Solution Manual for Principles of Animal Physiology, 3rd Edition
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ANSWER KEY
Principles of
Animal Physiology
Third Edition
Christopher D. Moyes, Ph.D.
Queen’s University
Patricia M. Schulte, Ph.D.
University of British Columbia
Principles of
Animal Physiology
Third Edition
Christopher D. Moyes, Ph.D.
Queen’s University
Patricia M. Schulte, Ph.D.
University of British Columbia
1
Chapter 1 Introduction to Physiological Principles
Answers to Concept Check Questions
1. How would you define physiology?
Answer
It is the study of the functioning of biological structures and systems, or how organisms work.
2. What is a model organism in the context of physiological research?
Answer
The August Krogh Principle suggests that “for any biological question, there is an organism on which it can be most
conveniently studied.” A model organism is a convenient animal on which to study a biological question. Squid, for
example, was an early model to study neuronal function because of the size of its giant axon.
3. Why do the rates of biochemical reactions increase as temperature increases? Do they do so infinitely?
Answer
Temperature increases the thermal energy of molecules and increases the number of collisions between molecules.
Because most reactions require molecular collisions, increasing the rate of collisions will increase the rate of
reactions. This increase does not continue to infinity as temperature increases because at high temperatures many of
the intermolecular bonds that stabilize protein structure start to break, causing proteins to unfold and denature. When
proteins are unfolded they are unable to perform their functions. Because most biochemical reactions only occur at
high rates because of the actions of protein catalysts, reaction rates decline when the catalysts begin to denature.
4. What is allometric scaling?
Answer
Some processes or structures change in direct proportion to body mass, which is called isometric scaling. If the
process or structure changes disproportionately with body mass, it is considered to scale allometrically.
5. What is an adaptation?
Answer
An adaptation is a trait that arose via a process such as natural selection and that causes an increase in reproductive
success.
6. Distinguish between homology and analogy.
Answer
Homology describes a pattern where a trait that is present in two taxa is inherited from a common ancestor. These
traits may or may not be similar in appearance and function in the two taxa. For example, bird wings and human arms
appear to be quite different, but they are actually homologous because they both evolved from the forelimbs of a four-
legged ancestor.
Chapter 1 Introduction to Physiological Principles
Answers to Concept Check Questions
1. How would you define physiology?
Answer
It is the study of the functioning of biological structures and systems, or how organisms work.
2. What is a model organism in the context of physiological research?
Answer
The August Krogh Principle suggests that “for any biological question, there is an organism on which it can be most
conveniently studied.” A model organism is a convenient animal on which to study a biological question. Squid, for
example, was an early model to study neuronal function because of the size of its giant axon.
3. Why do the rates of biochemical reactions increase as temperature increases? Do they do so infinitely?
Answer
Temperature increases the thermal energy of molecules and increases the number of collisions between molecules.
Because most reactions require molecular collisions, increasing the rate of collisions will increase the rate of
reactions. This increase does not continue to infinity as temperature increases because at high temperatures many of
the intermolecular bonds that stabilize protein structure start to break, causing proteins to unfold and denature. When
proteins are unfolded they are unable to perform their functions. Because most biochemical reactions only occur at
high rates because of the actions of protein catalysts, reaction rates decline when the catalysts begin to denature.
4. What is allometric scaling?
Answer
Some processes or structures change in direct proportion to body mass, which is called isometric scaling. If the
process or structure changes disproportionately with body mass, it is considered to scale allometrically.
5. What is an adaptation?
Answer
An adaptation is a trait that arose via a process such as natural selection and that causes an increase in reproductive
success.
6. Distinguish between homology and analogy.
Answer
Homology describes a pattern where a trait that is present in two taxa is inherited from a common ancestor. These
traits may or may not be similar in appearance and function in the two taxa. For example, bird wings and human arms
appear to be quite different, but they are actually homologous because they both evolved from the forelimbs of a four-
legged ancestor.
1
Chapter 1 Introduction to Physiological Principles
Answers to Concept Check Questions
1. How would you define physiology?
Answer
It is the study of the functioning of biological structures and systems, or how organisms work.
2. What is a model organism in the context of physiological research?
Answer
The August Krogh Principle suggests that “for any biological question, there is an organism on which it can be most
conveniently studied.” A model organism is a convenient animal on which to study a biological question. Squid, for
example, was an early model to study neuronal function because of the size of its giant axon.
3. Why do the rates of biochemical reactions increase as temperature increases? Do they do so infinitely?
Answer
Temperature increases the thermal energy of molecules and increases the number of collisions between molecules.
Because most reactions require molecular collisions, increasing the rate of collisions will increase the rate of
reactions. This increase does not continue to infinity as temperature increases because at high temperatures many of
the intermolecular bonds that stabilize protein structure start to break, causing proteins to unfold and denature. When
proteins are unfolded they are unable to perform their functions. Because most biochemical reactions only occur at
high rates because of the actions of protein catalysts, reaction rates decline when the catalysts begin to denature.
4. What is allometric scaling?
Answer
Some processes or structures change in direct proportion to body mass, which is called isometric scaling. If the
process or structure changes disproportionately with body mass, it is considered to scale allometrically.
5. What is an adaptation?
Answer
An adaptation is a trait that arose via a process such as natural selection and that causes an increase in reproductive
success.
6. Distinguish between homology and analogy.
Answer
Homology describes a pattern where a trait that is present in two taxa is inherited from a common ancestor. These
traits may or may not be similar in appearance and function in the two taxa. For example, bird wings and human arms
appear to be quite different, but they are actually homologous because they both evolved from the forelimbs of a four-
legged ancestor.
Chapter 1 Introduction to Physiological Principles
Answers to Concept Check Questions
1. How would you define physiology?
Answer
It is the study of the functioning of biological structures and systems, or how organisms work.
2. What is a model organism in the context of physiological research?
Answer
The August Krogh Principle suggests that “for any biological question, there is an organism on which it can be most
conveniently studied.” A model organism is a convenient animal on which to study a biological question. Squid, for
example, was an early model to study neuronal function because of the size of its giant axon.
3. Why do the rates of biochemical reactions increase as temperature increases? Do they do so infinitely?
Answer
Temperature increases the thermal energy of molecules and increases the number of collisions between molecules.
Because most reactions require molecular collisions, increasing the rate of collisions will increase the rate of
reactions. This increase does not continue to infinity as temperature increases because at high temperatures many of
the intermolecular bonds that stabilize protein structure start to break, causing proteins to unfold and denature. When
proteins are unfolded they are unable to perform their functions. Because most biochemical reactions only occur at
high rates because of the actions of protein catalysts, reaction rates decline when the catalysts begin to denature.
4. What is allometric scaling?
Answer
Some processes or structures change in direct proportion to body mass, which is called isometric scaling. If the
process or structure changes disproportionately with body mass, it is considered to scale allometrically.
5. What is an adaptation?
Answer
An adaptation is a trait that arose via a process such as natural selection and that causes an increase in reproductive
success.
6. Distinguish between homology and analogy.
Answer
Homology describes a pattern where a trait that is present in two taxa is inherited from a common ancestor. These
traits may or may not be similar in appearance and function in the two taxa. For example, bird wings and human arms
appear to be quite different, but they are actually homologous because they both evolved from the forelimbs of a four-
legged ancestor.
2
Analogy describes a pattern where a trait is used for a similar function in two taxa, but is not inherited from a common
ancestor. For example, the camera-type eyes of vertebrates and cephalopods were derived from the non-camera eyes
of the closest relatives of each of these groups. This independent derivation suggests that these eyes are not
homologous, but instead are analogous.
7. What is homeostasis?
Answer
Homeostasis is the regulation or maintenance of internal conditions within a narrow range, despite changes in the
external environment.
8. Distinguish between acclimation, acclimatization, polyphenism, and phenotypic plasticity.
Answer
Acclimatization is a reversible phenotypic change produced from variations in natural environmental conditions,
usually working in combination (for example, low temperature and short day length in the winter).
