Cellular Respiration: Obtaining Energy from Food

Cellular Respiration: Obtaining Energy from Food
Chapter 6 Cellular Respiration: Obtaining Energy from Food

Biology and Society: Marathoners versus Sprinters
Slow-twitch fibers last longer, do not generate a lot of quick power, and generate ATP using oxygen (aerobically). © 2013 Pearson Education, Inc. 2

Biology and Society: Marathoners versus Sprinters
Fast-twitch fibers contract more quickly and powerfully, fatigue more quickly, and can generate ATP without using oxygen (anaerobically). All human muscles contain both types of fibers but in different ratios. © 2013 Pearson Education, Inc. 3

ENERGY FLOW AND CHEMICAL CYCLING IN THE BIOSPHERE
Animals depend on plants to convert the energy of sunlight to chemical energy of sugars and other organic molecules we consume as food. Photosynthesis uses light energy from the sun to power a chemical process and make organic molecules. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students should be cautioned against making statements that “energy is created” when it is converted from one form to another. This might be a good time to review the principle of conservation of energy (the first law of thermodynamics). 2. Students frequently think that plants have chloroplasts instead of mitochondria. Care should be taken to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips 1. You might wish to elaborate on the amount of solar energy striking Earth. Every day Earth is bombarded with solar radiation equal to the energy of 100 million atomic bombs. Of the tiny fraction of light that reaches photosynthetic organisms, only about 1% is converted to chemical energy by photosynthesis. 2. You might share with your students that it takes about 10 million ATP molecules per second to power one active muscle cell. 3. Energy coupling at the cellular level may be new to many students, but it is a familiar concept when related to the use of money in our society. Students might be discouraged if the only benefit of work was the ability to make purchases from the employer. (We all might soon tire of a fast-food job that pays its employees only in food!) Money permits the coupling of the generation of value (a paycheck, analogous to an energy-releasing reaction) to an energy-consuming reaction (money, which enables us to make purchases in distant locations). This idea of “earn and spend” is a common concept we all know well. 4

Producers and Consumers
Plants and other autotrophs (self-feeders) make their own organic matter from inorganic nutrients. Heterotrophs (other-feeders) include humans and other animals that cannot make organic molecules from inorganic ones. Autotrophs are producers because ecosystems depend upon them for food. Heterotrophs are consumers because they eat plants or other animals. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students should be cautioned against making statements that “energy is created” when it is converted from one form to another. This might be a good time to review the principle of conservation of energy (the first law of thermodynamics). 2. Students frequently think that plants have chloroplasts instead of mitochondria. Care should be taken to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips 1. You might wish to elaborate on the amount of solar energy striking Earth. Every day Earth is bombarded with solar radiation equal to the energy of 100 million atomic bombs. Of the tiny fraction of light that reaches photosynthetic organisms, only about 1% is converted to chemical energy by photosynthesis. 2. You might share with your students that it takes about 10 million ATP molecules per second to power one active muscle cell. 3. Energy coupling at the cellular level may be new to many students, but it is a familiar concept when related to the use of money in our society. Students might be discouraged if the only benefit of work was the ability to make purchases from the employer. (We all might soon tire of a fast-food job that pays its employees only in food!) Money permits the coupling of the generation of value (a paycheck, analogous to an energy-releasing reaction) to an energy-consuming reaction (money, which enables us to make purchases in distant locations). This idea of “earn and spend” is a common concept we all know well. 5

Chemical Cycling between Photosynthesis and Cellular Respiration
The ingredients for photosynthesis are carbon dioxide (CO2) and water (H2O). CO2 is obtained from the air by a plant’s leaves. H2O is obtained from the damp soil by a plant’s roots. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students should be cautioned against making statements that “energy is created” when it is converted from one form to another. This might be a good time to review the principle of conservation of energy (the first law of thermodynamics). 2. Students frequently think that plants have chloroplasts instead of mitochondria. Care should be taken to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips 1. You might wish to elaborate on the amount of solar energy striking Earth. Every day Earth is bombarded with solar radiation equal to the energy of 100 million atomic bombs. Of the tiny fraction of light that reaches photosynthetic organisms, only about 1% is converted to chemical energy by photosynthesis. 2. You might share with your students that it takes about 10 million ATP molecules per second to power one active muscle cell. 3. Energy coupling at the cellular level may be new to many students, but it is a familiar concept when related to the use of money in our society. Students might be discouraged if the only benefit of work was the ability to make purchases from the employer. (We all might soon tire of a fast-food job that pays its employees only in food!) Money permits the coupling of the generation of value (a paycheck, analogous to an energy-releasing reaction) to an energy-consuming reaction (money, which enables us to make purchases in distant locations). This idea of “earn and spend” is a common concept we all know well. 6

Chloroplasts in the cells of leaves use light energy to rearrange the atoms of CO2 and H2O, which produces sugars (such as glucose), other organic molecules, and oxygen gas. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students should be cautioned against making statements that “energy is created” when it is converted from one form to another. This might be a good time to review the principle of conservation of energy (the first law of thermodynamics). 2. Students frequently think that plants have chloroplasts instead of mitochondria. Care should be taken to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips 1. You might wish to elaborate on the amount of solar energy striking Earth. Every day Earth is bombarded with solar radiation equal to the energy of 100 million atomic bombs. Of the tiny fraction of light that reaches photosynthetic organisms, only about 1% is converted to chemical energy by photosynthesis. 2. You might share with your students that it takes about 10 million ATP molecules per second to power one active muscle cell. 3. Energy coupling at the cellular level may be new to many students, but it is a familiar concept when related to the use of money in our society. Students might be discouraged if the only benefit of work was the ability to make purchases from the employer. (We all might soon tire of a fast-food job that pays its employees only in food!) Money permits the coupling of the generation of value (a paycheck, analogous to an energy-releasing reaction) to an energy-consuming reaction (money, which enables us to make purchases in distant locations). This idea of “earn and spend” is a common concept we all know well. 7

Plant and animal cells perform cellular respiration, a chemical process that primarily occurs in mitochondria, harvests energy stored in organic molecules, uses oxygen, and generates ATP. The waste products of cellular respiration are CO2 and H2O, used in photosynthesis. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students should be cautioned against making statements that “energy is created” when it is converted from one form to another. This might be a good time to review the principle of conservation of energy (the first law of thermodynamics). 2. Students frequently think that plants have chloroplasts instead of mitochondria. Care should be taken to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips 1. You might wish to elaborate on the amount of solar energy striking Earth. Every day Earth is bombarded with solar radiation equal to the energy of 100 million atomic bombs. Of the tiny fraction of light that reaches photosynthetic organisms, only about 1% is converted to chemical energy by photosynthesis. 2. You might share with your students that it takes about 10 million ATP molecules per second to power one active muscle cell. 3. Energy coupling at the cellular level may be new to many students, but it is a familiar concept when related to the use of money in our society. Students might be discouraged if the only benefit of work was the ability to make purchases from the employer. (We all might soon tire of a fast-food job that pays its employees only in food!) Money permits the coupling of the generation of value (a paycheck, analogous to an energy-releasing reaction) to an energy-consuming reaction (money, which enables us to make purchases in distant locations). This idea of “earn and spend” is a common concept we all know well. 8

