firewood for cooking or keeping warm and no wood for building large canoes used to catch fish, shellfish, and other forms of seafood. They also hypothesized that, with the forest cover gone, soils eroded, crop yields plummeted, famine struck, the population dwindled, violence broke out, and the civilization collapsed.
In 2001, anthropologist Terry L. Hunt and archeologist Carl Lippo carried out new research to test the older hypotheses about what happened on Easter Island. They used radiocarbon data and other analyses to propose some new hypotheses. First, their research indicated that the Polynesians arrived on the island about 800 years ago, not 2,900 years ago, as had been thought. Second, their population size probably never exceeded 3,000, contrary to the earlier estimate of up to 15,000.
Third, the Polynesians did use the island’s trees and other vegetation in an unsustainable manner, and visitors reported that by 1722, most of the island’s trees were gone. However, one question not answered by the earlier hypothesis was, why did the trees never grow back? Based on new evidence Hunt and Lippo hypothesized that rats, which either came along with the original settlers as stowaways or were brought along as a source of protein for the long voyage, played a key role in the island’s permanent deforestation. Over the years, the rats multiplied rapidly into the millions and devoured the seeds, palm nuts, and shoots that would have regenerated large areas of the forests. According to this new hypothesis, the rats played a key role in the fall of the civilization on Easter Island.
Fourth, evidence led Hunt, Lippo and others to propose when faced with the loss of trees and poor soil, the islanders developed rock gardens to protect plants from the wind and replenish soil nutrients. In other words, they found ways to sustain themselves.
Fifth, the collapse of the island’s civilization was not due to famine and warfare. Earlier researchers found tools that they contended were weapons, but to Hunt and Lippo they were farming tools. In addition, skeletal remains indicated that lethal injuries from widespread fighting were rare.
Sixth, the collapse of the island’s civilization likely resulted from epidemics when European visitors unintentionally exposed the islanders to infectious diseases to which they had no immunity. This was followed by invaders who raided the island and took away some islanders as slaves. Later Europeans took over the land, used the remaining islanders for slave labor, and introduced sheep that devastated the island’s vegetation.
Hunt and Lippo’s research and hypotheses indicate that the Easter Island tragedy may not be as clear an example of the islanders bringing about their own ecological collapse as was once thought. This story is an excellent example of how science works. The gathering of new scientific data and the reevaluation of older data led to revised hypotheses that challenged some of the earlier thinking about the decline of civilization on Easter Island. Scientists are gathering new evidence to test these two versions of what happened on Easter Island. This could lead to some new hypotheses.
Critical Thinking
Does the new doubt about the original hypothesis about the collapse of Easter Island’s civilization mean that we should not be concerned about using resources unsustainably on the island in space that we call Earth? Explain.
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2.1cCritical Thinking and Creativity Are Important in Science
Scientists use logical reasoning and critical thinking skills to learn about nature. (See Improve Your Critical Thinking Skills in the Learning Skills section following the Table of Contents.) Thinking critically involves three steps:
1. Be skeptical about everything you read or hear.
2. Evaluate evidence and hypotheses using inputs and opinions from a variety of reliable sources.
3. Identify and evaluate your personal assumptions, biases, and beliefs and distinguish between facts and opinions before coming to a conclusion.
Logic and critical thinking are important tools in science, but imagination, creativity, and intuition are also vital. According to Albert Einstein, “There is no completely logical way to a new scientific idea.”
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2.1dScientific Theories and Laws: The Most Important and Certain Results of Science
We should never take a scientific theory lightly. It has been tested widely, is supported by extensive evidence, and is accepted by most scientists in a particular field or related fields of study as being a useful explanation of some phenomenon. So when you hear someone say, “Oh, that’s just a theory,” you will know that he or she does not have a clear understanding of what a scientific theory is and how it is one of the key outcomes of science.
Another important and reliable outcome of science is a scientific law , or law of nature —a well-tested and widely accepted description of what we find always happening in the same way in nature. An example is the law of gravity. After making many thousands of observations and measurements of objects falling from different heights, scientists developed the following scientific law: all objects fall to the earth’s surface at predictable speeds. Scientific laws cannot be broken.
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2.1eReliable, Unreliable, and Tentative Science
Reliable science consists of data, hypotheses, models, theories, and laws that are accepted by most of the scientists who are considered experts in the field under study. Scientific results and hypotheses that are presented as reliable without having undergone peer review, or that are discarded because of peer review or additional research, are considered to be unreliable science .
Preliminary scientific results that have not undergone adequate testing and peer review are viewed as tentative science . Some of these results and hypotheses will be validated and classified as reliable. Others may be discredited and classified as unreliable. This is how scientific knowledge advances.
