Suggested Answers to Collaborative Questions Principles of Biology

Chapter 11.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 thefollowing: 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 21. Protons—These are positively charged particles that are found in thecenter of the atom which is referred to as the nucleus. The numberof protons an atom has is called the atomic number, and this defineseach type of element. This particle makes up approximately half ofthe mass of an atom, which is referred to as the atomic mass.

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

Electrons—These are negatively charged particles that are found inorbitals around the nucleus. For atoms, the number of protons isequal to the number of electrons. Therefore, an atom has no overallnet charge. If electrons are added to an atom or taken away, this willchange the charge of the atom, which is now called an ion, therebychanging its properties and reactivity.

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

Water can directly participate in types of chemical reactions calledhydrolysis reactions, which among other things are important in theconversion of certain large molecules into smaller units that are biologicallyimportant.

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

Water also has a high heat of fusion and requires considerableenergy to be removed from it to turn it from a liquid to a solid. As aresult of this, liquid water is very stable and resistant to temperaturechange, making it ideal for living organisms.Also see Figure 2.13.

Chapter 3

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

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

Polysaccharides—These are polymers that consist of many monosaccharidesbonded 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. Organismsdevelop specific proteins to fight against specific diseases.

Enzymes—increase the rates of chemical reactions. Without theseproteins, 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 cellularmembranes.

Chapter 41.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 51.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 61.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 increasingthe 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 71.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 81. 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 91. 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 101.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 111.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 feedbackinhibition 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 121. A mutation is a heritable change in the genetic material. A mutationcan be passed from mother cell to daughter cell or the mutationcan occur during gamete formation and be passed from parent tooffspring. The word mutation is often associated with negative effectsbut this is not always the case. Mutation increases the genetic variability

of a species. If a mutation is favorable, it will be beneficial tothat individual and may increase its reproductive success. Likewise,such favorable mutations may be passed to offspring. Over time, thisprocess may increase the frequency of the mutation in a population.On the other hand, however, most mutations are unfavorable anddecrease the survival or reproductive success of individuals. Thesemutations 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 mutagensare and thereby avoid them. On the other hand, one might arguethat 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 diseasessuch as cancer or help us to prevent mutations. On the other hand,it may not.c. Similarly, investigating DNA repair mechanisms may lead to waysof preventing mutations. On the other hand, it may not.d. Other places: educating the public about mutagens; tighter regulationsof substances that contain mutagens; alternative methods ofagriculture that may diminish the level of mutagens in food; andmany others.

Chapter 131. During interphase, the chromosomes are greatly extended. In thisconformation, they might get tangled up with each other and not sortproperly during meiosis and mitosis. The condensation process probablyoccurs so that the chromosomes easily align along the equatorialplate during metaphase without getting tangled up.

2. It’s not possible to give a direct answer, but the point is for studentsto be able to draw chromosomes in different configurations andunderstand the various phases. The chromosomes may or maynot 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 141. The discussion is a matter of opinion. Some may say that Mendelwithheld data, but others may not feel that way.

2. a. Chromosomes contain the genetic information that is passed fromparent to offspring and from one cell to another. Genes, the basicunits 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 divisionand gamete formation.c. The nucleus of a diploid cell contains two sets of chromosomes thatare found in homologous pairs. Half of these chromosomes comefrom the mother, and the other half come from the father, and eachset of chromosomes carry a full complement of genes.d. During meiosis, one member of each chromosome pair segregatesinto one daughter nucleus, and its homologue segregates into theother daughter nucleus. Each of the resulting haploid cells containsonly one set of chromosomes. During the formation of haploidcells, the members of different chromosome pairs segregate independentlyof each other.e. Gametes are haploid cells that combine to form diploid cells duringfertilization, with each gamete transmitting one set of chromosomesto the offspring.

Tenets 2, 3, and 4 were largely determined via microscopy. Tenets 1and 5 were deduced both via crosses and via microscopy. Moderntechniques to verify this theory could involve a variety of cloningtechniques that are described in Chapters 20 and 21.

Chapter 151.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 parentsproduce gametes that unite to form a new individual. However, conjugationis similar to sexual reproduction in the sense that the geneticmaterial from two cells is somewhat mixed. In conjugation, there isnot the mixing of two genomes, one from each gamete. Instead, thereis a transfer of genetic material from one cell to another. This transfercan alter the combination of genetic traits in the recipient cell.

