Cellular Respiration: Obtaining Energy from Food

Cellular Respiration: Obtaining Energy from Food
Chapter 6 Cellular Respiration: Obtaining Energy from Food © 2016 Pearson Education, Inc.

Why Cellular Respiration Matters
Figure 6.0-1 Figure Why cellular respiration matters

Biology and Society: Getting the Most Out of Your Muscles
For many endurance athletes, the rate at which oxygen is provided to working muscles is the limiting factor in their performance. Your muscles need a continuous supply of energy to perform work. Muscle cells obtain this energy from the sugar glucose through a series of chemical reactions that depend upon a constant input of oxygen (O2). When there is enough oxygen reaching your cells to support their energy needs, metabolism is said to be aerobic. 3

Your aerobic capacity is the maximum rate at which O2 can be taken in and used by your muscle cells and therefore the most strenuous exercise that your body can maintain aerobically. Chapter Thread: Exercise Science 4

If you work even harder and exceed your aerobic capacity, the demand for oxygen in your muscles will outstrip your body’s ability to deliver it, metabolism then becomes anaerobic, and your muscle cells switch to an “emergency mode” in which they break down glucose very inefficiently and produce lactic acid as a by-product. Every living organism depends on processes that provide energy. Cells harvest food energy and put it to work with the help of oxygen. 5

Energy Flow and Chemical Cycling in the Biosphere
All life requires energy. In almost all ecosystems on Earth, this energy originates with the sun. During photosynthesis, plants convert the energy of sunlight to the chemical energy of sugars and other organic molecules. Humans and other animals depend on this conversion for food and more. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students should be cautioned against making statements that “energy is created” when it is converted from one form to another. This might be a good time to review the principle of conservation of energy (the first law of thermodynamics). 2. Students frequently think that plants have chloroplasts instead of mitochondria. Care should be taken to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips 1. You might wish to elaborate on the amount of solar energy striking Earth. Every day Earth is bombarded with solar radiation equal to the energy of 100 million atomic bombs. Of the tiny fraction of light that reaches photosynthetic organisms, only about 1% is converted to chemical energy by photosynthesis. 2. You might share with your students that it takes about 10 million ATP molecules per second to power one active muscle cell. 3. Energy coupling at the cellular level may be new to many students, but it is a familiar concept when related to the use of money in our society. Students might be discouraged if the only benefit of work was the ability to make purchases from the employer. (We all might soon tire of a fast-food job that pays its employees only in food!) Money permits the coupling of the generation of value (a paycheck, analogous to an energy-releasing reaction) to an energy-consuming reaction (money, which enables us to make purchases in distant locations). This idea of “earn and spend” is a common concept we all know well. Active Lecture Tips 1. See the activity Photosynthesis and Respiration: Are They Similar? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 6

Producers and Consumers
Autotrophs (self-feeders) include plants and other photosynthetic organisms Make their own organic matter (carbohydrates, lipids, proteins and nucleic acids) from inorganic nutrients (CO2, H2O, and minerals from the sol). Are the producers of the ecosystem because the other ecosystem members depend upon them for food. Heterotrophs (other-feeders): Include humans and other animals that cannot make organic molecules from inorganic ones. Heterotrophs are consumers of the ecosystem because they eat plants or other animals. We depend upon plants for more than food - dress, wood for house, books

Producer and consumer Figure 6.1 Figure 6.1 Producer and consumer

Chemical Cycling between Photosynthesis and Cellular Respiration
The chemical ingredients for photosynthesis are carbon dioxide and water. CO2 is gas obtained from the air into the plant through tiny pores of the leaves H2O is obtained from the damp soil by a plant’s roots Chloroplasts inside the leaf cells of plant leaves: use light energy to rearrange the atoms of CO2 and H2O, to produces Sugars (such as glucose), and other organic molecules Oxygen (O2) a by-product of all this which is vital to living organisms

Cellular respiration, a chemical process that: primarily occurs in mitochondria harvests energy stored in sugar and other organic molecules to generates ATP (which cell need for everything) is an aerobic process (uses oxygen) The waste products of cellular respiration are: CO2 and H2O used in photosynthesis In other words, plants store chemical energy through photosynthesis and then harvest it through cellular respiration

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

Animals perform only cellular respiration. Plants perform Photosynthesis and Cellular respiration Plants usually make more organic molecules than they need for fuel. This surplus provides material that can be used for the plant to grow or stored as starch in potatoes People have always taken advantage of plants’ photosynthetic abilities by eating them.