Animals perform only cellular respiration. Plants perform photosynthesis and cellular respiration. Plants usually make more organic molecules than they need for fuel. This surplus provides material that can be used for the plant to grow or stored as starch in potatoes. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students should be cautioned against making statements that “energy is created” when it is converted from one form to another. This might be a good time to review the principle of conservation of energy (the first law of thermodynamics). 2. Students frequently think that plants have chloroplasts instead of mitochondria. Care should be taken to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips 1. You might wish to elaborate on the amount of solar energy striking Earth. Every day Earth is bombarded with solar radiation equal to the energy of 100 million atomic bombs. Of the tiny fraction of light that reaches photosynthetic organisms, only about 1% is converted to chemical energy by photosynthesis. 2. You might share with your students that it takes about 10 million ATP molecules per second to power one active muscle cell. 3. Energy coupling at the cellular level may be new to many students, but it is a familiar concept when related to the use of money in our society. Students might be discouraged if the only benefit of work was the ability to make purchases from the employer. (We all might soon tire of a fast-food job that pays its employees only in food!) Money permits the coupling of the generation of value (a paycheck, analogous to an energy-releasing reaction) to an energy-consuming reaction (money, which enables us to make purchases in distant locations). This idea of “earn and spend” is a common concept we all know well. 9

Photosynthesis Cellular respiration
Figure 6.2 Sunlight energy enters ecosystem Photosynthesis C6H12O6 CO2 O2 H2O Cellular respiration drives cellular work ATP Heat energy exits ecosystem Figure 6.2 Energy flow and chemical cycling in ecosystems

CELLULAR RESPIRATION: AEROBIC HARVEST OF FOOD ENERGY
Cellular respiration is the main way that chemical energy is harvested from food and converted to ATP and an aerobic process—it requires oxygen. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.6 can be especially helpful to provide physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37ºC (98–99ºF). This is about the same amount of heat generated by a 100-watt incandescent lightbulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30ºC (86ºF) outside if their core body temperature is 37ºC (98.6ºF). Shouldn’t they feel cold? The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a body temperature around 37ºC. Thus, we sweat and behave in ways that help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100ºC. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 100 Calories raises 1 L of water 100ºC. Note: It takes much more energy to melt ice or evaporate water as steam.) 2. The location within a cell of each of the following reactions is often lost in the details of the processes; yet the locations are important. The “Evolution Connection” section at the end of this chapter discusses the significance of glycolysis occurring in the cytosol. To emphasize the location of each stage, consider pointing to Figure 6.6, with mitochondrial detail, as you discuss cellular respiration. 3. As you relate the structure of the inner mitochondrial membrane to its functions, challenge the students to suggest an adaptive advantage of the many folds of this inner membrane. These folds greatly increase the membrane region available for the associated reactions. 4. The production of NADH by glycolysis and the citric acid cycle, instead of just the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have energy “value,” to be “cashed in” by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the “electron transport” cashier. 5. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding back water. As the hydrogen ions move down their concentration gradient, they “spin” the ATP synthase, which helps generate ATP. In a dam, water rushing downhill turns giant turbines, which generate electricity. 6. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under ideal conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. 11

CELLULAR RESPIRATION: AEROBIC HARVEST OF FOOD ENERGY
Cellular respiration and breathing are closely related. Cellular respiration requires a cell to exchange gases with its surroundings. Cells take in oxygen gas. Cells release waste carbon dioxide gas. Breathing exchanges these same gases between the blood and outside air. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.6 can be especially helpful to provide physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37ºC (98–99ºF). This is about the same amount of heat generated by a 100-watt incandescent lightbulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30ºC (86ºF) outside if their core body temperature is 37ºC (98.6ºF). Shouldn’t they feel cold? The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a body temperature around 37ºC. Thus, we sweat and behave in ways that help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100ºC. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 100 Calories raises 1 L of water 100ºC. Note: It takes much more energy to melt ice or evaporate water as steam.) 2. The location within a cell of each of the following reactions is often lost in the details of the processes; yet the locations are important. The “Evolution Connection” section at the end of this chapter discusses the significance of glycolysis occurring in the cytosol. To emphasize the location of each stage, consider pointing to Figure 6.6, with mitochondrial detail, as you discuss cellular respiration. 3. As you relate the structure of the inner mitochondrial membrane to its functions, challenge the students to suggest an adaptive advantage of the many folds of this inner membrane. These folds greatly increase the membrane region available for the associated reactions. 4. The production of NADH by glycolysis and the citric acid cycle, instead of just the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have energy “value,” to be “cashed in” by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the “electron transport” cashier. 5. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding back water. As the hydrogen ions move down their concentration gradient, they “spin” the ATP synthase, which helps generate ATP. In a dam, water rushing downhill turns giant turbines, which generate electricity. 6. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under ideal conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. 12

O2 CO2 O2 CO2 Cellular respiration
Figure 6.3 O2 CO2 Breathing Lungs O2 CO2 Muscle cells Cellular respiration Figure 6.3 How breathing is related to cellular respiration

The Simplified Equation for Cellular Respiration
A common fuel molecule for cellular respiration is glucose. Cellular respiration can produce up to 32 ATP molecules for each glucose molecule consumed. The overall equation for what happens to glucose during cellular respiration is glucose & oxygen  CO2, H2O, & a release of energy. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.6 can be especially helpful to provide physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37ºC (98–99ºF). This is about the same amount of heat generated by a 100-watt incandescent lightbulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30ºC (86ºF) outside if their core body temperature is 37ºC (98.6ºF). Shouldn’t they feel cold? The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a body temperature around 37ºC. Thus, we sweat and behave in ways that help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100ºC. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 100 Calories raises 1 L of water 100ºC. Note: It takes much more energy to melt ice or evaporate water as steam.) 2. The location within a cell of each of the following reactions is often lost in the details of the processes; yet the locations are important. The “Evolution Connection” section at the end of this chapter discusses the significance of glycolysis occurring in the cytosol. To emphasize the location of each stage, consider pointing to Figure 6.6, with mitochondrial detail, as you discuss cellular respiration. 3. As you relate the structure of the inner mitochondrial membrane to its functions, challenge the students to suggest an adaptive advantage of the many folds of this inner membrane. These folds greatly increase the membrane region available for the associated reactions. 4. The production of NADH by glycolysis and the citric acid cycle, instead of just the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have energy “value,” to be “cashed in” by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the “electron transport” cashier. 5. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding back water. As the hydrogen ions move down their concentration gradient, they “spin” the ATP synthase, which helps generate ATP. In a dam, water rushing downhill turns giant turbines, which generate electricity. 6. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under ideal conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. 14

Figure 6.UN01 During cellular respiration, hydrogen and its bonding electrons change partners from sugar to oxygen, forming water as a product. C6H12O6 6 O2 6 CO2 6 H2O ATP Glucose Oxygen Carbon dioxide Water Energy Chemical reactions that transfer electrons from one substance to another are called oxidation-reduction reactions or redox reactions for short. Figure 6.UN01 In-text figure, cellular respiration equation, p. 94