Chapter 161. There are many possible answers. Examples include researchadvances, 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 171. The prokaryotic genome typically consists of a single chromosomeranging from several hundred thousand to a few million base pairs in length. Most prokaryotes contain only a single chromosome althoughthere may be multiple copies present within a single cell. Bacterialchromosomes are predominantly circular in structure although linearchromosomes are found in several species. When compared to theeukaryotic genome, the prokaryotic genome is less complex, lackingcentromeres 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 linearchromosomes. The genome of simple eukaryotes carries only a fewthousand genes, whereas the genome of more complex eukaryotesmay contain tens of thousands of genes. Unlike the genome ofprokaryotes, the chromosomes found in eukaryotes are much morecomplex, having centromeres, telomeres, and multiple origins ofreplication. 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 181. The reducing atmosphere hypothesis—This hypothesis is basedlargely on geological evidence. By examining what chemicals werein the primitive atmosphere at the time when life arose, scientistshave determined that the basic chemicals needed to form organicmolecules were present. By combining these primitive inorganic molecules,more complex molecules such as amino acids and nucleotidescould be formed.

The extraterrestrial hypothesis—This hypothesis postulates that thefirst organic molecules may have come from fallen bodies from spacesuch as meteorites. Because certain meteorites called carbonaceous

chondrites contain organic carbon, these bodies may have added thefirst organic molecules to our planet.Deep sea vents—This hypothesis proposes that the key organic moleculesthat started life may have originated in deep sea vents. Becausethese vents have the necessary chemicals and high temperatures, lifeon 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 separatedthe internal contents of the protobiont from the external environment; (2) polymers inside the protobiont contained information;(3) polymers inside had enzymatic functions; and (4) protobiontswere capable of self-replication. However, they were not as biochemicallycomplex as living cells and were not capable of preciseself-reproduction. However, it’s difficult to describe a clear distinctionbetween a protobiont and a living cell.

Chapter 191.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 maylead to antibiotic resistance. A random mutation may create anantibiotic-resistance allele. This could occur in different ways.Many antibiotics exert their effects by binding to an essential cellularprotein within the microorganism and inhibiting its function.A random mutation could occur in the gene that encodes suchan essential cellular protein; this could alter the structure of theprotein in a way that would prevent the antibiotic from binding tothe 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 occurin a gene that encodes a degradative enzyme so that the enzymenow recognizes the antibiotic and degrades it.

b. When random mutations occur, they may be lost due to geneticdrift. This is particularly likely when the frequency of the mutationis very low in a large population. Alternatively (and much lesslikely), a random mutation that confers antibiotic resistance couldbecome fixed in a population.

c. If a random mutation occurs that confers antibiotic resistance and ifthe mutation is not lost by genetic drift, natural selection will favorthe growth of microorganisms that carry the antibiotic-resistanceallele if the organisms are exposed to the antibiotic. Therefore, ifantibiotics are widely used, this will kill microorganisms that aresensitive and favor the proliferation of ones that happen to carryantibiotic-resistance alleles.

Chapter 201. A species is a population of organisms that maintains a distinctive setof 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 geographicisolation. If a population is geographically isolated from anotherpopulation of the same species, then genes will not mix betweenthese two populations. As a result of this isolation, any mutations or

shifts in allele frequency which occur in one population will be independentof those that occur in the other. As different genetic changesaccumulate in the two populations, they may eventually becomereproductively isolated. In other cases, such as polyploidy, abruptgenetic events can cause reproductive isolation.

2. a. Allopatric speciation may occur because the offspring would begeographically isolated from the original population.b. Sympatric speciation may occur if polyploidy plants are formedthat cannot successfully interbreed with members of the originalpopulation. c. Allopatric speciation may occur due to geographic isolation, thoughsome limited inbreeding may occur in hybrid zones where the narrowstreams are found.

Chapter 211. Taxonomy is the field of biology that is concerned with the theory,practice, and rules of classifying living and extinct organisms andviruses. In taxonomy, scientists place organisms into distinct groupsbased on similarities and differences. This allows scientists to moreeasily appreciate the similarities and differences between groups ofspecies. With regard to applications, many are possible. In the field ofconservation, knowing that a group is a unique species may intensifyits conservation efforts if its population becomes small. In agriculture,knowing that two species are or are not closely related may influencewhether or not a breeder will attempt to make interspecies hybrids.

