1. Control of Body Temperature and Water Balance
Chapter 25
Control of Body Temperature and Water Balance

2. Introduction During cold winters, bears are often dormant.
Physiological processes aid homeostasis, keeping the body temperature about 5ºC below normal.
Body fat and dense fur provide insulation.
Blood flow to extremities is reduced.
Nitrogen-containing wastes are metabolized differently.
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3. Introduction
Homeostasis is the maintenance of steady internal conditions despite fluctuations in the external environment.
Examples of homeostasis include
thermoregulation—the maintenance of internal temperature within narrow limits,
osmoregulation—the control of the gain and loss of water and solutes, and
excretion—the disposal of nitrogen-containing wastes.
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4. Osmoregulation and Excretion
Figure 25.0_1
Chapter 25: Big Ideas
Figure 25.0_1 Chapter 25: Big Ideas
Thermoregulation
Osmoregulation and Excretion 4

5. Figure 25.0_2
Figure 25.0_2 Grizzly bears (Ursus arctos horribilis) 5

6. THERMOREGULATION
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7. 25.1 An animal’s regulation of body temperature helps maintain homeostasis
Thermoregulation is
the process by which animals maintain an internal temperature within a tolerable range and
a form of homeostasis.
Student Misconceptions and Concerns
1. The concept of homeostasis may be new to some students, who have never considered how organisms must adjust to subtle changes in environmental conditions. Analogies to other systems that engage in self-regulation, such as the water regulation of a toilet or the temperature regulation of a furnace, may help.
2. One role of the circulatory system rarely discussed is the transport of heat. Blood vessels near the surface of the body expand when we are overheated, releasing some of this excess to the environment. Conversely, during periods of exposure to cold, blood is shunted away from the skin to conserve heat.
Teaching Tips
1. The terms warm-blooded and cold-blooded are less precise than endotherm and ectotherm. Encourage students to discuss why the latter two terms are preferable.
2. Ask your students to explain the adaptive advantages of endothermy and ectothermy. You might prompt the discussion by noting that endotherms consume about 10 times as many calories as ectotherms of equivalent body mass. What advantages might be worth this additional “cost” for endotherms?
3. The heat generated by aerobic metabolism is analogous to the heat generated by the engine of an automobile. In both cases, the heat is a by-product of the process. In the winter, this excess heat helps keep the body and the interior of the car warm. In the summer, both the body and the automobile’s engine must work to keep from overheating.
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8. 25.1 An animal’s regulation of body temperature helps maintain homeostasis
Ectothermic animals
gain most of their heat from external sources and
include many fish, most amphibians, lizards, and most invertebrates.
Endothermic animals
derive body heat mainly from their metabolism and
include birds, mammals, a few reptiles and fish, and many insects.
Student Misconceptions and Concerns
1. The concept of homeostasis may be new to some students, who have never considered how organisms must adjust to subtle changes in environmental conditions. Analogies to other systems that engage in self-regulation, such as the water regulation of a toilet or the temperature regulation of a furnace, may help.
2. One role of the circulatory system rarely discussed is the transport of heat. Blood vessels near the surface of the body expand when we are overheated, releasing some of this excess to the environment. Conversely, during periods of exposure to cold, blood is shunted away from the skin to conserve heat.
Teaching Tips
1. The terms warm-blooded and cold-blooded are less precise than endotherm and ectotherm. Encourage students to discuss why the latter two terms are preferable.
2. Ask your students to explain the adaptive advantages of endothermy and ectothermy. You might prompt the discussion by noting that endotherms consume about 10 times as many calories as ectotherms of equivalent body mass. What advantages might be worth this additional “cost” for endotherms?
3. The heat generated by aerobic metabolism is analogous to the heat generated by the engine of an automobile. In both cases, the heat is a by-product of the process. In the winter, this excess heat helps keep the body and the interior of the car warm. In the summer, both the body and the automobile’s engine must work to keep from overheating.
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9. 25.2 Heat is gained or lost in four ways
Heat exchange with the environment may occur by
conduction—the transfer of heat by direct contact,
convection—the transfer of heat by movement of air or liquid past a surface,
radiation—the emission of electromagnetic waves, or
evaporation—the loss of heat from the surface of a liquid that is losing some of its molecules as a gas.
Student Misconceptions and Concerns
1. The concept of homeostasis may be new to some students, who have never considered how organisms must adjust to subtle changes in environmental conditions. Analogies to other systems that engage in self-regulation, such as the water regulation of a toilet or the temperature regulation of a furnace, may help.
2. One role of the circulatory system rarely discussed is the transport of heat. Blood vessels near the surface of the body expand when we are overheated, releasing some of this excess to the environment. Conversely, during periods of exposure to cold, blood is shunted away from the skin to conserve heat.
Teaching Tips
1. Have students list the many factors that affect heat gain and loss during periods of physical activity, then have them identify which of the four physical processes for exchanging heat are involved. The factors include (a) the person’s physical condition, (b) the level of physical activity, (c) the age of the person (younger people tend to have higher metabolic rates), (d) the person’s level of hydration (which in turn affects the amount of sweating and evaporative cooling), (e) the external level of humidity (higher levels decrease evaporative cooling), (f) the intensity of the wind (greater intensity promotes evaporative cooling), (g) the intensity of sunlight, and (h) the color of the person’s clothing (which affects the amount of light energy the body absorbs).
2. You can extend the exercise above by challenging your class to identify environmental conditions when it would be too hot to play an outdoor sport. That is, when as a parent or coach would you want to prevent practice or a game because it is dangerously hot?
3. As an alternative to the above, challenge students to identify a human example of each of the four physical processes that involve heat exchange with the environment and that promote thermoregulation. Or, to check student comprehension, describe such examples and challenge the class to match the examples to the correct terminology.
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10. Evaporation Radiation Convection Conduction Figure 25.2
Figure 25.2 Mechanisms of heat exchange 10

