Suggested Answers to Collaborative Questions Principles of Biology

Chapter 1 1.This is a matter of opinion. For people who base their belief system on experimentation, they would tend to believe the theories of biology. Outside of biology, there are many ways that people judge things to be true including the following: experimentation, hearing it from an expert; seeing an event happen over and over again; and many others.

2. There are many examples. Here are a few: hummingbirds have long beaks that fit into flowers; many insects have evolved structures so they can visit flowers; many prey have evolved structures to avoid predators while the predators have evolved structures that overcome the prey’s defenses.

Chapter 2 1. Protons—These are positively charged particles that are found in the center of the atom which is referred to as the nucleus. The number of protons an atom has is called the atomic number, and this defines each type of element. This particle makes up approximately half of the mass of an atom, which is referred to as the atomic mass.

Neutrons—These are neutral (uncharged) particles that are found in the nucleus of the atom. For most atoms of biological importance, the number of neutrons is equal to the number of protons in an atom, but this is not always the case. Atoms with the same number of protons but different numbers of neutrons are called isotopes of each other.

Electrons—These are negatively charged particles that are found in orbitals around the nucleus. For atoms, the number of protons is equal to the number of electrons. Therefore, an atom has no overall net charge. If electrons are added to an atom or taken away, this will change the charge of the atom, which is now called an ion, thereby changing its properties and reactivity.

2. The partial electric charges around the hydrogen and oxygen atoms in a water molecule make water a good solvent for many of the chemicals important for life in organisms, such as ions and polar compounds.

Water can directly participate in types of chemical reactions called hydrolysis reactions, which among other things are important in the conversion of certain large molecules into smaller units that are biologically important.

Water has a high heat of vaporization, which means that it takes a great deal of heat to change its state from a liquid to a gas. As a result of this, most of the water in our planet is in liquid form, which is required to support life.

Water also has a high heat of fusion and requires considerable energy to be removed from it to turn it from a liquid to a solid. As a result of this, liquid water is very stable and resistant to temperature change, making it ideal for living organisms. Also see Figure 2.13. Chapter 3

1. Monosaccharides—These are monomers and the most simple of the sugars, carbohydrates that often, but not always, taste sweet. A prime example of this type of carbohydrate is glucose, which is used by many organisms in the production of ATP.

Disaccharides—These consist of two monosaccharides covalently bonded together. This is accomplished through a dehydration reaction by removing hydrogen from one monosaccharide and a hydroxyl from the other, resulting in the loss of a molecule of water. Sucrose is an example of this type of carbohydrate.

Polysaccharides—These are polymers that consist of many monosaccharides bonded together. Some examples of polysaccharides are

Glycogen—this is the storage form of glucose in animals.

Starch—this is the storage form of glucose in plants.

Cellulose—this molecule serves as a support molecule in plants.

2. Protection—protect organisms from attack against disease. Organisms develop specific proteins to fight against specific diseases.

Enzymes—increase the rates of chemical reactions. Without these proteins, metabolism would slow down and stop.

Gene expression and regulation—involved in transcribing genes (converting DNA into RNA), and regulating the activity of genes.

Cell signaling— provide the basis for communication between cells

Motor proteins—allow cellular movements.

Transporters—allow the movement of ions and molecules across cellular membranes.

Chapter 4 1.The genome has a storage function. The genome stores the information to make all of a cell’s proteins. The proteome, which is a collection of many different cellular proteins, are the active participants in cell structure and function. Proteins are involved with forming cellular structures, such as the cytoskeleton, and they also play a role in carrying out many cellular functions, such as metabolism, transport, etc. Proteins are also involved in the synthesis other cellular molecules, such as lipids, carbohydrates, and nucleic acids.

2. See Figures 4.5 and 4.7 for drawings. These three organelles are interconnected and are required in eukaryotic cells to function properly. The nucleus is the control center of the cell and houses the DNA of the cell. DNA is the blueprint for maintaining and building structures such as proteins inside the cell. Without the nucleus, the cell cannot repair or maintain itself and cannot live indefinitely under his condition. The rough endoplasmic reticulum (RER) is the place in the cell where proteins are made. It does this with the help of structures called the ribosomes. But the RER cannot build a protein without instructions from the nucleus. Therefore information from the nucleus must be delivered to the RER in the form of messenger RNA. After most protein are made at the RER, they are sent to the Golgi apparatus via membrane vesicles. From the Golgi, most proteins are then sorted to other locations such as the ER, lysosomes, vacuoles, and plasma membrane, or they are secreted from the cell. Chapter 5 1.Membrane proteins that span the plasma membrane may have sites that are exposed on the cell surface. This makes it easy for the drug to bind to the protein because it doesn’t have to cross the plasma membrane. Also, many membrane protein carry out important functions that can be affected by drugs.

2. Diffusion does not require the synthesis of a protein and does not use energy. However, it only applies to hydrophobic solutes that can cross the membrane. Facilitated diffusion requires the synthesis of a protein, but the transport process doesn’t require energy. Both diffusion and facilitated diffusion can only transport solutes downhill. By comparison, active transport can transport solutes against a gradient, but it does require the input of energy. Finally, an advantage of endocytosis is that it can transport large solutes and even things like bacteria into the cell.

Chapter 6 1.We are not defying the second law of thermodynamics. Our bodies are using energy to maintain our internal organization. However, in the process, we are increasing the entropy of the universe even though our bodies are fairly well ordered.

2.PET scans are good at detecting solid tumors. When solid tumors become hypoxic, this favors glycolysis, which makes them more easily detected via PET scans. Chapter 7 1.An advantage of being a heterotroph is that you don’t have to expend energy making organic molecules from inorganic sources. A disadvantage is that you have to expend energy trying to find food. The autotrophs are just the opposite.