Summary: Chemical cycling
The chemical reaction takes glucose and oxygen and turns it into carbon dioxide, water, and ATP energy. This is not a single chemical reaction, but a series of three main reactions : Glycolysis, the citric acid cycle (Krebs cycle), and electron transport. Heat C6H12O6 Sunlight O2 ATP Cellular respiration Photosynthesis CO2 H2O Figure 6.UN6 Summary: Chemical cycling

Check yourself What chemical ingredients do plants require from the environment in order to synthesize their own food? Check yourself What chemical ingredients do plants require from the environment in order to synthesize their own food?

CELLULAR RESPIRATION: AEROBIC HARVEST OF FOOD ENERGY
Cellular respiration is the main way that chemical energy is harvested from food and converted to ATP. - It is an aerobic process—it requires oxygen Cellular respiration and breathing are closely related. Cellular respiration requires a cell to exchange two gases with its surroundings; that cells take in oxygen gas (O2) and release waste carbon dioxide gas (CO2 ) a waste Breathing exchanges these same gases between the blood and outside air Respiration means breathing results in exchange of gases between your blood and the outside sir Cellular respiration requires a cell to exchange two gases with its surroundings

How breathing is related to cellular respiration
CO2 Lungs Air 79% N2 (inert) 21% O2 0.2% CO2 O2 CO2 O2 CO2 Muscle cells Cellular respiration Figure 6.3-1 Figure How breathing is related to cellular respiration (part 1: detail)

The Overall Equation for Cellular Respiration
A common fuel molecule for cellular respiration is glucose. Cellular respiration can produce up to 32 ATP molecules for each glucose molecule consumed Overall equation for what happens to glucose during cellular respiration: C6H12O6 CO2 ATP O2 H2O  6 6  Approx. 32 C6H12O6 CO2 ATP O2 H2O Oxidation: Glucose loses electrons (and hydrogens) Reduction: Oxygen gains electrons (and hydrogens) Electrons

The Role of Oxygen in Cellular Respiration
During cellular respiration, hydrogen and its bonding electrons change partners from sugar to oxygen, forming water as a product. Hydrogen ions (H+) and its electrons (e) go from sugar to oxygen, forming water. This hydrogen transfer is why oxygen is so vital to cellular respiration. glucose oxygen  carbon dioxide + water + energy C6H12O6 6O2 6CO2 6H2O ATP  + + heat respiration combustion = making heat energy by burning fuels in one step respiration = making ATP (& less heat) by burning fuels in many small steps ATP fuel (carbohydrates) CO2 + H2O + heat CO2 + H2O + ATP (+ heat) Movement of hydrogen atoms from glucose to water

Energy Transformations: An Overview of Cellular Respiration
consists of many chemical steps, with more than two dozen reactions in all, involves a specific enzyme to catalyze each reaction, constitutes one of the most important metabolic pathways for nearly every eukaryotic cell, and provides the energy these cells need to maintain the functions of life. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.4 can be especially helpful in providing physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37°C (98–99°F). This is about the same amount of heat generated by a 75-watt incandescent light bulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). Shouldn’t they feel cold? The answer is that 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 help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 200 Calories raises 2 L of water 100°C. (Note: It takes much more energy to melt ice or evaporate water as steam.) 2. 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. 3. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding water back. 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. 4. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under the best conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. Active Lecture Tips 1. As you relate the structure of the inner mitochondrial membrane to its functions, challenge students to explain the adaptive advantage of the many folds of this inner membrane. (These folds greatly increase the surface area available for the associated reactions.) 2. See the activity Cell Respiration: Pair and Share on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. See the activity Demonstration of Electron Transport and ATP Production in Aerobic Respiration Using Students and Balloons on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. Challenge your students to explain why most extra energy in the human body is stored as fat and not sugars or proteins. Have students work with others seated nearby. The general answer is this. The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) as an equivalent mass of protein or carbohydrates (about 4.5 kcal per gram). Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 lb overweight, you would be nearly 40 lb overweight if the same energy were stored as carbohydrates or proteins instead of fat.) 19