11. 25.3 Thermoregulation involves adaptations that balance heat gain and loss
Five general categories of adaptations help animals thermoregulate.
Student Misconceptions and Concerns
1. The concept of homeostasis may be new to some students, who have never considered how organisms must adjust to subtle changes in environmental conditions. Analogies to other systems that engage in self-regulation, such as the water regulation of a toilet or the temperature regulation of a furnace, may help.
2. One role of the circulatory system rarely discussed is the transport of heat. Blood vessels near the surface of the body expand when we are overheated, releasing some of this excess to the environment. Conversely, during periods of exposure to cold, blood is shunted away from the skin to conserve heat.
Teaching Tips
1. Have students list the many factors that affect heat gain and loss during periods of physical activity, then have them identify which of the four physical processes for exchanging heat are involved. The factors include (a) the person’s physical condition, (b) the level of physical activity, (c) the age of the person (younger people tend to have higher metabolic rates), (d) the person’s level of hydration (which in turn affects the amount of sweating and evaporative cooling), (e) the external level of humidity (higher levels decrease evaporative cooling), (f) the intensity of the wind (greater intensity promotes evaporative cooling), (g) the intensity of sunlight, and (h) the color of the person’s clothing (which affects the amount of light energy the body absorbs).
2. You can extend the exercise above by challenging your class to identify environmental conditions when it would be too hot to play an outdoor sport. That is, when as a parent or coach would you want to prevent practice or a game because it is dangerously hot?
3. As an alternative to the above, challenge students to identify a human example of each of the four physical processes that involve heat exchange with the environment and that promote thermoregulation. Or, to check student comprehension, describe such examples and challenge the class to match the examples to the correct terminology.
4. Some students will be familiar with the type of foam insulation wrap surrounding interior pipes. These forms of insulation are especially necessary when hot- and cold-water pipes run parallel and in close proximity to each other. Without the insulation, heat would be easily transferred from hot-water to cold-water pipes, in a situation similar to countercurrent heat exchange systems in animals.
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12. 25.3 Thermoregulation involves adaptations that balance heat gain and loss
Increased metabolic heat production occurs when
hormonal changes boost the metabolic rate in birds and mammals,
birds and mammals shiver,
organisms increase their physical activity, and
honeybees cluster and shiver.
Student Misconceptions and Concerns
1. The concept of homeostasis may be new to some students, who have never considered how organisms must adjust to subtle changes in environmental conditions. Analogies to other systems that engage in self-regulation, such as the water regulation of a toilet or the temperature regulation of a furnace, may help.
2. One role of the circulatory system rarely discussed is the transport of heat. Blood vessels near the surface of the body expand when we are overheated, releasing some of this excess to the environment. Conversely, during periods of exposure to cold, blood is shunted away from the skin to conserve heat.
Teaching Tips
1. Have students list the many factors that affect heat gain and loss during periods of physical activity, then have them identify which of the four physical processes for exchanging heat are involved. The factors include (a) the person’s physical condition, (b) the level of physical activity, (c) the age of the person (younger people tend to have higher metabolic rates), (d) the person’s level of hydration (which in turn affects the amount of sweating and evaporative cooling), (e) the external level of humidity (higher levels decrease evaporative cooling), (f) the intensity of the wind (greater intensity promotes evaporative cooling), (g) the intensity of sunlight, and (h) the color of the person’s clothing (which affects the amount of light energy the body absorbs).
2. You can extend the exercise above by challenging your class to identify environmental conditions when it would be too hot to play an outdoor sport. That is, when as a parent or coach would you want to prevent practice or a game because it is dangerously hot?
3. As an alternative to the above, challenge students to identify a human example of each of the four physical processes that involve heat exchange with the environment and that promote thermoregulation. Or, to check student comprehension, describe such examples and challenge the class to match the examples to the correct terminology.
4. Some students will be familiar with the type of foam insulation wrap surrounding interior pipes. These forms of insulation are especially necessary when hot- and cold-water pipes run parallel and in close proximity to each other. Without the insulation, heat would be easily transferred from hot-water to cold-water pipes, in a situation similar to countercurrent heat exchange systems in animals.
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13. Figure 25.3_UN01
Figure 25.3_UN01 Honeybees clustering together and shivering to produce heat 13

14. 25.3 Thermoregulation involves adaptations that balance heat gain and loss
Insulation is provided by
hair,
feathers, and
fat layers.
Student Misconceptions and Concerns
1. The concept of homeostasis may be new to some students, who have never considered how organisms must adjust to subtle changes in environmental conditions. Analogies to other systems that engage in self-regulation, such as the water regulation of a toilet or the temperature regulation of a furnace, may help.
2. One role of the circulatory system rarely discussed is the transport of heat. Blood vessels near the surface of the body expand when we are overheated, releasing some of this excess to the environment. Conversely, during periods of exposure to cold, blood is shunted away from the skin to conserve heat.
Teaching Tips
1. Have students list the many factors that affect heat gain and loss during periods of physical activity, then have them identify which of the four physical processes for exchanging heat are involved. The factors include (a) the person’s physical condition, (b) the level of physical activity, (c) the age of the person (younger people tend to have higher metabolic rates), (d) the person’s level of hydration (which in turn affects the amount of sweating and evaporative cooling), (e) the external level of humidity (higher levels decrease evaporative cooling), (f) the intensity of the wind (greater intensity promotes evaporative cooling), (g) the intensity of sunlight, and (h) the color of the person’s clothing (which affects the amount of light energy the body absorbs).
2. You can extend the exercise above by challenging your class to identify environmental conditions when it would be too hot to play an outdoor sport. That is, when as a parent or coach would you want to prevent practice or a game because it is dangerously hot?
3. As an alternative to the above, challenge students to identify a human example of each of the four physical processes that involve heat exchange with the environment and that promote thermoregulation. Or, to check student comprehension, describe such examples and challenge the class to match the examples to the correct terminology.
4. Some students will be familiar with the type of foam insulation wrap surrounding interior pipes. These forms of insulation are especially necessary when hot- and cold-water pipes run parallel and in close proximity to each other. Without the insulation, heat would be easily transferred from hot-water to cold-water pipes, in a situation similar to countercurrent heat exchange systems in animals.
© 2012 Pearson Education, Inc. 14