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2.1fLimitations of Science
Environmental science and science in general have several limitations. First, scientific research cannot prove that anything is absolutely true. This is because there is always some degree of uncertainty in measurements, observations, models, and the resulting hypotheses and theories. Instead, scientists try to establish that a particular scientific theory has a very high probability or certainty (typically 90–95%) of being useful for understanding some aspect of the natural world. It is rare but a scientific theory can be modified and or even discarded if new data strongly support a new conclusion.
Many scientists do not use the word proof because it can falsely imply “absolute proof.” For example, most scientists would not say: “Science has proven that cigarette smoking causes lung cancer.” Instead, they might say: “Overwhelming evidence from thousands of studies indicates that people who smoke regularly for many years have a greatly increased chance of developing lung cancer.”
Critical Thinking
1. Does the fact that science can never prove anything absolutely mean that its results are not valid or useful? Explain.
A second limitation of science is that some scientists are not always free of bias about their own results and hypotheses. However, the high standards for evidence and peer review uncover or greatly reduce personal bias and falsified scientific results.
A third limitation is that many systems in the natural world involve a huge number of variables with complex interactions. This makes it too difficult, costly, and time consuming to test one variable at a time in controlled experiments such as the one described in this chapter’s Core Case Study . To deal with this, scientists develop mathematical models that can take into account the interactions of many variables, and they run the models on high-speed computers.
A fourth limitation of science involves the use of statistical tools. For example, there is no way to measure accurately the number of metric tons of soil eroded annually worldwide. Instead, scientists use statistical sampling and mathematical methods to estimate such numbers.
Despite these limitations, science is the most useful way that we have of learning about how nature works and projecting how it might behave in the future.
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2.2Matter and Changes in Matter
· LO 2.2AList the three major types of subatomic particles.
· LO 2.2BExplain why the atomic number of a carbon atom is 6 and its mass number is 12.
· LO 2.2CList two examples of each of the four major types of organic polymers.
· LO 2.2EDescribe the difference between a physical change and a chemical change in matter in terms of how such changes affect a common object.
· LO 2.2FState the Law of Conservation of Matter.
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2.2aMatter Consists of Elements and Compounds
Matter is anything that has mass and takes up space. Matter can exist in three physical states—solid, liquid, and gas—at a given temperature and pressure and in two chemical forms—elements and compounds.
An element such as gold or mercury ( Figure 2.3 ) is a fundamental type of matter with a unique set of properties that cannot be broken down into simpler substances by chemical means. Chemists refer to each element with a unique one- or two-letter symbol such as C for carbon and Au for gold. They have arranged the known elements based on their chemical behavior in a chart known as the periodic table of elements .
Figure 2.3
Mercury (left) and gold (right) are chemical elements. Each has a unique set of properties and cannot be broken down into simpler substances.
Andraz Cerar/ shutterstock.com; Hurst Photo/ Shutterstock.com
Some matter is composed of one element, such as carbon (C) and oxygen gas . However, most matter consists of compounds , which are combinations of two or more different elements held together in fixed proportions. For example, carbon and oxygen gas combine to form the compound carbon dioxide . Water is a compound containing the elements hydrogen and oxygen, and sodium chloride (NaCl) contains the elements sodium and chlorine.
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2.2bAtoms, Molecules, and Ions
The basic building block of matter is an atom —the smallest unit of matter into which an element can be divided and still have its distinctive chemical properties. The idea that all elements are made up of atoms is called the atomic theory and is the most widely accepted scientific theory in chemistry.
Atoms are incredibly small. For example, more than 3 million hydrogen atoms could sit side by side on the period at the end of this sentence. If you could view atoms with a super microscope, you would find that each different type of atom contains a certain number of three types of subatomic particles: neutrons , with no electrical charge; protons , each with a positive electrical charge (+); and electrons , each with a negative electrical charge (−).
Each atom has an extremely small center called the nucleus , which contains one or more protons and, in most cases, one or more neutrons. Outside of the nucleus, we find one or more electrons in rapid motion (Figure 2.4).
Figure 2.4
Simplified model of a carbon-12 atom. It consists of a nucleus containing six protons, each with a positive electrical charge, and six neutrons with no electrical charge. Six negatively charged electrons are found outside its nucleus.
Each element has a unique atomic number equal to the number of protons in the nucleus of its atom. Carbon (C), with 6 protons in its nucleus, has an atomic number of 6, whereas uranium (U), has 92 protons in its nucleus and thus an atomic number of 92.