Acclimation is similar but describes the process of reversible phenotypic adjustment in response to a single
environmental variable, usually in an artificial (e.g. laboratory) environment.
Polyphenism occurs when different environments lead to discrete alternative phenotypes. For example, developmental
plasticity can lead to polyphenism that is often irreversible.
Phenotypic plasticity is a general term that reflects the ability of a single genotype to result in multiple phenotypes as
a result of the environment; thus acclimation, acclimatization, and polyphenism are all types of phenotypic plasticity.
Analogy describes a pattern where a trait is used for a similar function in two taxa, but is not inherited from a common
ancestor. For example, the camera-type eyes of vertebrates and cephalopods were derived from the non-camera eyes
of the closest relatives of each of these groups. This independent derivation suggests that these eyes are not
homologous, but instead are analogous.
7. What is homeostasis?
Answer
Homeostasis is the regulation or maintenance of internal conditions within a narrow range, despite changes in the
external environment.
8. Distinguish between acclimation, acclimatization, polyphenism, and phenotypic plasticity.
Answer
Acclimatization is a reversible phenotypic change produced from variations in natural environmental conditions,
usually working in combination (for example, low temperature and short day length in the winter).
Acclimation is similar but describes the process of reversible phenotypic adjustment in response to a single
environmental variable, usually in an artificial (e.g. laboratory) environment.
Polyphenism occurs when different environments lead to discrete alternative phenotypes. For example, developmental
plasticity can lead to polyphenism that is often irreversible.
Phenotypic plasticity is a general term that reflects the ability of a single genotype to result in multiple phenotypes as
a result of the environment; thus acclimation, acclimatization, and polyphenism are all types of phenotypic plasticity.
1
Chapter 1 Introduction to Physiological Principles
Answers to Review Questions
1. Where would organelles such as the mitochondrion fit in the levels of organization shown in Figure 1.3?
Answer
Organelles such as mitochondria would fit between the molecular and the cellular levels in Figure 1.3. Molecules
work together in complex biochemical pathways to form the complex structures that are assembled to make
organelles. These organelles are parts of a cell.
2. What is the Krogh principle, and why is it useful for animal physiologists?
Answer
The Krogh Principle states that for every biological problem there is an organism on which it can be most
conveniently studied. This means that medical physiologists interested in a function in humans (or veterinary
physiologists interested in cows) might choose to study these functions in an animal such as a mouse, because they are
much smaller and easier to maintain.
3. All organisms have a maximum temperature at which they can function. Suggest a possible physical basis for this
observation.
Answer
The maximum temperature that an organism can function at must be the lowest temperature at which a critical process
required to sustain life fails. Not all physiological functions are likely to fail at exactly the same temperature, but when
a critical process fails, life will end. Processes could fail at high temperatures for a variety of reasons, but ultimately
this failure must be due to changes in intermolecular interactions at high temperatures.
4. How might size-related changes in surface area-to-volume ratios affect physiological functions?
Answer
Surface area increases less with size than does volume, so surface area for exchange becomes limiting as size
increases, unless there is a change in shape. This pattern explains why physiological systems such as the respiratory
system have extremely high surface area compared with their volume. This increases the area available for gas
exchange.
5. What are three fundamental requirements for adaptive evolution of a trait to occur?
Answer
For adaptive evolution to occur:
1. There must be variation among individuals in the trait.
2. The trait must be heritable.
3. The trait must increase the fitness.
Chapter 1 Introduction to Physiological Principles
Answers to Review Questions
1. Where would organelles such as the mitochondrion fit in the levels of organization shown in Figure 1.3?
Answer
Organelles such as mitochondria would fit between the molecular and the cellular levels in Figure 1.3. Molecules
work together in complex biochemical pathways to form the complex structures that are assembled to make
organelles. These organelles are parts of a cell.
2. What is the Krogh principle, and why is it useful for animal physiologists?
Answer
The Krogh Principle states that for every biological problem there is an organism on which it can be most
conveniently studied. This means that medical physiologists interested in a function in humans (or veterinary
physiologists interested in cows) might choose to study these functions in an animal such as a mouse, because they are
much smaller and easier to maintain.
3. All organisms have a maximum temperature at which they can function. Suggest a possible physical basis for this
observation.
Answer
The maximum temperature that an organism can function at must be the lowest temperature at which a critical process
required to sustain life fails. Not all physiological functions are likely to fail at exactly the same temperature, but when
a critical process fails, life will end. Processes could fail at high temperatures for a variety of reasons, but ultimately
this failure must be due to changes in intermolecular interactions at high temperatures.
4. How might size-related changes in surface area-to-volume ratios affect physiological functions?
Answer
Surface area increases less with size than does volume, so surface area for exchange becomes limiting as size
increases, unless there is a change in shape. This pattern explains why physiological systems such as the respiratory
system have extremely high surface area compared with their volume. This increases the area available for gas
exchange.
5. What are three fundamental requirements for adaptive evolution of a trait to occur?
Answer
For adaptive evolution to occur:
1. There must be variation among individuals in the trait.
2. The trait must be heritable.
3. The trait must increase the fitness.
2
6. Are the eyes of vertebrates and cephalopod mollusks homologous or analogous? Justify your answer.
Answer
The eyes of vertebrates and cephalopod mollusks are analogous. Both are camera-type eyes that can form a focused
image, but they arose independently from different ancestors that lacked camera-type eyes. Thus, they did not share a
common ancestor and cannot be homologous, despite their similarity of function.
7. What is the main benefit of having antagonistic controls in physiological systems?
Answer
Antagonistic controls allow more precise control over a physiological system by having two separate control
mechanisms: one that increases, and one that decreases, the activity of the system. This is analogous to having both a
brake and an accelerator on a car.
8. Explain why a positive feedback loop is unlikely to be involved in a control system that maintains homeostasis.
Answer
Positive feedback loops are organized so that the output of the system tends to increase the activity of the system. This
results in a rapid response and an amplification of the output of the system, resulting in a large response to a small
stimulus. This control mechanism is unlikely to be appropriate for a control system that maintains homeostasis,
because homeostasis involves maintaining the system within a narrow range around the set point.
6. Are the eyes of vertebrates and cephalopod mollusks homologous or analogous? Justify your answer.
Answer
The eyes of vertebrates and cephalopod mollusks are analogous. Both are camera-type eyes that can form a focused
image, but they arose independently from different ancestors that lacked camera-type eyes. Thus, they did not share a
common ancestor and cannot be homologous, despite their similarity of function.
7. What is the main benefit of having antagonistic controls in physiological systems?
Answer
Antagonistic controls allow more precise control over a physiological system by having two separate control
mechanisms: one that increases, and one that decreases, the activity of the system. This is analogous to having both a
brake and an accelerator on a car.
8. Explain why a positive feedback loop is unlikely to be involved in a control system that maintains homeostasis.
Answer
Positive feedback loops are organized so that the output of the system tends to increase the activity of the system. This
results in a rapid response and an amplification of the output of the system, resulting in a large response to a small
stimulus. This control mechanism is unlikely to be appropriate for a control system that maintains homeostasis,
because homeostasis involves maintaining the system within a narrow range around the set point.
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1
Chapter 1 Introduction to Physiological Principles
Answers to Synthesis Questions
1. What physical, chemical, or physiological constraints might lead to allometric scaling?
Answer
Allometric scaling refers to variables that do not change linearly with body mass; thus, a given trait in a 1-kg animal
will not be twice as large in a 2-kg animal. A major constraint that leads to allometric scaling is the surface area-to-
volume ratio, which decreases as mass increases. This affects many physical and chemical processes (such as
diffusion rates and heat exchange) that in turn affect the scaling of physiological functions. But surface area-to-
volume constraints do not fully explain all instances of allometric scaling. For example, metabolic rate does not
always have a scaling exponent of 0.67, as would be expected if surface area-to-volume ratios were the only important
factor. A variety of physical, chemical, and physiological mechanisms have been proposed to explain this pattern, but
the actual mechanism remains a matter of debate among physiologists.