Practice What is the correct general equation for cellular respiration? [Hint] 6 CO2 + 6 H2O + ATP energy → C6H12O6 + 6 O2 C6H12O6 + 6 CO2 → 6 O2 + 6 H2O + ATP energy 6 O2 + 6 H2O + ATP energy → C6H12O6 + 6 CO2 C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + ATP energy C6H12O H2O → 6 CO2 + 6 O2 + ATP energy

An Overview of Cellular Respiration
Cellular respiration is an example of a metabolic pathway, which is a series of chemical reactions in cells Each reaction is catalyzed by specific enzyme All of the reactions in cellular respiration can be grouped into four metabolic stages: Anaerobic respiration: without O2 in the cytoplasm Glycolysis Anaerobic respiration with O2 in the mitochondria 2. Linking Step or Pyruvate oxidation 3. The citric acid cycle 4. Electron transport The enzyme for glycolysis are located in the cytoplasm The enzyme for citric acid cycle are dissolved in the fluid within mitochondria The protein and other molecules that make up ETC are embedded within the inner mitochondrial membrane

BioFlix Animation: Cellular Respiration
© 2016 Pearson Education, Inc.

Practice Which statement best describes cellular respiration?
1. It is the conversion of light energy into chemical energy. 2. It is the release of oxygen from the cells of an organism. 3. It is the release of stored chemical energy in food to produce ATP. 4. It is the excretion of materials out of the cells of an organism.

The overall equation for cellular respiration shows that the atoms of the reactant molecules glucose and oxygen are rearranged to form the products carbon dioxide and water. The main function of cellular respiration is to generate ATP for cellular work. The process can produce around 32 ATP molecules for each glucose molecule consumed. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.4 can be especially helpful in providing physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37°C (98–99°F). This is about the same amount of heat generated by a 75-watt incandescent light bulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). Shouldn’t they feel cold? The answer is that 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 help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 200 Calories raises 2 L of water 100°C. (Note: It takes much more energy to melt ice or evaporate water as steam.) 2. 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. 3. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding water back. 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. 4. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under the best conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. Active Lecture Tips 1. As you relate the structure of the inner mitochondrial membrane to its functions, challenge students to explain the adaptive advantage of the many folds of this inner membrane. (These folds greatly increase the surface area available for the associated reactions.) 2. See the activity Cell Respiration: Pair and Share on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. See the activity Demonstration of Electron Transport and ATP Production in Aerobic Respiration Using Students and Balloons on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. Challenge your students to explain why most extra energy in the human body is stored as fat and not sugars or proteins. Have students work with others seated nearby. The general answer is this. The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) as an equivalent mass of protein or carbohydrates (about 4.5 kcal per gram). Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 lb overweight, you would be nearly 40 lb overweight if the same energy were stored as carbohydrates or proteins instead of fat.) 24

A road map for cellular respiration
Mitochondria Cytoplasm Cytoplasm Animal cell Plant cell Cytoplasm Mitochondrion High-energy electrons via carrier molecules   Glycolysis 2 Pyruvic acid Citric Acid Cycle  Electron Transport Chain Glucose ATP ATP ATP Figure 6.4 Figure 6.4 A road map for cellular respiration

