1 Cellular Respiration: Obtaining Energy from FoodChapter 6 Cellular Respiration: Obtaining Energy from Food

2 Biology and Society: Marathoners versus SprintersSprinters do not usually compete at short and long distances. Natural differences in the muscles of these athletes favor sprinting or long-distance running.

3 The muscles that move our legs contain two main types of muscle fibers:Slow-twitch fibers: Generate less power Last longer Generate ATP using oxygen Fast-twitch fibers: Generate more power Fatigue much more quickly Can generate ATP without using oxygen All human muscles contain both types of fibers but in different ratios.

4 ENERGY FLOW AND CHEMICAL CYCLING IN THE BIOSPHEREAnimals depend on plants to convert solar energy to: Chemical energy of sugars Other molecules we consume as food Photosynthesis: Uses light energy from the sun to power a chemical process that makes organic molecules. © 2010 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 the Earth. Every day the 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 only pays its employees in food!) Money permits the coupling of a generation of value (a paycheck, analogous to an energy releasing reaction) to an energy consuming reaction, (money, which allows us to make purchases in distant locations). This idea of earn and spend is a common concept we all know well.

5 Producers and ConsumersPlants 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. 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 the Earth. Every day the 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 only pays its employees in food!) Money permits the coupling of a generation of value (a paycheck, analogous to an energy releasing reaction) to an energy consuming reaction, (money, which allows us to make purchases in distant locations). This idea of earn and spend is a common concept we all know well.

6 Chemical Cycling between Photosynthesis and Cellular RespirationThe ingredients for photosynthesis are carbon dioxide and water. CO2 is obtained from the air by a plant’s leaves. H2O is obtained from the damp soil by a plant’s roots. 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 Oxygen © 2010 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 the Earth. Every day the 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 only pays its employees in food!) Money permits the coupling of a generation of value (a paycheck, analogous to an energy releasing reaction) to an energy consuming reaction, (money, which allows us to make purchases in distant locations). This idea of earn and spend is a common concept we all know well.

7 The waste products of cellular respiration are:Plant and animal cells perform cellular respiration, a chemical process that: Primarily occurs in mitochondria Harvests energy stored in organic molecules Uses oxygen Generates ATP The waste products of cellular respiration are: CO2 and H2O Used in photosynthesis 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 the Earth. Every day the 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 only pays its employees in food!) Money permits the coupling of a generation of value (a paycheck, analogous to an energy releasing reaction) to an energy consuming reaction, (money, which allows 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 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 the Earth. Every day the 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 only pays its employees in food!) Money permits the coupling of a generation of value (a paycheck, analogous to an energy releasing reaction) to an energy consuming reaction, (money, which allows us to make purchases in distant locations). This idea of earn and spend is a common concept we all know well.

9 Figure 6.2 Sunlight energy enters ecosystem Photosynthesis C6H12O6Glucose O2 Oxygen CO2 Carbon dioxide H2O Water Cellular respiration ATP drives cellular work Heat energy exits ecosystem Figure 6.2 Figure 6.2 Energy flow and chemical cycling in ecosystems

10 CELLULAR RESPIRATION: AEROBIC HARVEST OF FOOD ENERGYCellular respiration is: The main way that chemical energy is harvested from food and converted to ATP An aerobic process—it requires oxygen 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. © 2010 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. 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 becomes 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 37°C (98–99°F). This is about the same amount of heat generated by a 100-watt incandescent light bulb. 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 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). 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 37°C. Thus, we sweat and behave in ways that helps us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending upon 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 liters of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-liter bottle as a visual aid, or ten 2-liter bottles to make the point above; 100 Calories raises 1 liter of water 100C; 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. Consider pointing to a diagram of a cell, with mitochondrial detail, as you lecture on cellular respiration to emphasize the location of each stage. 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 two 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 38 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 Figure 6.3 O2 CO2 Breathing Lungs O2 CO2 Muscle cells Cellularrespiration Figure 6.3 Figure 6.3 How breathing is related to cellular respiration.

12 O2 CO2 Breathing O2 CO2 Muscle cells Cellular respirationLungs O2 CO2 Muscle cells Cellular respiration Figure 6.3a Figure 6.3a How breathing is related to cellular respiration.