2. The advantage of converting C3 plants to C4 plants is that they would be more tolerant of hot and dry conditions. To achieve this goal, you might try to transfer genes that encode the proteins found in C4 and CAM plants.

Chapter 8 1. Here are some examples: Direct intercellular signaling- In multicellular organisms, there is usually some form of direct contact between adjacent cells so they can communicate with each other and exchange chemicals between cells. Without this communication, organs and tissues would not work correctly. In the lungs, cilia are needed to work in rhythmic movements to sweep unwanted particles out of the lungs. This could not be achieved if there was not direct cell-to-cell communication.

Contact-dependent signaling- In this type of signaling, membrane bound signals on one cell bind to the receptors on an adjacent cell. This occurs when portions of nerve cells grow and make contact with other nerve cells or muscle cells, thus allowing the cells to work together.

Autocrine signaling- Some cells secrete signals that act on themselves as well as cells of the same type that are close by.

Paracrine signaling- In paracrine signaling, a specific cell secretes a signaling molecule that influences the behavior of target cells in close proximity to the signaling cell. This signal is usually short lived, thereby keeping the effects very local. An example of this is found in the nervous system and the signaling chemicals are called neurotransmitters. These neurotransmitters communicate specific messages to the target cells.

Hormone signaling- This form of signaling acts over long distances. Certain cells secrete hormones that are carried through vessels in plants and animals and cause a cellular response in distant cells. Epinephrine in humans is an example.

2. Second messengers can relay signals of molecules that bind to cell surface receptors. Two advantages are speed and amplification of the signal. A disadvantage is that the cell has to use energy to synthesize the components of the second messenger pathways. Chapter 9 1. Step 1. Isolate and purify DNA from resistant bacteria. Step 2. In three separate tubes, add DNase, RNase, or protease. Step 3. Add sensitive bacteria to each tube. A small percentage maybe transformed. Step 4. Plate on Petri plates containing tetracycline. Expected results: Tetracycline-resistant colonies should grow only when the DNA has been exposed to RNase and protease, but not to DNase.

2. There are many possibilities. You could use a DNA-specific chemical and show that it causes heritable mutations. Perhaps you could inject an oocyte with a piece of DNA and produce a mouse with a new trait.

Chapter 10 1.The RNA components of spliceosomes and ribosomes perform both structural and catalytic roles. In the case of spliceosomes, the RNA is thought to catalyze the splicing reactions. In ribosomes, an rRNA catalyzes the peptidyl transfer reaction. Proteins are needed in spliceosomes and ribosomes to perform a structural role. They hold the RNA in the correct configuration so that its catalytic function is achieved.

2. This could be a very long list. There are similarities along several lines: 1. There is a lot of molecular recognition going on, either between two nucleic acid molecules or between proteins and nucleic acid molecules. Students may see these as similarities or differences, depending on their point of view. 2. There is biosynthesis going on in both processes. Small building blocks are being connected together. This requires an input of energy. 3. There are genetic signals that determine the beginning and ending of these processes.

There are also many differences: 1. Transcription produces an RNA molecule with a similar structure to the DNA, whereas translation produces a polypeptide with a structure that is very different from RNA. 2. Depending on your point of view, it seems that translation is more biochemically complex, requiring more proteins and RNA molecules to accomplish the task.

Chapter 11 1.Transcriptional regulation is the most efficient form of regulation from the point of view of energy. If a protein is not needed by a cell, turning off the gene (via a repressor protein) prevents the synthesis of the mRNA as well as the protein itself. Therefore, the cell does not waste energy making a protein it doesn’t need. On the other hand, transcriptional control is fairly slow because it takes time to transcribe a gene and synthesize a polypeptide. By comparison, the regulation of protein function via feedback inhibition or covalent modification is very fast. Translational control, which involves the regulation of mRNA translation, is in the middle. It is not as efficient as transcriptional control because mRNA is made, but it is faster than transcriptional control. However, it is not as fast as the regulation of protein function.

2.The advantages of gene regulation via combinatorial are that genes are carefully regulated so they are expressed under the correct environmental conditions, in the correct cell types, and at the proper stage of development. A disadvantage is that it does require some extra energy due to all of the different types of proteins and events (e.g., DNA methylation) that are involved in this process.

Chapter 12 1. A mutation is a heritable change in the genetic material. A mutation can be passed from mother cell to daughter cell or the mutation can occur during gamete formation and be passed from parent to offspring. The word mutation is often associated with negative effects but this is not always the case. Mutation increases the genetic variability of a species. If a mutation is favorable, it will be beneficial to that individual and may increase its reproductive success. Likewise, such favorable mutations may be passed to offspring. Over time, this process may increase the frequency of the mutation in a population. On the other hand, however, most mutations are unfavorable and decrease the survival or reproductive success of individuals. These mutations tend to be eliminated from populations.

2. It’s a matter of opinion. Some ideas might be the following: a. Testing of mutagens would enable us to know what the mutagens are and thereby avoid them. On the other hand, one might argue that there are so many now, that it’s difficult to avoid them anyway. b. Investigating molecular effects may help us fi nd a cure for diseases such as cancer or help us to prevent mutations. On the other hand, it may not. c. Similarly, investigating DNA repair mechanisms may lead to ways of preventing mutations. On the other hand, it may not. d. Other places: educating the public about mutagens; tighter regulations of substances that contain mutagens; alternative methods of agriculture that may diminish the level of mutagens in food; and many others.

Chapter 13 1. During interphase, the chromosomes are greatly extended. In this conformation, they might get tangled up with each other and not sort properly during meiosis and mitosis. The condensation process probably occurs so that the chromosomes easily align along the equatorial plate during metaphase without getting tangled up.

2. It’s not possible to give a direct answer, but the point is for students to be able to draw chromosomes in different configurations and understand the various phases. The chromosomes may or may not be 1. in homologous pairs; 2. connected as sister chromatids; 3. associated in bivalents; 4. lined up in metaphase; 5. moving toward the poles; and so on.