2. Why do physiologists need to understand evolution?
Answer
There is a great deal of diversity in physiological traits expressed by animals. These traits (an animal’s phenotype) are
the result of interactions between the animal’s genotype and its environment. An individual’s genotype reflects its
evolutionary history, shaped by natural selection and genetic drift. As a consequence, closely related organisms share
more traits than distantly related ones. Evolution therefore allows physiologists to understand the significance of the
diversity of physiological traits (both the proximal and ultimate causes).
3. Compare and contrast adaptive evolution and genetic drift.
Chapter 1 Introduction to Physiological Principles
Answers to Synthesis Questions
1. What physical, chemical, or physiological constraints might lead to allometric scaling?
Answer
Allometric scaling refers to variables that do not change linearly with body mass; thus, a given trait in a 1-kg animal
will not be twice as large in a 2-kg animal. A major constraint that leads to allometric scaling is the surface area-to-
volume ratio, which decreases as mass increases. This affects many physical and chemical processes (such as
diffusion rates and heat exchange) that in turn affect the scaling of physiological functions. But surface area-to-
volume constraints do not fully explain all instances of allometric scaling. For example, metabolic rate does not
always have a scaling exponent of 0.67, as would be expected if surface area-to-volume ratios were the only important
factor. A variety of physical, chemical, and physiological mechanisms have been proposed to explain this pattern, but
the actual mechanism remains a matter of debate among physiologists.
2. Why do physiologists need to understand evolution?
Answer
There is a great deal of diversity in physiological traits expressed by animals. These traits (an animal’s phenotype) are
the result of interactions between the animal’s genotype and its environment. An individual’s genotype reflects its
evolutionary history, shaped by natural selection and genetic drift. As a consequence, closely related organisms share
more traits than distantly related ones. Evolution therefore allows physiologists to understand the significance of the
diversity of physiological traits (both the proximal and ultimate causes).
3. Compare and contrast adaptive evolution and genetic drift.
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2
point, the thermostat will stop sending the “on” signal to the heating system. This process qualifies as a negative
feedback because the response (turning on the heat to warm the air) is in the opposite direction to the stimulus (cold
air temperature).
6. Make an argument for or against adopting the use of the term allostasis.
Answer
Argument for: The term allostasis is useful because it points out that set points for homeostatic systems can change
with the environment, for example between seasons or with the phases of the reproductive cycle, which is not
explicitly included in the definition of homeostasis.
Argument against: The term allostasis is not necessary because the original definition of homeostasis already includes
the concept that it is necessary to alter the functions of some physiological systems to maintain homeostasis in others.
7. Dogs typically shed some hair in the spring. Is this an example of acclimation or acclimatization? How might you
experimentally distinguish between these two possibilities?
Answer
It is probably an example of acclimatization, as the observation was not made under controlled conditions in the
laboratory, and multiple factors likely changed in the spring (temperature, day length, amount of time spent outside
and exercising, and probably many others). However, it might also be a developmentally programmed event that is
independent of environmental factors. The way to test this experimentally would be to take a dog into the laboratory
and expose it to changes in each of the possible environmental factors individually and in combination and then to
observe the dog’s hair to see whether the thickness of the coat increases or decreases. Ideally, this experiment should
be done with many different individual dogs to see whether it is a consistent response for the species.
point, the thermostat will stop sending the “on” signal to the heating system. This process qualifies as a negative
feedback because the response (turning on the heat to warm the air) is in the opposite direction to the stimulus (cold
air temperature).
6. Make an argument for or against adopting the use of the term allostasis.
Answer
Argument for: The term allostasis is useful because it points out that set points for homeostatic systems can change
with the environment, for example between seasons or with the phases of the reproductive cycle, which is not
explicitly included in the definition of homeostasis.
Argument against: The term allostasis is not necessary because the original definition of homeostasis already includes
the concept that it is necessary to alter the functions of some physiological systems to maintain homeostasis in others.
7. Dogs typically shed some hair in the spring. Is this an example of acclimation or acclimatization? How might you
experimentally distinguish between these two possibilities?
Answer
It is probably an example of acclimatization, as the observation was not made under controlled conditions in the
laboratory, and multiple factors likely changed in the spring (temperature, day length, amount of time spent outside
and exercising, and probably many others). However, it might also be a developmentally programmed event that is
independent of environmental factors. The way to test this experimentally would be to take a dog into the laboratory
and expose it to changes in each of the possible environmental factors individually and in combination and then to
observe the dog’s hair to see whether the thickness of the coat increases or decreases. Ideally, this experiment should
be done with many different individual dogs to see whether it is a consistent response for the species.
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1
Chapter 2 Physiological Evolution of Animals
Answers to Concept Check Questions
1. Distinguish between the terms protist, protozoan, metazoan, and eumetazoan.
Answer
Unicellular eukaryotes are collectively called protists, though they are a polyphyletic group. Protozoans are those
protists with “animal-like” abilities to move. These two terms include many unrelated organisms. Metazoan can be
used synonymously with “animal” though some researchers separate sponges from true metazoans, or eumetazoans.
Inother words, eumetazoans is used to distinguish animals with tissue layers from sponges, which have no discrete
tissue layers.
2. What is a coelom?
Answer
In triploblastic animals the early stages of embryonic development lead to three distinct tissue layers: endoderm,
mesoderm, and ectoderm. In coelomate animals, a gap can occur within the early embryo, either through splitting of
the mesoderm or folding of the mesoderm. The gap is a coelom. A pseudocoelom is like a coelom in that it is a
internal body cavity. However, a true coelom is lined by mesoderm, whereas a pseudocoelom is only partially lined by
mesoderm.
3. Distinguish between metamers and tagmata.
Chapter 2 Physiological Evolution of Animals
Answers to Concept Check Questions
1. Distinguish between the terms protist, protozoan, metazoan, and eumetazoan.
Answer
Unicellular eukaryotes are collectively called protists, though they are a polyphyletic group. Protozoans are those
protists with “animal-like” abilities to move. These two terms include many unrelated organisms. Metazoan can be
used synonymously with “animal” though some researchers separate sponges from true metazoans, or eumetazoans.
Inother words, eumetazoans is used to distinguish animals with tissue layers from sponges, which have no discrete
tissue layers.
2. What is a coelom?
Answer
In triploblastic animals the early stages of embryonic development lead to three distinct tissue layers: endoderm,
mesoderm, and ectoderm. In coelomate animals, a gap can occur within the early embryo, either through splitting of
the mesoderm or folding of the mesoderm. The gap is a coelom. A pseudocoelom is like a coelom in that it is a
internal body cavity. However, a true coelom is lined by mesoderm, whereas a pseudocoelom is only partially lined by
mesoderm.
3. Distinguish between metamers and tagmata.
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2
Myosin appeared in unicellular eukaryotes long before animals arose. It retains a role in cytoskeletal trafficking, but in
animals it has derived roles in muscle. The myosin family amplified many times in animals, leading to the origin of
different myosin isoforms.
8. When did collagen evolve and what is its significance?
Answer
Collagen first appeared in the earliest animals, and is used to construct many forms of extracellular matrix.
9. What are cadherins?
Answer
Cadherins are cell membrane adhesion proteins. Though they appear in animals, their origins predate the appearance
of metazoans. Cadherin genes occur in protists, in particular the choanoflagellates that are thought to share a common
ancestor with metazoans.
10. What is cephalization?
Answer
Cephalization is an evolutionary trend whereby animals concentrate important sensory, nervous, and digestive system
components toward the anterior, giving rise to a discrete head region.
11. Why is metabolism more diverse in bacteria than in animals?
Answer
Bacteria have little capacity to evolve structurally because of their structural simplicity. Their best evolutionary option
for surviving environmental stress is through their biochemistry. Animals are able to evolve changes in structure,
which can offer different routes for resisting and surviving environmental stress. Nonetheless, biochemical adaptations
are important in many aspects of animal evolutionary physiology.