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

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 221. Cataloging the microbial species associated with a host organism is useful because many symbiotic microorganisms are beneficial to the hostand identifying the microbiome of a host allows research into the ways themicrobes 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 microorganismsas a defense, to inhibit the growth of other types of microorganisms, thereby reducing competition. In order to find new antibiotic compounds, it is best tolook where bacteria are present. Most commercially produced antibiotics originated from the phylum Actinobacteria. These are soil bacteria, but theyalso exist in freshwater and so looking in soil or freshwater habitats may yield

new antibiotic compounds.

Chapter 231. 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 fromtheir parents. This food allows embryos to grow into sporophytes thatcan produce many more spores than could zygotes. Sporangia protectdeveloping spores. Plant spores are protected by tough sporopolleninwalls during their dispersal in air. Gametophytes produce gametangiathat protect delicate gametes. Vascular tissues allow food and waterconduction to occur within the bodies of sporophytes. Waxy cuticlesprotect sporophytes from drying and attack by disease organisms.Stomata allow for gas exchange when conditions are moist but aidwater conservation under arid conditions. Seeds allow plants to growin a wide array of habitats. Flowers foster the development of seeds,and fruits aid seed dispersal.

Chapter 241. Many fungi live within the soil, where they break down organiccompounds in dead organisms. These decomposers get rid of wastesand help recycle minerals, making them available for uptake byplants. Other soil fungi trap and kill nematodes, small soil animalsfrom which the fungi obtain organic food. By so doing, fungi help tocontrol populations of nematodes that attack plants, thereby protectingplants. Some fungi are parasites that live within the bodies ofplants and animals, absorbing nutrients from them, and often killingthe host in the process. Such fungi help to control populations ofweeds and insects. Certain fungi live compatibly within plants, especiallygrasses, helping the plants to withstand biological and physicalstresses. Most plants have mycorrhizal fungal partners that help themobtain water and minerals from soil. Lichens are very common ontree trunks, rocks, and soil. These partnerships of fungi and algae orcyanobacteria help to generate soils and add to its fertility. The fruitingbodies of fungi serve as food for animals (but experts recommendthat people generally should not collect fungi from the wild for use asfood, because many fungal fruiting bodies are toxic to humans).

2. You could search for information about the ectomycorrhizal fungi thatare normally present in natural populations of Pinus resinosa. Youcould search for information about how to inoculate the roots of yourpine seedlings with the appropriate strains of mycorrhizal fungi. Thismight include locating a source of soil harboring such fungi, perhapsfrom an undisturbed natural pine forest. Bearing in mind that suchnatural soil might also harbor fungal pathogens that might attack thedelicate seedlings, you might also try to locate a source of laboratory grownfungal inoculum.

Chapter 251. Positive impacts: food sources, pets, transportation, drug testing,guide dogs, jewelry, clothes, pollination of flowers and agriculturalcrops, ecotourism, decomposition, nutrient cycling, and biologicalcontrol of pests.

Negative impacts: parasites, pests, vectors of disease, competitors forfood, 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 261. Vertebrates can swim, crawl, walk or hop or run, burrow, slither, orfly. Fishes most commonly swim, though some may be able to crawlon land. Many amphibians, such as frogs, can swim and hop, whilesalamanders walk. Caecilians, however, burrow in the ground. Manyreptiles can swim, walk, and even run, but the snakes slither alongthe ground. Most birds fly and all can walk or run, while penguinsand some others can swim. Among the mammals, all these forms oflocomotion are utilized, from flying bats and swimming whales torunning dogs and burrowing moles.

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

Chapter 271. On a cut tree stump you would be able to locate the outer bark,secondary xylem, and annual rings, but the inner bark and vascularcambium would likely be too thin for you to see without the use of amicroscope.

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 wouldexpect soil water, soil minerals, obstructing soil particles (such asrocks), and gravity to most strongly affect the growth of undergroundroot systems.

Chapter 281. Natural plants produce bad-tasting secondary metabolites that keepherbivores from completely destroying them. Humans have tastereceptors similar to those of other animals. Thus, the defensivechemicals taste bad to us also.

