2 THE CHEMISTRY OF LIFE CHAPTER OUTLINE

LEARNING OBJECTIVES

• Describe the basic structure of an atom in terms of three atomic particles (2.1.1). • Explain why electrons determine the chemical behavior of atoms (2.1.2). • Explain how electrons carry energy (2.1.3). • Differentiate between a cation and an anion (2.2.1). • Differentiate between an ion and an isotope (2.2.2). • Define a chemical bond and describe the three principal kinds (2.3.1). • Explain how ionic bonds promote crystal formation (2.3.2). • Explain why most chemical bonds in organisms are covalent bonds, and distinguish between polar and

nonpolar covalent bonds (2.3.3). • Predict which molecules will form hydrogen bonds with each other (2.3.4). • Distinguish between a chemical bond and van der Waals interactions (2.3.5). • Explain why water heats up so slowly (2.4.1). • Explain why ice floats (2.4.2). • Explain why sweating cools you (2.4.3). • Distinguish cohesion from adhesion (2.4.4). • Explain why oil will not dissolve in water (2.4.5). • Define pH and predict the change in hydrogen ion concentration represented by a difference of 1 on

the pH scale (2.5.1).

Some Simple Chemistry (p. 34)

2.1 Atoms (p. 34; Figs. 2.1, 2.2, 2.3, 2.4; Table 2.1) A. All matter is composed of atoms and atoms are the smallest particles into which a substance

can be divided and still retain its chemical properties. B. An atom has positively charged protons and neutrally charged neutrons in the nucleus, with

tiny negatively charged electrons whizzing around the nucleus. C. The number of protons of an atom is referred to as its atomic number. D. Atomic mass includes the number of protons and neutrons. E. Electrons Determine What Atoms Are Like

1. Electrons determine the behavior of atoms because they are the parts of the atom that come into contact with each other.

F. Electrons Carry Energy 1. Electrons possess potential energy, and energy levels surrounding the nucleus reflect the

amount of energy possessed by an electron existing there. 2. Less energy is present in electrons closer to the nucleus. 3. Electrons are most likely to be found in volumes of space called orbitals. 4. Each orbital can hold only two electrons. 5. The first energy level has one orbital, for a total of two electrons. 6. The second and third energy levels each have four orbitals, and can hold up to eight

electrons apiece. 7. When orbitals are not filled with electrons, the atoms are likely to react with atoms to fill

orbitals. 2.2 Ions and Isotopes (p. 36; Figs. 2.5, 2.6, 2.7)

A. Ions 1. In an electrically neutral atom, there are equal numbers of protons and electrons. 2. Ions form when atoms do not have equal numbers of electrons and protons.

B. Isotopes 1. The number of neutrons for atoms of an element can vary, giving rise to isotopes of that

element. 2. Some isotopes of elements break apart by radioactive decay.

C. Medical Uses of Radioactive Isotopes 1. Radioactive tracers are used for both the detection and treatment of human disorders.

2.3 Molecules (p. 37; Figs. 2.8, 2.9, 2.10, 2.11) A. A molecule is made up of two or more atoms held together by energy in the form of a

chemical bond. B. There are three types of chemical bonds: ionic bonds, covalent bonds, and hydrogen bonds;

van der Waals forces are another type of chemical attraction. C. Ionic Bonds

1. Ionic bonds form when ions are electrically attracted to each other by opposite charges. 2. Table salt is built of ionic bonds. 3. Sodium gives up an electron to chlorine; sodium then bears a positive charge while

chloride bears a negative charge; these two ions combine to form table salt (NaCl). 4. Ionic bonds are strong and not directional, two properties that help them form crystals.

D. Covalent Bonds 1. Covalent bonds form when electrons are shared between atoms. 2. Most organic molecules are formed from covalent bonds. 3. Two key properties make covalent bonds ideal for use in biological molecules: they are

strong and they are very directional. 4. The nucleus of a particular atom may be better at attracting the shared electrons of a

covalent bond, causing the electrons to spend more time in the vicinity of this atom; this creates tiny partial negative and positive charges within the molecule, which is called a polar molecule.

E. Hydrogen Bonds 1. Hydrogen bonds are the result of weak electrical attractions between the positive end of

one polar molecule and the negative end of another. 2. Hydrogen bonds are weak and highly directional, and thus play an important role in maintaining the conformation of large, biologically important molecules.

Water: Cradle of Life (p. 42)

2.4 Unique Properties of Water (p. 42; Figs. 2.12, 2.13, 2.14; Table 2.2) A. All organisms are made up of a large quantity of water. B. Water is biologically important because it is a polar molecule and forms hydrogen bonds

between its own molecules. C. Heat Storage

1. Water has the capacity for heat storage because of its many hydrogen bonds. 2. Water changes temperature slowly, an attribute that is beneficial to living organisms.

D. Ice Formation 1. When water freezes, the hydrogen bonds space water molecules apart, making ice less

dense than liquid water. E. High Heat of Vaporization

1. Considerable energy is required to break the hydrogen bonds in water and turn liquid water into vapor.

2. The high heat of vaporization of water helps to explain why evaporative cooling removes heat from the body.

F. Cohesion 1. When the polar molecules of water are attracted to other molecules of water, this

property is called cohesion.

2. The surface tension of water is created by cohesion. 3. When water molecules are attracted to the polar molecules of a substance other than

water, the property is called adhesion. 4. Water clings to other substances, making them wet, as a result of adhesion.