Myosin appeared in unicellular eukaryotes long before animals arose. It retains a role in cytoskeletal trafficking, but in
animals it has derived roles in muscle. The myosin family amplified many times in animals, leading to the origin of
different myosin isoforms.
8. When did collagen evolve and what is its significance?
Answer
Collagen first appeared in the earliest animals, and is used to construct many forms of extracellular matrix.
9. What are cadherins?
Answer
Cadherins are cell membrane adhesion proteins. Though they appear in animals, their origins predate the appearance
of metazoans. Cadherin genes occur in protists, in particular the choanoflagellates that are thought to share a common
ancestor with metazoans.
10. What is cephalization?
Answer
Cephalization is an evolutionary trend whereby animals concentrate important sensory, nervous, and digestive system
components toward the anterior, giving rise to a discrete head region.
11. Why is metabolism more diverse in bacteria than in animals?
Answer
Bacteria have little capacity to evolve structurally because of their structural simplicity. Their best evolutionary option
for surviving environmental stress is through their biochemistry. Animals are able to evolve changes in structure,
which can offer different routes for resisting and surviving environmental stress. Nonetheless, biochemical adaptations
are important in many aspects of animal evolutionary physiology.
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1
Chapter 2 Physiological Evolution of Animals
Answers to Review Questions
1. What is the significance of the similarity between choanoflagellates and choanocytes?
Answer
It is likely that choanoflagellates are the modern protist that is most closely related to the earliest metazoan. There is a
striking similarity in the general structure of choanoflagellates and choanocytes of sponges.
2. Why aren’t protozoans considered animals?
Answer
Protozoans are a polyphyletic group of single-celled eukarytotes, which include groups that are plantlike, fungilike,
and animal-like. Animals are, by definition, multicellular, so a single-celled eukaryotic organism could not be an
animal. Some protists have the animal-like trait of locomotion, but that is not an indicator of how closely a protist is
related to the ancestors of animals.
3. Which animals are diploblasts?
Answer
Diploblasts have only two embryonic cell layers, endoderm and ectoderm. Sponges lack cell layers, and most animals
have three embryonic cell layers. Only cnidarians and probably ctenophores are diploblasts.
4. Explain why arthropods are considered Ecdysozoans.
Answer
Ecdysozoans share the ability to moult at some stage in their development. Arthropods moult.
5. Did all jawed animals evolve from the same agnathan ancestors?
Answer
No. Agnathans are a large group of jawless fish that gave rise to multiple lineages of fish and their descendants. It
appears likely that sharks and bony fish arose from different agnathan ancestors, which were distinct from those that
gave rise to lamprey and hagfish. It now appears likely that hagfish and lamprey, despite their divergence, shared a
common ancestor.
6. How many times did terrestriality arise in animal lineages?
Answer
Many times. Land was invaded by multiple arthropod lineages, including myriapods, hexapods, and chelicerates.
Amphibians were the first tetrapod group that had a major terrestrial presence. Many invertebrate phyla have groups
that live on land, although in many cases they live in wet environments, such as moss, or live as endoparasites in the
fluids of land animals. Of course, select groups of fish can spend periods of time on land.
Chapter 2 Physiological Evolution of Animals
Answers to Review Questions
1. What is the significance of the similarity between choanoflagellates and choanocytes?
Answer
It is likely that choanoflagellates are the modern protist that is most closely related to the earliest metazoan. There is a
striking similarity in the general structure of choanoflagellates and choanocytes of sponges.
2. Why aren’t protozoans considered animals?
Answer
Protozoans are a polyphyletic group of single-celled eukarytotes, which include groups that are plantlike, fungilike,
and animal-like. Animals are, by definition, multicellular, so a single-celled eukaryotic organism could not be an
animal. Some protists have the animal-like trait of locomotion, but that is not an indicator of how closely a protist is
related to the ancestors of animals.
3. Which animals are diploblasts?
Answer
Diploblasts have only two embryonic cell layers, endoderm and ectoderm. Sponges lack cell layers, and most animals
have three embryonic cell layers. Only cnidarians and probably ctenophores are diploblasts.
4. Explain why arthropods are considered Ecdysozoans.
Answer
Ecdysozoans share the ability to moult at some stage in their development. Arthropods moult.
5. Did all jawed animals evolve from the same agnathan ancestors?
Answer
No. Agnathans are a large group of jawless fish that gave rise to multiple lineages of fish and their descendants. It
appears likely that sharks and bony fish arose from different agnathan ancestors, which were distinct from those that
gave rise to lamprey and hagfish. It now appears likely that hagfish and lamprey, despite their divergence, shared a
common ancestor.
6. How many times did terrestriality arise in animal lineages?
Answer
Many times. Land was invaded by multiple arthropod lineages, including myriapods, hexapods, and chelicerates.
Amphibians were the first tetrapod group that had a major terrestrial presence. Many invertebrate phyla have groups
that live on land, although in many cases they live in wet environments, such as moss, or live as endoparasites in the
fluids of land animals. Of course, select groups of fish can spend periods of time on land.
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7. What is meant by the term “a new head”?
Answer
The “new head” hypothesis suggests that the evolutionary diversification and success of vertebrates was made
possible by the development of structures anterior to the notochord. In different lineages, these structures become
important musculoskeletal features such as the jaw.
8. What is the significance of the evolution of the Na+/K+ATPase?
Answer
The evolution of the Na+ /K+ ATPase gave animals a mechanism by which to pump Na+ and K+ across their cell
membranes, creating the electrochemical potential that is used to drive many transport processes and permit the
formation of excitable tissues. The transporters linked indirectly to Na+/K+ ATPase help animals regulate their cell
volume, which was important in this group of organisms because they lack cell walls.
9. When did endothermy arise in animal evolution?
Answer
Endothermy arose several times in animals. Endothermy arose independently in the ancestors of two groups of
vertebrates, birds and mammals. Birds arose about 150 million years ago and mammals about 300 million years ago.
7. What is meant by the term “a new head”?
Answer
The “new head” hypothesis suggests that the evolutionary diversification and success of vertebrates was made
possible by the development of structures anterior to the notochord. In different lineages, these structures become
important musculoskeletal features such as the jaw.
8. What is the significance of the evolution of the Na+/K+ATPase?
Answer
The evolution of the Na+ /K+ ATPase gave animals a mechanism by which to pump Na+ and K+ across their cell
membranes, creating the electrochemical potential that is used to drive many transport processes and permit the
formation of excitable tissues. The transporters linked indirectly to Na+/K+ ATPase help animals regulate their cell
volume, which was important in this group of organisms because they lack cell walls.
9. When did endothermy arise in animal evolution?
Answer
Endothermy arose several times in animals. Endothermy arose independently in the ancestors of two groups of
vertebrates, birds and mammals. Birds arose about 150 million years ago and mammals about 300 million years ago.
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Chapter 2 Physiological Evolution of Animals
Answers to Synthesis Questions
1. Speculate on how animals might have evolved if the ancestral protist possessed a cell wall.
Answer
Rather than giving you possible answers, consider the significance of the cell wall in other organisms. It provides
resistance to cell swelling, and how is cell volume controlled in animals? It provides a physical barrier that makes it
difficult for large molecules to cross, so how might that affect cell-to-cell signaling? It is a rigid structural support for
cells that can be connected together to make tissues. It also precludes connections between adjacent cells, obviating
direct cell-cell communication.
2. What critical events led to the origin and diversification of tetrapods?
Answer
To answer this you probably need to draw on material from outside this chapter and from other courses. Think about
the diversity in tetrapods, and how those differences may have arisen. Within vertebrates, the two whole-genome
duplications created the genetic raw material for specialization of genes. A number of events occurred in tetrapod
evolution that contributed to their diversity. From the developmental perspective, the flexibility associated with the
“new head” allowed different configurations of jaws. Environmental changes, such as air density and oxygen levels,
permitted some groups to elevate metabolic rate, and others to evolve flight. Changes in global temperature and
seasonality contributed to constraints on range limits; evolutionary changes in anatomy and physiology permitted the
invasion of new environments.