Stage 1: Glycolysis 6C 3C glucose      pyruvate 2x
Glycolysis usually located in the cytoplasm split in half six-carbon glucose molecule forming two 3-carbon molecules (pyruvate) The 3-carbon molecules then donate high-energy e- to NAD+ (electron carrier), forming NADH In addition to NADH, glycolysis makes four ATP molecules directly when enzymes transfer phosphate group from food molecules to ADP However, glycolysis uses two ATP molecules per glucose to split the six-carbon glucose Thus, glycolysis produces a net of two molecules of ATP per glucose molecule. glucose      pyruvate 6C 2x 3C

Glycolysis EA Convert 6C to 3C You put 2 ATP in &
INPUT OUTPUT – – NADH P P 2 ATP NAD 2 ADP EA Adenosine diphosphate 2 3 2 ATP P 2 ADP P 2 Pyruvic acid 1 P P P 2 3 Glucose 2 ADP NAD 2 ATP P – – NADH Energy investment phase Energy harvest phase Key Carbon atom Convert 6C to 3C You put 2 ATP in & we end up with 4 ATP, but it is a NET GAIN of 2ATP P Phosphate group – High-energy electron Figure 6.7 Figure 6.7 Glycolysis During glycolysis, a six-carbon glucose molecule is broken in half forming two 3-carbon molecules The 3-carbon molecules then donate high-energy e- to NAD+, the electron carrier, forming NADH In addition to NADH, glycolysis also makes four ATP molecules directly when enzymes transfer phosphate group from food molecules to ADP

INPUT OUTPUT 2 Pyruvic acid Glucose Big things in Small things out
Figure 6.7a Figure 6.7 Glycolysis (part 1)

Practice In glycolysis,
1. there is a net ATP loss. 2. aerobic processes occur. 3. glucose is produced. 4. four ATP molecules are produced. 5. four ADP molecules are produced. In eukaryotes, where do the glycolytic reactions take place? 1. cytoplasm of the cell 2. ribosomes of the cell 3. Golgi bodies of the cell 4. mitochondria of the cell 5. endoplasmic reticulum of each cell

Practice What is the first stage of cellular respiration
(and the oldest in terms of evolution)? 1. deamination 2. chemiosmosis 3. glycolysis 4. fermentation 5. decarboxylation What is not an end product of glycolysis? 1. pyruvate 2. NAD+ 3. energy 4. ATP 5. NADH

Stage 2: Linking Step Step between glycolysis & citric acid cycle where pyruvic acid from glycolysis must be “groomed” or converted to a form the citric acid cycle can use to complete the breakdown of sugar Each pyruvic acid loses a carbon as CO2 (gas release as you breath) The remaining fuel molecule, with only two carbons left, is acetic acid. Electrons are stripped (oxydation) from these molecules and transferred to another molecule of NAD+, forming more NADH. Finally, each acetic acid is attached to a molecule called coenzyme A to form acetyl CoA. The CoA escorts the acetic acid into the first reaction of the citric acid cycle. The CoA is then stripped and recycled

Stage 2: Linking Step between Glycolysis & Citric acid cycle
Pyruvic acid from glycolysis is transformed into acetyl-coenzyme A which can enter the citric acid cycle INPUT OUTPUT 2 Breakdown of the fuel generates NADH (from glycolysis) (to citric acid cycle)   NAD+ NADH CoA 1 Pyruvic acid loses a carbon as CO2 Breath out Acetic acid 3 Acetic acid attaches to coenzyme A Acetyl CoA Pyruvic acid CO2 Coenzyme A Yield = 2C sugar + CO2 + NADH Figure 6.7 The link between glycolysis and the citric acid cycle: the conversion of pyruvic acid to acetyl CoA

2 Breakdown of the fuel generates NADH NADH NAD+ 1 3 Pyruvic acid
Figure 6.7-2 2 Breakdown of the fuel generates NADH   NADH NAD+ 1 Pyruvic acid loses a carbon as CO2 3 Acetic acid Acetic acid attaches to coenzyme A CO2 Coenzyme A Figure The link between glycolysis and the citric acid cycle: the conversion of pyruvic acid to acetyl CoA (part 2: steps)