G. High Polarity 1. Other polar, hydrophilic, molecules are “welcomed” by water molecules, which form

shells of water molecules around each of the other polar molecules such that these molecules are soluble in water.

2. Nonpolar molecules, by contrast, are hydrophobic.

2.5 Water Ionizes (p. 44; Fig. 2.15) A. Water ionizes spontaneously, forming hydrogen ions and hydroxide ions. B. pH

1. The amount of hydrogen ions present in solution can be measured by the pH scale, which indicates substances that are acids and bases.

C. Acids 1. An acid is a substance that increases the hydrogen ion concentration in a solution, thus

decreasing the pH of the solution. D. Bases

1. A base is a substance that combines with hydrogen ions in solution, thus increasing pH. E. Buffers

1. Buffers resist changes in pH by either taking up or giving off hydrogen ions as needed.

KEY TERMS

• atom (p. 34) An atom is typically described by the number of protons in its nucleus, and atoms with the same number of protons belong to the same element.

• atomic number (p. 34) • element (p. 34) • mass number (p. 34) • orbital (p. 35) An orbital is not an actual path, but a volume of space that electrons are predicted to

occupy. • ions (p. 36) • isotopes (p. 36) Most elements in nature exist as mixtures of different isotopes; some unstable isotopes

are radioactive. • radioactive decay (p. 36) • molecule (p. 37) • chemical bond (p. 37) • polar molecule (p. 38) The polarity of water molecules is responsible for the degree of hydrogen

bonding that occurs between water molecules. Hydrogen bonding is responsible for most of the unique attributes of water.

• hydrophilic (p. 43) • hydrophobic (p. 43) • pH scale (p. 44) • buffer (p. 44)

CRITICAL THINKING QUESTIONS

1. The human body uses several methods to carefully regulate the pH of the blood, including the bicarbonate system within the blood and adjustments to breathing depth and rate that alter the CO2 content of the blood. Why are several buffer systems needed?

2. Which unique features of water help to support pond life, even in the winter months when water is frozen? Which other physical properties of water are beneficial to pond water organisms? How might these properties have played a part in sustaining life during the progression of an ice age?

3 MOLECULES OF LIFE CHAPTER OUTLINE

LEARNING OBJECTIVES • Distinguish between a polymer and a monomer (3.1.1). • Contrast hydrolysis with dehydration synthesis (3.1.2). • Explain what proteins do by listing five functional groupings of proteins (3.2.1). • Diagram the structure of an amino acid, and the formation of a peptide bond (3.2.2). • Describe the four general levels of protein structure, and how the polar nature of water influences

them (3.2.3). • Explain the forces that cause a protein to denature (3.2.4). • Describe how the structure of an enzyme enables it to catalyze a chemical reaction (3.2.5). • Name the three parts of a nucleotide (3.3.1). • State the two major chemical differences between DNA and RNA (3.3.2). • Identify what two base pairings are possible in DNA, and explain why the other four potential

base pairings do not occur (3.3.3). • Define carbohydrate. Distinguish between monosaccharides and polysaccharides (3.4.1). • Distinguish between saturated and unsaturated fats, and explain why one is a solid and the other a

liquid at room temperature (3.5.1).

Forming Macromolecules (p. 50) 3.1 Building Big Molecules (p.50; Figs. 3.1 -3.4)

A. Organic molecules consist of a carbon-based core with functional groups attached that give the molecules their unique properties.

B. Four major categories of organic molecules are found in living things: proteins, nucleic acids, carbohydrates, and lipids.

C. Large organic molecules are called macromolecules because of their size and complexity. D. A macromolecule is a polymer built from repeating subunits called monomers. E. Making (and Breaking) Macromolecules

1. Subunits of macromolecules are joined together using enzymes and dehydration synthesis.

2. Adding water to macromolecules to break them into subunits is called hydrolysis.

Types of Macromolecules (p. 52) 3.2 Proteins (p. 52; Figs. 3.5–3.9)

A. Proteins can serve as enzymes, play structural roles, and act as chemical messengers. B. Proteins are polypeptides made up of amino acids joined together by peptide bonds. C. Protein Structure

1. The sequence of amino acids within a protein is called the primary structure. 2. The secondary structure is the initial folding of the primary chain. 3. Globular, three-dimensional shapes are the tertiary structure of a protein. 4. When more than one polypeptide chain composes the protein, the spatial arrangement of

the different component chains is the quaternary structure of the protein. D. Protein Folding and Denaturation

1. A protein is denatured when changes in its environment cause it to unfold, which prevents it from functioning properly.

E. Protein Structure Determines Function 1. Proteins that serve architectural and structural roles are often long and cable-like. 2. Proteins that serve as enzymes are globular and help chemical reactions to occur.

3.3 Nucleic Acids (p. 56; Figs. 3.10 - 3.13) A. Nucleic acids (polynucleotides) store information for cells and are made up of subunits called

nucleotides. 1. Each nucleotide is composed of three parts: a five-carbon sugar, a phosphate group, and a

nitrogenous base that can be adenine, guanine, cytosine, thymine, or uracil. B. DNA and RNA

1. Deoxyribonucleic acid (DNA) exists as a double helix of polynucleotides, exhibiting base pairing within the helix. a. DNA nucleotides contain the five-carbon sugar deoxyribose. b. DNA contains the thymine nucleotide. c. DNA encodes genetic instructions for the cell.

2. Ribonucleic acid (RNA) is single-stranded. a. RNA nucleotides contain the five-carbon sugar ribose. b. RNA uses the nitrogen base uracil instead of thymine. c. RNA is involved in protein synthesis

C. The Double Helix 1. The reason that DNA forms a double helix is because only two base pairs are possible.

a. Adenine pairs with thymine and cytosine pairs with guanine, due to the alignment of hydrogen bonds.