Chapter 14 1. The discussion is a matter of opinion. Some may say that Mendel withheld data, but others may not feel that way.

2. a. Chromosomes contain the genetic information that is passed from parent to offspring and from one cell to another. Genes, the basic units of genetics, are found on these chromosomes. b. Chromosomes are replicated, and each chromosome retains its individuality (the same number and type of genes) during cell division and gamete formation. c. The nucleus of a diploid cell contains two sets of chromosomes that are found in homologous pairs. Half of these chromosomes come from the mother, and the other half come from the father, and each set of chromosomes carry a full complement of genes. d. During meiosis, one member of each chromosome pair segregates into one daughter nucleus, and its homologue segregates into the other daughter nucleus. Each of the resulting haploid cells contains only one set of chromosomes. During the formation of haploid cells, the members of different chromosome pairs segregate independently of each other. e. Gametes are haploid cells that combine to form diploid cells during fertilization, with each gamete transmitting one set of chromosomes to the offspring. Tenets 2, 3, and 4 were largely determined via microscopy. Tenets 1 and 5 were deduced both via crosses and via microscopy. Modern techniques to verify this theory could involve a variety of cloning techniques that are described in Chapters 20 and 21.

Chapter 15 1.The answer to this question depends on which virus you choose. Some of the societal and medical issues center around how to control its spread, which could involve a variety of factors such as: the use of drugs that stop the proliferation of the virus; vaccination; isolating people who have been infected, etc.

2. It is not a form of sexual reproduction, in which two distinct parents produce gametes that unite to form a new individual. However, conjugation is similar to sexual reproduction in the sense that the genetic material from two cells is somewhat mixed. In conjugation, there is not the mixing of two genomes, one from each gamete. Instead, there is a transfer of genetic material from one cell to another. This transfer can alter the combination of genetic traits in the recipient cell.

Chapter 16 1. There are many possible answers. Examples include research advances, such as studying and sequencing genes, and practical applications, such as making human insulin in bacteria or making Bt corn.

2. Many issues could be discussed. These include philosophical issues, religious issues, etc.

Chapter 17 1. The prokaryotic genome typically consists of a single chromosome ranging from several hundred thousand to a few million base pairs in length. Most prokaryotes contain only a single chromosome although there may be multiple copies present within a single cell. Bacterial chromosomes are predominantly circular in structure although linear chromosomes are found in several species. When compared to the eukaryotic genome, the prokaryotic genome is less complex, lacking centromeres and telomeres, and having a single origin of replication. In addition, the prokaryote genome has relatively little repetitive DNA.

The genome found in eukaryotes is usually found in sets of linear chromosomes. The genome of simple eukaryotes carries only a few thousand genes, whereas the genome of more complex eukaryotes may contain tens of thousands of genes. Unlike the genome of prokaryotes, the chromosomes found in eukaryotes are much more complex, having centromeres, telomeres, and multiple origins of replication. Unlike prokaryotes, eukaryotes have more repetitive DNA, ranging from moderate to high.

2. This sequence is from the b-globin gene found in humans.

Chapter 18 1. The reducing atmosphere hypothesis—This hypothesis is based largely on geological evidence. By examining what chemicals were in the primitive atmosphere at the time when life arose, scientists have determined that the basic chemicals needed to form organic molecules were present. By combining these primitive inorganic molecules, more complex molecules such as amino acids and nucleotides could be formed.

The extraterrestrial hypothesis—This hypothesis postulates that the first organic molecules may have come from fallen bodies from space such as meteorites. Because certain meteorites called carbonaceous chondrites contain organic carbon, these bodies may have added the first organic molecules to our planet. Deep sea vents—This hypothesis proposes that the key organic molecules that started life may have originated in deep sea vents. Because these vents have the necessary chemicals and high temperatures, life on our planet may have began here.

The favored hypothesis is a matter of opinion.

2. Protobionts had (1) a boundary, such as a membrane, that separated the internal contents of the protobiont from the external environment; (2) polymers inside the protobiont contained information; (3) polymers inside had enzymatic functions; and (4) protobionts were capable of self-replication. However, they were not as biochemically complex as living cells and were not capable of precise self-reproduction. However, it’s difficult to describe a clear distinction between a protobiont and a living cell.

Chapter 19 1.Natural selection is a process in which individuals with greater reproductive success are more likely to contribute genes to the next generation. Evolution is a change in the genetic composition of a population from one generation to next. Natural selection can cause evolution to happen. However, other processes can cause evolution to happen such as genetic drift, which is a random change in allele frequencies from one generation to the next.

2. a. Random mutation is the source of genetic variation that may lead to antibiotic resistance. A random mutation may create an antibiotic-resistance allele. This could occur in different ways. Many antibiotics exert their effects by binding to an essential cellular protein within the microorganism and inhibiting its function. A random mutation could occur in the gene that encodes such an essential cellular protein; this could alter the structure of the protein in a way that would prevent the antibiotic from binding to the protein or inhibiting its function. As another possibility, microorganisms, which are killed by antibiotics, possess many enzymes, which degrade related compounds. A random mutation could occur in a gene that encodes a degradative enzyme so that the enzyme now recognizes the antibiotic and degrades it. b. When random mutations occur, they may be lost due to genetic drift. This is particularly likely when the frequency of the mutation is very low in a large population. Alternatively (and much less likely), a random mutation that confers antibiotic resistance could become fixed in a population. c. If a random mutation occurs that confers antibiotic resistance and if the mutation is not lost by genetic drift, natural selection will favor the growth of microorganisms that carry the antibiotic-resistance allele if the organisms are exposed to the antibiotic. Therefore, if antibiotics are widely used, this will kill microorganisms that are sensitive and favor the proliferation of ones that happen to carry antibiotic-resistance alleles.