15. 25.3 Thermoregulation involves adaptations that balance heat gain and loss
Circulatory adaptations include
increased or decreased blood flow to skin and
countercurrent heat exchange, with warm and cold blood flowing in opposite directions.
Student Misconceptions and Concerns
1. The concept of homeostasis may be new to some students, who have never considered how organisms must adjust to subtle changes in environmental conditions. Analogies to other systems that engage in self-regulation, such as the water regulation of a toilet or the temperature regulation of a furnace, may help.
2. One role of the circulatory system rarely discussed is the transport of heat. Blood vessels near the surface of the body expand when we are overheated, releasing some of this excess to the environment. Conversely, during periods of exposure to cold, blood is shunted away from the skin to conserve heat.
Teaching Tips
1. Have students list the many factors that affect heat gain and loss during periods of physical activity, then have them identify which of the four physical processes for exchanging heat are involved. The factors include (a) the person’s physical condition, (b) the level of physical activity, (c) the age of the person (younger people tend to have higher metabolic rates), (d) the person’s level of hydration (which in turn affects the amount of sweating and evaporative cooling), (e) the external level of humidity (higher levels decrease evaporative cooling), (f) the intensity of the wind (greater intensity promotes evaporative cooling), (g) the intensity of sunlight, and (h) the color of the person’s clothing (which affects the amount of light energy the body absorbs).
2. You can extend the exercise above by challenging your class to identify environmental conditions when it would be too hot to play an outdoor sport. That is, when as a parent or coach would you want to prevent practice or a game because it is dangerously hot?
3. As an alternative to the above, challenge students to identify a human example of each of the four physical processes that involve heat exchange with the environment and that promote thermoregulation. Or, to check student comprehension, describe such examples and challenge the class to match the examples to the correct terminology.
4. Some students will be familiar with the type of foam insulation wrap surrounding interior pipes. These forms of insulation are especially necessary when hot- and cold-water pipes run parallel and in close proximity to each other. Without the insulation, heat would be easily transferred from hot-water to cold-water pipes, in a situation similar to countercurrent heat exchange systems in animals.
© 2012 Pearson Education, Inc. 15

16. Figure 25.3_1
Figure 25.3_1 Heat dissipation via ear flapping (convection) and via water spray (evaporative cooling) 16

17. Blood returning to body core in vein
Figure 25.3_2
Blood returning to body core in vein
Blood from body core in artery
Blood from body core in artery
35
33C
Blood returning to body core in vein
30
27
Figure 25.3_2 Countercurrent heat exchange
20
18
10 9 17

18. 25.3 Thermoregulation involves adaptations that balance heat gain and loss
Evaporative cooling may involve
sweating,
panting, or
spreading saliva on body surfaces.
Student Misconceptions and Concerns
1. The concept of homeostasis may be new to some students, who have never considered how organisms must adjust to subtle changes in environmental conditions. Analogies to other systems that engage in self-regulation, such as the water regulation of a toilet or the temperature regulation of a furnace, may help.
2. One role of the circulatory system rarely discussed is the transport of heat. Blood vessels near the surface of the body expand when we are overheated, releasing some of this excess to the environment. Conversely, during periods of exposure to cold, blood is shunted away from the skin to conserve heat.
Teaching Tips
1. Have students list the many factors that affect heat gain and loss during periods of physical activity, then have them identify which of the four physical processes for exchanging heat are involved. The factors include (a) the person’s physical condition, (b) the level of physical activity, (c) the age of the person (younger people tend to have higher metabolic rates), (d) the person’s level of hydration (which in turn affects the amount of sweating and evaporative cooling), (e) the external level of humidity (higher levels decrease evaporative cooling), (f) the intensity of the wind (greater intensity promotes evaporative cooling), (g) the intensity of sunlight, and (h) the color of the person’s clothing (which affects the amount of light energy the body absorbs).
2. You can extend the exercise above by challenging your class to identify environmental conditions when it would be too hot to play an outdoor sport. That is, when as a parent or coach would you want to prevent practice or a game because it is dangerously hot?
3. As an alternative to the above, challenge students to identify a human example of each of the four physical processes that involve heat exchange with the environment and that promote thermoregulation. Or, to check student comprehension, describe such examples and challenge the class to match the examples to the correct terminology.
4. Some students will be familiar with the type of foam insulation wrap surrounding interior pipes. These forms of insulation are especially necessary when hot- and cold-water pipes run parallel and in close proximity to each other. Without the insulation, heat would be easily transferred from hot-water to cold-water pipes, in a situation similar to countercurrent heat exchange systems in animals.
© 2012 Pearson Education, Inc. 18