2. You could try to identify secondary metabolites that are distastefulto the particular herbivores but not distasteful or toxic to humans. Ifsuch compounds can be identified, you could determine which pathwayenzymes for synthesizing these metabolites are missing from thecrop plant or expressed at too low a level. You could try to use geneticengineering or conventional breeding techniques to add the missingenzymes to the crop genome, or increase the levels of metaboliteexpression. Alternatively, you could try to modify the crop so that itexudes volatile compounds that attract the enemies of the herbivores.

Chapter 291. You could experimentally determine how effectively your crop plantsobtain water and soil nutrient ions and how resistant your plant isto water loss under different simulated climate regimes. You couldmeasure the relative water content of plants grown under differentconditions of soil moisture. You might want to examine the extent ofthe root system, how thick the cuticle is, how responsive the stomataare to drought conditions, and whether or not your crop can use rootpressure to refill xylem that has become embolized as the result ofcold or drought. You might want to examine your crop for its abilityto balance cytoplasmic osmotic conditions with solutes and protectmembranes from plasmolysis damage.

2. If you see or imagine tall trees growing closely together, you canassume that soil moisture is high on average, because trees transpire

huge quantities of water obtained from the soil. If you see or imagineabundant or low-growing plants, such as might occur in a grassland,you can deduce that soil water is relatively low, but constant enoughto prevent plant death. If you see or imagine a desert, with relativelyfew plants visible, you can deduce that soil water is very low orsporadically available and that the plants present likely have specificadaptations allowing them to cope with water stress.

Chapter 301. Orchid flowers are bilaterally symmetrical because they can be cutby only one plane that would produce two identical halves. Bilateralsymmetry is associated with bee pollination, and, in fact, bees do pollinatemany orchids, though other pollination processes are involvedin some cases. For example, Chinese botanists recently reported thecase of an orchid that inhabits a windless site that is too dry foranimal pollinators. This orchid has adapted to its unusual pollinationcircumstances by producing anthers that grow in a pattern thatallows self-pollination. Because the gene CYCLOIDEA is involved inthe development of bilaterally symmetrical flowers in at least two distantlyrelated eudicot plants (snapdragon and Gerbera), it is reasonableto hypothesize that orchids, which are monocots, might possessa similar gene.

Chapter 311. Negative feedback loop—In a negative feedback loop, the system isworking to return to homeostasis. Sometimes there is a physiologicaldisturbance 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 willoccur 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 movingtoward homeostasis, the system is moving away from homeostasis.Positive feedback is much less common in nature than negativefeedback. The process of birth in mammals is an example of apositive feedback loop. As the fetus pushes against the cervix of themother, nerve signals from the cervix relay a signal to the brain andendocrine system, which, in turn, produce hormones that cause strongeruterine 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 ofmany cells, unlike unicellular organisms such as bacteria. The cellsin an animal’s body are organized into groups of similar cells calledtissues, 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 overallfunction, it is called an organ system. The digestive, reproductive, andnervous systems are all major organ systems found in most animals.

Chapter 321. The nervous system of many animals is divided into the centralnervous system (CNS) and the peripheral nervous system (PNS). TheCNS is composed of a brain and a nerve cord, which in vertebrates isthe spinal cord. A major function of the brain is to interpret stimulifrom all parts of the body. Once the stimulus is interpreted, the braindetermines what response is necessary. The PNS consists of neuronsand processes that are outside of the CNS but which connect

to it. The PNS receives stimuli from the body and the environmentand conveys it to the CNS for interpretation. In addition to receivingstimuli, the PNS is what allows the animal to respond to stimuli if aresponse is necessary. The distinction between a CNS and PNS is lessclear 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 331. 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 341. 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 animaland provides support, protection, and an anchoring place for musclesinvolved in movement. The complexity, shape, thickness, and durabilityvary greatly from species to species, depending on where theorganism lives and how it moves. In most instances, the exoskeletondoes not grow along with the organism and must periodically be shedto accommodate an increase in body size. Exoskeletons can be foundin arthropods.

Endoskeleton—Unlike exoskeletons, endoskeletons are internal andgrow along with the organism. In all cases, endoskeletons are madeup of minerals such as calcium, magnesium, and phosphate, but theircomplexity and exact composition depend on the type of organismand 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 involvedin locomotion and the movement of limbs and other body structures.It is under voluntary control. Due to its striped appearance whenviewed under a microscope, skeletal muscle is also referred to as striatedmuscle. The striations are the myofibrils arranged in sarcomeres.