13 The Overall Equation for Cellular RespirationA common fuel molecule for cellular respiration is glucose. The overall equation for what happens to glucose during cellular respiration: Oxidation Glucose loses electrons (and hydrogens) C6H12O6  6 O2 6 CO2  6 H2O Glucose Oxygen Carbon dioxide Water Reduction Oxygen gains electrons (and hydrogens) 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. 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 becomes 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 37°C (98–99°F). This is about the same amount of heat generated by a 100-watt incandescent light bulb. 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 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). 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 37°C. Thus, we sweat and behave in ways that helps us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending upon 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 liters of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-liter bottle as a visual aid, or ten 2-liter bottles to make the point above; 100 Calories raises 1 liter of water 100C; 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. Consider pointing to a diagram of a cell, with mitochondrial detail, as you lecture on cellular respiration to emphasize the location of each stage. 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 two 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 38 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 The Role of Oxygen in Cellular RespirationCellular respiration can produce up to 38 ATP molecules for each glucose molecule consumed. During cellular respiration, hydrogen and its bonding electrons change partners. Hydrogen and its electrons go from sugar to oxygen, forming water. This hydrogen transfer is why oxygen is so vital to cellular respiration. 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. 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 becomes 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 37°C (98–99°F). This is about the same amount of heat generated by a 100-watt incandescent light bulb. 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 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). 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 37°C. Thus, we sweat and behave in ways that helps us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending upon 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 liters of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-liter bottle as a visual aid, or ten 2-liter bottles to make the point above; 100 Calories raises 1 liter of water 100C; 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. Consider pointing to a diagram of a cell, with mitochondrial detail, as you lecture on cellular respiration to emphasize the location of each stage. 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 two 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 38 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.

15 Redox Reactions Chemical reactions that transfer electrons from one substance to another are called: Oxidation-reduction reactions or Redox reactions for short The loss of electrons during a redox reaction is called oxidation. The acceptance of electrons during a redox reaction is called reduction. During cellular respiration glucose is oxidized while oxygen is reduced. 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. 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 becomes 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 37°C (98–99°F). This is about the same amount of heat generated by a 100-watt incandescent light bulb. 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 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). 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 37°C. Thus, we sweat and behave in ways that helps us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending upon 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 liters of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-liter bottle as a visual aid, or ten 2-liter bottles to make the point above; 100 Calories raises 1 liter of water 100C; 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. Consider pointing to a diagram of a cell, with mitochondrial detail, as you lecture on cellular respiration to emphasize the location of each stage. 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 two 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 38 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 Citric Acid Cycle Electron Transport Glycolysis ATP ATP ATPFigure 6.UN03 Figure 6.UN3 Glycosis orientation diagram

17 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 A stepwise cascade much like going down a staircase 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. 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 becomes 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 37°C (98–99°F). This is about the same amount of heat generated by a 100-watt incandescent light bulb. 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 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). 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 37°C. Thus, we sweat and behave in ways that helps us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending upon 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 liters of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-liter bottle as a visual aid, or ten 2-liter bottles to make the point above; 100 Calories raises 1 liter of water 100C; 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. Consider pointing to a diagram of a cell, with mitochondrial detail, as you lecture on cellular respiration to emphasize the location of each stage. 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 two 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 38 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 1 H2 O2 2 Release of heat energy H2OFigure 6.4 Figure 6.4 A simple redox reaction

19 NADH and Electron Transport ChainsThe path that electrons take on their way down from glucose to oxygen involves many steps. The first step is an electron acceptor called NAD+. 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 Ultimately leads to the production of large amounts of ATP 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. 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 becomes 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 37°C (98–99°F). This is about the same amount of heat generated by a 100-watt incandescent light bulb. 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 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). 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 37°C. Thus, we sweat and behave in ways that helps us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending upon 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 liters of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-liter bottle as a visual aid, or ten 2-liter bottles to make the point above; 100 Calories raises 1 liter of water 100C; 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. Consider pointing to a diagram of a cell, with mitochondrial detail, as you lecture on cellular respiration to emphasize the location of each stage. 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 two 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 38 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 chainElectrons from food e e Stepwise release of energy used to make NAD NADH ATP 2 H 2 e Electron transport chain 2 e 2 1 2 H O2 Hydrogen, electrons, and oxygen combine to produce water H2O Figure 6.5 Figure 6.5 The role of oxygen in harvesting food energy.

21 An Overview of Cellular RespirationIs 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: Glycolysis The citric acid cycle Electron transport 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. 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 becomes 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 37°C (98–99°F). This is about the same amount of heat generated by a 100-watt incandescent light bulb. 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 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). 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 37°C. Thus, we sweat and behave in ways that helps us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending upon 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 liters of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-liter bottle as a visual aid, or ten 2-liter bottles to make the point above; 100 Calories raises 1 liter of water 100C; 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. Consider pointing to a diagram of a cell, with mitochondrial detail, as you lecture on cellular respiration to emphasize the location of each stage. 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 two 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 38 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.