19. 25.3 Thermoregulation involves adaptations that balance heat gain and loss
Behavioral responses
are used by endotherms and ectotherms and
include
moving to the sun or shade,
migrating, and
bathing.
Student Misconceptions and Concerns
1. The concept of homeostasis may be new to some students, who have never considered how organisms must adjust to subtle changes in environmental conditions. Analogies to other systems that engage in self-regulation, such as the water regulation of a toilet or the temperature regulation of a furnace, may help.
2. One role of the circulatory system rarely discussed is the transport of heat. Blood vessels near the surface of the body expand when we are overheated, releasing some of this excess to the environment. Conversely, during periods of exposure to cold, blood is shunted away from the skin to conserve heat.
Teaching Tips
1. Have students list the many factors that affect heat gain and loss during periods of physical activity, then have them identify which of the four physical processes for exchanging heat are involved. The factors include (a) the person’s physical condition, (b) the level of physical activity, (c) the age of the person (younger people tend to have higher metabolic rates), (d) the person’s level of hydration (which in turn affects the amount of sweating and evaporative cooling), (e) the external level of humidity (higher levels decrease evaporative cooling), (f) the intensity of the wind (greater intensity promotes evaporative cooling), (g) the intensity of sunlight, and (h) the color of the person’s clothing (which affects the amount of light energy the body absorbs).
2. You can extend the exercise above by challenging your class to identify environmental conditions when it would be too hot to play an outdoor sport. That is, when as a parent or coach would you want to prevent practice or a game because it is dangerously hot?
3. As an alternative to the above, challenge students to identify a human example of each of the four physical processes that involve heat exchange with the environment and that promote thermoregulation. Or, to check student comprehension, describe such examples and challenge the class to match the examples to the correct terminology.
4. Some students will be familiar with the type of foam insulation wrap surrounding interior pipes. These forms of insulation are especially necessary when hot- and cold-water pipes run parallel and in close proximity to each other. Without the insulation, heat would be easily transferred from hot-water to cold-water pipes, in a situation similar to countercurrent heat exchange systems in animals.
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20. OSMOREGULATION AND EXCRETION
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21. 25.4 Animals balance the level of water and solutes through osmoregulation
Osmoregulation is the homeostatic control of the uptake and loss of water and solutes such as salt and other ions.
Osmosis is one process whereby animals regulate their uptake and loss of fluids.
Student Misconceptions and Concerns
The idea that a freshwater fish never drinks can be conceptually challenging, especially for students who have heard the old saying “drinks like a fish”! Consider introducing your discussion of osmoregulation with this remarkable and seemingly counterintuitive fact to generate interest.
Teaching Tips
Students may better understand the challenges of osmoregulation in freshwater fish if they are reminded of what occurs when humans soak their hands in water. Students will likely recall that this causes the skin on their hands to wrinkle, and some may have noticed that their skin wrinkles even faster in soapy water. Skin absorbs water by osmosis (just as a freshwater fish gains water). Oils on our skin reduce the influx of water. Soapy water, which washes away these oils, speeds up the process. The wrinkling occurs because the skin can expand only in certain areas, creating puckers.
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22. 25.4 Animals balance the level of water and solutes through osmoregulation
Osmoconformers
have body fluids with a solute concentration equal to that of seawater,
face no substantial challenges in water balance, and
include many marine invertebrates.
Student Misconceptions and Concerns
The idea that a freshwater fish never drinks can be conceptually challenging, especially for students who have heard the old saying “drinks like a fish”! Consider introducing your discussion of osmoregulation with this remarkable and seemingly counterintuitive fact to generate interest.
Teaching Tips
Students may better understand the challenges of osmoregulation in freshwater fish if they are reminded of what occurs when humans soak their hands in water. Students will likely recall that this causes the skin on their hands to wrinkle, and some may have noticed that their skin wrinkles even faster in soapy water. Skin absorbs water by osmosis (just as a freshwater fish gains water). Oils on our skin reduce the influx of water. Soapy water, which washes away these oils, speeds up the process. The wrinkling occurs because the skin can expand only in certain areas, creating puckers.
© 2012 Pearson Education, Inc. 22

23. 25.4 Animals balance the level of water and solutes through osmoregulation
Osmoregulators
have body fluids whose solute concentrations differ from that of their environment,
must actively regulate water movement, and
include
many land animals,
freshwater animals such as trout, and
marine vertebrates such as sharks.
Student Misconceptions and Concerns
The idea that a freshwater fish never drinks can be conceptually challenging, especially for students who have heard the old saying “drinks like a fish”! Consider introducing your discussion of osmoregulation with this remarkable and seemingly counterintuitive fact to generate interest.
Teaching Tips
Students may better understand the challenges of osmoregulation in freshwater fish if they are reminded of what occurs when humans soak their hands in water. Students will likely recall that this causes the skin on their hands to wrinkle, and some may have noticed that their skin wrinkles even faster in soapy water. Skin absorbs water by osmosis (just as a freshwater fish gains water). Oils on our skin reduce the influx of water. Soapy water, which washes away these oils, speeds up the process. The wrinkling occurs because the skin can expand only in certain areas, creating puckers.
© 2012 Pearson Education, Inc. 23

24. 25.4 Animals balance the level of water and solutes through osmoregulation
Freshwater fish
gain water by osmosis (mainly through gills),
lose salt by diffusion to the more dilute environment,
take in salt through their gills and in food, and
excrete excess water in dilute urine.
Student Misconceptions and Concerns
The idea that a freshwater fish never drinks can be conceptually challenging, especially for students who have heard the old saying “drinks like a fish”! Consider introducing your discussion of osmoregulation with this remarkable and seemingly counterintuitive fact to generate interest.
Teaching Tips
Students may better understand the challenges of osmoregulation in freshwater fish if they are reminded of what occurs when humans soak their hands in water. Students will likely recall that this causes the skin on their hands to wrinkle, and some may have noticed that their skin wrinkles even faster in soapy water. Skin absorbs water by osmosis (just as a freshwater fish gains water). Oils on our skin reduce the influx of water. Soapy water, which washes away these oils, speeds up the process. The wrinkling occurs because the skin can expand only in certain areas, creating puckers.
© 2012 Pearson Education, Inc. 24

25. Osmotic water gain through gills and other parts of body surface
Figure 25.4_1
Osmotic water gain through gills and other parts of body surface
Uptake of some ions in food
Uptake of salt ions by gills
Figure 25.4_1 Osmoregulation in a rainbow trout, a freshwater fish
Excretion of large amounts of water in dilute urine from kidneys
Fresh water 25

26. 25.4 Animals balance the level of water and solutes through osmoregulation
Saltwater fish
lose water by osmosis from the gills and body surface,
drink seawater, and
use their gills and kidneys to excrete excess salt.
Student Misconceptions and Concerns
The idea that a freshwater fish never drinks can be conceptually challenging, especially for students who have heard the old saying “drinks like a fish”! Consider introducing your discussion of osmoregulation with this remarkable and seemingly counterintuitive fact to generate interest.
Teaching Tips
Students may better understand the challenges of osmoregulation in freshwater fish if they are reminded of what occurs when humans soak their hands in water. Students will likely recall that this causes the skin on their hands to wrinkle, and some may have noticed that their skin wrinkles even faster in soapy water. Skin absorbs water by osmosis (just as a freshwater fish gains water). Oils on our skin reduce the influx of water. Soapy water, which washes away these oils, speeds up the process. The wrinkling occurs because the skin can expand only in certain areas, creating puckers.
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27. Gain of water and salt ions from food and by intake of seawater
Figure 25.4_2
Gain of water and salt ions from food and by intake of seawater
Osmotic water loss through gills and other parts of body surface
Excretion of salt from gills
Excretion of excess ions and small amounts of water in concentrated urine from kidneys
Figure 25.4_2 Osmoregulation in a bluefin tuna, a saltwater fish
Salt water 27