Chapter 20 1. A species is a population of organisms that maintains a distinctive set of attributes in nature. According to de Quieroz’s general lineage concept, each species is a population of an independently evolving lineage. One of the major driving forces behind speciation is geographic isolation. If a population is geographically isolated from another population of the same species, then genes will not mix between these two populations. As a result of this isolation, any mutations or shifts in allele frequency which occur in one population will be independent of those that occur in the other. As different genetic changes accumulate in the two populations, they may eventually become reproductively isolated. In other cases, such as polyploidy, abrupt genetic events can cause reproductive isolation.

2. a. Allopatric speciation may occur because the offspring would be geographically isolated from the original population. b. Sympatric speciation may occur if polyploidy plants are formed that cannot successfully interbreed with members of the original population. c. Allopatric speciation may occur due to geographic isolation, though some limited inbreeding may occur in hybrid zones where the narrow streams are found.

Chapter 21 1. Taxonomy is the field of biology that is concerned with the theory, practice, and rules of classifying living and extinct organisms and viruses. In taxonomy, scientists place organisms into distinct groups based on similarities and differences. This allows scientists to more easily appreciate the similarities and differences between groups of species. With regard to applications, many are possible. In the field of conservation, knowing that a group is a unique species may intensify its conservation efforts if its population becomes small. In agriculture, knowing that two species are or are not closely related may influence whether or not a breeder will attempt to make interspecies hybrids.

2. Systematics is the study of biological diversity based on evolutionary relationships that places organisms into taxonomic groups. By studying similarities and differences among species, biologists gain information about the evolutionary history of an organism (its phylogeny), and this helps scientists understand the relationship between ancestors and their descendants. A goal of systematics is to create a phylogenetic tree, which is a diagram that describes an organism’s phylogeny. By studying the branching points of a phylogenetic tree, biologists can group species according to common ancestors. Systematics attempts to organize species into monophyletic groups, which means that each group includes an ancestral species and all of its descendants leading to the species in question. As new information becomes available to scientists, trees are revised to accommodate that information.

The rationale behind the principle of parsimony is that a hypothesis that requires a fewer number of evolutionary changes is more likely to be correct compared to one that requires more changes. In other words, a simpler hypothesis is favored over a more complicated hypothesis. This concept applies to phylogenetic trees, which are hypotheses about the evolutionary histories of species.

Chapter 22 1. Cataloging the microbial species associated with a host organism is useful because many symbiotic microorganisms are beneficial to the host and identifying the microbiome of a host allows research into the ways the microbes and their host are interdependent, finding ways to enhance the benefit the microbes present to their host.

2. Natural antibiotics are produced by bacteria and other microorganisms as a defense, to inhibit the growth of other types of microorganisms, thereby reducing competition. In order to find new antibiotic compounds, it is best to look where bacteria are present. Most commercially produced antibiotics originated from the phylum Actinobacteria. These are soil bacteria, but they also exist in freshwater and so looking in soil or freshwater habitats may yield new antibiotic compounds.

Chapter 23 1. The plants of the Coal Age stored up carbon and as a result atmospheric CO2 levels dropped and atmospheric oxygen levels rose. Modern plants experience higher CO2 levels in the atmosphere than the Coal Age plants.

2. Placental transfer tissues supply developing embryos with food from their parents. This food allows embryos to grow into sporophytes that can produce many more spores than could zygotes. Sporangia protect developing spores. Plant spores are protected by tough sporopollenin walls during their dispersal in air. Gametophytes produce gametangia that protect delicate gametes. Vascular tissues allow food and water conduction to occur within the bodies of sporophytes. Waxy cuticles protect sporophytes from drying and attack by disease organisms. Stomata allow for gas exchange when conditions are moist but aid water conservation under arid conditions. Seeds allow plants to grow in a wide array of habitats. Flowers foster the development of seeds, and fruits aid seed dispersal.

Chapter 24 1. Many fungi live within the soil, where they break down organic compounds in dead organisms. These decomposers get rid of wastes and help recycle minerals, making them available for uptake by plants. Other soil fungi trap and kill nematodes, small soil animals from which the fungi obtain organic food. By so doing, fungi help to control populations of nematodes that attack plants, thereby protecting plants. Some fungi are parasites that live within the bodies of plants and animals, absorbing nutrients from them, and often killing the host in the process. Such fungi help to control populations of weeds and insects. Certain fungi live compatibly within plants, especially grasses, helping the plants to withstand biological and physical stresses. Most plants have mycorrhizal fungal partners that help them obtain water and minerals from soil. Lichens are very common on tree trunks, rocks, and soil. These partnerships of fungi and algae or cyanobacteria help to generate soils and add to its fertility. The fruiting bodies of fungi serve as food for animals (but experts recommend that people generally should not collect fungi from the wild for use as food, because many fungal fruiting bodies are toxic to humans).

2. You could search for information about the ectomycorrhizal fungi that are normally present in natural populations of Pinus resinosa. You could search for information about how to inoculate the roots of your pine seedlings with the appropriate strains of mycorrhizal fungi. This might include locating a source of soil harboring such fungi, perhaps from an undisturbed natural pine forest. Bearing in mind that such natural soil might also harbor fungal pathogens that might attack the delicate seedlings, you might also try to locate a source of laboratory grown fungal inoculum.

Chapter 25 1. Positive impacts: food sources, pets, transportation, drug testing, guide dogs, jewelry, clothes, pollination of flowers and agricultural crops, ecotourism, decomposition, nutrient cycling, and biological control of pests.

Negative impacts: parasites, pests, vectors of disease, competitors for food, some potentially harmful to humans.