Because electrons have so little mass compared to protons and neutrons, most of an atom’s mass is concentrated in its nucleus. The mass of an atom is described by its mass number , the total number of neutrons and protons in its nucleus. For example, a carbon atom with 6 protons and 6 neutrons in its nucleus (Figure 2.4) has a mass number of and a uranium atom with 92 protons and 143 neutrons in its nucleus has a mass number of .
Each atom of a particular element has the same number of protons in its nucleus. However, the nuclei of atoms of a particular element can vary in the number of neutrons they contain, and, therefore, in their mass numbers. The forms of an element having the same atomic number but different mass numbers are called isotopes of that element. Scientists identify isotopes by attaching their mass numbers to the name or symbol of the element. For example, the three most common isotopes of carbon are carbon-12 (with six protons and six neutrons, Figure 2.4), carbon-13 (with six protons and seven neutrons), and carbon-14 (with six protons and eight neutrons). Carbon-12 makes up about 98.9% of all naturally occurring carbon.
A second building block of matter is a molecule , a combination of two or more atoms of the same or different elements held together by chemical bonds. Molecules are the basic building blocks of many compounds. Examples are water and hydrogen gas .
A third building block of some types of matter is an ion . It is an atom or a group of atoms with one or more net positive (+) or negative (−) electrical charges resulting from the loss or gain of negatively charged electrons. Chemists use a superscript after the symbol of an ion to indicate the number of positive or negative electrical charges. The hydrogen ion and sodium ion are examples of positive ions. Examples of negative ions are the hydroxide ion and chloride ion . Another example of a negative ion is the nitrate ion , a nutrient essential for plant growth. In this chapter’s Core Case Study, Bormann and Likens measured the loss of nitrate ions (Figure 2.5) from the deforested area (Figure 2.1, right) in their controlled experiment. Table 2.1 lists the chemical ions used in this book.
Figure 2.5
Loss of nitrate ions from a deforested watershed in the Hubbard Brook Experimental Forest (Core Case Study, Figure 2.1).
Data Analysis:
1. By what percent did the nitrate concentration increase between 1965 and the peak concentration between 1967 and 1968?
Compiled by the authors using data from F H Bormann and Gene Likens.
Table 2.1
Chemical Ions Used in This Book
|
Positive Ion |
Symbol |
Negative Ion |
Symbol |
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Hydrogen ion |
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Chloride ion |
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Sodium ion |
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Hydroxide ion |
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Calcium ion |
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Nitrate ion |
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Aluminum ion |
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Carbonate ion |
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Ammonium ion |
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Sulfate ion |
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Phosphate ion |
|
Ions are important for measuring a substance’s acidity , a measure of the comparative amounts of hydrogen ions and hydroxide ions in a particular volume of a water solution. Scientists use pH as a measure of acidity. Pure water (not tap water or rainwater) has an equal number of and ions. It is called a neutral solution and has a pH of 7. An acidic solution has more hydrogen ions than hydroxide ions and has a pH less than 7. A basic solution has more hydroxide ions than hydrogen ions and has a pH greater than 7.
Each change of a whole number unit on the pH scale represents a tenfold increase or decrease in the concentration of hydrogen ions in a liter of solution. For example, an acidic solution with a pH of 3 is 10 times more acidic than a solution with a pH of 4. Figure 2.6 shows the approximate pH and hydrogen ion concentration per liter of solution for various common substances.
Figure 2.6
The pH scale measures the acidity of solutions. A neutral solution has a pH of 7, an acidic solution has a pH less than 7, and a basic solution has a pH greater than 7. A one-unit change in pH means a tenfold change, that is, a tenfold increase or decrease in acidity.
Data Analysis:
1. How many times more acidic is a solution with a pH of 2 than one with a pH of 6?
Chemists use a chemical formula to show the number of each type of atom or ion in a compound. The formula contains the symbol for each element present and uses subscripts to show the number of atoms or ions of each element in the compound’s basic structural unit. Examples of compounds and their formulas encountered in this book are sodium chloride (NaCl) and water (, read as “H-two-O”). Sodium chloride is an ionic compound that is held together in a three-dimensional array by the attraction between oppositely charged sodium ions and chloride ions (Figure 2.7). Sodium chloride and many other compounds tend to dissolve in water and beak apart into their individual ions and .
Figure 2.7
A solid crystal of an ionic compound such as sodium chloride (NaCl) consists of a three-dimensional array of oppositely charged ions held together by the strong forces of attraction between oppositely charged ions.
Other compounds called covalent compounds are made up of uncharged atoms. An example is water . The bonds between the hydrogen and oxygen atoms in water molecules are called covalent bonds and form when the atoms in the molecule share one or more pairs of their electrons. Figure 2.8 shows the chemical formulas and shapes of molecules that are the building blocks for several common covalent compounds. Table 2.2 lists compounds important to the study of environmental science in this book.