3. Would you expect the underlying metabolic pathways to be similar or different in animal models of metabolic arrest?
Chapter 2 Physiological Evolution of Animals
Answers to Synthesis Questions
1. Speculate on how animals might have evolved if the ancestral protist possessed a cell wall.
Answer
Rather than giving you possible answers, consider the significance of the cell wall in other organisms. It provides
resistance to cell swelling, and how is cell volume controlled in animals? It provides a physical barrier that makes it
difficult for large molecules to cross, so how might that affect cell-to-cell signaling? It is a rigid structural support for
cells that can be connected together to make tissues. It also precludes connections between adjacent cells, obviating
direct cell-cell communication.
2. What critical events led to the origin and diversification of tetrapods?
Answer
To answer this you probably need to draw on material from outside this chapter and from other courses. Think about
the diversity in tetrapods, and how those differences may have arisen. Within vertebrates, the two whole-genome
duplications created the genetic raw material for specialization of genes. A number of events occurred in tetrapod
evolution that contributed to their diversity. From the developmental perspective, the flexibility associated with the
“new head” allowed different configurations of jaws. Environmental changes, such as air density and oxygen levels,
permitted some groups to elevate metabolic rate, and others to evolve flight. Changes in global temperature and
seasonality contributed to constraints on range limits; evolutionary changes in anatomy and physiology permitted the
invasion of new environments.
3. Would you expect the underlying metabolic pathways to be similar or different in animal models of metabolic arrest?
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Chapter 3 Chemistry, Biochemistry, and Cell Physiology
Answers to Concept Check Questions
1. What are the five main forms of energy used by animals? Provide biological and nonbiological examples of processes that
represent conversion of energy from one form to another.
Answer
The five main forms of energy used by animals are radiant, mechanical, electrical, thermal, and chemical energy. If
you are having difficulty coming up with examples, consider Figure 3.2 as a starting point.
2. What is the difference between thermal energy, heat and temperature?
Answer
Thermal energy of a system is the total energy associated with molecular motion of that system: vibration, rotation,
and translocation. Heat is the transfer of thermal energy between objects or systems at a different temperature. When
an animal’s body heats the air around it, thermal energy is transferred from the molecules of the body to the molecules
of the surrounding air. Both thermal energy and heat are forms of energy, measured in Joules. Temperature is a
convenient measure of the average thermal energy of a system
Chapter 3 Chemistry, Biochemistry, and Cell Physiology
Answers to Concept Check Questions
1. What are the five main forms of energy used by animals? Provide biological and nonbiological examples of processes that
represent conversion of energy from one form to another.
Answer
The five main forms of energy used by animals are radiant, mechanical, electrical, thermal, and chemical energy. If
you are having difficulty coming up with examples, consider Figure 3.2 as a starting point.
2. What is the difference between thermal energy, heat and temperature?
Answer
Thermal energy of a system is the total energy associated with molecular motion of that system: vibration, rotation,
and translocation. Heat is the transfer of thermal energy between objects or systems at a different temperature. When
an animal’s body heats the air around it, thermal energy is transferred from the molecules of the body to the molecules
of the surrounding air. Both thermal energy and heat are forms of energy, measured in Joules. Temperature is a
convenient measure of the average thermal energy of a system
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6. What is the difference between osmolarity and tonicity?
Answer
Osmolarity describes the number of osmotically active solutes (osmolytes) in a solution, whereas tonicity refers to a
solution in terms of its effects on a cell.
7. Distinguish between allosteric and covalent regulation of enzymes.
Answer
Allosteric regulation occurs when a molecule reversibly binds an enzyme at a site somewhere distant from the active
site, and causes a change in structure that influences function. Covalent modification of an enzyme is when another
molecule is added to or removed from the enzyme. Common molecules include phosphate groups (phosphorylation),
methyl groups (methylation), or acetate groups (acetylation). Covalent modifications are usually mediated by
enzymes.
8. Distinguish between the following types of reactions: anabolic, catabolic, and amphibolic.
Answer
Anabolic reactions are synthetic, catabolic are degradative, amphibolic are a combination of both synthetic and
degradative processes.
9. Why is ATP considered a “high-energy” molecule?
Answer
The breakdown of ATP to ADP and phosphate liberates energy because of the thermodynamics of the reaction and the
relative concentrations of the reactants.
10. Distinguish between primary, secondary, tertiary, and quaternary structure.
Answer
For a protein, the primary structure is the amino acid sequence. This strand can be arranged into spirals or sheets to
form the secondary structure. The protein can then be folded i
6. What is the difference between osmolarity and tonicity?
Answer
Osmolarity describes the number of osmotically active solutes (osmolytes) in a solution, whereas tonicity refers to a
solution in terms of its effects on a cell.
7. Distinguish between allosteric and covalent regulation of enzymes.
Answer
Allosteric regulation occurs when a molecule reversibly binds an enzyme at a site somewhere distant from the active
site, and causes a change in structure that influences function. Covalent modification of an enzyme is when another
molecule is added to or removed from the enzyme. Common molecules include phosphate groups (phosphorylation),
methyl groups (methylation), or acetate groups (acetylation). Covalent modifications are usually mediated by
enzymes.
8. Distinguish between the following types of reactions: anabolic, catabolic, and amphibolic.
Answer
Anabolic reactions are synthetic, catabolic are degradative, amphibolic are a combination of both synthetic and
degradative processes.
9. Why is ATP considered a “high-energy” molecule?
Answer
The breakdown of ATP to ADP and phosphate liberates energy because of the thermodynamics of the reaction and the
relative concentrations of the reactants.
10. Distinguish between primary, secondary, tertiary, and quaternary structure.
Answer
For a protein, the primary structure is the amino acid sequence. This strand can be arranged into spirals or sheets to
form the secondary structure. The protein can then be folded i
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13. Distinguish between starch, glycogen, and cellulose.
Answer
All three are polysaccharides formed from glucose. Starch is a mixture of amylose, which has few branches, and
amylopectin, which has some branches. Glycogen is similar in structure but much more highly branched. Both starch
and glycogen are composed of glucose chains linked by α1,4 glycoside bonds. Cellulose is also a chain of glucose, but
these are linked by β1,4 glycoside bonds.
14. What is the purpose of a redox shuttle?
Answer
NADH produced in the cytoplasm cannot enter mitochondria. A series of cyclic enzymatic reactions allows the
transfer of reducing energy across the mitochondrial membrane. NADH is oxidized to reduce a metabolite that can be
transported across the inner mitochondrial membrane. When reoxidized in the mitochondria, the resulting NADH can
be oxidized by the electron transport chain.
15. What happens to glycolytic pyruvate under hypoxic conditions?
Answer
Pyruvate can be reduced to form lactate, oxidizing NADH in the process. Lactate may be subsequently converted to
other alternate end products. In some species, pyruvate can be processed to form ethanol, oxidizing NADH.
16. How is energy derived from triglyceride breakdown?
Answer
The triglyceride can be broken down into glycerol and three fatty acids. Glycerol can enter the glycolytic pathway via
conversion to glycerol 3-phosphate. The fatty acids enter beta-oxidation, with ATP produced by the oxidation of the
NADH and FADH
13. Distinguish between starch, glycogen, and cellulose.
Answer
All three are polysaccharides formed from glucose. Starch is a mixture of amylose, which has few branches, and
amylopectin, which has some branches. Glycogen is similar in structure but much more highly branched. Both starch
and glycogen are composed of glucose chains linked by α1,4 glycoside bonds. Cellulose is also a chain of glucose, but
these are linked by β1,4 glycoside bonds.
14. What is the purpose of a redox shuttle?
Answer
NADH produced in the cytoplasm cannot enter mitochondria. A series of cyclic enzymatic reactions allows the
transfer of reducing energy across the mitochondrial membrane. NADH is oxidized to reduce a metabolite that can be
transported across the inner mitochondrial membrane. When reoxidized in the mitochondria, the resulting NADH can
be oxidized by the electron transport chain.