2. Insects possess a number of critical innovations. They evolved wings but retained their walking legs. This means they can fly yet thrive in a variety of habitats. They have evolved a variety of mouthparts which enables them to feed on a variety of different food, from foliage and plant sap to rotting fruits and vertebrate blood. Many insects undergo complete metamorphosis, allowing larvae to occupy completely different habitats from the adults.

Chapter 26 1. Vertebrates can swim, crawl, walk or hop or run, burrow, slither, or fly. Fishes most commonly swim, though some may be able to crawl on land. Many amphibians, such as frogs, can swim and hop, while salamanders walk. Caecilians, however, burrow in the ground. Many reptiles can swim, walk, and even run, but the snakes slither along the ground. Most birds fly and all can walk or run, while penguins and some others can swim. Among the mammals, all these forms of locomotion are utilized, from flying bats and swimming whales to running dogs and burrowing moles.

2. Amphibians breathe through their skin and are particularly susceptible to pollutants which may be present in their environment.

Chapter 27 1. On a cut tree stump you would be able to locate the outer bark, secondary xylem, and annual rings, but the inner bark and vascular cambium would likely be too thin for you to see without the use of a microscope.

2. You would expect shoot growth to be particularly responsive to light, humidity, temperature, wind, and carbon dioxide concentration, because these physical factors influence photosynthesis. You would expect soil water, soil minerals, obstructing soil particles (such as rocks), and gravity to most strongly affect the growth of underground root systems.

Chapter 28 1. Natural plants produce bad-tasting secondary metabolites that keep herbivores from completely destroying them. Humans have taste receptors similar to those of other animals. Thus, the defensive chemicals taste bad to us also.

2. You could try to identify secondary metabolites that are distasteful to the particular herbivores but not distasteful or toxic to humans. If such compounds can be identified, you could determine which pathway enzymes for synthesizing these metabolites are missing from the crop plant or expressed at too low a level. You could try to use genetic engineering or conventional breeding techniques to add the missing enzymes to the crop genome, or increase the levels of metabolite expression. Alternatively, you could try to modify the crop so that it exudes volatile compounds that attract the enemies of the herbivores.

Chapter 29 1. You could experimentally determine how effectively your crop plants obtain water and soil nutrient ions and how resistant your plant is to water loss under different simulated climate regimes. You could measure the relative water content of plants grown under different conditions of soil moisture. You might want to examine the extent of the root system, how thick the cuticle is, how responsive the stomata are to drought conditions, and whether or not your crop can use root pressure to refill xylem that has become embolized as the result of cold or drought. You might want to examine your crop for its ability to balance cytoplasmic osmotic conditions with solutes and protect membranes from plasmolysis damage.

2. If you see or imagine tall trees growing closely together, you can assume that soil moisture is high on average, because trees transpire huge quantities of water obtained from the soil. If you see or imagine abundant or low-growing plants, such as might occur in a grassland, you can deduce that soil water is relatively low, but constant enough to prevent plant death. If you see or imagine a desert, with relatively few plants visible, you can deduce that soil water is very low or sporadically available and that the plants present likely have specific adaptations allowing them to cope with water stress.

Chapter 30 1. Orchid flowers are bilaterally symmetrical because they can be cut by only one plane that would produce two identical halves. Bilateral symmetry is associated with bee pollination, and, in fact, bees do pollinate many orchids, though other pollination processes are involved in some cases. For example, Chinese botanists recently reported the case of an orchid that inhabits a windless site that is too dry for animal pollinators. This orchid has adapted to its unusual pollination circumstances by producing anthers that grow in a pattern that allows self-pollination. Because the gene CYCLOIDEA is involved in the development of bilaterally symmetrical flowers in at least two distantly related eudicot plants (snapdragon and Gerbera), it is reasonable to hypothesize that orchids, which are monocots, might possess a similar gene.

Chapter 31 1. Negative feedback loop—In a negative feedback loop, the system is working to return to homeostasis. Sometimes there is a physiological disturbance that pushes a system away from homeostasis. An example of this is when the human body temperature exceeds 37°C. When this occurs, compensatory mechanisms such as perspiring will occur until normal body temperature (37°C) is achieved; this removes the signals for dissipating heat and thus homeostasis is restored.

Positive feedback loop—In a positive feedback loop, instead of moving toward homeostasis, the system is moving away from homeostasis. Positive feedback is much less common in nature than negative feedback. The process of birth in mammals is an example of a positive feedback loop. As the fetus pushes against the cervix of the mother, nerve signals from the cervix relay a signal to the brain and endocrine system, which, in turn, produce hormones that cause stronger uterine contractions. The strong contractions stimulate the brain and endocrine system to make more hormones that intensify the contractions even more, eventually resulting in the birth of the newborn.

2. All animals are multicellular, which means they are composed of many cells, unlike unicellular organisms such as bacteria. The cells in an animal’s body are organized into groups of similar cells called tissues, such as epithelial, connective, muscle, and nervous tissue. When two or more types of tissues are arranged in a specific pattern, the resulting structure is called an organ. The lungs, heart, kidney, and liver are all examples of organs that are found in many animals. When several different organs work together to perform an overall function, it is called an organ system. The digestive, reproductive, and nervous systems are all major organ systems found in most animals.

Chapter 32 1. The nervous system of many animals is divided into the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS is composed of a brain and a nerve cord, which in vertebrates is the spinal cord. A major function of the brain is to interpret stimuli from all parts of the body. Once the stimulus is interpreted, the brain determines what response is necessary. The PNS consists of neurons and processes that are outside of the CNS but which connect to it. The PNS receives stimuli from the body and the environment and conveys it to the CNS for interpretation. In addition to receiving stimuli, the PNS is what allows the animal to respond to stimuli if a response is necessary. The distinction between a CNS and PNS is less clear in many invertebrates with simpler nervous systems.