2. The advantage of the double helix is that it contains two copies of the information—one the mirror image of the other.

3.4 Carbohydrates (p. 58; Figs. 3.14, 3.15; Table 3.1) A. Carbohydrates are used as structural molecules in some cells and as energy sources. B. Simple Carbohydrates

1. The simple sugars, or monosaccharides, consist of one subunit. 2. Another simple carbohydrate is a disaccharide, built of two subunits.

C. Complex Carbohydrates 1. Animals and plants store energy in polysaccharides formed from glucose. 2. In plants, energy is stored in a polysaccharide called starch; in animals, energy is stored

in a polysaccharide called glycogen. 3. Organisms also use polysaccharides as building materials, cellulose in plants and chitin

in fungi and invertebrates. 3.5 Lipids (p. 60; Figs. 3.16, 3.17)

A. Fats and all other biological molecules that are not soluble in water are lipids. B. Fats are employed for long-term storage of energy. C. Fats

1. Fats are made up of glycerol attached to three fatty acids. 2. The fatty acids may be saturated or unsaturated with hydrogens along the carbon chain.

D. Other Types of Lipids 1. Phospholipids and cholesterol are used to build biological membranes. 2. The steroids testosterone and estradiol serve as the male and female sex hormones.

KEY TERMS • macromolecules (p. 50) A macromolecule is any large organic molecule, such as a carbohydrate, a protein, a lipid, or a nucleic acid. • proteins (p.52 ) • nucleic acids (p.56) The “building blocks” of nucleic acids are nucleotides. Because the building blocks of proteins are amino acids, students often mistakenly think nucleic acids are the building blocks of nucleotides. • carbohydrates (p.58)

• lipids (p.60)

CRITICAL THINKING QUESTION 1. Based on what you know about how macromolecules are synthesized and degraded, why is adequate

water in the diet necessary to aid digestion and cell metabolic reactions? 2. Why do you think that it is important that enzymes are generally very specific to certain

macromolecules? Would you expect this to be the case in all mammals? Why or why not?

4 CELLS CHAPTER OUTLINE

LEARNING OBJECTIVES • State the cell theory, and outline its three principles (4.1.1). • Explain why most cells are so small (4.1.2). • Explain visualizing cells (4.1.3). • Describe the interior of a prokaryotic cell. (4.2.1). • List the organelles unique to eukaryotic cells, and state which of them are not present in plant

cells (4.3.1). • Explain why a lipid bilayer forms spontaneously, and how proteins are anchored within it (4.4.1). • Recount two functions of the cell nucleus (4.5.1).

The World of Cells (p. 65) 4.1 Cells (p. 66; Figs. 4.1 - 4.3)

A. The human body is made up of cells, almost all of which are too small to be seen with the naked eye.

B. The Cell Theory 1. Robert Hooke first described cells in 1665 and coined the term that eventually came to

be “cells.” 2. Modern cell theory includes three principles, as follows:

a. All living organisms are composed of cells. b. Nothing smaller than a cell is considered to be alive. c. Cells arise only from preexisting cells.

C. Most Cells Are Very Small. 1. Cells vary in size, but most are less than 20 micrometers in diameter.

D. Why Aren’t Cells Larger? 1. Cells are small because larger cells do not function efficiently. 2. Cell size is limited by two factors: (1) surface area-to-volume relationships that make

distribution of materials throughout a large cell difficult, and (2) the volume of cytoplasm the nucleus can control.

E. Visualizing Cells 1. Cells can be viewed through microscopes. 2. Transmission and scanning electron microscopes can resolve smaller objects than light

microscopes. Kinds of Cells (p. 69) 4.2 Prokaryotic Cells (p. 69; Figs. 4.4, 4.5)

A. Cells can be divided into prokaryotic cells or eukaryotic cells based on whether or not the cytoplasm of the cells is divided into compartments by internal membranes.

B. Prokaryotic cells lack internal membranes and are evolutionarily more primitive. C. Prokaryotes include the bacteria and archaea. D. Prokaryotic cells contain ribosomes and DNA but no internal membrane-bounded organelles; most prokaryotic cells are surrounded by a cell wall.

4.3 Eukaryotic Cells (p.72; Figs. 4.6, 4.7)

A. Eukaryotic cells are more complex and can compartmentalize different chemical reactions into membrane-bounded interior compartments and organelles.

B. Eukaryotic cells, as their name implies, have a true nucleus, while prokaryotes lack one.

Tour of a Eukaryotic Cell (p. 72) 4.4 The Plasma Membrane (p. 72)

A. All cells are surrounded by a plasma membrane composed of proteins embedded in a bilayer of phospholipids, according to the fluid mosaic model.

B. The polar heads of phospholipids interact with the fluid interior and exterior environments of the cell, while the nonpolar tails form the interior of the membrane.

C. The phospholipids are arranged in a bilayer, with nonpolar tails extending to the inside. D. Proteins Within the Membrane

1. Floating within the lipid bilayer are a variety of membrane proteins that function either to transport materials across the membrane (transmembrane proteins) or to serve as identification markers or receptors in cell communication (cell surface proteins).

4.5 The Nucleus: The Cell’s Control Center (p. 74; Fig. 4.8, Table 4.1) A. The nucleus is the command and control center of the eukaryotic cell, directing all of its activities.