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

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

Chapter 351. 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 isneeded 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 animalscannot be made by cellular metabolism and must be obtained throughthe diet. Without these essential amino acids, animals would not beable to manufacture the proteins required for the animal to live. Manyherbivores, however, cannot obtain these amino acids through theirdiet; such animals have the ability to manufacture these amino acidsthemselves.

Essential fatty acids—Many of the fatty acids that animals need tofunction cannot be made by the animal’s cells. These fatty acids mustbe obtained through the animal’s diet and are known as essentialfatty acids. These fatty acids can be obtained by either eating plantsor animals.

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

Minerals—These are important inorganic molecules that animalsrequire to build skeletons, balance salt concentrations in theirbody fluids, and produce electric currents for normal function ofthe nervous system and muscles. Many of these important mineralsare required only in trace amounts and can be stored in certainbody structures, such as the skeleton, to reduce the risk of mineraldeficiency.

Chapter 361. 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 systemfound in fishes and is the simplest type of circulation found invertebrates. In this system, deoxygenated blood from the tissues is

returned to the two-chambered heart, which then pumps the blood tothe gills. In the gills, blood picks up oxygen and unloads carbon dioxide,then circulates to the tissues to drop off oxygen and nutrients andpick up carbon dioxide and wastes. Arteries are the blood vessels thatcarry 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 incrocodiles, birds, and mammals and is divided into two parts: the systemicand pulmonary circulations. In the systemic circulation, blood ispumped from the left side of the heart to the body to drop off oxygenand nutrients and pick up carbon dioxide and wastes. The blood thenreturns to the right side of the heart. In the pulmonary circulation,the right side of the heart provides a second pumping mechanismthat sends blood to the lungs to release carbon dioxide and pick upoxygen from the atmosphere. Due to the fact that the heart is dividedinto a right and left side, it acts as two hearts in one, which increasesthe efficiency of the circulation. Amphibians and most reptiles have acirculation with features of both types.

Chapter 371. Animals exchange gases with an aqueous environment in two majorways: (1) across the skin or body surface and (2) via gills. In smallinvertebrates with bodies that are only a few cell layers thick, oxygenand carbon dioxide can rapidly diffuse across the body surface andto the interior parts of the animal. As a result, they require no specialrespiratory organs such as lungs or gills. Diffusion of gases across thebody surface occurs in most amphibians; they have skin that is highlypermeable to oxygen and carbon dioxide. Although these amphibiansrequire gills or lungs for most of their oxygen and carbon dioxideexchange, diffusion of gases across the skin represents an importantadaptation for amphibious life.

Most exclusively aquatic animals other than marine mammals havespecialized respiratory structures called gills. These can be eitheruncovered extensions from the body surface called external gills, orthey can be enclosed in a protective cavity, in which case they arecalled internal gills. External gills may be concentrated in one part ofthe body, or they may be scattered over a large area. Having externalgills has two major drawbacks. One is that the gills can be damagedby the environment, and the other is that the constant waving of theelaborate-looking gills that occurs for adequate ventilation to takeplace can draw the attention of predators.

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

2. Air enters either through the nose or the mouth and passes on to thepharynx. The nose and pharynx help to filter, warm, and moisturizethe air that enters from the outside world. This part of the respiratorysystem also produces mucus, which helps to trap particles from theair. After the pharynx, the air moves to the larynx and then to thetrachea. The trachea is also lined with mucus-producing cells, whichtrap particles that were missed by the nose and pharynx. In addition,the trachea is lined with ciliated epithelium that moves the mucus tothe pharynx where it is swallowed. After the trachea, the respiratorysystem divides into two tubes—the right bronchus and the left bronchus—before dividing into smaller tubes called bronchioles. At theends of the bronchioles there are saclike structures called alveoli that

are surrounded by capillaries. It is at the alveoli that the exchangeof oxygen and carbon dioxide takes place. The breathing process isfacilitated by the intercostal muscles, which lie between the ribs and alarge dome-shaped muscle called the diaphragm. The action of thesetwo groups of muscles creates a decreased pressure that enables theanimal to inhale air.