The loss of electrons during a redox reaction is oxidation.
Redox Reactions The loss of electrons during a redox reaction is oxidation. The acceptance of electrons during a redox reaction is reduction. During cellular respiration glucose is oxidized and oxygen is reduced. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.6 can be especially helpful to provide physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37ºC (98–99ºF). This is about the same amount of heat generated by a 100-watt incandescent lightbulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30ºC (86ºF) outside if their core body temperature is 37ºC (98.6ºF). Shouldn’t they feel cold? The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a body temperature around 37ºC. Thus, we sweat and behave in ways that help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100ºC. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 100 Calories raises 1 L of water 100ºC. Note: It takes much more energy to melt ice or evaporate water as steam.) 2. The location within a cell of each of the following reactions is often lost in the details of the processes; yet the locations are important. The “Evolution Connection” section at the end of this chapter discusses the significance of glycolysis occurring in the cytosol. To emphasize the location of each stage, consider pointing to Figure 6.6, with mitochondrial detail, as you discuss cellular respiration. 3. As you relate the structure of the inner mitochondrial membrane to its functions, challenge the students to suggest an adaptive advantage of the many folds of this inner membrane. These folds greatly increase the membrane region available for the associated reactions. 4. The production of NADH by glycolysis and the citric acid cycle, instead of just the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have energy “value,” to be “cashed in” by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the “electron transport” cashier. 5. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding back water. As the hydrogen ions move down their concentration gradient, they “spin” the ATP synthase, which helps generate ATP. In a dam, water rushing downhill turns giant turbines, which generate electricity. 6. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under ideal conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. 16

Glucose loses electrons Oxygen gains electrons (and hydrogens)
Figure 6.UN02 Oxidation Glucose loses electrons (and hydrogens) C6H12O6 6 O2 6 CO2 6 H2O Glucose Oxygen Carbon dioxide Water Reduction Oxygen gains electrons (and hydrogens) Figure 6.UN02 In-text figure, redox reaction, p. 95

Why does electron transfer to oxygen release energy?
Redox Reactions Why does electron transfer to oxygen release energy? When electrons move from glucose to oxygen, it is as though the electrons were falling. This “fall” of electrons releases energy during cellular respiration. Cellular respiration is a controlled fall of electrons and a stepwise cascade much like going down a staircase. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.6 can be especially helpful to provide physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37ºC (98–99ºF). This is about the same amount of heat generated by a 100-watt incandescent lightbulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30ºC (86ºF) outside if their core body temperature is 37ºC (98.6ºF). Shouldn’t they feel cold? The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a body temperature around 37ºC. Thus, we sweat and behave in ways that help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100ºC. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 100 Calories raises 1 L of water 100ºC. Note: It takes much more energy to melt ice or evaporate water as steam.) 2. The location within a cell of each of the following reactions is often lost in the details of the processes; yet the locations are important. The “Evolution Connection” section at the end of this chapter discusses the significance of glycolysis occurring in the cytosol. To emphasize the location of each stage, consider pointing to Figure 6.6, with mitochondrial detail, as you discuss cellular respiration. 3. As you relate the structure of the inner mitochondrial membrane to its functions, challenge the students to suggest an adaptive advantage of the many folds of this inner membrane. These folds greatly increase the membrane region available for the associated reactions. 4. The production of NADH by glycolysis and the citric acid cycle, instead of just the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have energy “value,” to be “cashed in” by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the “electron transport” cashier. 5. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding back water. As the hydrogen ions move down their concentration gradient, they “spin” the ATP synthase, which helps generate ATP. In a dam, water rushing downhill turns giant turbines, which generate electricity. 6. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under ideal conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. 18

H2 O2 H2O Release of heat energy 1 2 Figure 6.4
Figure 6.4 A simple redox reaction

NADH and Electron Transport Chains
The path that electrons take on their way down from glucose to oxygen involves many steps. The first step is an electron acceptor called NAD+. NAD is made by cells from niacin, a B vitamin. The transfer of electrons from organic fuel to NAD+ reduces it to NADH. The rest of the path consists of an electron transport chain, which involves a series of redox reactions and ultimately leads to the production of large amounts of ATP. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.6 can be especially helpful to provide physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37ºC (98–99ºF). This is about the same amount of heat generated by a 100-watt incandescent lightbulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30ºC (86ºF) outside if their core body temperature is 37ºC (98.6ºF). Shouldn’t they feel cold? The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a body temperature around 37ºC. Thus, we sweat and behave in ways that help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100ºC. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 100 Calories raises 1 L of water 100ºC. Note: It takes much more energy to melt ice or evaporate water as steam.) 2. The location within a cell of each of the following reactions is often lost in the details of the processes; yet the locations are important. The “Evolution Connection” section at the end of this chapter discusses the significance of glycolysis occurring in the cytosol. To emphasize the location of each stage, consider pointing to Figure 6.6, with mitochondrial detail, as you discuss cellular respiration. 3. As you relate the structure of the inner mitochondrial membrane to its functions, challenge the students to suggest an adaptive advantage of the many folds of this inner membrane. These folds greatly increase the membrane region available for the associated reactions. 4. The production of NADH by glycolysis and the citric acid cycle, instead of just the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have energy “value,” to be “cashed in” by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the “electron transport” cashier. 5. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding back water. As the hydrogen ions move down their concentration gradient, they “spin” the ATP synthase, which helps generate ATP. In a dam, water rushing downhill turns giant turbines, which generate electricity. 6. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under ideal conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. 20

Electron transport chain
Figure 6.5 e e Electrons from food e e Stepwise release of energy used to make NAD NADH ATP 2 H 2 e Electron transport chain 2 e 2 H 2 1 O2 Hydrogen, electrons, and oxygen combine to produce water H2O Figure 6.5 The role of oxygen in harvesting food energy

H Electron transport chain 2 e H 2
Figure 6.5a Stepwise release of energy used to make ATP ATP 2 H 2 e Electron transport chain 2 e H 2 1 2 O2 Hydrogen, electrons, and oxygen combine to produce water H2O Figure 6.5 The role of oxygen in harvesting food energy (detail)

An Overview of Cellular Respiration
Cellular respiration is an example of a metabolic pathway, which is a series of chemical reactions in cells. All of the reactions involved in cellular respiration can be grouped into three main stages: 1. glycolysis, 2. the citric acid cycle, and 3. electron transport. BioFlix Animation: Cellular Respiration © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.6 can be especially helpful to provide physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37ºC (98–99ºF). This is about the same amount of heat generated by a 100-watt incandescent lightbulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30ºC (86ºF) outside if their core body temperature is 37ºC (98.6ºF). Shouldn’t they feel cold? The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a body temperature around 37ºC. Thus, we sweat and behave in ways that help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100ºC. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 100 Calories raises 1 L of water 100ºC. Note: It takes much more energy to melt ice or evaporate water as steam.) 2. The location within a cell of each of the following reactions is often lost in the details of the processes; yet the locations are important. The “Evolution Connection” section at the end of this chapter discusses the significance of glycolysis occurring in the cytosol. To emphasize the location of each stage, consider pointing to Figure 6.6, with mitochondrial detail, as you discuss cellular respiration. 3. As you relate the structure of the inner mitochondrial membrane to its functions, challenge the students to suggest an adaptive advantage of the many folds of this inner membrane. These folds greatly increase the membrane region available for the associated reactions. 4. The production of NADH by glycolysis and the citric acid cycle, instead of just the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have energy “value,” to be “cashed in” by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the “electron transport” cashier. 5. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding back water. As the hydrogen ions move down their concentration gradient, they “spin” the ATP synthase, which helps generate ATP. In a dam, water rushing downhill turns giant turbines, which generate electricity. 6. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under ideal conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. 23