B. Nuclear Membrane 1. The nucleus is enclosed by a double lipid bilayer, the nuclear envelope, which contains

pores to regulate the passage of materials into and out of the nucleus. C. Chromosomes

1. The DNA of eukaryotes is divided into segments associated with protein, forming chromosomes.

2. When the cell is not dividing, the chromosomes exist as threadlike strands called chromatin.

D. Ribosomes 1. A darker staining area inside the nucleus is the nucleolus, which contains information

for the construction of ribosomes that are needed for protein synthesis.

KEY TERMS • cells (p. 66) • cell theory (p. 66) This is one of the major themes of biology. • prokaryotes (p. 69) • eukaryotes (p. 70) • cytoplasm (p. 71) • organelle (p. 70) • plasma membrane (p. 72) • fluid-mosaic model (p. 72) One of the amazing features of a plasma membrane is the ability of the

phospholipids to exchange places as needed, such as during endocytosis, and is the reason for the term “fluid” in the name.

• lipid bilayer (p. 73) • nucleus (p. 74) • ribosome (p. 74) • endoplasmic reticulum (p. 76) • flagella (p. 81) • cilia (p. 81)

CRITICAL THINKING QUESTIONS 1. Do the number of mitochondria vary within a given cell? Between different tissues in a multicellular

organism? Explain.

14 EVOLUTION AND NATURAL SELECTION CHAPTER OUTLINE

LEARNING OBJECTIVES • List Recount the story of Darwin's voyage on the Beagle (14.1.1). • Describe the fossils and patterns of life Darwin observed on the voyage of HMS Beagle (14.2.1). • Explain how Malthus's proposition implies that nature acts to limit population numbers, and how this

leads to the process Darwin called natural selection (14.3.1). • Contrast the work of Darwin and that of the Grants on Galápagos finch evolution (14.4.1). • Describe the four ecological niches occupied by Galápagos finches and their impact on the evolution

of finch beaks (14.5.1). • Outline a four-step procedure to test the theory of evolution using fossil evidence (14.6.1). • Evaluate the scientific merit of common criticisms of Darwin’s theory of evolution (14.7.1). • Discuss five evolutionary forces that have the potential to significantly alter allele and genotype

frequencies in populations (genetic variations )(14.9.1). • Compare the operations of stabilizing, disruptive, and directional selection (14.9.2). • Explain how stabilizing selection maintains sickle-cell disease in Central Africa (14.10.1). • Assess the evidence that natural selection has led to melanism in moths (14.11.1). • Analyze how predation might be altering coloration in Trinidad guppies (14.12.1). • Define the biological species concept (14.13.1). • Describe five prezygotic isolating mechanisms, comparing them to postzygotic mechanisms (14.14.1).

Evolution (p. 250) 14.1 Darwin’s Voyage on H.M.S. Beagle (p. 250; Figs. 14.1 - 14.3)

A. English naturalist Charles Darwin (1809–1882) was the first to propose natural selection as a mechanism of evolution in On the Origin of Species by Means of Natural Selection.

B. In Darwin’s time, most people believed that species were specially created once and remained unchanged through time.

C. One of the most influential events in Darwin’s life was his five-year journey as ship’s naturalist aboard HMS Beagle. 1. During the voyage around the coasts of South America, Darwin observed tropical

forests, fossils of extinct mammals in Patagonia, and related but distinct species on the Galápagos Islands.

14.2 Darwin’s Evidence (p. 252; Figs. 14.4, 14.5) A. The fossils and patterns of life that Darwin observed on his voyage led to his conclusion that

evolution had occurred. B. The writings of geologist Charles Lyell (1797–1875) were highly influential to Darwin during

his voyage. 1. Lyell believed, unlike most people of his day, that the earth was extremely old.

C. What Darwin Saw 1. Fossils of extinct armadillos were similar in form to living species. 2. On the Galápagos Islands, Darwin saw several species of finches that differed slightly.

3. Darwin saw that plants and animals on these islands resembled those on the mainland, but were distinctly different.

14.3 The Theory of Natural Selection (p. 253; Figs. 14.6 - 14.8)

A. Darwin and Malthus 1. Mathematician Thomas Malthus wrote Essay on the Principle of Population (1798) in

which he pointed out that human populations tend to increase geometrically while food supplies increase arithmetically.

2. However, populations remain fairly constant year after year because death limits population size.

3. Malthus’ ideas provided the key that was needed for Darwin to develop his hypothesis that evolution occurs by natural selection.

B. Natural Selection 1. Darwin now saw that each population could produce enough offspring to outstrip its

food supply, but only a limited number survived to reproduce. 2. This led Darwin to the idea of “survival of the fittest” in which only those organisms

that were well-adapted survived long enough to reproduce. 3. The traits of organisms that survive to produce more offspring will be more common in

future generations. 4. Darwin’s theory provides a simple and direct explanation for biological diversity.

C. Darwin Drafts His Argument 1. Darwin wrote a draft of his ideas in 1842, and then turned to other research for sixteen

years. D. Wallace Has the Same Idea

1. English naturalist Alfred Russel Wallace (1823–1913) wrote an essay about his own ideas on evolution by natural selection from his observations in Malaysia.

2. Darwin and Wallace gave a joint presentation, then Darwin expanded his 1842 manuscript and submitted it for publication.

E. Publication of Darwin’s Theory 1. Darwin’s book appeared in 1859 and began a controversy about the origin of humans. 2. The views of Darwin put him at odds with most people of his time. 3. After 1860, Darwin’s ideas were widely accepted in the intellectual community of Great

Britain.