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

ATP synthesis by direct phosphate transfer
Phosphate groups can be transferred directly to ADP in a process called substrate-level phosphorylation Enzyme P ADP ATP Substrate: P and ADP P P Figure 6.6 Figure 6.6 ATP synthesis by direct phosphate transfer

Stage 3: THE CITRIC ACID CYCLE
The citric acid cycle (also called the Krebs cycle) extracts the energy of sugar by completing the breaking down of acetic acid molecules all the way down to CO2 uses some of this energy to make ATP and also uses enzymes that are dissolved in the fluid within mitochondria and forms NADH and FADH2 (Flavin Adenine Dinucleotide) Two turns of the cycle are required for each glucose molecule that is being broken down

Stage 3: The citric acid cycle
Acetic acid joins a 4-carbon acceptor molecule to form a 6-carbon product called citric acid (for which the cycle is named) For every acetic acid molecule that enters the cycle as fuel, Two CO2 molecules (release as you breath) exit as a waste product and along the way the citric acid cycle harvests energy from the fuel These energy are used to produce ATP directly The cycle also captures energy in the form of NADH and a second closely related electron carrier, FADH2 All the carbon atoms that entered the cycle as fuel are accounted for as CO2 exhaust, and the 4-carbon acceptor molecule is recycled

Most important things to knows is what goes in and what goes out
INPUT OUTPUT Citric acid Acetic acid 2 CO2 2 ADP  P Citric Acid Cycle ATP 3 NAD 3 NADH FAD FADH2 Acceptor molecule NADH and FADH2 go to the ETC Citric cycle produces large quantities of electron carriers Figure 6.10 The citric acid cycle Acetic acid joins a 4-carbon acceptor molecule to form a 6-carbon product called citric acid Two CO2 molecules exit as a waste product and along the way some energy is released These energy are used to produce ATP directly It also captures energy in the form of NADH and a second closely related electron carrier, FADH2 4-carbon acceptor molecule is recycled

Energy accounting of Krebs cycle
[ ] Net gain = 2 ATP = 8 NADH + 2 FADH2 4 NAD + 1 FAD 4 NADH + 1 FADH2 2x pyruvate          CO2 1 ADP 1 ATP 3C 3x 1C

1 and 2. Glycolysis and the citric acid cycle generate a small amount of ATP directly and much more ATP indirectly, via reactions that transfer electrons from fuel molecules to a molecule called NAD+ (nicotinamide adenine dinucleotide). The electron transfer forms a molecule called NADH, which acts as a shuttle carrying high-energy electrons from one area of the cell to another. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.4 can be especially helpful in providing physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37°C (98–99°F). This is about the same amount of heat generated by a 75-watt incandescent light bulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). Shouldn’t they feel cold? The answer is that 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 help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 200 Calories raises 2 L of water 100°C. (Note: It takes much more energy to melt ice or evaporate water as steam.) 2. 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. 3. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding water back. 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. 4. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under the best conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. Active Lecture Tips 1. As you relate the structure of the inner mitochondrial membrane to its functions, challenge students to explain the adaptive advantage of the many folds of this inner membrane. (These folds greatly increase the surface area available for the associated reactions.) 2. See the activity Cell Respiration: Pair and Share on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. See the activity Demonstration of Electron Transport and ATP Production in Aerobic Respiration Using Students and Balloons on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. Challenge your students to explain why most extra energy in the human body is stored as fat and not sugars or proteins. Have students work with others seated nearby. The general answer is this. The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) as an equivalent mass of protein or carbohydrates (about 4.5 kcal per gram). Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 lb overweight, you would be nearly 40 lb overweight if the same energy were stored as carbohydrates or proteins instead of fat.) 40

Practice Which of these is NOT a product of the citric acid cycle?
A. ATP B. NADH + H+ C. FADH2 D. CO2 E. acetyl CO2 Pyruvate is the end product of the ______ reactions. A) citric acid cycle B) Calvin cycle C) electron transport system D) glycolysis E) preparatory reaction The enzymes of the Krebs cycle are located in the 1. outer membrane of the mitochondria. 2. vesicles of the ER. 3. matrix of the mitochondria. 4. inter-membrane space of mitochondria. 5. cytoplasm.