Mitochondrion Cytoplasm Cytoplasm Animal cell Plant cell Cytoplasm
Figure 6.6 Mitochondrion Cytoplasm Cytoplasm Animal cell Plant cell Cytoplasm Mitochondrion High-energy electrons via carrier molecules Glycolysis Citric Acid Cycle 2 Pyruvic acid Electron Transport Glucose ATP ATP ATP Figure 6.6 A road map for cellular respiration

Cytoplasm Mitochondrion High-energy electrons via carrier molecules
Figure 6.6a Cytoplasm Mitochondrion High-energy electrons via carrier molecules Glycolysis Citric Acid Cycle 2 Pyruvic acid Electron Transport Glucose ATP ATP ATP Figure 6.6 A road map for cellular respiration (detail)

Stage 1: Glycolysis A six-carbon glucose molecule is split in half to form two molecules of pyruvic acid. These two molecules then donate high energy electrons to NAD+, forming NADH. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.6 can be especially helpful to provide physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37ºC (98–99ºF). This is about the same amount of heat generated by a 100-watt incandescent lightbulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30ºC (86ºF) outside if their core body temperature is 37ºC (98.6ºF). Shouldn’t they feel cold? The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a body temperature around 37ºC. Thus, we sweat and behave in ways that help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100ºC. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 100 Calories raises 1 L of water 100ºC. Note: It takes much more energy to melt ice or evaporate water as steam.) 2. The location within a cell of each of the following reactions is often lost in the details of the processes; yet the locations are important. The “Evolution Connection” section at the end of this chapter discusses the significance of glycolysis occurring in the cytosol. To emphasize the location of each stage, consider pointing to Figure 6.6, with mitochondrial detail, as you discuss cellular respiration. 3. As you relate the structure of the inner mitochondrial membrane to its functions, challenge the students to suggest an adaptive advantage of the many folds of this inner membrane. These folds greatly increase the membrane region available for the associated reactions. 4. The production of NADH by glycolysis and the citric acid cycle, instead of just the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have energy “value,” to be “cashed in” by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the “electron transport” cashier. 5. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding back water. As the hydrogen ions move down their concentration gradient, they “spin” the ATP synthase, which helps generate ATP. In a dam, water rushing downhill turns giant turbines, which generate electricity. 6. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under ideal conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. 26

Figure 6.7 INPUT OUTPUT – – NADH P P 2 ATP NAD 2 ADP 2 3 2 ATP P 2 ADP P 2 Pyruvic acid 1 P P P 2 3 Glucose 2 ADP NAD 2 ATP P – – NADH Energy investment phase Energy harvest phase Key Carbon atom P Phosphate group – High-energy electron Figure 6.7 Glycolysis

INPUT OUTPUT 2 Pyruvic acid Glucose Figure 6.7a
Figure 6.7 Glycolysis (part 1)

Energy investment phase
Figure 6.7b-1 P 2 ATP 2 ADP 1 P Energy investment phase Figure 6.7 Glycolysis (part 2, step 1)

Energy investment phase Energy harvest phase
Figure 6.7b-2 – – NADH P P NAD 2 P 2 ATP 2 ADP P 1 P P P 2 NAD P – – NADH Energy investment phase Energy harvest phase Figure 6.7 Glycolysis (part 2, step 2)

Energy investment phase Energy harvest phase
Figure 6.7b-3 – – NADH P P 2 ATP NAD 2 ADP 2 3 P 2 ATP 2 ADP P 1 P P P 2 3 2 ADP NAD 2 ATP P – – NADH Energy investment phase Energy harvest phase Figure 6.7 Glycolysis (part 2, step 3)

Stage 1: Glycolysis Glycolysis
uses two ATP molecules per glucose to split the six-carbon glucose and makes four additional ATP directly when enzymes transfer phosphate groups from fuel molecules to ADP. Thus, glycolysis produces a net of two molecules of ATP per glucose molecule. Glycolysis © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.6 can be especially helpful to provide physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37ºC (98–99ºF). This is about the same amount of heat generated by a 100-watt incandescent lightbulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30ºC (86ºF) outside if their core body temperature is 37ºC (98.6ºF). Shouldn’t they feel cold? The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a body temperature around 37ºC. Thus, we sweat and behave in ways that help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100ºC. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 100 Calories raises 1 L of water 100ºC. Note: It takes much more energy to melt ice or evaporate water as steam.) 2. The location within a cell of each of the following reactions is often lost in the details of the processes; yet the locations are important. The “Evolution Connection” section at the end of this chapter discusses the significance of glycolysis occurring in the cytosol. To emphasize the location of each stage, consider pointing to Figure 6.6, with mitochondrial detail, as you discuss cellular respiration. 3. As you relate the structure of the inner mitochondrial membrane to its functions, challenge the students to suggest an adaptive advantage of the many folds of this inner membrane. These folds greatly increase the membrane region available for the associated reactions. 4. The production of NADH by glycolysis and the citric acid cycle, instead of just the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have energy “value,” to be “cashed in” by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the “electron transport” cashier. 5. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding back water. As the hydrogen ions move down their concentration gradient, they “spin” the ATP synthase, which helps generate ATP. In a dam, water rushing downhill turns giant turbines, which generate electricity. 6. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under ideal conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. 32

Enzyme P ADP ATP P P Figure 6.8
Figure 6.8 ATP synthesis by direct phosphate transfer

Stage 2: The Citric Acid Cycle
In the citric acid cycle, pyruvic acid from glycolysis is first “groomed.” Each pyruvic acid loses a carbon as CO2. The remaining fuel molecule, with only two carbons left, is acetic acid. Oxidation of the fuel generates NADH. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.6 can be especially helpful to provide physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37ºC (98–99ºF). This is about the same amount of heat generated by a 100-watt incandescent lightbulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30ºC (86ºF) outside if their core body temperature is 37ºC (98.6ºF). Shouldn’t they feel cold? The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a body temperature around 37ºC. Thus, we sweat and behave in ways that help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100ºC. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 100 Calories raises 1 L of water 100ºC. Note: It takes much more energy to melt ice or evaporate water as steam.) 2. The location within a cell of each of the following reactions is often lost in the details of the processes; yet the locations are important. The “Evolution Connection” section at the end of this chapter discusses the significance of glycolysis occurring in the cytosol. To emphasize the location of each stage, consider pointing to Figure 6.6, with mitochondrial detail, as you discuss cellular respiration. 3. As you relate the structure of the inner mitochondrial membrane to its functions, challenge the students to suggest an adaptive advantage of the many folds of this inner membrane. These folds greatly increase the membrane region available for the associated reactions. 4. The production of NADH by glycolysis and the citric acid cycle, instead of just the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have energy “value,” to be “cashed in” by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the “electron transport” cashier. 5. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding back water. As the hydrogen ions move down their concentration gradient, they “spin” the ATP synthase, which helps generate ATP. In a dam, water rushing downhill turns giant turbines, which generate electricity. 6. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under ideal conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. 34