28. 25.4 Animals balance the level of water and solutes through osmoregulation
Land animals
face the risk of dehydration,
lose water by evaporation and waste disposal,
gain water by drinking and eating, and
conserve water by
reproductive adaptations,
behavior adaptations,
waterproof skin, and
efficient kidneys.
Student Misconceptions and Concerns
The idea that a freshwater fish never drinks can be conceptually challenging, especially for students who have heard the old saying “drinks like a fish”! Consider introducing your discussion of osmoregulation with this remarkable and seemingly counterintuitive fact to generate interest.
Teaching Tips
Students may better understand the challenges of osmoregulation in freshwater fish if they are reminded of what occurs when humans soak their hands in water. Students will likely recall that this causes the skin on their hands to wrinkle, and some may have noticed that their skin wrinkles even faster in soapy water. Skin absorbs water by osmosis (just as a freshwater fish gains water). Oils on our skin reduce the influx of water. Soapy water, which washes away these oils, speeds up the process. The wrinkling occurs because the skin can expand only in certain areas, creating puckers.
© 2012 Pearson Education, Inc. 28

29. 25.5 EVOLUTION CONNECTION: A variety of ways to dispose of nitrogenous wastes has evolved in animals
Metabolism produces toxic by-products.
Nitrogenous wastes are toxic breakdown products of proteins and nucleic acids.
Animals dispose of nitrogenous wastes in different ways.
Student Misconceptions and Concerns
The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store.
Teaching Tips
Student experience with osmoregulation not pertaining to their bodies may be quite limited. However, many students are familiar with the pasty white color of bird droppings. Consider beginning your discussion of nitrogenous wastes by asking your class to explain why bird droppings are white.
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30. 25.5 EVOLUTION CONNECTION: A variety of ways to dispose of nitrogenous wastes has evolved in animals
Ammonia (NH3) is
poisonous,
too toxic to be stored in the body,
soluble in water, and
easily disposed of by aquatic animals.
Student Misconceptions and Concerns
The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store.
Teaching Tips
Student experience with osmoregulation not pertaining to their bodies may be quite limited. However, many students are familiar with the pasty white color of bird droppings. Consider beginning your discussion of nitrogenous wastes by asking your class to explain why bird droppings are white.
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31. 25.5 EVOLUTION CONNECTION: A variety of ways to dispose of nitrogenous wastes has evolved in animals
Urea is
produced in the vertebrate liver by combining ammonia and carbon dioxide,
less toxic,
easier to store, and
highly soluble in water.
Student Misconceptions and Concerns
The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store.
Teaching Tips
Student experience with osmoregulation not pertaining to their bodies may be quite limited. However, many students are familiar with the pasty white color of bird droppings. Consider beginning your discussion of nitrogenous wastes by asking your class to explain why bird droppings are white.
© 2012 Pearson Education, Inc. 31

32. 25.5 EVOLUTION CONNECTION: A variety of ways to dispose of nitrogenous wastes has evolved in animals
Uric acid is
excreted by some land animals (insects, land snails, and many reptiles),
relatively nontoxic,
largely insoluble in water,
excreted as a semisolid paste, conserving water, but
more energy expensive to produce.
Student Misconceptions and Concerns
The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store.
Teaching Tips
Student experience with osmoregulation not pertaining to their bodies may be quite limited. However, many students are familiar with the pasty white color of bird droppings. Consider beginning your discussion of nitrogenous wastes by asking your class to explain why bird droppings are white.
© 2012 Pearson Education, Inc. 32

33. Most aquatic animals, including most bony fishes
Figure 25.5
Proteins
Amino acids
Nitrogenous bases
Nucleic acids
NH2 (amino groups)
Most aquatic animals, including most bony fishes
Mammals, most amphibians, sharks,
some bony fishes
Birds and many other reptiles, insects, land snails
Figure 25.5 Nitrogen-containing metabolic waste products
Uric acid
Ammonia
Urea 33

34. 25.6 The urinary system plays several major roles in homeostasis
forms and excretes urine and
regulates water and solutes in body fluids.
In humans, the kidneys are the main processing centers of the urinary system.
Student Misconceptions and Concerns
1. The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store.
2. Before addressing the human urinary system, challenge each student in your class to explain how a drink of water may end up as urine. Consider having students write out their answers on a 3  5 card in class. This quick survey will likely reveal misunderstandings that would otherwise be concealed by quiet students’ reluctance to speak up. Students might suggest that some sort of tube transports fluid from the digestive tract to the kidneys or urinary bladder. Such surveys provide a useful means of gauging the initial assumptions of your students as they approach a new subject.
Teaching Tips
1. A moderately full human urinary bladder holds about 500 ml (or 1 pint) of fluid. The bladder’s maximum capacity may be up to double that volume, although if overdistended, it may burst!
2. Students must understand that blood consists of two main components, cells and plasma. If your course has not covered Chapter 23, consider assigning Module to ensure that they have this important background knowledge.
3. During the production of urine, blood cells remain within blood vessels, and components of the plasma are filtered out and selectively reabsorbed. Students may appreciate your making this important distinction early on in the discussion of renal functions.
© 2012 Pearson Education, Inc. 34