Chapter 381. 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 beforethe 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 thefiltrate from the glomerular capillaries enters Bowman’s capsule. Fromthere, the filtrate passes on to the proximal tubule, wheremost of the reabsorption of useful solutes occurs. After the proximaltubule, fluid moves into the loop of Henle, where additional waterand ions are reabsorbed. Next, the fluid enters the distal convolutedtubule, where fine-tuning of solute reabsorption and secretion takesplace. Finally, the fluid in the distal tubule empties intoa collecting duct, where the final composition of urine is establishedbefore 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 391. Two hormones, 20-hydroxyecdysone and juvenile hormone, playmajor roles in insect development. Ecdysone is secreted by a pairof glands called the prothoracic glands. Twenty-hydroxyecdysonestimulates rapid differentiation and causes the larva to molt. Juvenilehormone is secreted by the corpus allatum, and its main responsibilityis to control the nature of the molt induced by 20-hydroxyecdysone.Not until the levels of juvenile hormone decline to nearly zero doesthe 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 areproduced in the testes. Progesterone and estrogens such as estradioland progesterone control reproduction in females and are producedin the ovaries. Mineralocorticoids such as aldosterone are producedby the glomerulosa cells of the adrenal cortex and act to regulate saltand water balance. Glucocorticoids such as cortisol are produced bythe fasciculata cells of the adrenal cortex; these hormones are catabolic,suppress the immune system, and are an important part of theresponse to stress. The hormone 1,25-dihydroxyvitamin D is derivedfrom precursors in the skin or formed from dietary vitamin D. It actsto 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 401. 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 411. 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 421. Just as with geese, young cranes exhibit imprinting behavior. Humanresearchers took advantage of this behavior and encouraged youngcranes to imprint on humans dressed in crane suits. They even flewbehind ultralight planes piloted by crane-suited researchers, followingthem to their overwintering sites.

2. Chemical—Chemical communication is often used among animals tomark territory or food sources or to attract mates.Sound—This method of communication has a long range. It is a goodmethod 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 toidentify and select potential mates. One drawback is that by the timevisual communication has been established, the two organisms willbe in close proximity to each other and conflict could occur.

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

Chapter 431. Ensure the park is burned frequently. More frequent fi res use up fuelsupplies 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 outsidethe park hadn’t had a big fi re for 20 years, leaving bushes and shrubsto grow unchecked. The recent proliferation of homes in the areadecreased the opportunities for controlled burns.

2. The answer depends on where the course is being taught. Answeringthis question is an excellent way to get students to think about theworld 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 441. 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 451.

2.

Chapter 461. As we learned in Chapter 43, most scientists believe atmospheric CO2levels will have reached about 700 ppm by the end of the century,though extrapolation from Figure 59.18 puts the level closer to550 ppm. The effects of such an increase are many and varied. Globalwarming will increase and cause a shift in the distribution of many

organisms. Other organisms that cannot easily move, such as thoseon islands or mountain tops, will go extinct. Precipitation rates willchange with most areas getting wetter, but some deserts and continentalinteriors becoming drier. As we learned from Chapter 43, suchchanges may affect the frequency of disease. Changing temperatureswill also alter the phenology, or timing, of many events, such as budburst 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 lowerherbivory levels. In theory, reduced foliar nitrogen in leaf litter couldchange decomposition rates and affect rates of nutrient cycling inboth terrestrial and aquatic ecosystems. Greater plant productivitycould also elevate litterfall, increasing the frequency and severityof 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 enzymesand 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 471. Introduced species, also referred to as exotic species, are species thatare moved by humans from their native habitat to a different location.As a result, the introduced species may interfere with and possiblyoutcompete native species for resources or feed on native species. Ifthe introduced species outcompetes or preys heavily on the nativespecies, then the native species may become threatened, endangered,or extinct.

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

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

2. Because your goal is to maximize biodiversity, you would choosean area rich in species, not necessarily endemic species. Accordingto the principles we discussed in Chapter 44, you would try to selectan area where the individuals are spread fairly evenly among species,maximizing the Shannon diversity index. According to the theoreticaltenets laid out in Figure 47.10, you might establish a series of smallparks, containing a diverse array of habitats, rather than one largepark. You might minimize the amount of edge in each of these parksby maximizing the area : perimeter ratio. You might also decide tolink 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.