Stage 2: The Citric Acid Cycle
Finally, each acetic acid is attached to a molecule called coenzyme A to form acetyl CoA. The CoA escorts the acetic acid into the first reaction of the citric acid cycle. The CoA is then stripped and recycled. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.6 can be especially helpful to provide physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37ºC (98–99ºF). This is about the same amount of heat generated by a 100-watt incandescent lightbulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30ºC (86ºF) outside if their core body temperature is 37ºC (98.6ºF). Shouldn’t they feel cold? The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a body temperature around 37ºC. Thus, we sweat and behave in ways that help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100ºC. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 100 Calories raises 1 L of water 100ºC. Note: It takes much more energy to melt ice or evaporate water as steam.) 2. The location within a cell of each of the following reactions is often lost in the details of the processes; yet the locations are important. The “Evolution Connection” section at the end of this chapter discusses the significance of glycolysis occurring in the cytosol. To emphasize the location of each stage, consider pointing to Figure 6.6, with mitochondrial detail, as you discuss cellular respiration. 3. As you relate the structure of the inner mitochondrial membrane to its functions, challenge the students to suggest an adaptive advantage of the many folds of this inner membrane. These folds greatly increase the membrane region available for the associated reactions. 4. The production of NADH by glycolysis and the citric acid cycle, instead of just the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have energy “value,” to be “cashed in” by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the “electron transport” cashier. 5. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding back water. As the hydrogen ions move down their concentration gradient, they “spin” the ATP synthase, which helps generate ATP. In a dam, water rushing downhill turns giant turbines, which generate electricity. 6. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under ideal conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. 35

INPUT OUTPUT 2 Oxidation of the fuel generates NADH (from glycolysis)
Figure 6.9 INPUT OUTPUT 2 Oxidation of the fuel generates NADH (from glycolysis) (to citric acid cycle) – – NAD NADH CoA 1 Pyruvic acid loses a carbon as CO2 3 Acetic acid Acetic acid attaches to coenzyme A Acetyl CoA Pyruvic acid CO2 Coenzyme A Figure 6.9 The link between glycolysis and the citric acid cycle: the conversion of pyruvic acid to acetyl CoA

(from glycolysis) (to citric acid cycle)
Figure 6.9a INPUT OUTPUT (from glycolysis) (to citric acid cycle) CoA Acetyl CoA Pyruvic acid Figure 6.9 The link between glycolysis and the citric acid cycle: the conversion of pyruvic acid to acetyl CoA (part 1)

2 Oxidation of the fuel generates NADH – – NAD NADH 1 3 Pyruvic acid
Figure 6.9b 2 Oxidation of the fuel generates NADH – – OUTPUT NAD NADH 1 3 Pyruvic acid loses a carbon as CO2 Acetic acid Acetic acid attaches to coenzyme A CO2 Coenzyme A Figure 6.9 The link between glycolysis and the citric acid cycle: the conversion of pyruvic acid to acetyl CoA (part 2)

Blast Animation: Harvesting Energy: Krebs Cycle
Stage 2: The Citric Acid Cycle The citric acid cycle extracts the energy of sugar by breaking the acetic acid molecules all the way down to CO2, uses some of this energy to make ATP, and forms NADH and FADH2. Blast Animation: Harvesting Energy: Krebs Cycle © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.6 can be especially helpful to provide physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37ºC (98–99ºF). This is about the same amount of heat generated by a 100-watt incandescent lightbulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30ºC (86ºF) outside if their core body temperature is 37ºC (98.6ºF). Shouldn’t they feel cold? The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a body temperature around 37ºC. Thus, we sweat and behave in ways that help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100ºC. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 100 Calories raises 1 L of water 100ºC. Note: It takes much more energy to melt ice or evaporate water as steam.) 2. The location within a cell of each of the following reactions is often lost in the details of the processes; yet the locations are important. The “Evolution Connection” section at the end of this chapter discusses the significance of glycolysis occurring in the cytosol. To emphasize the location of each stage, consider pointing to Figure 6.6, with mitochondrial detail, as you discuss cellular respiration. 3. As you relate the structure of the inner mitochondrial membrane to its functions, challenge the students to suggest an adaptive advantage of the many folds of this inner membrane. These folds greatly increase the membrane region available for the associated reactions. 4. The production of NADH by glycolysis and the citric acid cycle, instead of just the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have energy “value,” to be “cashed in” by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the “electron transport” cashier. 5. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding back water. As the hydrogen ions move down their concentration gradient, they “spin” the ATP synthase, which helps generate ATP. In a dam, water rushing downhill turns giant turbines, which generate electricity. 6. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under ideal conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. 39

INPUT OUTPUT 2 CO2 ATP – – – – FAD FADH2
Figure 6.10 INPUT OUTPUT Citric acid 1 Acetic acid 2 2 CO2 3 ADP  P ATP Citric Acid Cycle – – 3 NAD 4 3 NADH – – FAD 5 FADH2 6 Acceptor molecule Figure 6.10 The citric acid cycle

INPUT OUTPUT 1 Acetic acid 2 2 CO2 3 ADP  P ATP – – 3 NAD 4 3 NADH –
Figure 6.10a INPUT OUTPUT 1 Acetic acid 2 2 CO2 3 ADP  P ATP – – 3 NAD 4 3 NADH – – FAD 5 FADH2 Figure 6.10 The citric acid cycle (part 1)

Citric acid Citric Acid Cycle Acceptor molecule INPUT OUTPUT
Figure 6.10b Citric acid INPUT OUTPUT Citric Acid Cycle Acceptor molecule Figure 6.10 The citric acid cycle (part 2)

Stage 3: Electron Transport
Electron transport releases the energy your cells need to make the most of their ATP. The molecules of the electron transport chain are built into the inner membranes of mitochondria. The chain functions as a chemical machine, which uses energy released by the “fall” of electrons to pump hydrogen ions across the inner mitochondrial membrane, and uses these ions to store potential energy. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.6 can be especially helpful to provide physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37ºC (98–99ºF). This is about the same amount of heat generated by a 100-watt incandescent lightbulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30ºC (86ºF) outside if their core body temperature is 37ºC (98.6ºF). Shouldn’t they feel cold? The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a body temperature around 37ºC. Thus, we sweat and behave in ways that help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100ºC. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 100 Calories raises 1 L of water 100ºC. Note: It takes much more energy to melt ice or evaporate water as steam.) 2. The location within a cell of each of the following reactions is often lost in the details of the processes; yet the locations are important. The “Evolution Connection” section at the end of this chapter discusses the significance of glycolysis occurring in the cytosol. To emphasize the location of each stage, consider pointing to Figure 6.6, with mitochondrial detail, as you discuss cellular respiration. 3. As you relate the structure of the inner mitochondrial membrane to its functions, challenge the students to suggest an adaptive advantage of the many folds of this inner membrane. These folds greatly increase the membrane region available for the associated reactions. 4. The production of NADH by glycolysis and the citric acid cycle, instead of just the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have energy “value,” to be “cashed in” by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the “electron transport” cashier. 5. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding back water. As the hydrogen ions move down their concentration gradient, they “spin” the ATP synthase, which helps generate ATP. In a dam, water rushing downhill turns giant turbines, which generate electricity. 6. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under ideal conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. 43