22 Cytoplasm Mitochondrion Glycolysis 2 Pyruvic acid ATP ATP ATPHigh-energy electrons carried by NADH High-energy electrons carried mainly by NADH Glycolysis Citric Acid Cycle 2 Pyruvic acid Electron Transport Glucose ATP ATP ATP Figure 6.6a Figure 6.6a A road map for cellular respiration

23 The Three Stages of Cellular RespirationWith the big-picture view of cellular respiration in mind, let’s examine the process in more detail. 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. 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 becomes 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 37°C (98–99°F). This is about the same amount of heat generated by a 100-watt incandescent light bulb. 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 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). 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 37°C. Thus, we sweat and behave in ways that helps us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending upon 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 liters of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-liter bottle as a visual aid, or ten 2-liter bottles to make the point above; 100 Calories raises 1 liter of water 100C; 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. Consider pointing to a diagram of a cell, with mitochondrial detail, as you lecture on cellular respiration to emphasize the location of each stage. 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 two 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 38 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.

24 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. Glycolysis: Uses two ATP molecules per glucose to split the six-carbon glucose 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. 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. 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 becomes 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 37°C (98–99°F). This is about the same amount of heat generated by a 100-watt incandescent light bulb. 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 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). 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 37°C. Thus, we sweat and behave in ways that helps us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending upon 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 liters of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-liter bottle as a visual aid, or ten 2-liter bottles to make the point above; 100 Calories raises 1 liter of water 100C; 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. Consider pointing to a diagram of a cell, with mitochondrial detail, as you lecture on cellular respiration to emphasize the location of each stage. 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 two 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 38 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.

25 Energy investment phaseINPUT OUTPUT NADH 2 ATP NAD 2 ADP 2 ATP 2 ADP 2 Pyruvic acid Glucose 2 ADP Key NAD 2 ATP Carbon atom NADH Phosphate group High-energy electron Energy investment phase Energy harvest phase Figure 6.7-3 Figure 6.7 Glycolysis (Step 3)

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

27 Stage 2: The Citric Acid CycleThe citric acid cycle completes the breakdown of sugar. In the citric acid cycle, pyruvic acid from glycolysis is first “prepped.” 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. 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 becomes 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 37°C (98–99°F). This is about the same amount of heat generated by a 100-watt incandescent light bulb. 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 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). 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 37°C. Thus, we sweat and behave in ways that helps us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending upon 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 liters of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-liter bottle as a visual aid, or ten 2-liter bottles to make the point above; 100 Calories raises 1 liter of water 100C; 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. Consider pointing to a diagram of a cell, with mitochondrial detail, as you lecture on cellular respiration to emphasize the location of each stage. 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 two 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 38 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.

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

29 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 Forms NADH and FADH2 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. 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 becomes 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 37°C (98–99°F). This is about the same amount of heat generated by a 100-watt incandescent light bulb. 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 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). 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 37°C. Thus, we sweat and behave in ways that helps us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending upon 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 liters of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-liter bottle as a visual aid, or ten 2-liter bottles to make the point above; 100 Calories raises 1 liter of water 100C; 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. Consider pointing to a diagram of a cell, with mitochondrial detail, as you lecture on cellular respiration to emphasize the location of each stage. 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 two 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 38 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.

30 INPUT OUTPUT ATP Citric Acid Cycle Citric acid Acetic acid 2 CO2ADP  P ATP Citric Acid Cycle 3 NAD 3 NADH FAD FADH2 Acceptor molecule Figure 6.10 Figure 6.10 The citric acid cycle

31 Stage 3: Electron TransportElectron 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 that uses energy released by the “fall” of electrons to pump hydrogen ions across the inner mitochondrial membrane. These ions store potential energy. 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. 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 becomes 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 37°C (98–99°F). This is about the same amount of heat generated by a 100-watt incandescent light bulb. 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 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). 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 37°C. Thus, we sweat and behave in ways that helps us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending upon 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 liters of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-liter bottle as a visual aid, or ten 2-liter bottles to make the point above; 100 Calories raises 1 liter of water 100C; 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. Consider pointing to a diagram of a cell, with mitochondrial detail, as you lecture on cellular respiration to emphasize the location of each stage. 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 two 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 38 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 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 Synthesizes ATP 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. 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 becomes 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 37°C (98–99°F). This is about the same amount of heat generated by a 100-watt incandescent light bulb. 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 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). 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 37°C. Thus, we sweat and behave in ways that helps us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending upon 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 liters of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-liter bottle as a visual aid, or ten 2-liter bottles to make the point above; 100 Calories raises 1 liter of water 100C; 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. Consider pointing to a diagram of a cell, with mitochondrial detail, as you lecture on cellular respiration to emphasize the location of each stage. 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 two 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 38 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.