35. 25.6 The urinary system plays several major roles in homeostasis
Nephrons
are the functional units of the kidneys,
extract a fluid filtrate from the blood, and
refine the filtrate to produce urine.
Urine is
drained from the kidneys by ureters,
stored in the urinary bladder, and
expelled through the urethra.
Student Misconceptions and Concerns
1. The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store.
2. Before addressing the human urinary system, challenge each student in your class to explain how a drink of water may end up as urine. Consider having students write out their answers on a 3 x 5 card in class. This quick survey will likely reveal misunderstandings that would otherwise be concealed by quiet students’ reluctance to speak up. Students might suggest that some sort of tube transports fluid from the digestive tract to the kidneys or urinary bladder. Such surveys provide a useful means of gauging the initial assumptions of your students as they approach a new subject.
Teaching Tips
1. A moderately full human urinary bladder holds about 500 ml (or 1 pint) of fluid. The bladder’s maximum capacity may be up to double that volume, although if overdistended, it may burst!
2. Students must understand that blood consists of two main components, cells and plasma. If your course has not covered Chapter 23, consider assigning Module to ensure that they have this important background knowledge.
3. During the production of urine, blood cells remain within blood vessels, and components of the plasma are filtered out and selectively reabsorbed. Students may appreciate your making this important distinction early on in the discussion of renal functions.
© 2012 Pearson Education, Inc. 35

36. Animation: Nephron Introduction
Student Misconceptions and Concerns
1. The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store.
2. Before addressing the human urinary system, challenge each student in your class to explain how a drink of water may end up as urine. Consider having students write out their answers on a 3 x 5 card in class. This quick survey will likely reveal misunderstandings that would otherwise be concealed by quiet students’ reluctance to speak up. Students might suggest that some sort of tube transports fluid from the digestive tract to the kidneys or urinary bladder. Such surveys provide a useful means of gauging the initial assumptions of your students as they approach a new subject.
Teaching Tips
1. A moderately full human urinary bladder holds about 500 ml (or 1 pint) of fluid. The bladder’s maximum capacity may be up to double that volume, although if overdistended, it may burst!
2. Students must understand that blood consists of two main components, cells and plasma. If your course has not covered Chapter 23, consider assigning Module to ensure that they have this important background knowledge.
3. During the production of urine, blood cells remain within blood vessels, and components of the plasma are filtered out and selectively reabsorbed. Students may appreciate your making this important distinction early on in the discussion of renal functions.
Animation: Nephron Introduction
Right click on animation / Click play
© 2012 Pearson Education, Inc. 36

37. Figure 25.6 Anatomy of the human excretory system
Renal cortex
Aorta
Renal medulla
Inferior vena cava
Renal artery (red) and vein (blue)
Kidney
Ureter
Urinary bladder
Renal pelvis
Urethra
The urinary system
Ureter
Bowman’s capsule 1
Proximal tubule
Arteriole from renal artery
Glomerulus
Capillaries
The kidney 3
Distal tubule
Bowman’s capsule
Arteriole from glomerulus
Collecting duct
Tubule
Renal cortex
Branch of renal vein
From another nephron
Branch of renal artery
Figure 25.6 Anatomy of the human excretory system
Branch of renal vein
Collecting duct
Renal medulla 2
Loop of Henle with capillary network
To renal pelvis
Detailed structure of a nephron
Orientation of a nephron within the kidney 37

38. The urinary system Aorta Inferior vena cava
Figure 25.6_1
Aorta
Inferior vena cava
Renal artery (red) and vein (blue)
Kidney
Ureter
Figure 25.6_1 Anatomy of the human excretory system: the urinary system (part 1)
Urinary bladder
Urethra
The urinary system 38

39. Renal cortex Renal medulla Renal pelvis Ureter The kidney
Figure 25.6_2
Renal cortex
Renal medulla
Renal pelvis
Ureter
Figure 25.6_2 Anatomy of the human excretory system: the kidney (part 2)
The kidney 39

40. Orientation of a nephron within the kidney
Figure 25.6_3
Bowman’s capsule
Tubule
Renal cortex
Branch of renal artery
Branch of renal vein
Collecting duct
Renal medulla
Figure 25.6_3 Anatomy of the human excretory system: nephron orientation (part 3)
To renal pelvis
Orientation of a nephron within the kidney 40

41. Arteriole from renal artery Glomerulus Capillaries
Figure 25.6_4
Bowman’s capsule 1
Proximal tubule
Arteriole from renal artery
Glomerulus
Capillaries 3
Distal tubule Collecting Duct
Arteriole from glomerulus
Branch of renal vein
From another nephron
Figure 25.6_4 Anatomy of the human excretory system: nephron structure (part 4) 2
Loop of Henle with capillary network
Detailed structure of a nephron 41

42. 25.7 Overview: The key processes of the urinary system are filtration, reabsorption, secretion, and excretion
Filtration
Blood pressure forces water and many small molecules through a capillary wall into the start of the kidney tubule.
Reabsorption
refines the filtrate,
reclaims valuable solutes (such as glucose, salt, and amino acids) from the filtrate, and
returns these to the blood.
Student Misconceptions and Concerns
The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store.
Teaching Tips
1. Students must understand that blood consists of two main components, cells and plasma. If your course has not covered Chapter 23, consider assigning Module to ensure that they have this important background knowledge.
2. During the production of urine, blood cells remain within blood vessels, and components of the plasma are filtered out and selectively reabsorbed. Students may appreciate your making this important distinction early on in the discussion of renal functions.
3. Some drugs are excreted in urine. This is the basis of drug testing using samples of a person’s urine. Making this simple connection can help generate interest and improve comprehension in your students.
4. Many students do not know about interstitial fluid or its functions. They may think that blood delivers nutrients directly to cells, perhaps through direct contact between capillaries and cells. Instead, interstitial fluids typically act as an intermediate and promote homeostasis in many ways. Interstitial fluid is discussed in detail in Module 23.7, which may not have been addressed previously in your class.
© 2012 Pearson Education, Inc. 42

43. Figure 25.7 Major processes of the urinary system
Bowman’s capsule
From renal artery
Filtration
Reabsorption
Secretion
Excretion
Nephron tubule
H2O, other small molecules
Urine
Interstitial fluid
Capillary
To renal vein
Figure 25.7 Major processes of the urinary system 43