Darwin’s Finches: Evolution in Action (p. 255)

14.4 The Beaks of Darwin’s Finches (p. 255; Figs. 14.9 -14.11) A. Darwin’s finches from the Galápagos Islands are a classic example of evolution by natural

selection. B. The Importance of the Beak

1. Beak shape of this group of 14 species of finches indicated a correspondence between shape and food source.

C. Checking to See if Darwin Was Right 1. In 1973, the Grants of Princeton University discovered a relationship between beak

shape, seed size, and climatic conditions which indicated that beak size was adjusted to the food supply and was passed on from one generation to the next.

2. Natural selection does seem to be operating to adjust the beak to its food supply. 14.5 How Natural Selection Produces Diversity (p. 257; Fig. 14.12)

A. Darwin’s finches, all derived from one similar mainland species, underwent an adaptive radiation on the Galápagos Islands in the absence of competition.

B. Four groups of finches have been recognized from these islands: ground finches, tree finches, a vegetarian finch, and warbler finches.

The Theory of Evolution (p. 258) 14.6 The Evidence for Evolution (p. 258; Figs. 14.13–14.18) A. The Fossil Record

1. The most direct evidence of evolution is found in the fossil record. 2. Fossils are the preserved remains, traces, or tracks of once-living creatures; fossils are

created when organisms or their markings become buried in sand and sediment.

3. By dating the rocks in which fossils occur, biologists can determine the age of the fossil. 4. Rocks are dated by measuring the rate of decay of certain radioisotopes contained in the

rock. B. Using Fossils to Test the Theory of Evolution

a. When fossils are lined up according to their age, they often provide evidence of successive evolutionary change.

b. Many examples serve to illustrate a record of successive change and confirm Darwin’s theory.

C. The Anatomical Record 1. Many diverse organisms go through the same early stages of embryologic development,

which is evidence for evolutionary relatedness. 2. In vertebrates, homologous structures can be seen from the study of anatomy. 3. Vertebrate forelimbs have diverged to perform different functions, but consist of the

same bone structure, indicating a common ancestry. 4. Sometimes analogous structures are found in animals that have evolved the same solution

to a problem, although they did not share a common ancestor. 5. Vestigial organs, which served a function in an ancestor but have no function in the

modern counterpart (such as the appendix that has no function in humans but functions as a reservoir for cellulose bacteria in apes), are also anatomical evidence for evolution.

D. The Molecular Record 1. The evolutionary past is also evident at the molecular level. 2. Since the record of evolutionary change is linked to changes in DNA, organisms that are

more distantly related will have accumulated a greater number of genetic changes in DNA.

3. When analyzing nucleotide sequences for the gene encoding the protein cytochrome c, biologists can construct a molecular clock showing the relatedness of organisms based on how many nucleotide sequences they are away from each other.

14.7 Evolution’s Critics (p. 262; Figs. 14.19, 14.20, 14.21) A. Critics have raised a variety of objections to Darwin’s theory, all of which can be either

explained by biologists or do not necessarily refute evolutionary theory. C. The Irreducible Complexity Fallacy

1. Irreducible complexity is an idea that states that individual parts of a complex, interconnected process cannot evolve independently.

2. However, using the mammalian blood clotting system as an example, each protein at each step in the cascade can indeed be acted upon by natural selection, but evolution has acted on the system as a whole; the parts have evolved together.

How Populations Evolve (p. 266) 14.9 Agents of Evolution (p. 268; Figs. 14.23 - 14.25; Table 14.1)

A. Five factors alter the proportions of homozygotes and heterozygotes enough to produce significant deviations from the proportions predicted by the Hardy-Weinberg rule.

B. Mutation 1. Genetic mutations, or alterations in DNA nucleotide sequences, are rare but are the

ultimate source of genetic variation. C. Migration

1. Migration from the movement of individuals into or out of the population can alter the genetic composition of a population.

D. Genetic Drift 1. In small populations, by random chance alone, it is possible for the allele frequencies to

change from one generation to the next. 2. Such a phenomenon is termed genetic drift. 3. The founder effect occurs when a few individuals are separated from the rest and give

rise, over time, to a new population; this effect often occurs on islands. E. Nonrandom Mating

1. Nonrandom mating and inbreeding (mating with relatives) also lead to changes in gene frequencies from one generation to the next.

F. Selection 1. Selection, whether artificial selection by humans or natural selection, operates to select

certain fit phenotypes, which are able to leave more offspring and thus pass on their genes to successive generations.

G. Stabilizing Selection 1. In stabilizing selection, individuals toward the middle of a range of phenotypes are

selected. H. Disruptive Selection

1. In disruptive selection, both extremes of a phenotype are favored, and individuals in the middle of the range of phenotypes are selected against.

I. Directional Selection 1. Directional selection favors a phenotype at one extreme or the other of an array of phenotypes.

Adaptation Within Population (p. 272) 14.10 Sickle-Cell Disease (p. 272; Figs. 14.26 -14.28)

A. Sickle-cell disease is a hereditary disease affecting hemoglobin molecules in the blood; the homozygous condition is often lethal.

B. The disorder results from a single nucleotide change in the gene encoding beta-hemoglobin, a key protein used by red blood cells to transport oxygen. 1. The altered gene causes the sixth amino acid in the chain to change from glutamic acid

(very polar) to valine (nonpolar). 2. As a result, the hemoglobin molecules clump together and deform the red blood cell into

“sickle-shape.” C. Persons homozygous for the sickle-cell genetic mutation frequently have a reduced lifespan

because the sickled form of hemoglobin does not carry oxygen atoms and the red blood cells that are sickled do not flow smoothly through capillaries.