Figure 2.8
Chemical formulas and shapes for some covalent compound molecules.
Compounds Used in This Book
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Compound |
Formula |
Compound |
Formula |
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Sodium chloride |
NaCl |
Methane |
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Sodium hydroxide |
NaOH |
Glucose |
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Carbon monoxide |
CO |
Water |
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Carbon dioxide |
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Hydrogen sulfide |
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Nitric oxide |
NO |
Sulfur dioxide |
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Nitrogen dioxide |
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Sulfuric acid |
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Nitrous oxide |
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Ammonia |
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Nitric acid |
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Calcium carbonate |
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2.2cOrganic Compounds
Plastics, table sugar, vitamins, aspirin, penicillin, and most of the chemicals in your body are called organic compounds , which contain at least two carbon atoms combined with atoms of one or more other elements. The exception is methane , with only one carbon atom.
The millions of known organic (carbon-based) compounds include hydrocarbons—compounds of carbon and hydrogen atoms—such as methane , the main component of natural gas. They also include simple carbohydrates (simple sugars) that contain carbon, hydrogen, and oxygen atoms. An example is glucose , which most plants and animals break down in their cells to obtain energy.
Several types of larger and more complex organic compounds essential to life are called polymers. They form when a number of simple organic molecules (monomers) are linked together by chemical bonds, somewhat like rail cars linked in a freight train. Four types of organic polymers—complex carbohydrates, proteins, nucleic acids, and lipids—are the molecular building blocks of life.
Complex carbohydrates consist of two or more monomers of simple sugars (such as glucose, linked together. One example is the starches that plants use to store energy and to provide energy for animals that feed on plants. Another is cellulose, the earth’s most abundant organic compound, which is found in the cell walls of bark, leaves, stems, and roots.
Proteins are large polymer molecules formed by linking together long chains of monomers called amino acids. Living organisms use about 20 different amino acid molecules to build a variety of proteins. Some proteins store energy. Others are components of the immune system and chemical messengers, or hormones, which turn various bodily functions of animals on or off. In animals, proteins are also components of hair, skin, muscle, and tendons. In addition, some proteins act as enzymes that catalyze or speed up certain chemical reactions.
Nucleic acids are large polymer molecules made by linking large numbers of monomers called nucleotides. Each nucleotide consists of a phosphate group, a sugar molecule, and one of four different nucleotide bases (represented by A, G, C, and T, the first letter in each of their names). Two nucleic acids—DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)—help build proteins and carry hereditary information used to pass traits from parent to offspring. Hydrogen bonds between parts of the nucleotides in DNA hold two DNA strands together like a spiral staircase, forming a double helix ( Figure 2.9 ).
Figure 2.9
Portion of a DNA molecule, which is composed of spiral (helical) strands of nucleotides. Each nucleotide contains three units: phosphate (P), a sugar (S), which is deoxyribose, and one of four different nucleotide bases represented by the letters A, G, C, and T.
The different molecules of DNA in the millions of species found on the earth are like a vast and diverse genetic library. Each species is a unique book in that library. If the DNA coiled in your body were unwound, it would stretch about 960 million kilometers (600 million miles)—more than six times the distance between the sun and the earth.
Lipids , a fourth building block of life, are a chemically diverse group of large organic compounds that do not dissolve in water. Examples are fats and oils for storing energy, waxes for structure, and steroids for producing hormones.
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2.2dCells, Genes, and Chromosomes
All organisms are composed of one or more cells —the fundamental structural and functional units of life. The idea that all living things are composed of cells is called the cell theory . It is the most widely accepted scientific theory in biology.
Within some DNA molecules ( Figure 2.9 ) are certain sequences of nucleotides called genes . Each of these segments of DNA contains instructions, or codes, called genetic information for making specific proteins. The coded information in each segment of DNA is a trait that passes from parents to offspring during reproduction in an animal or plant.
Thousands of genes make up a single chromosome , a double helix DNA molecule wrapped around one or more proteins. Genetic information coded in your chromosomal DNA is what makes you different from an oak leaf, a mosquito, and your parents. Figure 2.10 shows the relationships of genetic material to cells.
Figure 2.10
The relationships among cells, nuclei, chromosomes, DNA, and genes.
Photo: Flashon Studio/ Shutterstock.com
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2.2ePhysical and Chemical Changes
Matter can undergo physical and chemical changes. When matter undergoes a physical change , there is no change in its chemical composition. A piece of aluminum foil cut into small pieces is still aluminum foil. When solid water (ice) melts and when liquid water boils, the resulting liquid water and water vapor remain as molecules.