2. Reflexes are beneficial because they may protect an animal from various types of danger; they also occur very rapidly because they generally involve only one or a few synaptic connections. Common examples are cringing in response to a noise, grasping in young primates (to help hold onto their mother's fur), closing the eyes when something contacts them, the pupillary reflex in response to bright light, postural reflexes that allow us to maintain balance even on a moving subway train, the diving reflex of many animals in which the heart rate slows and breathing stops when water contacts the face, and many others.

Chapter 33 1. Animals may sense tactile, olfactory, auditory, gustatory, electromagnetic, painful and temperature stimuli. Tactile and auditory stimuli are detected by mechanoreceptors. Olfactory and gustatory stimuli are detected by chemoreceptors, and electromagnetic stimuli are detected by photoreceptors. Pain is sensed by nociceptors and temperature by thermoreceptors.

2. Structurally, both types of eyes include one or more lenses and photoreceptors, and in both cases the photoreceptors are highly specialized with large amounts of surface area in which the light-sensitive molecules are located. Functionally, both types of eye sense both the intensity and color (wavelength) of light.

Chapter 34 1. Two basic types of skeletons are found in animals: exoskeletons, and endoskeletons. For both types of skeletons, the main functions are support, protection, and locomotion.

Exoskeleton—This is an external skeleton that surrounds the animal and provides support, protection, and an anchoring place for muscles involved in movement. The complexity, shape, thickness, and durability vary greatly from species to species, depending on where the organism lives and how it moves. In most instances, the exoskeleton does not grow along with the organism and must periodically be shed to accommodate an increase in body size. Exoskeletons can be found in arthropods.

Endoskeleton—Unlike exoskeletons, endoskeletons are internal and grow along with the organism. In all cases, endoskeletons are made up of minerals such as calcium, magnesium, and phosphate, but their complexity and exact composition depend on the type of organism and how it moves and lives. Endoskeletons can be found in all echinoderms, some sponges, and all vertebrates.

2. Skeletal muscle attaches via connective tissue to bone and is involved in locomotion and the movement of limbs and other body structures. It is under voluntary control. Due to its striped appearance when viewed under a microscope, skeletal muscle is also referred to as striated muscle. The striations are the myofibrils arranged in sarcomeres.

Smooth muscle gets its name because it has no striations when viewed under a microscope. It surrounds and forms the outer lining of hollow organs and tubes, including organs of the digestive, cardiovascular, and respiratory systems. Unlike skeletal muscle, smooth muscle is not under voluntary control; it contracts and relaxes spontaneously or in response to changes in neural input.

Cardiac muscle is found in the heart. This striated type of muscle is responsible for generating the force that propels blood out of the heart and throughout the circulatory system.

Chapter 35 1. Three major processes- glycogenolysis, gluconeogenesis, and lipolysis- contribute to glucose homeostasis when an animal is fasted. The first two are stimulated in the liver by the hormone glucagon and the neurotransmitter norepinephrine, which also stimulates lipolysis in adipose cells. The glucose provided by the liver enters the blood; fatty acids released by lipolysis of triglycerides in adipose tissue provide an alternate energy source for cells outside the central nervous system, thus "sparing" glucose for the CNS.

2. A nutrient is any substance that is consumed by an organism and is needed for survival, growth, development, tissue repair, or reproduction. By that definition, water is a nutrient.

Essential amino acids—These are amino acids that in many animals cannot be made by cellular metabolism and must be obtained through the diet. Without these essential amino acids, animals would not be able to manufacture the proteins required for the animal to live. Many herbivores, however, cannot obtain these amino acids through their diet; such animals have the ability to manufacture these amino acids themselves.

Essential fatty acids—Many of the fatty acids that animals need to function cannot be made by the animal’s cells. These fatty acids must be obtained through the animal’s diet and are known as essential fatty acids. These fatty acids can be obtained by either eating plants or animals.

Vitamins—These are organic nutrients that serve as coenzymes for many metabolic pathways in animal bodies. For metabolism to function, these vitamins must be obtained through the diet. Without the proper balance of vitamins, severe health issues can occur.

Minerals—These are important inorganic molecules that animals require to build skeletons, balance salt concentrations in their body fluids, and produce electric currents for normal function of the nervous system and muscles. Many of these important minerals are required only in trace amounts and can be stored in certain body structures, such as the skeleton, to reduce the risk of mineral deficiency.

Chapter 36 1. The cardiac cycle consists of ventriclular filling (diastole) and ventricular contraction (systole). Blood fills the ventricles from the atria through the av valves. When the ventricles become electrically excited, they contract, closing the av valves and opening the semilunar valves. This propels blood out into the aorta or pulmonary trunk. When the ventricles become electrically repolarized, they relax. As pressure decreases in the relaxing ventricles, the semilunar valves close. Eventually the av valves re-open, and the cycle starts again. Valves must open in one direction so that blood may be propelled forward; for example, if the av valves could open in both directions, some ventricular blood would be ejected back into the atria instead of into the arteries.

2. Single circulation—This is the type of closed circulatory system found in fishes and is the simplest type of circulation found in vertebrates. In this system, deoxygenated blood from the tissues is returned to the two-chambered heart, which then pumps the blood to the gills. In the gills, blood picks up oxygen and unloads carbon dioxide, then circulates to the tissues to drop off oxygen and nutrients and pick up carbon dioxide and wastes. Arteries are the blood vessels that carry blood away from the heart, and veins carry blood to the heart. There is no boost in blood pressure after blood leaves the gills.

Double circulation—This is the type of circulatory system found in crocodiles, birds, and mammals and is divided into two parts: the systemic and pulmonary circulations. In the systemic circulation, blood is pumped from the left side of the heart to the body to drop off oxygen and nutrients and pick up carbon dioxide and wastes. The blood then returns to the right side of the heart. In the pulmonary circulation, the right side of the heart provides a second pumping mechanism that sends blood to the lungs to release carbon dioxide and pick up oxygen from the atmosphere. Due to the fact that the heart is divided into a right and left side, it acts as two hearts in one, which increases the efficiency of the circulation. Amphibians and most reptiles have a circulation with features of both types.