D. Heterozygous individuals make enough functional hemoglobin to keep their red blood cells healthy.

E. The Puzzle: Why So Common? 1. In central Africa, one in 100 people are homozygous for the disorder and develops sickle-

cell disease. 2. Why is the sickle-cell allele so common in Africa?

F. The Answer: Stabilizing Selection 1. It turns out that individuals who are heterozygous for the sickle-cell allele are resistant to

the malarial parasite that otherwise kills the person with normal hemoglobin. 2. Sickle-cell anemia in humans is an example of stabilizing selection in which the middle

phenotype, in this case the heterozygote with sickle-cell trait but not anemia, is more adapted to an environment that hosts the malarial parasite.

14.11 Peppered Moths and Industrial Melanism (p. 274; Figs. 14.29. 14.30) A. The frequency of dark individuals relative to light individuals of the peppered moth (Biston

betularia) has increased in industrialized areas. 1. Darker forms may be less susceptible to predation.

B. Industrial melanism describes the evolutionary process in which darker individuals become more common than light individuals in a population as a result of natural selection. 1. This phenomenon has been observed in other species of moths in industrialized areas in

Eurasia and North America. 14.12 Selection on Color in Guppies (p. 276; Figs. 14.31, 14.32) A. Guppies Live in Different Environments

1. Guppies living in high-predation pools exhibit drab coloration and have a small adult size. 2. In absence of predators, male guppies are larger and exhibit gaudy colors.

B. The Experiments

1. A controlled experiment was conducted by John Endler in a laboratory to test the response to differences in strength of predation.

2. The results established that predation can lead to rapid evolutionary change. 3. A field experiment was conducted by Endler that revealed that natural selection can lead

to rapid evolutionary change.

How Species Form (p. 279)

14.13 The Biological Species Concept (p. 279; Table 14.2) A. According to Darwin's ideas, species form slowly over time as microevolutionary changes

accumulate and give rise to macroevolution, or the formation of new species. B. A species is defined as a group of potentially or actually interbreeding organisms that is

reproductively isolated from other groups in nature. C. What causes reproductive isolation?

1. Two kinds of barriers act to isolate species: prezygotic and postzygotic isolation mechanisms.

14.14 Isolating Mechanisms (p. 280; Figs. 14.33, 14.34) A. Prezygotic Isolating Mechanisms

1. Prezygotic isolating mechanisms lead to reproductive isolation by preventing the formation of hybrid zygotes.

2. Prezygotic isolating mechanisms include geographical isolation, ecological isolation, temporal isolation, behavioral isolation, mechanical isolation, and prevention of gamete fusion.

B. Postzygotic Isolating Mechanisms 1. Postzygotic isolating mechanisms prevent the proper functioning of hybrid zygotes, and

they include the improper development of hybrids, the failure of the hybrids to become established in either parental habitat, or sterility of hybrid adults.

KEY TERMS • evolution (p. 250) • natural selection (p. 250) • On the Origin of Species (p. 250) If possible, get a copy of this book from the school library and show

it to the students during lecture. Read a few excerpts to help your students understand the depth of Darwin’s ideas.

• Galápagos Islands (p. 251) • adaptive radiation (p. 257) Evidence from island biogeography and adaptive radiation are among the

most convincing arguments for evolution as a result of natural selection. Point out any local examples from your own ecosystem.

• fossil (p. 258) • homologous structures (p. 260) These are derived from a common ancestry. • analogous structures (p. 260) These result from similar environmental pressure but have separate

evolutionary histories. • allele frequency (p. 268) Allele frequency refers to the proportion of alleles of a particular type in a

population. • Hardy-Weinberg equilibrium (p. 266) • genetic drift (p. 268) • founder effect (p. 269) • artificial selection (p. 269) • stabilizing selection (p. 271) Human infant birth weight is a good example of this type of selection. • disruptive selection (p. 271) • directional selection (p. 271) • sickle-cell disease (p. 272)

• heterozygote advantage (p. 273) • industrial melanism (p. 274) • biological species concept (p. 279) • reproductive isolating mechanisms (p. 280)

CRITICAL THINKING QUESTIONS 3. Devise a scenario where two populations become reproductively isolated. 4. How can selection pressure influence evolution? 5. What effect does directional selection have on phenotypic ratios in a population over time?

22 HOW HUMANS INFLUENCE THE LIVING WORLD CHAPTER OUTLINE

LEARNING OBJECTIVES • Explain how modern industry and agriculture are leading to higher levels of chemical pollution

(22.1.1). • Explain the sources and consequences of acid precipitation (22.2.1). • Assess the proposition that global warming is the consequence of increased CO2 in the atmosphere

(22.3.1). • Identify the three main causes of today's loss of biodiversity (22.4.1). • Explain how CFCs caused the ozone hole over Antarctica, and describe the consequences (22.5.1). • Describe how economists estimate the "optimal" level of pollution, and how it might be achieved

(22.6.1). • Evaluate the importance of three nonreplaceable resources (22.7.1). • Describe the growth of the human population over the last 10,000 years (22.8.1). • Explain why population pyramids with broader bases indicate more rapid future population growth

(22.8.2). • Explain how the design of recovery plans for endangered species is related in each instance to the

cause of species loss (22.9.1). • Discuss renewable alternatives to fossil fuels, and evaluate what role biomass may play (22.10.1). • Recount how Lake Washington and the Nashua River were restored through individual action

(22.11.1).