When a chemical change , or chemical reaction , takes place, there is a change in the chemical composition of the substances involved. Chemists use a chemical equation to show how chemicals are rearranged in a chemical reaction. For example, coal is made up almost entirely of the element carbon (C). When coal is burned completely in a power plant, the solid carbon in the coal combines with oxygen gas from the atmosphere to form the gaseous compound carbon dioxide . Chemists use the following shorthand chemical equation to represent this chemical reaction:
2.2fLaw of Conservation of Matter
Elements and compounds can change from one physical form (solid, liquid, or gas) and elements and compounds can interact in chemical reactions and change from one chemical form to another. However, atoms are never created or destroyed in any physical or chemical change. Instead, atoms, ions, or molecules can only be rearranged into different spatial patterns (physical changes) or chemical combinations (chemical changes). This finding, based on many thousands of measurements, describes an unbreakable scientific law known as the law of conservation of matter : Whenever matter undergoes a physical or chemical change, no atoms are created or destroyed.
This equation is unbalanced because one atom of oxygen is on the left side of the equation but two oxygen atoms are on the right side. We cannot change the subscripts of any of the formulas to balance this equation because that would change the arrangements of the atoms, leading to different substances. Instead, we must use different numbers of the molecules involved to balance the equation. For example, we could use two water molecules:
This equation is still unbalanced. Although the numbers of oxygen atoms on both sides of the equation are now equal, the numbers of hydrogen atoms are not. We can correct this problem by recognizing that the reaction must produce two hydrogen molecules:
Now the equation is balanced, and the law of conservation of matter has been observed.
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2.3Energy and Changes in Energy
· LO 2.3AExplain the difference between potential energy and kinetic energy in terms of something you do every day.
· LO 2.3BList two examples each of renewable energy sources and nonrenewable energy sources.
· LO 2.3CExplain the difference between high-quality and low-quality energy in terms of common examples.
· LO 2.3DState the First Law of Thermodynamics.
· LO 2.3EState the Second Law of Thermodynamics.
· LO 2.3FExplain why some light bulbs are more energy-efficient than others.
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2.3aEnergy Comes in Many Forms
Energy is the capacity to do work or to transfer heat. Suppose you find a book on the floor and you pick it up and put it on your desktop. In doing this, you have to do work, by using certain amount of muscular force to move the book from one place to another. In scientific terms, work is done when any object is moved a certain distance . When you touch a hot object such as a stove, heat (or thermal energy) flows from the stove to your finger. Both of these examples involve energy.
There are two major types of energy: moving energy (called kinetic energy) and stored energy (called potential energy). Matter in motion has kinetic energy . Examples are flowing water, a car speeding down a highway, electricity (electrons flowing through a wire or other conducting material), and wind (a mass of moving air that we can use to produce electricity, as shown in Figure 2.11 ). Electric power is the rate at which electric energy is transferred through a wire or other conducting material.
Figure 2.11
Kinetic energy, created by the gaseous molecules in a mass of moving air, turns the blades of these wind turbines. The turbines then convert this kinetic energy to electrical energy, which is another form of kinetic energy.
In another form of kinetic energy called electromagnetic radiation , energy travels from one place to another in the form of waves formed from changes in electrical and magnetic fields. There are many different forms of electromagnetic radiation ( Figure 2.12 ). Each form has a different wavelength—the distance between successive peaks or troughs in the wave—and energy content. Those with short wavelengths have more energy than do those with longer wavelengths. Visible light makes up most of the spectrum of electromagnetic radiation emitted by the sun.
Figure 2.12
The electromagnetic spectrum consists of a range of electromagnetic waves, which differ in wavelength (the distance between successive peaks or troughs) and energy content.
Another form of kinetic energy is heat , or thermal energy . It is the total kinetic energy of all moving atoms, ions, or molecules in an object, a body of water, or a volume of gas such as the atmosphere. The hotter an object is, the faster the motion of the atoms, ions, or molecules inside that object. Temperature is a measure of the average heat or thermal energy of the atoms, ions, or molecules in a sample of matter. When two objects at different temperatures make contact with each another, heat flows from the warmer object to the cooler object. You learned this the first time you touched a hot stove.
Heat is transferred from one place to another by three methods—radiation, conduction, and convection. Radiation is the transfer of heat energy through space by electromagnetic radiation in the form of infrared radiation ( Figure 2.12 ). This is how heat from the sun reaches the earth and how heat from a fireplace is transferred to the surrounding air. Conduction is the transfer of heat from one solid substance to another cooler one when they are in physical contact. It occurs when you touch a hot object or when an electric stove burner heats a pan. Convection is the transfer of heat energy within liquids or gases when warmer areas of the liquid or gas rise to cooler areas and cooler liquid or gas takes its place. As a result, heat circulates through the air or liquid such as water being heated in a pan.