15. What happens to glycolytic pyruvate under hypoxic conditions?
Answer
Pyruvate can be reduced to form lactate, oxidizing NADH in the process. Lactate may be subsequently converted to
other alternate end products. In some species, pyruvate can be processed to form ethanol, oxidizing NADH.
16. How is energy derived from triglyceride breakdown?
Answer
The triglyceride can be broken down into glycerol and three fatty acids. Glycerol can enter the glycolytic pathway via
conversion to glycerol 3-phosphate. The fatty acids enter beta-oxidation, with ATP produced by the oxidation of the
NADH and FADH
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20. What is the proton motive force?
Answer
The proton motive force is the combination of a pH gradient and membrane potential. This electrochemical gradient is
produced by the electron transport chain and utilized for ATP synthesis.
21. How is oxidation coupled to phosphorylation in mitochondrial oxidative phosphorylation?
Answer
Oxidation is coupled to phosphorylation in mitochondrial oxidative phosphorylation via the electron transport system.
The regeneration of NAD+ and FAD via the actions of complexes I to IV and cytochrome c creates a proton gradient,
whose energy is utilized, via complex V, to phosphorylate ADP to ATP. This process requires the reduction of oxygen
at complex IV, so that the electrons the complex IV received from cytochrome c can be passed on and new electrons
accepted.
22. How does glucose catabolism differ under (a) high versus low energy conditions and (b) normal versus low oxygen
conditions?
Answer
Anaerobic glycolysis may be advantageous under high energy and/or low oxygen conditions as it produces ATP
rapidly from glucose stores and does not require access to oxygen. Oxidative metabolism of glucose may be
advantageous under low energy and/or normal oxygen conditions,
20. What is the proton motive force?
Answer
The proton motive force is the combination of a pH gradient and membrane potential. This electrochemical gradient is
produced by the electron transport chain and utilized for ATP synthesis.
21. How is oxidation coupled to phosphorylation in mitochondrial oxidative phosphorylation?
Answer
Oxidation is coupled to phosphorylation in mitochondrial oxidative phosphorylation via the electron transport system.
The regeneration of NAD+ and FAD via the actions of complexes I to IV and cytochrome c creates a proton gradient,
whose energy is utilized, via complex V, to phosphorylate ADP to ATP. This process requires the reduction of oxygen
at complex IV, so that the electrons the complex IV received from cytochrome c can be passed on and new electrons
accepted.
22. How does glucose catabolism differ under (a) high versus low energy conditions and (b) normal versus low oxygen
conditions?
Answer
Anaerobic glycolysis may be advantageous under high energy and/or low oxygen conditions as it produces ATP
rapidly from glucose stores and does not require access to oxygen. Oxidative metabolism of glucose may be
advantageous under low energy and/or normal oxygen conditions,
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by favoring phospholipids with longer or shorter tails or with greater or lesser degrees of saturation. Increasing the
concentration of cholesterol also increases the fluidity of the membrane.
27. What is the relationship between the Nernst equation and the equilibrium potential?
Answer
The Nernst equation can be solved to determine the membrane potential at which net movement of a specific ion
ceases at a given chemical gradient, i.e. the equilibrium potential for that ion.
28. Distinguish between depolarization, repolarization, and hyperpolarization.
Answer
Depolarization is a change in membrane potential toward a value of 0 mV. After depolarization, a cell should return to
its normal resting membrane potential via repolarization. Often, the nature of ion movements leads to an overshoot,
causing hyperpolarization, where the membrane is even more polarized than at rest.
29. Summarize the roles of the different subcellular compartments within a cell, and discuss how they influence physiological
function.
Answer
Compartments that should be discussed here include the nucleus, the mitochondria, the rough and smooth
endoplasmic reticulum, and the Golgi apparatus.
30. What does the Na+/ K+ ATPase do in a typical cell?
Answer
The sodium pump, or Na+/ K+ ATPase, uses the energy associated with ATP hydrolysis to pump 3Na+ out of a cell in
by favoring phospholipids with longer or shorter tails or with greater or lesser degrees of saturation. Increasing the
concentration of cholesterol also increases the fluidity of the membrane.
27. What is the relationship between the Nernst equation and the equilibrium potential?
Answer
The Nernst equation can be solved to determine the membrane potential at which net movement of a specific ion
ceases at a given chemical gradient, i.e. the equilibrium potential for that ion.
28. Distinguish between depolarization, repolarization, and hyperpolarization.
Answer
Depolarization is a change in membrane potential toward a value of 0 mV. After depolarization, a cell should return to
its normal resting membrane potential via repolarization. Often, the nature of ion movements leads to an overshoot,
causing hyperpolarization, where the membrane is even more polarized than at rest.
29. Summarize the roles of the different subcellular compartments within a cell, and discuss how they influence physiological
function.
Answer
Compartments that should be discussed here include the nucleus, the mitochondria, the rough and smooth
endoplasmic reticulum, and the Golgi apparatus.
30. What does the Na+/ K+ ATPase do in a typical cell?
Answer
The sodium pump, or Na+/ K+ ATPase, uses the energy associated with ATP hydrolysis to pump 3Na+ out of a cell in
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34. What are whole-genome duplications and when did they occur in animal evolution?
Answer
Many genes or chromosomal regions can be duplicated and persist as extra copies. At several points in evolution,
animals experienced a duplication of the entire genome. For a period, the organism was essentially tetraploid but with
time the duplicate genes diverged and the progeny were considered diploid, retaining extra paralogs of many genes.
34. What are whole-genome duplications and when did they occur in animal evolution?
Answer
Many genes or chromosomal regions can be duplicated and persist as extra copies. At several points in evolution,
animals experienced a duplication of the entire genome. For a period, the organism was essentially tetraploid but with
time the duplicate genes diverged and the progeny were considered diploid, retaining extra paralogs of many genes.
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Chapter 3 Chemistry, Biochemistry, and Cell Physiology
Answers to Review Questions
1. What are the four types of weak bonds and how do they differ from each other and from covalent bonds?
Answer
The four types of weak bonds are van der Waals forces, hydrogen bonds, ionic bonds, and hydrophobic interactions.
Covalent bonds are stronger, meaning more energy is required to break them. Hydrophobic interactions are
strengthened at high temperature whereas van der Waals forces, hydrogen bonds, ionic bonds are weakened at high
temperature.
2. Why are reaction rates influenced by temperature?
Answer
The influence of temperature on chemical reactions depends on many factors. For a simple chemical reaction that
requires energy to proceed spontaneously, increasing temperature will increase the reaction rate because a greater
fraction of the substrate molecules will possess activation energy. For enzymatic reactions, other factors come into
play because of how temperature affects the thermodynamics and kinetics. As with simple chemical reactions,
increasing temperature could increase reaction rates by imparting more energy to the substrates, enabling a greater
fraction to reach the activation energy barrier. Some reactions are very temperature sensitive in vivo and accelerate
when temperature increases. Typically, a 10oC temperature increase increases reaction rate 2- to 3-fold.. However,
many enzymes, such as catalase, have almost no thermal sensitivity and proceed at the same rate regardless of
Chapter 3 Chemistry, Biochemistry, and Cell Physiology
Answers to Review Questions
1. What are the four types of weak bonds and how do they differ from each other and from covalent bonds?
Answer
The four types of weak bonds are van der Waals forces, hydrogen bonds, ionic bonds, and hydrophobic interactions.
Covalent bonds are stronger, meaning more energy is required to break them. Hydrophobic interactions are
strengthened at high temperature whereas van der Waals forces, hydrogen bonds, ionic bonds are weakened at high
temperature.