44. H2O, other small molecules
Figure 25.7_1
Bowman’s capsule
From renal artery
Filtration
Nephron tubule
H2O, other small molecules
Interstitial fluid
Figure 25.7_1 Major processes of the urinary system (part 1)
Capillary 44

45. Reabsorption Secretion Excretion Nephron tubule Urine To renal vein
Figure 25.7_2
Reabsorption
Secretion
Excretion
Nephron tubule
Urine
To renal vein
Figure 25.7_2 Major processes of the urinary system (part 2)
Capillary 45

46. 25.7 Overview: The key processes of the urinary system are filtration, reabsorption, secretion, and excretion
Substances in the blood are transported into the filtrate by the process of secretion.
By excretion the final product, urine, is excreted via the ureters, urinary bladder, and urethra.
Student Misconceptions and Concerns
The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store.
Teaching Tips
1. Students must understand that blood consists of two main components, cells and plasma. If your course has not covered Chapter 23, consider assigning Module to ensure that they have this important background knowledge.
2. During the production of urine, blood cells remain within blood vessels, and components of the plasma are filtered out and selectively reabsorbed. Students may appreciate your making this important distinction early on in the discussion of renal functions.
3. Some drugs are excreted in urine. This is the basis of drug testing using samples of a person’s urine. Making this simple connection can help generate interest and improve comprehension in your students.
4. Many students do not know about interstitial fluid or its functions. They may think that blood delivers nutrients directly to cells, perhaps through direct contact between capillaries and cells. Instead, interstitial fluids typically act as an intermediate and promote homeostasis in many ways. Interstitial fluid is discussed in detail in Module 23.7, which may not have been addressed previously in your class.
© 2012 Pearson Education, Inc. 46

47. Figure 25.7 Major processes of the urinary system
Bowman’s capsule
From renal artery
Filtration
Reabsorption
Secretion
Excretion
Nephron tubule
H2O, other small molecules
Urine
Interstitial fluid
Capillary
To renal vein
Figure 25.7 Major processes of the urinary system 47

48. 25.8 Blood filtrate is refined to urine through reabsorption and secretion
Reabsorption in the proximal and distal tubules removes
nutrients,
salt, and
water.
pH is regulated by
reabsorption of HCO3– and
secretion of H+.
Student Misconceptions and Concerns
The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store.
Teaching Tips
Many students do not know about interstitial fluid or its functions. They may think that blood delivers nutrients directly to cells, perhaps through direct contact between capillaries and cells. Instead, interstitial fluids typically act as an intermediate and promote homeostasis in many ways. Interstitial fluid is discussed in detail in Module 23.7, which may not have been addressed previously in your class.
© 2012 Pearson Education, Inc. 48

49. 25.8 Blood filtrate is refined to urine through reabsorption and secretion
High NaCl concentration in the medulla promotes reabsorption of water.
Student Misconceptions and Concerns
The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store.
Teaching Tips
Many students do not know about interstitial fluid or its functions. They may think that blood delivers nutrients directly to cells, perhaps through direct contact between capillaries and cells. Instead, interstitial fluids typically act as an intermediate and promote homeostasis in many ways. Interstitial fluid is discussed in detail in Module 23.7, which may not have been addressed previously in your class.
© 2012 Pearson Education, Inc. 49

50. Animation: Bowman’s Capsule and Proximal Tubule
Student Misconceptions and Concerns
The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store.
Teaching Tips
Many students do not know about interstitial fluid or its functions. They may think that blood delivers nutrients directly to cells, perhaps through direct contact between capillaries and cells. Instead, interstitial fluids typically act as an intermediate and promote homeostasis in many ways. Interstitial fluid is discussed in detail in Module 23.7, which may not have been addressed previously in your class.
Animation: Bowman’s Capsule and Proximal Tubule
Right click on animation / Click play
© 2012 Pearson Education, Inc. 50

51. Animation: Collecting Duct
Student Misconceptions and Concerns
The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store.
Teaching Tips
Many students do not know about interstitial fluid or its functions. They may think that blood delivers nutrients directly to cells, perhaps through direct contact between capillaries and cells. Instead, interstitial fluids typically act as an intermediate and promote homeostasis in many ways. Interstitial fluid is discussed in detail in Module 23.7, which may not have been addressed previously in your class.
Animation: Collecting Duct
Right click on animation / Click play
© 2012 Pearson Education, Inc. 51

52. Animation: Effect of ADH
Student Misconceptions and Concerns
The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store.
Teaching Tips
Many students do not know about interstitial fluid or its functions. They may think that blood delivers nutrients directly to cells, perhaps through direct contact between capillaries and cells. Instead, interstitial fluids typically act as an intermediate and promote homeostasis in many ways. Interstitial fluid is discussed in detail in Module 23.7, which may not have been addressed previously in your class.
Animation: Effect of ADH
Right click on animation / Click play
© 2012 Pearson Education, Inc. 52

53. Animation: Loop of Henle and Distal Tubule
Student Misconceptions and Concerns
The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store.
Teaching Tips
Many students do not know about interstitial fluid or its functions. They may think that blood delivers nutrients directly to cells, perhaps through direct contact between capillaries and cells. Instead, interstitial fluids typically act as an intermediate and promote homeostasis in many ways. Interstitial fluid is discussed in detail in Module 23.7, which may not have been addressed previously in your class.
Animation: Loop of Henle and Distal Tubule
Right click on animation / Click play
© 2012 Pearson Education, Inc. 53

54. Urine (to renal pelvis)
Figure 25.8
Bowman’s capsule
Proximal tubule
Distal tubule
Nutrients H2O 1
H2O
NaCl
HCO3
NaCl
HCO3
Blood
Some drugs and poisons H K H 3
Collecting duct
Cortex
Filtrate composition
Medulla
H2O Salts (NaCl and others) HCO3 H Urea Glucose Amino acids Some drugs
Interstitial fluid
Loop of Henle 2
NaCl
NaCl
H2O
Urea
Figure 25.8 Reabsorption and secretion in a nephron
NaCl
H2O
Reabsorption
Secretion
Filtrate movement
Urine (to renal pelvis) 54