The other major type of energy is potential energy , which is stored and potentially available for use. Examples of this type of energy include a rock held in your hand, the water in a reservoir behind a dam, the chemical energy stored in the carbon atoms of coal or in the molecules of the food you eat, and nuclear energy stored in the strong forces that hold the particles (protons and neutrons) in the nuclei of atoms together.
You can change potential energy to kinetic energy. If you hold a book in your hand, it has potential energy. If you drop it on your foot, the book’s potential energy changes to kinetic energy during its fall. When a car engine burns gasoline, the potential energy stored in the chemical bonds of the gasoline molecules changes into kinetic energy that propels the car, and into heat that flows into the environment. When water in a reservoir flows through channels in a dam ( Figure 2.13 ), its potential energy becomes kinetic energy used to spin turbines in the dam to produce electricity—yet another form of kinetic energy.
Figure 2.13
The water stored in this reservoir behind Hoover dam has potential energy, which becomes kinetic energy when the water flows through channels built into the dam where it spins a turbine and produces electricity—another form of kinetic energy.
Andrew Zarivny/ Shutterstock.com
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2.3bRenewable and Nonrenewable Energy
Scientists divide energy resources into two major categories: renewable energy and nonrenewable energy. Renewable energy is energy gained from resources that are replenished by natural processes in a relatively short time. Examples are solar energy, wind, moving water, firewood from trees, and heat that comes from the earth’s interior (geothermal energy).
Learning from Nature
One of the fastest growing sources of energy is solar power, a prominent example of how scientists and engineers are learning from nature by studying how plants and animals use solar energy to stay alive.
Nonrenewable energy is energy from resources that can be depleted and are not replenished by natural processes within a human time scale. Examples are energy produced by the burning of oil, coal, and natural gas, and nuclear energy released when the nuclei of atoms of uranium fuel are split apart.
About 99% of the energy that keeps us warm and supports the plants that we and other organisms eat is electromagnetic radiation that comes from the sun. This is the basis of the solar energy principle of sustainability (Figure 1.2). Without this essentially inexhaustible solar energy, the earth would be frozen and life as we know it would not exist.
85%
Percentage of the commercial energy used in the world that is provided by fossil fuels.
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2.3cEnergy Quality
Some types of energy are more useful than others. Energy quality is a measure of the capacity of energy to do useful work. High-quality energy is concentrated energy that has a high capacity to do useful work. Examples are high-temperature heat, concentrated sunlight, high-speed wind, and the energy released when we burn wood, gasoline, natural gas, or coal.
By contrast, low-quality energy is so dispersed that it has little capacity to do useful work. For example, the enormous number of moving molecules in the atmosphere or in an ocean together has a huge amount of energy. However, it is low-quality energy because it is widely dispersed and has such a low temperature, that we cannot use it to move things or to heat things to high temperatures.
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2.3dEnergy Changes Obey Two Scientific Laws
From millions of observations and measurements of energy changing from one form to another in physical and chemical changes, scientists have summarized their results in the first law of thermodynamics , also known as the law of conservation of energy . According to this scientific law, whenever energy is converted from one form to another in a physical or chemical change, no energy is created or destroyed. It can only be changed from one form of energy to another or transferred from one place to another.
Because energy cannot be created or destroyed, only converted from one form to another, you may think we will never run out of energy. Think again. If you fill a car’s tank with gasoline and drive around all day or run your cell phone battery down, something has been lost. What is it? The answer is energy quality, the amount of energy available for performing useful work.
Thousands of experiments have shown that whenever energy is converted from one form to another in a physical or chemical change, we end up with lower-quality or less-usable energy than we started with. This is a statement of the second law of thermodynamics . The low-quality energy usually takes the form of heat that flows into the environment. The random motion of air or water molecules further disperses this heat, decreasing its temperature to the point where its energy quality is too low to do much useful work.
In other words, when energy is changed from one form to another, it always goes from a more useful to a less useful form. This means we cannot recycle or reuse high-quality energy to perform useful work. Once the high-quality energy in a serving of food, a tank of gasoline, or a chunk coal is released, it is degraded to low-quality heat and dispersed into the environment. The second law of thermodynamics is another basic rule of nature that we cannot violate.