Chapter 37 1. Animals exchange gases with an aqueous environment in two major ways: (1) across the skin or body surface and (2) via gills. In small invertebrates with bodies that are only a few cell layers thick, oxygen and carbon dioxide can rapidly diffuse across the body surface and to the interior parts of the animal. As a result, they require no special respiratory organs such as lungs or gills. Diffusion of gases across the body surface occurs in most amphibians; they have skin that is highly permeable to oxygen and carbon dioxide. Although these amphibians require gills or lungs for most of their oxygen and carbon dioxide exchange, diffusion of gases across the skin represents an important adaptation for amphibious life.

Most exclusively aquatic animals other than marine mammals have specialized respiratory structures called gills. These can be either uncovered extensions from the body surface called external gills, or they can be enclosed in a protective cavity, in which case they are called internal gills. External gills may be concentrated in one part of the body, or they may be scattered over a large area. Having external gills has two major drawbacks. One is that the gills can be damaged by the environment, and the other is that the constant waving of the elaborate-looking gills that occurs for adequate ventilation to take place can draw the attention of predators.

In internal gills—which are found in fishes—the gills are covered by a bony plate called an operculum. This structure acts to aid in ventilation by helping to draw oxygenated water over the gills. In addition, the operculum provides protection to the gills and decreases the chances of damage by the environment.

2. Air enters either through the nose or the mouth and passes on to the pharynx. The nose and pharynx help to filter, warm, and moisturize the air that enters from the outside world. This part of the respiratory system also produces mucus, which helps to trap particles from the air. After the pharynx, the air moves to the larynx and then to the trachea. The trachea is also lined with mucus-producing cells, which trap particles that were missed by the nose and pharynx. In addition, the trachea is lined with ciliated epithelium that moves the mucus to the pharynx where it is swallowed. After the trachea, the respiratory system divides into two tubes—the right bronchus and the left bronchus— before dividing into smaller tubes called bronchioles. At the ends of the bronchioles there are saclike structures called alveoli that are surrounded by capillaries. It is at the alveoli that the exchange of oxygen and carbon dioxide takes place. The breathing process is facilitated by the intercostal muscles, which lie between the ribs and a large dome-shaped muscle called the diaphragm. The action of these two groups of muscles creates a decreased pressure that enables the animal to inhale air.

Chapter 38 1. Metanephridia of annelids. Metanephridia are pairs of tubules in each body segment of annelid worms. Interstitial fluid is filtered through structures called nephrostomes. As the filtrate passes down the tubule of the metanephridia, ions and other beneficial solutes are reabsorbed into capillaries before the dilute urine is excreted via nephridiopores. In insects, cleansing occurs by secretion, with organs called Malpighian tubules. In vertebrates, filtration and secretion both occur in the kidneys. Animals that live in the water and produce ammonia or ammonium ions as a nitrogenous waste, excrete these substances across the skin surface or across the gills.

2. The first part of the nephron is called the renal corpuscle, where the filtrate from the glomerular capillaries enters Bowman’s capsule. From there, the filtrate passes on to the proximal tubule, where most of the reabsorption of useful solutes occurs. After the proximal tubule, fluid moves into the loop of Henle, where additional water and ions are reabsorbed. Next, the fluid enters the distal convoluted tubule, where fine-tuning of solute reabsorption and secretion takes place. Finally, the fluid in the distal tubule empties into a collecting duct, where the final composition of urine is established before it leaves the body. Transport occurs all along the nephron. However, reabsorption of organic molecules primarily occurs in the proximal tubule. Water is reabsorbed by osmosis in all parts of the nephron, but the amount of water reabsorbed depends on various factors such as the hormones aldosterone and antidiuretic hormone.

Chapter 39 1. Two hormones, 20-hydroxyecdysone and juvenile hormone, play major roles in insect development. Ecdysone is secreted by a pair of glands called the prothoracic glands. Twenty-hydroxyecdysone stimulates rapid differentiation and causes the larva to molt. Juvenile hormone is secreted by the corpus allatum, and its main responsibility is to control the nature of the molt induced by 20-hydroxyecdysone. Not until the levels of juvenile hormone decline to nearly zero does the molt result in the transition from a larva to a pupa. In vertebrates, thyroid hormone, growth hormone, and insulin-like growth factor-1 have numerous developmental functions ranging from metamorphosis in frogs, to lung formation in fetal mammals.

2. Androgens such as testosterone control reproduction in males and are produced in the testes. Progesterone and estrogens such as estradiol and progesterone control reproduction in females and are produced in the ovaries. Mineralocorticoids such as aldosterone are produced by the glomerulosa cells of the adrenal cortex and act to regulate salt and water balance. Glucocorticoids such as cortisol are produced by the fasciculata cells of the adrenal cortex; these hormones are catabolic, suppress the immune system, and are an important part of the response to stress. The hormone 1,25-dihydroxyvitamin D is derived from precursors in the skin or formed from dietary vitamin D. It acts to increase Ca2_ absorption from the intestines. Unlike other hormones, steroid hormones are derived from cholesterol and are therefore hydrophobic. They act by binding to intracellular receptors and altering transcription of one or more genes. Most other hormones (thyroid hormone is a notable exception) act on plasma membrane receptors and activate intracellular signaling pathways.

Chapter 40 1. The major events of animal development are cleavage, gastrulation, neurulation, and organogenesis. In cleavage, the embryo divides into a mass of smaller cells. In gastrulation, the three cell layers of ectoderm, mesoderm and endoderm are formed. The future nervous system and a segmented body develop during neurulation. Tissues are organized into differentiated organs during organogenesis.