Global Change (p. 452) 22.1 Pollution (p. 452; Fig. 22.1)

A. Global change occurs because of the wide-ranging effects of each of man's activities. B. Chemical Pollution

1. The growth of industry and the casual attitude many have toward industrial chemicals augments problems of chemical pollution.

2. Chemical pollution comes from a wide variety of sources, and its effects are far-reaching.

3. Air Pollution a. Air pollution is a major problem in the world’s large cities. b. Certain cities are called gray-air cities because of sulfur oxides emitted by industry. c. Other cities have been called brown-air cities because air pollutants undergo

chemical changes in sunlight to form smog. 4. Water Pollution

a. Water pollution is an ever-growing problem due to the enormous amount of substances produced by the human population.

b. Lakes and rivers worldwide are becoming increasingly polluted. C. Agricultural Chemicals

1. Many different types of fertilizers, pesticides, and herbicides have been applied to agricultural fields.

2. Certain agricultural chemicals undergo biological magnification and are toxic to organisms high on the food chain.

22.2 Acid Precipitation (p. 453; Figs. 22.2, 22.3)

A. Sulfur-containing air pollution from coal-fired power plants is the main cause of acid rain, rain that is considerably more acidic than would fall naturally.

B. The effects of acid rain are far-reaching, especially when industries install tall smokestacks to distribute the pollutants high into the air.

C. Acid precipitation kills life; many forests and lakes have been seriously damaged. D. The solutions are available, such as installing “scrubbers” on smokestacks to remove sulfur

from the emissions. E. But these methods are costly, and industry does not want to pay the cost. F. New legislation has begun to address the problems of acid rain.

22.3 Global Warming (p. 454; Fig. 22.4) A. The growth of our industrialized society has been fueled by cheap energy, such as burning

fossil fuels. B. When we burn fossil fuels, we add carbon dioxide to the atmosphere. C. Carbon dioxide is a natural feature of our atmosphere and contributes to the warmer climate

we enjoy on the planet; this is known as the greenhouse effect. D. Global Warming Due to Greenhouse Gases

1. Excess carbon dioxide and other gases could be intensifying the greenhouse effect and causing global warming.

2. Scientists are not all in agreement that we are seeing global warming yet, but substantial evidence is mounting.

3. The projected consequences of global warming could be serious, including affecting rain patterns, agriculture, and sea levels.

22.4 Loss of Biodiversity (p. 455; Figs. 22.5, 22.6) A. More than 99% of species known to science are now extinct. B. Factors Responsible for Extinction

1. Habitat Loss a. Habitat loss is the single most important cause of extinction. b. Natural habitats may be affected by the following human influences: destruction,

pollution, human disruption, and habitat fragmentation. 2. Species Overexploitation

a. Species that are hunted and harvested by humans are at a risk for extinction. 3. Introduced Species

a. New species can enter a habitat and colonize it, usually at the expense of native species.

b. Species introductions are usually unintentional. 22.5 The Ozone Hole (p. 457; Fig. 22.7)

A. A layer of protective ozone formed in the earth's upper atmosphere after the early marine photosynthesizers began emitting oxygen.

B. Since then, living creatures have been able to invade land under the protection of the ozone layer.

C. But starting in 1975, the ozone shield surrounding the earth began to get thinner over the South Pole.

D. Scientists eventually determined that the cause was chlorofluorocarbons (CFCs) in the atmosphere.

E. These chemicals are used in abundance in refrigeration units, air conditioners, aerosol propellants, and Styrofoam.

F. When CFCs drift upward in the atmosphere, they react with ozone, converting it back to gaseous oxygen.

G. One CFC molecule can interact with huge numbers of ozone molecules without being altered. H. An ozone hole has now developed over Antarctica. I. A 1% drop in ozone content coincides with a 6% increase in skin cancer because of increased

exposure to ultraviolet radiation. J. Efforts have been undertaken to curtail the use of CFCs worldwide.

Saving Our Environment (p. 458) 22.6 Reducing Pollution (p. 458; Fig. 22.8)

A. One of the first challenges in solving environmental problems is to reduce pollution. B. When the true cost of industry is calculated, protecting the environment must be added in. C. Although it makes energy and products more expensive, the demand should decline, and the

environment will then be preserved. D. Antipollution Laws

1. Antipollution laws are an encouraging trend. 2. The Clean Air Act of 1990 requires that power plants eliminate sulfur emissions.

E. Pollution Taxes 1. Pollution taxes are being considered, making each of us pay more for the option to

pollute. 2. These taxes are sometimes imposed as “cap-and-trade pollution permits” and are

becoming more common. 22.7 Preserving Nonreplaceable Resources (p. 459; Figs. 22.9, 22.10)

A. Preserving nonrenewable resources, such as topsoil, groundwaters, and biodiversity, are extremely important measures.

B. Topsoil 1. One-quarter of the topsoil in this country has been lost since 1950. 2. If we can adopt ways of reducing tillage and saving our soils, we can ensure a means of

growing food in the future. C. Groundwater

1. Groundwater is rapidly becoming depleted and polluted, mostly because it is under the jurisdiction of local governments that lack the authority to control groundwater usage.

D. Biodiversity 1. Biodiversity is a nonrenewable resource that adds to the stability of ecosystems. 2. When we destroy habitat, species are destroyed too, and we will never know the potential

benefit we might have gained from learning about them. 22.8 Curbing Population Growth (p. 461; Figs. 22.11 - 22.16; Table 22.1)

A. The core problem behind much of the environmental degradation we cause is that our population is too large and growing too rapidly.