Energy efficiency is a measure of how much work results from each unit of energy that is put into a system. Suppose you turn on a lamp with an incandescent bulb powered by electricity produced by a coal-burning power plant. This electricity is transported by a power line to your house and then through house wires to the light bulb. Because of the second law of thermodynamics, some of the original energy produced by burning the coal is lost as waste heat to the environment in each step of this process. The amount of heat lost in each step depends on the energy efficiency of the technologies used. Because of these losses, only 5% of the chemical energy in the coal ends up producing the light from the bulb. The other 95% ends up as heat that flows into the environment. In other words, the highly inefficient incandescent light bulb is mostly a heat bulb not a light bulb.
Thus, 95% of the money spent for the light in this example was wasted. Some of this energy and money waste was the automatic result of the second law of thermodynamics. The rest was lost mostly because of low energy efficiency of the power plant (35%) and the light bulb (5%). A key to reducing this waste of energy and money is to improve the energy efficiency of the power plant and light bulb or replace them with newer, more energy-efficient technologies. We are still using the energy-wasting power plants, but we are shifting from inefficient incandescent light bulbs to much more efficient light-emitting diode (LED) light bulbs.
Scientists estimate that about 84% of the energy used in the United States is either unavoidably wasted because of the second law of thermodynamics (41%) or unnecessarily wasted (43%). Thus, thermodynamics teaches us an important lesson: the cheapest and quickest way to get more energy and cut energy bills is to stop wasting almost half the energy we use. One way to reduce the unnecessary waste of energy and money is to improve the energy efficiency of the power plants, automobile engines, and devices powered by electricity such as lights, refrigerators, and air conditioners. This will save money and sharply reduce air pollution, including emissions of climate-changing carbon dioxide.
43%
Percentage of the commercial energy used in the United States that is unnecessarily wasted
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2.4Systems and How They Respond to Change
· LO 2.4AExplain why the human body, a forest, and a car are all examples of systems.
· LO 2.4BDescribe the inputs, throughputs, and outputs involved in driving a car.
· LO 2.4CDescribe a common positive feedback loop.
· LO 2.4DDescribe a common negative, or corrective, feedback loop.
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2.4aSystems and Feedback Loops
A system is any set of components that function and interact in some regular way. Examples are a cell, the human body, a forest, an economy, a car, a TV set, and the earth.
Most systems have three key components: inputs of matter, energy, and information from the environment; flows or throughputs of matter, energy, and information within the system; and outputs of matter, energy, and information to the environment ( Figure 2.14 ). A system can become unsustainable if the throughputs of matter and energy resources exceed the ability of the system’s environment to provide the required resource inputs and to absorb or dilute the system’s outputs of matter and energy (mostly heat).
Figure 2.14
Simplified model of a system.
Most systems are affected by feedback, any process that increases (positive feedback) or decreases (negative feedback) a change to a system. Such a process, called a feedback loop, occurs when an output of matter, energy, or information is fed back into the system as an input and changes the system. A positive feedback loop causes a system to change further in the same direction. For example, when researchers removed the vegetation from a stream valley in the Hubbard Brook Experimental Forest ( Core Case Study ), they found that flowing water from precipitation caused erosion and losses of nutrients, which caused more vegetation to die ( Figure 2.15 ). With even less vegetation to hold soil in place, flowing water caused even more erosion and nutrient loss, which caused even more plants to die.
Figure 2.15
A positive feedback loop. Decreasing vegetation in a valley causes increasing erosion and nutrient losses that in turn cause more vegetation to die, resulting in more erosion and nutrient losses.
Learning from Nature
For many years, farmers have made use of the natural abilities of plants to hold soil and nutrients by planting cover crops to help retain topsoil and using rows of trees called windbreaks to protect open fields from wind erosion.
When a natural system becomes locked into a positive feedback loop, it can reach a tipping point . Beyond this point, the system can change so drastically that it suffers from severe degradation or collapse. Reaching and exceeding a tipping point is somewhat like stretching a rubber band. We can get away with stretching it to several times its original length. At some point, however, we reach an irreversible tipping point where the rubber band breaks. Similarly, if you lean back on the two rear legs of a chair, at some point the chair will tip back and you will land on the floor. Several types of ecological tipping points will be discussed throughout this book.
A negative , or corrective, feedback loop causes a system to change in the opposite direction. A simple example is a thermostat, a device that measures the temperature in a house and uses this information to turn its heating or cooling system on or off to achieve a desired temperature ( Figure 2.16 ).
Figure 2.16
A negative feedback loop. When a house being heated by a furnace gets to a certain temperature, its thermostat is set to turn off the furnace, and the house begins to cool instead of continuing to get warmer. When the house temperature drops below the set point, this information is fed back to turn the furnace on until the desired temperature is reached again.