33 Electron transport chainSpace between membranes H H H H H H H H Electron carrier H H H H H Protein complex Inner mitochondrial membrane FADH2 FAD Electron flow H 1 O2  2 H H2O 2 NADH NAD ADP  P ATP H H H H H ATP synthase Matrix Electron transport chain Figure 6.11a Figure 6.11a How electron transport drives ATP synthase machines

34 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 Stops the production of ATP 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. 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 becomes 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 37°C (98–99°F). This is about the same amount of heat generated by a 100-watt incandescent light bulb. 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 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). 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 37°C. Thus, we sweat and behave in ways that helps us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending upon 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 liters of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-liter bottle as a visual aid, or ten 2-liter bottles to make the point above; 100 Calories raises 1 liter of water 100C; 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. Consider pointing to a diagram of a cell, with mitochondrial detail, as you lecture on cellular respiration to emphasize the location of each stage. 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 two 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 38 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 The Versatility of Cellular RespirationIn addition to glucose, cellular respiration can “burn”: Diverse types of carbohydrates Fats Proteins 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. 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 becomes 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 37°C (98–99°F). This is about the same amount of heat generated by a 100-watt incandescent light bulb. 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 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). 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 37°C. Thus, we sweat and behave in ways that helps us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending upon 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 liters of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! (Note: Consider bringing a 2-liter bottle as a visual aid, or ten 2-liter bottles to make the point above; 100 Calories raises 1 liter of water 100C; 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. Consider pointing to a diagram of a cell, with mitochondrial detail, as you lecture on cellular respiration to emphasize the location of each stage. 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 two 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 38 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.

36 Food Polysaccharides Fats Proteins Sugars Glycerol Fatty acidsAmino acids Citric Acid Cycle Acetyl CoA Glycolysis Electron Transport ATP Figure 6.12 Figure 6.12 Energy from food

37 Figure 6.13 Cytoplasm Mitochondrion 6 NADH 2 NADH 2 NADH 2 FADH2Glycolysis 2 Acetyl CoA 2 Pyruvic acid Citric Acid Cycle Electron Transport Glucose Maximum per glucose: 2 ATP 2 ATP About 34 ATP About 38 ATP by direct synthesis by direct synthesis by ATP synthase Figure 6.13 Figure 6.13 A summary of ATP yield during cellular respiration

38 FERMENTATION: ANAEROBIC HARVEST OF FOOD ENERGYSome of your cells can actually work for short periods without oxygen. Fermentation is the anaerobic (without oxygen) harvest of food energy. After functioning anaerobically for about 15 seconds: Muscle cells will begin to generate ATP by the process of fermentation Fermentation relies on glycolysis to produce ATP. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and maybe even 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.

39 Pyruvic acid, produced by glycolysis, isDoes not require oxygen Produces two ATP molecules for each glucose broken down to pyruvic acid 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. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and maybe even 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.

40 INPUT OUTPUT Glycolysis Glucose2 ADP 2 ATP  2 P Glycolysis 2 NAD 2 NAD 2 NADH 2 NADH 2 Pyruvic acid  2 H 2 Lactic acid Glucose Figure 6.14a Figure 6.14a Fermentation: Producing lactic acid

41 The Process of Science: Does Lactic Acid Buildup Cause Muscle Burn?Observation: Muscles produce lactic acid under anaerobic conditions. Question: Does the buildup of lactic acid cause muscle fatigue? Hypothesis: The buildup of lactic acid would cause muscle activity to stop. Experiment: Tested frog muscles under conditions when lactic acid could and could not diffuse away. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and maybe even 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.

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

43 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. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and maybe even 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.

44 Fermentation in MicroorganismsFermentation 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 dairy products Soy sauce, pickles, olives Sausage meat products Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and maybe even 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.

45 Yeast are a type of microscopic fungus that:Use a different type of fermentation Produce CO2 and ethyl alcohol instead of lactic acid This type of fermentation, called alcoholic fermentation, is used to produce beer, wine, and breads Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and maybe even 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.

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

47 Evolution Connection: Life before and after OxygenGlycolysis 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 Is a metabolic heirloom of the first stage in the breakdown of organic molecules © 2010 Pearson Education, Inc. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and maybe even 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.

48 Figure 6.17 Earth’s atmosphere O2 present in 2.1Earth’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 Figure 6.17 A time line of oxygen and life on Earth

49 First eukaryotic organisms 2.2 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 6.17a Figure 6.17a A time line of oxygen and life on Earth

50 Figure 6.17b Figure 6.17b A time line of oxygen and life on Earth

51 Glucose loses electrons Oxygen gains electrons (and hydrogens)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 Figure 6.UN2 Redox reaction

52 C6H12O6  6 O2 6 CO2  6 H2O  ATP Glucose Oxygen Carbon dioxide WaterEnergy Figure 6.UN01 Figure 6.UN1 Overall equation of cellular respiration