When the hydrogen ions flow back through the membrane, they release energy. The hydrogen ions flow through ATP synthase. ATP synthase takes the energy from this flow and synthesizes ATP. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.6 can be especially helpful to provide physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37ºC (98–99ºF). This is about the same amount of heat generated by a 100-watt incandescent lightbulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30ºC (86ºF) outside if their core body temperature is 37ºC (98.6ºF). Shouldn’t they feel cold? The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a body temperature around 37ºC. Thus, we sweat and behave in ways that help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100ºC. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 100 Calories raises 1 L of water 100ºC. Note: It takes much more energy to melt ice or evaporate water as steam.) 2. The location within a cell of each of the following reactions is often lost in the details of the processes; yet the locations are important. The “Evolution Connection” section at the end of this chapter discusses the significance of glycolysis occurring in the cytosol. To emphasize the location of each stage, consider pointing to Figure 6.6, with mitochondrial detail, as you discuss cellular respiration. 3. As you relate the structure of the inner mitochondrial membrane to its functions, challenge the students to suggest an adaptive advantage of the many folds of this inner membrane. These folds greatly increase the membrane region available for the associated reactions. 4. The production of NADH by glycolysis and the citric acid cycle, instead of just the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have energy “value,” to be “cashed in” by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the “electron transport” cashier. 5. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding back water. As the hydrogen ions move down their concentration gradient, they “spin” the ATP synthase, which helps generate ATP. In a dam, water rushing downhill turns giant turbines, which generate electricity. 6. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under ideal conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. 44

Electron transport chain ATP synthase
Figure 6.11 Space between membranes H H H H H H H H Electron carrier H H H 3 H 5 H Protein complex Inner mitochondrial membrane – – FADH2 FAD H Electron flow 2 1 2 O2 2 H H2O 6 – – 4 NADH NAD ADP P ATP 1 H H H H H Matrix Electron transport chain ATP synthase Figure 6.11 How electron transport drives ATP synthase machines

Figure 6.11a Space between membranes H H H H H H H H Electron carrier H H H 3 H 5 H Protein complex Inner mitochondrial membrane – – FADH2 FAD H Electron flow 2 1 2 O2 2 H H2O 6 – – 4 NADH NAD ADP P ATP 1 H H H H H Matrix Electron transport chain ATP synthase Figure 6.11 How electron transport drives ATP synthase machines (part 1)

Figure 6.11b Space between membranes H H H H H H H Electron carrier H H H 3 H Protein complex Inner mitochondrial membrane – – FADH2 FAD H Electron flow 2 1 2 O2 2 H – – 4 NADH NAD 1 H H H H Matrix Electron transport chain Figure 6.11 How electron transport drives ATP synthase machines (part 2)

ATP synthase H H  H H H 5 H O2 6 H H2O 4 ADP P ATP H H 2
Figure 6.11c H H  H H H 5 H 1 2 O2 6 2 H H2O 4 ADP P ATP H H ATP synthase Figure 6.11 How electron transport drives ATP synthase machines (part 3)

Cyanide is a deadly poison that binds to one of the protein complexes in the electron transport chain, prevents the passage of electrons to oxygen, and stops the production of ATP. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.6 can be especially helpful to provide physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37ºC (98–99ºF). This is about the same amount of heat generated by a 100-watt incandescent lightbulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30ºC (86ºF) outside if their core body temperature is 37ºC (98.6ºF). Shouldn’t they feel cold? The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a body temperature around 37ºC. Thus, we sweat and behave in ways that help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100ºC. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 100 Calories raises 1 L of water 100ºC. Note: It takes much more energy to melt ice or evaporate water as steam.) 2. The location within a cell of each of the following reactions is often lost in the details of the processes; yet the locations are important. The “Evolution Connection” section at the end of this chapter discusses the significance of glycolysis occurring in the cytosol. To emphasize the location of each stage, consider pointing to Figure 6.6, with mitochondrial detail, as you discuss cellular respiration. 3. As you relate the structure of the inner mitochondrial membrane to its functions, challenge the students to suggest an adaptive advantage of the many folds of this inner membrane. These folds greatly increase the membrane region available for the associated reactions. 4. The production of NADH by glycolysis and the citric acid cycle, instead of just the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have energy “value,” to be “cashed in” by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the “electron transport” cashier. 5. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding back water. As the hydrogen ions move down their concentration gradient, they “spin” the ATP synthase, which helps generate ATP. In a dam, water rushing downhill turns giant turbines, which generate electricity. 6. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under ideal conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. 49

Cytoplasm Mitochondrion – – – – – – 6 NADH 2 NADH 2 NADH – – 2 FADH2
Figure 6.12 Cytoplasm Mitochondrion – – – – – – 6 NADH 2 NADH 2 NADH – – 2 FADH2 Glycolysis 2 Pyruvic acid 2 Acetyl CoA Citric Acid Cycle Electron Transport Glucose Maximum per glucose: 2 ATP 2 ATP About 28 ATP About 32 ATP by direct synthesis by direct synthesis by ATP synthase Figure 6.12 A summary of ATP yield during cellular respiration

2 Acetyl CoA 2 Pyruvic acid 2 ATP 2 ATP About 28 ATP
Figure 6.12a Glycolysis 2 Acetyl CoA 2 Pyruvic acid Citric Acid Cycle Electron Transport Glucose 2 ATP 2 ATP About 28 ATP by direct synthesis by direct synthesis by ATP synthase Figure 6.12 A summary of ATP yield during cellular respiration (detail)

The Results of Cellular Respiration
In addition to glucose, cellular respiration can “burn” diverse types of carbohydrates, fats, and proteins. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.6 can be especially helpful to provide physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37ºC (98–99ºF). This is about the same amount of heat generated by a 100-watt incandescent lightbulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30ºC (86ºF) outside if their core body temperature is 37ºC (98.6ºF). Shouldn’t they feel cold? The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a body temperature around 37ºC. Thus, we sweat and behave in ways that help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100ºC. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 100 Calories raises 1 L of water 100ºC. Note: It takes much more energy to melt ice or evaporate water as steam.) 2. The location within a cell of each of the following reactions is often lost in the details of the processes; yet the locations are important. The “Evolution Connection” section at the end of this chapter discusses the significance of glycolysis occurring in the cytosol. To emphasize the location of each stage, consider pointing to Figure 6.6, with mitochondrial detail, as you discuss cellular respiration. 3. As you relate the structure of the inner mitochondrial membrane to its functions, challenge the students to suggest an adaptive advantage of the many folds of this inner membrane. These folds greatly increase the membrane region available for the associated reactions. 4. The production of NADH by glycolysis and the citric acid cycle, instead of just the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have energy “value,” to be “cashed in” by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the “electron transport” cashier. 5. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding back water. As the hydrogen ions move down their concentration gradient, they “spin” the ATP synthase, which helps generate ATP. In a dam, water rushing downhill turns giant turbines, which generate electricity. 6. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under ideal conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. 52