2. Why are reaction rates influenced by temperature?
Answer
The influence of temperature on chemical reactions depends on many factors. For a simple chemical reaction that
requires energy to proceed spontaneously, increasing temperature will increase the reaction rate because a greater
fraction of the substrate molecules will possess activation energy. For enzymatic reactions, other factors come into
play because of how temperature affects the thermodynamics and kinetics. As with simple chemical reactions,
increasing temperature could increase reaction rates by imparting more energy to the substrates, enabling a greater
fraction to reach the activation energy barrier. Some reactions are very temperature sensitive in vivo and accelerate
when temperature increases. Typically, a 10oC temperature increase increases reaction rate 2- to 3-fold.. However,
many enzymes, such as catalase, have almost no thermal sensitivity and proceed at the same rate regardless of
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5. Distinguish between the types of polysaccharides relevant to animals.
Answer
Polysaccharides are simply chains of monosaccharides and in animals the most important ones are polymers of
glucose created when α-D-glucose molecules are attached between carbons 1 and 4 (α1,4 glycoside bonds). Amylose
is a plant polysaccharide with relatively few branches, whereas amylopectin has a side branch approximately every
thirty glucose molecules. Glycogen, produced by animals, is like amylopectin but with more frequent branches.
Cellulose, another plant-derived glucose polymer, is essentially indigestible in animals because the glucose units are
connected by β1,4 glycoside bonds.
Other polysaccharides can be made from different sugars. Arthropods build their exoskeletons with chitin, a
polysaccharide of N-acetyl-glucosamine. Vertebrates secrete hyaluronate, a polymer of N-acetyl-glucosamine and
glucuronic acid, into the extracellular space, where its gel-like properties act as a spacer between cells and tissues.
Hyaluronate is a member of a class of compounds called glycosaminoglycans that include chondroitin sulfate and
keratan sulfate.
6. Compare the structures of phospholipids.
Answer
Animal cells produce two classes of phospholipids: phosphoglycerides and sphingolipids. Phosphoglycerides are
built on a glycerol backbone, with fatty acid chains on two of the glycerol carbons, with the third position occupied by
a polar head group composed of an organic molecule linked via a phosphate. Sphingolipids have a similar three
5. Distinguish between the types of polysaccharides relevant to animals.
Answer
Polysaccharides are simply chains of monosaccharides and in animals the most important ones are polymers of
glucose created when α-D-glucose molecules are attached between carbons 1 and 4 (α1,4 glycoside bonds). Amylose
is a plant polysaccharide with relatively few branches, whereas amylopectin has a side branch approximately every
thirty glucose molecules. Glycogen, produced by animals, is like amylopectin but with more frequent branches.
Cellulose, another plant-derived glucose polymer, is essentially indigestible in animals because the glucose units are
connected by β1,4 glycoside bonds.
Other polysaccharides can be made from different sugars. Arthropods build their exoskeletons with chitin, a
polysaccharide of N-acetyl-glucosamine. Vertebrates secrete hyaluronate, a polymer of N-acetyl-glucosamine and
glucuronic acid, into the extracellular space, where its gel-like properties act as a spacer between cells and tissues.
Hyaluronate is a member of a class of compounds called glycosaminoglycans that include chondroitin sulfate and
keratan sulfate.
6. Compare the structures of phospholipids.
Answer
Animal cells produce two classes of phospholipids: phosphoglycerides and sphingolipids. Phosphoglycerides are
built on a glycerol backbone, with fatty acid chains on two of the glycerol carbons, with the third position occupied by
a polar head group composed of an organic molecule linked via a phosphate. Sphingolipids have a similar three
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9. What metabolic conditions can affect the values of the respiratory quotient? What metabolic conditions affect the
relationship between ATP produced and oxygen consumed?
Answer
The respiratory quotient is the ratio of CO2 produced to O2 consumed. While the amount of CO2 produced depends on
the number of carbons in the nutrient, the O2 consumed depends on the oxidation pathway. The oxidation of
carbohydrates leads to RQ values of 1, while the oxidation of fatty acids leads to RQ values around 0.7. Because
carbohydrates can be mobilized and oxidized rapidly, periods of short-term high-energy demands are characterized by
high RQ values, close to 1. Conversely, lipids are the major fuel source during sustained energy demands or during
starvation, which results in lower RQ values, near 0.7.
The oxidation of different fuels results in different ATP/O ratios. Carbohydrate oxidation relies mostly on NADH-
linked enzymes for which the ATP/O ratio is 3. Fatty acid oxidation, on the other hand, relies more on FAD-linked
enzymes for which the ATP/O ratio is 2. Therefore, the oxidation of carbohydrates leads to more ATP produced per
volume of oxygen consumed. Animals exposed to low levels of oxygen therefore favor the use of carbohydrates as a
fuel.
10. How do the pathways of gluconeogenesis and glycolysis overlap?
Answer
Most of the enzymes are shared between the two pathways, with these steps operating in opposite directions for
glycolysis and gluconeogenesis. However, there are three steps that are specific to each pathway.
(i) glucose to glucose 6-phosphate. In glycolysis, glucose is phosphorylated by hexokinase, consuming ATP and
releasing ADP. In gluconeogenesis, the reverse step is catalyzed by glucose 6-phosphatase, which cleaves off the
9. What metabolic conditions can affect the values of the respiratory quotient? What metabolic conditions affect the
relationship between ATP produced and oxygen consumed?
Answer
The respiratory quotient is the ratio of CO2 produced to O2 consumed. While the amount of CO2 produced depends on
the number of carbons in the nutrient, the O2 consumed depends on the oxidation pathway. The oxidation of
carbohydrates leads to RQ values of 1, while the oxidation of fatty acids leads to RQ values around 0.7. Because
carbohydrates can be mobilized and oxidized rapidly, periods of short-term high-energy demands are characterized by
high RQ values, close to 1. Conversely, lipids are the major fuel source during sustained energy demands or during
starvation, which results in lower RQ values, near 0.7.
The oxidation of different fuels results in different ATP/O ratios. Carbohydrate oxidation relies mostly on NADH-
linked enzymes for which the ATP/O ratio is 3. Fatty acid oxidation, on the other hand, relies more on FAD-linked
enzymes for which the ATP/O ratio is 2. Therefore, the oxidation of carbohydrates leads to more ATP produced per
volume of oxygen consumed. Animals exposed to low levels of oxygen therefore favor the use of carbohydrates as a
fuel.
10. How do the pathways of gluconeogenesis and glycolysis overlap?
Answer
Most of the enzymes are shared between the two pathways, with these steps operating in opposite directions for
glycolysis and gluconeogenesis. However, there are three steps that are specific to each pathway.
(i) glucose to glucose 6-phosphate. In glycolysis, glucose is phosphorylated by hexokinase, consuming ATP and
releasing ADP. In gluconeogenesis, the reverse step is catalyzed by glucose 6-phosphatase, which cleaves off the
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13. Many physiological processes require a change in the levels of proteins, such as membrane transporters. Discuss the
processes that cells can use to change the protein levels. Discuss how the subcellular compartment influences this pathway.
Answer
The levels of proteins can be controlled at multiple steps of synthesis and degradation. Some of these steps and
processes are shared by all proteins, regardless of their final destination. Other steps are unique to the final
compartment in which the protein finds itself. At the genetic level, cells can control whether specific genes are
transcribed or not. Transcription can be controlled through proteins that modify the three-dimensional organization of
DNA into nucleosomes. Once the promoter is accessible, DNA-binding proteins and coactivators control the
formation of the transcriptional machinery. The levels of transcription factors and chromatin remodeling enzymes are
often controlled by signaling pathways that change either the activity of these proteins or their subcellular localization.
For example, phosphorylation of a transcription factor might allow it dimerize or lead it to be imported into the
nucleus.
Once mRNA is synthesized and processed, it is exported to the cytoplasm, where it can be transcribed and eventually
degraded by RNases. For some proteins, the rate of protein synthesis is controlled by regulation of RNA degradation.
Few specific proteins are controlled through controls on translation. Cells alter global protein synthesis through the
phosphorylation of initiation and elongation factors, which affects the overall rate of translation in the cell. For
cytoplasmic and mitochondrial proteins, the mRNA is translated in the cytoplasm. In contrast, those proteins found in
the cell membrane and internal membrane network are translated into the ER. Once inside the ER, the protein is sent
to the correct location via transport vesicles.