Another example of a negative feedback loop is the recycling of aluminum. An aluminum can is an output of mining and manufacturing systems that requires large inputs of energy and matter and that produces pollution and solid waste. When we recycle, the output (the used can) it becomes an input that reduces the need for mining aluminum and manufacturing the can. This reduces the energy and matter inputs and the harmful environmental effects. This is an application of the chemical cycling principle of sustainability.
Most systems in nature use negative feedback to enhance their stability. For example, when we get too cold our brains send signals for us to shiver to produce more body heat. When we get too hot, our brains cause us to sweat, which cools us as the moisture evaporates from our skin.
Big Ideas
· According to the law of conservation of matter, no atoms are created or destroyed whenever matter undergoes a physical or chemical change. Thus, we cannot do away with matter; we can only change it from one physical state or chemical form to another.
· According to the first law of thermodynamics, or the law of conservation of energy, whenever energy is converted from one form to another in a physical or chemical change, no energy is created or destroyed. This means that in causing such changes, we cannot get more energy out than we put in.
· According to the second law of thermodynamics, whenever energy is converted from one form to another in a physical or chemical change, we always end up with a lower-quality or less-usable form of energy than we started with. This means that we cannot recycle or reuse high-quality energy.
Tying It All TogetherThe Hubbard Brook Forest Experiment and Sustainability
steve estvanik/ Shutterstock.com
In the controlled experiment discussed in this chapter’s Core Case Study, the clearing of a mature forest degraded some of its natural capital (Figure 1.3, and photo below). Specifically, the loss of trees and vegetation altered the ability of the forest to retain and recycle water and other critical plant nutrients—a crucial ecological function based on the chemical cycling principle of sustainability.
This clearing of vegetation also violated the solar energy and biodiversity principles of sustainability. For example, the cleared forest lost most of its plants that had used solar energy to produce food for the forest’s animals, which supplied nutrients to the soil when they died. Thus, the forest lost many of its key nutrients that would normally have been recycled. It also lost much of its life-sustaining biodiversity.
Many of the results of environmental science are based on this sort of experimentation. Throughout this textbook, we explore other examples of how scientists learn about nature. We will see how we can use these results to help us understand how the earth works, how our actions affect the environment, and how we can solve some of our environmental problems.
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Chapter Review
Critical Thinking
1. What ecological lesson can we learn from the controlled experiment on the clearing of forests described in the Core Case Study that opened this chapter?
2. Suppose you observe that all of the fish in a pond have disappeared. How might you use the scientific process described in the Core Case Study and in Figure 2.2 to determine the cause of this fish kill?
3. Respond to the following statements:
1. Scientists have not absolutely proven that anyone has ever died from smoking cigarettes.
2. The natural greenhouse effect—the warming effect of certain gases such as water vapor and carbon dioxide in the lower atmosphere—is not a reliable idea because it is just a scientific theory.
4. A tree grows and increases its mass. Explain why this is not a violation of the law of conservation of matter.
5. If there is no “away” where organisms can get rid of their wastes due to the law of conservation of matter, why is the world not filled with waste matter?
7. Use the second law of thermodynamics to explain why we can use oil only once as a fuel, or in other words, why we cannot recycle or reuse its high-quality energy.
8. For one day,
1. you have the power to revoke the law of conservation of matter, and
2. you have the power to violate the first law of thermodynamics.
For each of these scenarios, list three ways in which you would use your new power. Explain your choices.
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Chapter Review
Doing Environmental Science
1. Find a newspaper or magazine article or a report on the internet that attempts to discredit a scientific hypothesis because it has not been proven, or a report of a new scientific hypothesis that has the potential to be controversial. Analyze the piece by doing the following:
1. determine its source (authors or organization);
2. detect an alternative hypothesis, if any, that is offered by the authors;
3. determine the primary objective of the authors (for example, to debunk the original hypothesis, to state an alternative hypothesis, or to raise new questions);
4. summarize the evidence given by the authors for their position; and
5. compare the authors’ evidence with the evidence for the original hypothesis. Write a report summarizing your analysis and compare it with those of your classmates.
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Chapter Review
Data Analysis
Consider the graph below that compares the losses of calcium from the experimental and control sites in the Hubbard Brook Experimental Forest (Core Case Study). Note that this figure is very similar to Figure 2.5, which compares loss of nitrates from the two sites. After studying this graph, answer these questions.
1. In what year did the loss of calcium from the experimental site begin a sharp increase? In what year did it peak? In what year did it level off?
2. In what year were the calcium losses from the two sites closest together? In the span of time between 1963 and 1972, did they ever get that close again?
3. Does this graph support the hypothesis that cutting the trees from a forested area causes the area to lose nutrients more quickly than leaving the trees in place? Explain.