Food Polysaccharides Fats Proteins Sugars Glycerol Fatty acids
Figure 6.13 Food Polysaccharides Fats Proteins Sugars Glycerol Fatty acids Amino acids Citric Acid Cycle Acetyl CoA Glycolysis Electron Transport ATP Figure 6.13 Energy from food

FERMENTATION: ANAEROBIC HARVEST OF FOOD ENERGY
Some of your cells can actually work for short periods without oxygen. Fermentation is the anaerobic (without oxygen) harvest of food energy. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and perhaps carbon dioxide. Care should be taken to clarify the different possible products of fermentation in muscle cells and alcoholic fermentation used in the food and beverage industry. 2. The text notes that some microbes are useful in the dairy industry because they produce lactic acid. However, the impact of acids on milk may not be obvious to many students. Consider a simple demonstration mixing about equal portions of milk (skim or 2%) with some acid (vinegar will work). Notice the accumulation of strands of milk curd (protein) on the side of the container and stirring device. Teaching Tips 1. The carbon dioxide released from fermentation also makes beer and champagne bubbly. 2. Dry wines are produced when the yeast cells use up all or most of the sugar available. Sweet wines result when the alcohol accumulates enough to inhibit fermentation before the sugar is depleted. 3. Exposing fermenting yeast to oxygen will slow or stop the process, because the yeast will switch back to aerobic respiration. When fermentation is rapid, the carbon dioxide produced drives away the immediate oxygen above the wine. However, as fermentation slows down, the wine must be sealed to prevent oxygen exposure and permit the fermentation process to finish. 54

Fermentation in Human Muscle Cells
After functioning anaerobically for about 15 seconds, muscle cells begin to generate ATP by the process of fermentation. Fermentation relies on glycolysis to produce ATP. Glycolysis does not require oxygen and produces two ATP molecules for each glucose broken down to pyruvic acid. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and perhaps carbon dioxide. Care should be taken to clarify the different possible products of fermentation in muscle cells and alcoholic fermentation used in the food and beverage industry. 2. The text notes that some microbes are useful in the dairy industry because they produce lactic acid. However, the impact of acids on milk may not be obvious to many students. Consider a simple demonstration mixing about equal portions of milk (skim or 2%) with some acid (vinegar will work). Notice the accumulation of strands of milk curd (protein) on the side of the container and stirring device. Teaching Tips 1. The carbon dioxide released from fermentation also makes beer and champagne bubbly. 2. Dry wines are produced when the yeast cells use up all or most of the sugar available. Sweet wines result when the alcohol accumulates enough to inhibit fermentation before the sugar is depleted. 3. Exposing fermenting yeast to oxygen will slow or stop the process, because the yeast will switch back to aerobic respiration. When fermentation is rapid, the carbon dioxide produced drives away the immediate oxygen above the wine. However, as fermentation slows down, the wine must be sealed to prevent oxygen exposure and permit the fermentation process to finish. 55

Animation: Fermentation Overview
Fermentation in Human Muscle Cells Pyruvic acid, produced by glycolysis, is reduced by NADH, producing NAD+, which keeps glycolysis going. In human muscle cells, lactic acid is a by-product. Animation: Fermentation Overview © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and perhaps carbon dioxide. Care should be taken to clarify the different possible products of fermentation in muscle cells and alcoholic fermentation used in the food and beverage industry. 2. The text notes that some microbes are useful in the dairy industry because they produce lactic acid. However, the impact of acids on milk may not be obvious to many students. Consider a simple demonstration mixing about equal portions of milk (skim or 2%) with some acid (vinegar will work). Notice the accumulation of strands of milk curd (protein) on the side of the container and stirring device. Teaching Tips 1. The carbon dioxide released from fermentation also makes beer and champagne bubbly. 2. Dry wines are produced when the yeast cells use up all or most of the sugar available. Sweet wines result when the alcohol accumulates enough to inhibit fermentation before the sugar is depleted. 3. Exposing fermenting yeast to oxygen will slow or stop the process, because the yeast will switch back to aerobic respiration. When fermentation is rapid, the carbon dioxide produced drives away the immediate oxygen above the wine. However, as fermentation slows down, the wine must be sealed to prevent oxygen exposure and permit the fermentation process to finish. 56

Figure 6.14 Fermentation: producing lactic acid
INPUT OUTPUT 2 ADP 2 ATP 2 P Glycolysis – – – – 2 NAD 2 NADH 2 NADH 2 NAD 2 Pyruvic acid 2 H Glucose 2 Lactic acid Figure 6.14 Fermentation: producing lactic acid

INPUT OUTPUT 2 Lactic acid Glucose 2 ADP 2 ATP 2 P Glycolysis – – – –
Figure 6.14a INPUT OUTPUT 2 ADP 2 ATP 2 P Glycolysis – – – – 2 NAD 2 NADH 2 NADH 2 NAD 2 Pyruvic acid 2 H 2 Lactic acid Glucose Figure 6.14 Fermentation: producing lactic acid (part 1)

diffusion of lactic acid diffusion of lactic acid;
Figure 6.15 Battery Battery  –  – Force measured Force measured Frog muscle stimulated by electric current Solution prevents diffusion of lactic acid Solution allows diffusion of lactic acid; muscle can work for twice as long Figure 6.15 A. V. Hill’s 1929 apparatus for measuring muscle fatigue

The Process of Science: What Causes Muscle Burn?
Results: When lactic acid could diffuse away, performance improved greatly. Conclusion: Lactic acid accumulation is the primary cause of failure in muscle tissue. However, recent evidence suggests that the role of lactic acid in muscle function remains unclear. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and perhaps carbon dioxide. Care should be taken to clarify the different possible products of fermentation in muscle cells and alcoholic fermentation used in the food and beverage industry. 2. The text notes that some microbes are useful in the dairy industry because they produce lactic acid. However, the impact of acids on milk may not be obvious to many students. Consider a simple demonstration mixing about equal portions of milk (skim or 2%) with some acid (vinegar will work). Notice the accumulation of strands of milk curd (protein) on the side of the container and stirring device. Teaching Tips 1. The carbon dioxide released from fermentation also makes beer and champagne bubbly. 2. Dry wines are produced when the yeast cells use up all or most of the sugar available. Sweet wines result when the alcohol accumulates enough to inhibit fermentation before the sugar is depleted. 3. Exposing fermenting yeast to oxygen will slow or stop the process, because the yeast will switch back to aerobic respiration. When fermentation is rapid, the carbon dioxide produced drives away the immediate oxygen above the wine. However, as fermentation slows down, the wine must be sealed to prevent oxygen exposure and permit the fermentation process to finish. 60