B. Ten thousand years ago, the human population was 5 million. C. By the time of Christ, human population had increased to 130 million. D. Over the last 300 years, the average birth rate for humans has stabilized at about 21 births per

thousand people per year. E. However, with better sanitation and medical treatment, the death rate has declined to about 9

people per thousand per year. F. In 2008, the world's population reached 6.7 billion people, with an annual increase of about

80 million people. G. How each of these people will be fed and be able to lead a rewarding, meaningful life remains

to be determined. H. Population Growth Rate Starting to Decline

1. The population growth rate has been declining due to increased family planning efforts and increased economic power and social status of women.

2. Increased educational levels appear to follow a decrease in family size as a result of family planning.

3. The annual increase in population is still large, and it is uncertain whether or not the world can sustain the current population size or the much larger size expected in the future.

I. Population Pyramids 1. Human population growth is not occurring uniformly over the planet. 2. The rate at which a population can be expected to grow in the future can be assessed

graphically by means of a population pyramid. 3. The AIDS epidemic in Africa will have a huge impact on population sizes.

J. The Level of Consumption in the Developed World Is Also a Problem

1. We in the developed countries need to pay more attention to lessening the impact of our resource consumption.

2. An ecological footprint is the amount of productive land required to support an individual at the standard of living of a particular population through the course of his or her life.

3. The ecological footprint of an individual in the US is ten times greater than that of someone in India.

Solving Environmental Problems (p. 464)

22.9 Preserving Endangered Species (p. 464; Figs. 22.17 - 22.21) A. Preserving ecosystems and monitoring species before they are threatened is the means of

protecting the environment and preventing extinctions. B. Habitat Restoration

1. Pristine restoration is not usually possible because we rarely know the identity of all of the original inhabitants and the ecologies of each species.

2. Removing introduced species can restore a habitat. 3. Cleanup and rehabilitation, such as pollution removal, can successfully restore habitat.

C. Captive Propagation 1. Case History: The Peregrine Falcon

a. DDT use affected the egg shells of falcons causing them to break prematurely. b. DDT was banned in 1972, and falcons from other locations re-established

populations that had disappeared. D. Sustaining Genetic Diversity

1. Case History: The Black Rhino a. Mitochondrial DNA analysis suggests that populations are genetically very similar. b. This lack of genetic variability poses the greatest challenge to the species. c. Placing black rhinos from different locations together might increase genetic

diversity, and it might also be problematic. E. Preserving Keystone Species

1. Case History: Flying Foxes. a. The bats known as “flying foxes” are often the only pollinators and seed disperses of

certain plant species. b. Many plant species are suffering due to their dependence on the declining population

of these bats, which are hunted by humans. c. Some populations have been helped by legal protection, habitat restoration, and

captive breeding programs. F. Conservation of Ecosystems

1. Conservation biologists have recognized that the best way to preserve biodiversity is to focus on preserving intact ecosystems, rather than focusing on particular species.

22.10 Finding Other Sources of Energy (p. 467; Figs. 22.22 - 22.25) A. If we can find alternative sources of energy, we can curtail much air pollution and reduce

carbon dioxide emissions. B. Some countries have turned to nuclear power for their energy needs. C. In order for nuclear energy to be a viable alternative, there must be safe operation of the

power plant, proper waste disposal, and security against theft. D. Alternative Energy Sources

1. Solar, wind, and biomass are renewable sources of energy. E. Looking Closer at Ethanol

1. Plants like corn can be used to produce ethanol, which makes a good fuel. 22.11 Individuals Can Make the Difference (p. 469; Figs. 22.26, 22.27)

D. Environmental problems can be solved, but it will take everyone's help. E. One person can make a difference in solving environmental problems. F. The Nashua River

1. In the 1960s, Marion Stoddart organized a citizen’s campaign to clean up the severely polluted Nashua River in Massachusetts.

2. Her efforts led to the recovery of the river and contributed to the passage of the Massachusetts Clean Water Act of 1966.

G. Lake Washington 1. In the 1950s, W. T. Edmondson began a campaign to clean up Lake Washington, which

was being polluted by sewage plants.

KEY TERMS • global change (p. 452) The widespread effects of all environmental problems on the global ecosystem

are referred to as “global change.” • biological magnification (p. 452) Certain compounds magnify through the food chain. • acid rain (p.453) Perhaps more correctly called acid precipitation, increased acidity adversely affects

both aquatic and terrestrial ecosystems. • greenhouse effect (p. 454) Adding certain chemicals (mainly CO2) to the atmosphere enhances the

atmosphere’s natural property to insulate the earth and hold heat. • global warming (p. 454) While still a controversial idea in some circles, evidence for global warming

is mounting. • biodiversity (p. 455) • ozone hole (p. 457) The worldwide ozone loss is now at 3%. • CFCs (p. 457) Originally thought to be harmless, CFCs have been used in refrigerators and aerosols. • topsoil (p. 459) We have already lost at least one-quarter of the topsoil in the U.S. since 1950. • groundwater (p. 460) • ecological footprint (p.463)

CRITICAL THINKING QUESTIONS 6. Do you think the ozone hole will increase or decrease in size over the next few decades? Explain. 7. Describe alternatives you could use to reduce your use of energy and reduce the solid waste you

produce. 8. Design a recycling collection system for your campus, dorm, or immediate community. 9. Do you think groups need incentives to make sustainability initiatives work? What sort of incentives

may work for a campus community?