55. Bowman’s capsule Proximal tubule Nutrients H2O HCO3 NaCl Blood
Figure 25.8_1
Bowman’s capsule
Proximal tubule
Nutrients H2O
NaCl
HCO3
Blood
Some drugs and poisons H
Cortex
Filtrate composition
Medulla
H2O Salts (NaCl and others) HCO3 H Urea Glucose Amino acids Some drugs
Figure 25.8_1 Reabsorption and secretion in a nephron (part 1)
Reabsorption
Secretion
Filtrate movement 55

56.   Proximal tubule Distal tubule Nutrients H2O H2O NaCl HCO3 NaCl
Figure 25.8_2
Proximal tubule
Distal tubule
Nutrients
H2O 1
H2O
NaCl
HCO3
NaCl
HCO3
Some drugs and poisons H K  H  3
Collecting duct
Cortex
Medulla
Interstitial fluid
Loop of Henle 2
NaCl
NaCl
H2O
Figure 25.8_2 Reabsorption and secretion in a nephron (part 2)
Reabsorption
Urea
NaCl
Secretion
H2O
Filtrate movement
Urine (to renal pelvis) 56

57. 25.9 Hormones regulate the urinary system
Antidiuretic hormone (ADH) regulates the amount of water excreted by the kidneys by
signaling nephrons to reabsorb water from the filtrate, returning it to the blood, and
decreasing the amount of water excreted.
Diuretics
inhibit the release of ADH and
include alcohol and caffeine.
Student Misconceptions and Concerns
The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store.
Teaching Tips
Students may be particularly interested in the diuretic effects of alcohol and caffeine. The text notes that the diuretic effects of alcohol may contribute to some of the symptoms of a hangover. However, the concentration of alcohol and caffeine are important factors. Higher urine output resulting from the high consumption of low-alcohol (1–5%) beer may largely be the consequence of increased water consumption. Drinks with higher alcohol levels, such as shots of hard liquor (gin, vodka, whiskey) or higher caffeine levels (espresso) and low fluid volume would be expected to better reveal the diuretic effects.
© 2012 Pearson Education, Inc. 57

58. 25.10 CONNECTION: Kidney dialysis can be lifesaving
Kidney failure can result from
hypertension,
diabetes, and
prolonged use of common drugs, including alcohol.
A dialysis machine
removes wastes from the blood and
maintains its solute concentration.
Student Misconceptions and Concerns
The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store.
Teaching Tips
1. The loss of one kidney in a human typically results in enlargement of the remaining kidney, a process known as compensatory hypertrophy. As your time permits, this can provide material for a class discussion or for a special-topic assignment for students with a particular interest.
2. The unfortunate shortage of kidneys and other organs available for transplant is a major health issue. Consider discussing this problem with your class. Many state and federal organ donation organizations can by located by a quick Internet search. The National Kidney Foundation site includes information on kidney donation.
© 2012 Pearson Education, Inc. 58

59. Line from artery to apparatus
Figure 25.9
Line from artery to apparatus
Pump
Tubing made of a selectively permeable membrane
Dialyzing solution
Line from apparatus to vein
Figure 25.9 Kidney dialysis
Fresh dialyzing solution
Used dialyzing solution (with urea and excess ions) 59

60. Line from artery to apparatus
Figure 25.9_1
Line from artery to apparatus
Pump
Tubing made of a selectively permeable membrane
Dialyzing solution
Line from apparatus to vein
Figure 25.9_1 Kidney dialysis (part 1)
Fresh dialyzing solution
Used dialyzing solution (with urea and excess ions) 60

61. Figure 25.9_2
Figure 25.9_2 Kidney dialysis (part 2) 61

62. You should now be able to
Explain how bear physiology adjusts during dormancy.
Describe four ways that heat is gained or lost by an animal.
Describe five categories of adaptations that help animals thermoregulate.
Compare the osmoregulatory problems of freshwater fish, saltwater fish, and terrestrial animals.
© 2012 Pearson Education, Inc. 62

63. You should now be able to
Compare the three ways that animals eliminate nitrogenous wastes.
Describe the structure and functions of the human kidney.
Explain how the kidney promotes homeostasis.
Describe four major processes that produce urine.
Describe the key events in the conversion of filtrate into urine.
Explain why a dialysis machine is necessary and how it works.
© 2012 Pearson Education, Inc. 63

64. Figure 25.4_UN01
Figure 25.4_UN01 The tough, water-tight shell of a turtle egg 64

65. Figure 25.UN01
35
33C
30
27
20
18
10 9
Figure 25.UN01 Reviewing the Concepts, 25.3 65

66. Evaporation, urinary system
Figure 25.UN02
Gain Water
Lose Water
Salt
Freshwater Fish
Osmosis
Excretion
Pump in
Saltwater Fish
Drinking
Osmosis
Excrete, pump out
Land Animal
Drinking, eating
Evaporation, urinary system
Figure 25.UN02 Reviewing the Concepts, 25.4 66

67. Figure 25.UN03
Urea
Figure 25.UN03 Reviewing the Concepts, 25.5 67

68. Kidney Ureter Bladder Figure 25.UN04
Figure 25.UN04 Reviewing the Concepts, 25.7 68

69. requirements depend on form may be
Figure 25.UN05
Homeostasis
involves processes of
(a)
(b)
(c)
maintains balance of
involves removal of
both done by
animal may be
water and solutes
human kidney
nitrogenous wastes
(d)
requirements depend on
form may be
(e)
endotherm
mechanisms mostly
(f)
mechanisms include
(g)
Figure 25.UN05 Connecting the Concepts, question 1
depends on
(h)
(i)
reproduction (where embryo develops)
may be
heat production, insulation, countercurrent heat exchange
ocean, fresh water, land 69

70. (a) (b) (c) Bowman’s capsule From renal artery To renal vein
Figure 25.UN06
(a)
(b)
(c)
Bowman’s capsule
From renal artery
To renal vein
Collecting duct
Glomerulus
Tubule
Loop of Henle
Capillaries
Figure 25.UN06 Connecting the Concepts, question 2
(d) 70