2. The ovarian cycle is divided into the follicular phase- in which growth and maturation of follicles occurs- and the luteal phase- in which a corpus uteum is formed and produces progesterone to prepare for a possible pregnancy. The two secretory phase, the endometrium continues to grow and also develops glands that will secrete nutritive substances in the event of an embryo becoming implanted; this phase occurs in response to progesterone secreted during the luteal phase of the ovarian cycle.

Chapter 41 1. Immunoglobulins are made of four interlinked polypeptides, two heavy chains and two light chains held together by disulfide bonds. Each immunoglobulin contains within its structure a constant region that is the same from one molecule to another within a given immunoglobulin class, and a variable region. The variable region is what distinguishes one immunoglobulin from another, and is the region that specifically binds a particular antigen.

2. B cells differentiate into plasma cells upon binding an antigen. Plasma cells secrete antibodies. Cytotoxic T cells directly kill viruses, ancerous and transplanted cells. Helper T cells assist in the activation and function of both B cells and cytotoxic T cells and therefore participate in both humoral and cell mediated immunity. Natural killer cells have functions similar to cytotoxic T cells but also have certain nonspecific functions; therefore, they participate in both innate and acquired immunity.

Chapter 42 1. Just as with geese, young cranes exhibit imprinting behavior. Human researchers took advantage of this behavior and encouraged young cranes to imprint on humans dressed in crane suits. They even flew behind ultralight planes piloted by crane-suited researchers, following them to their overwintering sites.

2. Chemical—Chemical communication is often used among animals to mark territory or food sources or to attract mates. Sound—This method of communication has a long range. It is a good method of communication between members of the same species, especially members of the opposite sex.

Visual—In courtship, animals use a vast number of visual signals to identify and select potential mates. One drawback is that by the time visual communication has been established, the two organisms will be in close proximity to each other and conflict could occur.

Tactile—Many individuals of the same species communicate through direct contact with each other. Tactile information is often used by insects, for example, to convey information about food.

Chapter 43 1. Ensure the park is burned frequently. More frequent fi res use up fuel supplies and ensure future fi res do not burn out of control. Yosemite allows fi res to burn in 80% of the park. Prior to 2008, the area outside the park hadn’t had a big fi re for 20 years, leaving bushes and shrubs to grow unchecked. The recent proliferation of homes in the area decreased the opportunities for controlled burns.

2. The answer depends on where the course is being taught. Answering this question is an excellent way to get students to think about the world that surrounds them every day. Anthropogenic changes such as urban development or agriculture may result in much different vegetation than the biome predicted using temperature/precipitation profiles.

Chapter 44 1. In the future, human population growth may be limited by the emergence of new diseases which can spread quickly among members of a large population; food shortage or shortage of other resources; global climate change; pollution; or social change including increased conflicts.

2. Reduction in use of fossil fuels to reduce the need for forested land to absorb excess CO2.

Chapter 45 1.

Chapter 46 1. As we learned in Chapter 43, most scientists believe atmospheric CO2 levels will have reached about 700 ppm by the end of the century, though extrapolation from Figure 59.18 puts the level closer to 550 ppm. The effects of such an increase are many and varied. Global warming will increase and cause a shift in the distribution of many organisms. Other organisms that cannot easily move, such as those on islands or mountain tops, will go extinct. Precipitation rates will change with most areas getting wetter, but some deserts and continental interiors becoming drier. As we learned from Chapter 43, such changes may affect the frequency of disease. Changing temperatures will also alter the phenology, or timing, of many events, such as bud burst and the reproductive cycles of many organisms. For example, frogs and birds may start to breed earlier in the year. In addition, increased levels of CO2 will further reduce foliar nitrogen and lower herbivory levels. In theory, reduced foliar nitrogen in leaf litter could change decomposition rates and affect rates of nutrient cycling in both terrestrial and aquatic ecosystems. Greater plant productivity could also elevate litterfall, increasing the frequency and severity of wildfires. Elevated CO2 could increase the acidity of the oceans, increasing mortality of corals and other sensitive organisms.

2. Nitrogen molecules are held together by strong triple bonds which only certain bacteria can break apart using nitrogenase enzymes and large amount of energy. As a result, the whole nitrogen cycle is limited by this step. Nitrogen supply to plants is often supplemented using nitrogen-rich fertilizers produced by industrial processes.

Chapter 47 1. Introduced species, also referred to as exotic species, are species that are moved by humans from their native habitat to a different location. As a result, the introduced species may interfere with and possibly outcompete native species for resources or feed on native species. If the introduced species outcompetes or preys heavily on the native species, then the native species may become threatened, endangered, or extinct.

Habitat destruction is predominantly a result of deforestation through the removal of trees and plants from a habitat. As a result of this removal of habitat, species are forced into smaller and smaller habitats, thereby increasing the stress placed on the species who reside there. This habitat reduction, if left unchecked, may result in the extinction of one or many species.

Direct exploitation occurs when an organism is overharvested by humans. As a result, the number of individuals is greatly reduced, thus putting pressure on the population. If too many individuals are removed, reproduction becomes difficult, and due to the decrease in population size and genetic diversity, the species may become extinct.

2. Because your goal is to maximize biodiversity, you would choose an area rich in species, not necessarily endemic species. According to the principles we discussed in Chapter 44, you would try to select an area where the individuals are spread fairly evenly among species, maximizing the Shannon diversity index. According to the theoretical tenets laid out in Figure 47.10, you might establish a series of small parks, containing a diverse array of habitats, rather than one large park. You might minimize the amount of edge in each of these parks by maximizing the area : perimeter ratio. You might also decide to link the parks by a series of habitat corridors to minimize extinctions. Finally, you would try to ensure that the park is adequately patrolled, to minimize poaching.