Fermentation in Microorganisms
Fermentation alone is able to sustain many types of microorganisms. The lactic acid produced by microbes using fermentation is used to produce cheese, sour cream, and yogurt, soy sauce, pickles, and olives, and sausage meat products. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and perhaps carbon dioxide. Care should be taken to clarify the different possible products of fermentation in muscle cells and alcoholic fermentation used in the food and beverage industry. 2. The text notes that some microbes are useful in the dairy industry because they produce lactic acid. However, the impact of acids on milk may not be obvious to many students. Consider a simple demonstration mixing about equal portions of milk (skim or 2%) with some acid (vinegar will work). Notice the accumulation of strands of milk curd (protein) on the side of the container and stirring device. Teaching Tips 1. The carbon dioxide released from fermentation also makes beer and champagne bubbly. 2. Dry wines are produced when the yeast cells use up all or most of the sugar available. Sweet wines result when the alcohol accumulates enough to inhibit fermentation before the sugar is depleted. 3. Exposing fermenting yeast to oxygen will slow or stop the process, because the yeast will switch back to aerobic respiration. When fermentation is rapid, the carbon dioxide produced drives away the immediate oxygen above the wine. However, as fermentation slows down, the wine must be sealed to prevent oxygen exposure and permit the fermentation process to finish. 61

Fermentation in Microorganisms
Yeast is a microscopic fungus that uses a different type of fermentation and produces CO2 and ethyl alcohol instead of lactic acid. This type of fermentation, called alcoholic fermentation, is used to produce beer, wine, and breads. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and perhaps carbon dioxide. Care should be taken to clarify the different possible products of fermentation in muscle cells and alcoholic fermentation used in the food and beverage industry. 2. The text notes that some microbes are useful in the dairy industry because they produce lactic acid. However, the impact of acids on milk may not be obvious to many students. Consider a simple demonstration mixing about equal portions of milk (skim or 2%) with some acid (vinegar will work). Notice the accumulation of strands of milk curd (protein) on the side of the container and stirring device. Teaching Tips 1. The carbon dioxide released from fermentation also makes beer and champagne bubbly. 2. Dry wines are produced when the yeast cells use up all or most of the sugar available. Sweet wines result when the alcohol accumulates enough to inhibit fermentation before the sugar is depleted. 3. Exposing fermenting yeast to oxygen will slow or stop the process, because the yeast will switch back to aerobic respiration. When fermentation is rapid, the carbon dioxide produced drives away the immediate oxygen above the wine. However, as fermentation slows down, the wine must be sealed to prevent oxygen exposure and permit the fermentation process to finish. 62

Figure 6.16 Fermentation: producing ethyl alcohol
INPUT OUTPUT 2 ADP 2 ATP  2 P 2 CO2 released Glycolysis – – – – 2 NAD 2 NADH 2 NADH 2 NAD 2 Ethyl alcohol 2 Pyruvic acid  2 H Glucose Figure 6.16 Fermentation: producing ethyl alcohol

INPUT OUTPUT 2 ADP 2 ATP  2 P 2 CO2 released Glycolysis 2 NAD 2 NADH
Figure 6.16a INPUT OUTPUT 2 ADP 2 ATP  2 P 2 CO2 released Glycolysis – – – – 2 NAD 2 NADH 2 NADH 2 NAD 2 Ethyl alcohol 2 Pyruvic acid 2 H Glucose Figure 6.16 Fermentation: producing ethyl alcohol (part 1)

Evolution Connection: Life before and after Oxygen
Glycolysis could be used by ancient bacteria to make ATP when little oxygen was available, and before organelles evolved. Today, glycolysis occurs in almost all organisms and is a metabolic heirloom of the first stage in the breakdown of organic molecules. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and perhaps carbon dioxide. Care should be taken to clarify the different possible products of fermentation in muscle cells and alcoholic fermentation used in the food and beverage industry. 2. The text notes that some microbes are useful in the dairy industry because they produce lactic acid. However, the impact of acids on milk may not be obvious to many students. Consider a simple demonstration mixing about equal portions of milk (skim or 2%) with some acid (vinegar will work). Notice the accumulation of strands of milk curd (protein) on the side of the container and stirring device. Teaching Tips 1. The carbon dioxide released from fermentation also makes beer and champagne bubbly. 2. Dry wines are produced when the yeast cells use up all or most of the sugar available. Sweet wines result when the alcohol accumulates enough to inhibit fermentation before the sugar is depleted. 3. Exposing fermenting yeast to oxygen will slow or stop the process, because the yeast will switch back to aerobic respiration. When fermentation is rapid, the carbon dioxide produced drives away the immediate oxygen above the wine. However, as fermentation slows down, the wine must be sealed to prevent oxygen exposure and permit the fermentation process to finish. 65

First eukaryotic organisms 2.2
Figure 6.17 Earth’s atmosphere O2 present in 2.1 First eukaryotic organisms 2.2 Atmospheric oxygen reaches 10% of modern levels 2.7 Atmospheric oxygen first appears Billions of years ago 3.5 Oldest prokaryotic fossils 4.5 Origin of Earth Figure 6.17 A time line of oxygen and life on Earth

First eukaryotic organisms 2.2
Figure 6.17a Earth’s atmosphere O2 present in 2.1 First eukaryotic organisms 2.2 Atmospheric oxygen reaches 10% of modern levels 2.7 Atmospheric oxygen first appears Billions of years ago 3.5 Oldest prokaryotic fossils 4.5 Origin of Earth Figure 6.17 A time line of oxygen and life on Earth (part 1)

Citric Acid Cycle Electron Transport
Figure 6.UN03 Citric Acid Cycle Electron Transport Glycolysis ATP ATP ATP Figure 6.UN03 In-text figure, glycolysis, p. 97

Figure 6.UN04 Citric Acid Cycle Electron Transport Glycolysis ATP ATP ATP Figure 6.UN04 In-text figure, citric acid cycle, p. 98

Figure 6.UN05 Citric Acid Cycle Electron Transport Glycolysis ATP ATP ATP Figure 6.UN05 In-text figure, electron transport chain, p. 99

C6H12O6 Heat Sunlight O2 ATP Cellular respiration CO2 H2O
Figure 6.UN06 Heat C6H12O6 Sunlight O2 ATP Cellular respiration Photosynthesis CO2 H2O Figure 6.UN06 Summary of Key Concepts: Chemical Cycling between Photosynthesis and Cellular Respiration

Glucose loses electrons (and hydrogens)
Figure 6.UN08 Oxidation Glucose loses electrons (and hydrogens) C6H12O6 CO2 ATP Electrons (and hydrogens) O2 H2O Reduction Oxygen gains electrons (and hydrogens) Figure 6.UN08 Summary of Key Concepts: The Role of Oxygen in Cellular Respiration

Mitochondrion O2 – – – – – – 6 NADH 2 NADH 2 NADH – – 2 FADH2
Figure 6.UN09 Mitochondrion O2 – – – – – – 6 NADH 2 NADH 2 NADH – – 2 FADH2 Glycolysis 2 Acetyl CoA Citric Acid Cycle 2 Pyruvic acid Electron Transport Glucose 2 CO2 4 CO2 H2O About 28 ATP 2 ATP by direct synthesis by direct synthesis 2 ATP by ATP synthase About 32 ATP Figure 6.UN09 Summary of Key Concepts: An Overview of Cellular Respiration

Cellular Respiration: Obtaining Energy from Food

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