Once proteins are synthesized, their levels can be regulated by degradation (proteolysis). Again, the compartment
determines the pathway of proteolysis. Cytoplasmic proteins are degraded via the ubiquitin-proteasome pathway.
Proteins that are damaged or targeted for degradation are tagged with the protein ubiquitin, then degraded by
proteasomes. The level of cell membrane proteins can be altered through exocytosis and endocytosis. Once in
vesicles, the protein may be sent to lysosomes for degradation.
14. Other physiological processes require changes in the activities of proteins. While this can arise through changes in the
levels of proteins, it can also change through regulation of protein function. Discuss the various ways that cells can alter the
activity of enzymes or transporters.
Answer
Competitive inhibitors bind to the active sites of enzymes, preventing the binding of substrates and therefore
decreasing enzymatic activity. The binding of some molecules to enzyme
13. Many physiological processes require a change in the levels of proteins, such as membrane transporters. Discuss the
processes that cells can use to change the protein levels. Discuss how the subcellular compartment influences this pathway.
Answer
The levels of proteins can be controlled at multiple steps of synthesis and degradation. Some of these steps and
processes are shared by all proteins, regardless of their final destination. Other steps are unique to the final
compartment in which the protein finds itself. At the genetic level, cells can control whether specific genes are
transcribed or not. Transcription can be controlled through proteins that modify the three-dimensional organization of
DNA into nucleosomes. Once the promoter is accessible, DNA-binding proteins and coactivators control the
formation of the transcriptional machinery. The levels of transcription factors and chromatin remodeling enzymes are
often controlled by signaling pathways that change either the activity of these proteins or their subcellular localization.
For example, phosphorylation of a transcription factor might allow it dimerize or lead it to be imported into the
nucleus.
Once mRNA is synthesized and processed, it is exported to the cytoplasm, where it can be transcribed and eventually
degraded by RNases. For some proteins, the rate of protein synthesis is controlled by regulation of RNA degradation.
Few specific proteins are controlled through controls on translation. Cells alter global protein synthesis through the
phosphorylation of initiation and elongation factors, which affects the overall rate of translation in the cell. For
cytoplasmic and mitochondrial proteins, the mRNA is translated in the cytoplasm. In contrast, those proteins found in
the cell membrane and internal membrane network are translated into the ER. Once inside the ER, the protein is sent
to the correct location via transport vesicles.
Once proteins are synthesized, their levels can be regulated by degradation (proteolysis). Again, the compartment
determines the pathway of proteolysis. Cytoplasmic proteins are degraded via the ubiquitin-proteasome pathway.
Proteins that are damaged or targeted for degradation are tagged with the protein ubiquitin, then degraded by
proteasomes. The level of cell membrane proteins can be altered through exocytosis and endocytosis. Once in
vesicles, the protein may be sent to lysosomes for degradation.
14. Other physiological processes require changes in the activities of proteins. While this can arise through changes in the
levels of proteins, it can also change through regulation of protein function. Discuss the various ways that cells can alter the
activity of enzymes or transporters.
Answer
Competitive inhibitors bind to the active sites of enzymes, preventing the binding of substrates and therefore
decreasing enzymatic activity. The binding of some molecules to enzyme
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into an mRNA that encodes a functional protein (pseudogenization). The paralogs may be expressed at different times,
in different tissues, or change in expression in response to a physiological challenge. Since each gene appears
specialized for a specific cellular environment, this divergence is called subfunctionalization. In some cases, a parlog
can mutate and diverge, resulting in a protein that does a fundamentally different function. This is called
neofunctionalization. These processes, originating early in animal evolution and operating at the level of individual
cells, provide animals with physiological flexibility.
16. How does genetic variation provide physiological flexibility?
Answer
Genetic variation of direct relevance to physiology can arise in both coding and regulatory regions. Many genes exist
as duplicates and over evolutionary time, the duplicates (paralogs) diverge into genes that differ in expression patterns
and/or protein structure. Some animals will express one paralog under one set of conditions, then switch to another
when conditions change. This might influence how a given tissue responds to a challenge or allow the animal to
produce different forms in separate tissues (white versus red muscle) or regions of a tissue (small versus large
intestine). Within a population of a species, there may be polymorphisms of a particular gene (alleles) that affect gene
expression or protein structure. This variation may be unimportant under most circumstances but it may become
important when conditions change, such that one allele is better suited than another. This could lead to natural
selection of the favorable genotype, increasing its frequency in the population.
into an mRNA that encodes a functional protein (pseudogenization). The paralogs may be expressed at different times,
in different tissues, or change in expression in response to a physiological challenge. Since each gene appears
specialized for a specific cellular environment, this divergence is called subfunctionalization. In some cases, a parlog
can mutate and diverge, resulting in a protein that does a fundamentally different function. This is called
neofunctionalization. These processes, originating early in animal evolution and operating at the level of individual
cells, provide animals with physiological flexibility.
16. How does genetic variation provide physiological flexibility?
Answer
Genetic variation of direct relevance to physiology can arise in both coding and regulatory regions. Many genes exist
as duplicates and over evolutionary time, the duplicates (paralogs) diverge into genes that differ in expression patterns
and/or protein structure. Some animals will express one paralog under one set of conditions, then switch to another
when conditions change. This might influence how a given tissue responds to a challenge or allow the animal to
produce different forms in separate tissues (white versus red muscle) or regions of a tissue (small versus large
intestine). Within a population of a species, there may be polymorphisms of a particular gene (alleles) that affect gene
expression or protein structure. This variation may be unimportant under most circumstances but it may become
important when conditions change, such that one allele is better suited than another. This could lead to natural
selection of the favorable genotype, increasing its frequency in the population.
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2
6. Trace the path of a protein hormone, such as insulin, from its gene in the nucleus to secretion out of the cell.
Answer
In the nucleus, a gene, which is a segment of DNA, is transcribed into a mRNA. The mRNA transcript is processed to
remove introns and moves out of the nucleus into the rough endoplasmic reticulum. Here, the mRNA is translated by
ribosomes into a chain of amino acids, which will be folded with the help of chaperones and exported via a vesicle to
the Golgi apparatus. From the Golgi apparatus, the protein will be repackaged in a vesicle that will undergo exocytosis
to release its content in the extra-cellular space.
7. Discuss the ways in which a cell is able to alter its interactions with other cells.
Answer
An important part of the function of many cells is the ability to affect how it interacts with other cell types. Many of
these interactions are physical connections, mediated through cell membrane receptors and extracellular matrix
proteins. Cells can control their interactions with surrounding cells by changing the types of receptors they produce, or
by altering the nature of the surrounding extracellular matrix. The levels of membrane proteins and secreted proteins
can be controlled by synthesis (transcription, translation) degradation (proteolysis) and membrane trafficking
(exocytosis, endocytosis).
6. Trace the path of a protein hormone, such as insulin, from its gene in the nucleus to secretion out of the cell.
Answer
In the nucleus, a gene, which is a segment of DNA, is transcribed into a mRNA. The mRNA transcript is processed to
remove introns and moves out of the nucleus into the rough endoplasmic reticulum. Here, the mRNA is translated by
ribosomes into a chain of amino acids, which will be folded with the help of chaperones and exported via a vesicle to
the Golgi apparatus. From the Golgi apparatus, the protein will be repackaged in a vesicle that will undergo exocytosis
to release its content in the extra-cellular space.
7. Discuss the ways in which a cell is able to alter its interactions with other cells.
Answer
An important part of the function of many cells is the ability to affect how it interacts with other cell types. Many of
these interactions are physical connections, mediated through cell membrane receptors and extracellular matrix
proteins. Cells can control their interactions with surrounding cells by changing the types of receptors they produce, or
by altering the nature of the surrounding extracellular matrix. The levels of membrane proteins and secreted proteins
can be controlled by synthesis (transcription, translation) degradation (proteolysis) and membrane trafficking
(exocytosis, endocytosis).
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