Stage 3: Electron Transport
The third stage of cellular respiration is electron transport. Electrons captured from food by NADH are stripped of their energy, a little bit at a time, until they are finally combined with oxygen to form water. The proteins and other molecules that make up electron transport chains are embedded within the inner membrane of the mitochondria. Electron transport from NADH to oxygen releases the energy your cells use to make most of their ATP. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.4 can be especially helpful in providing physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37°C (98–99°F). This is about the same amount of heat generated by a 75-watt incandescent light bulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). Shouldn’t they feel cold? The answer is that 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 help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 200 Calories raises 2 L of water 100°C. (Note: It takes much more energy to melt ice or evaporate water as steam.) 2. 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. 3. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding water back. 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. 4. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under the best conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. Active Lecture Tips 1. As you relate the structure of the inner mitochondrial membrane to its functions, challenge students to explain the adaptive advantage of the many folds of this inner membrane. (These folds greatly increase the surface area available for the associated reactions.) 2. See the activity Cell Respiration: Pair and Share on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. See the activity Demonstration of Electron Transport and ATP Production in Aerobic Respiration Using Students and Balloons on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. Challenge your students to explain why most extra energy in the human body is stored as fat and not sugars or proteins. Have students work with others seated nearby. The general answer is this. The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) as an equivalent mass of protein or carbohydrates (about 4.5 kcal per gram). Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 lb overweight, you would be nearly 40 lb overweight if the same energy were stored as carbohydrates or proteins instead of fat.) 42

During cellular respiration, the electrons gathered from food molecules “fall” in a stepwise cascade down an energy staircase, unlocking chemical energy in small amounts, bit by bit, that cells can put to productive use. The transfer of electrons from organic fuel (food) to NAD+ converts it to NADH. The rest of the staircase consists of an electron transport chain. The overall effect of all this transfer of electrons during cellular respiration is a “downward” trip for electrons from glucose, to NADH, to an electron transport chain, and to oxygen Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.4 can be especially helpful in providing physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37°C (98–99°F). This is about the same amount of heat generated by a 75-watt incandescent light bulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). Shouldn’t they feel cold? The answer is that 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 help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 200 Calories raises 2 L of water 100°C. (Note: It takes much more energy to melt ice or evaporate water as steam.) 2. 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. 3. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding water back. 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. 4. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under the best conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. Active Lecture Tips 1. As you relate the structure of the inner mitochondrial membrane to its functions, challenge students to explain the adaptive advantage of the many folds of this inner membrane. (These folds greatly increase the surface area available for the associated reactions.) 2. See the activity Cell Respiration: Pair and Share on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. See the activity Demonstration of Electron Transport and ATP Production in Aerobic Respiration Using Students and Balloons on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. Challenge your students to explain why most extra energy in the human body is stored as fat and not sugars or proteins. Have students work with others seated nearby. The general answer is this. The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) as an equivalent mass of protein or carbohydrates (about 4.5 kcal per gram). Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 lb overweight, you would be nearly 40 lb overweight if the same energy were stored as carbohydrates or proteins instead of fat.) 43

The role of oxygen in harvesting food energy
Figure 6.9 e e Electrons from food NAD+ e– e– NAD+ NADH Stepwise release of energy used to make ATP ATP 2 e   Electron transport chain 2 e 1 O2 2 The role of oxygen in harvesting food energy H2O Hydrogens, electrons, and oxygen combine to form water 2 H+ Figure 6.9 The role of oxygen in harvesting food energy

NADH and FADH2 transfer electrons to ETC Electrons move down (from one e- acceptor to the next & to an over lower energy state) the ETC to the final electron acceptor, Oxygen (magnet pulling e- toward it) The ETC uses the energy released from this electron flow to pump H+ across the inner mitochondrial membrane This produces a H+ gradient, a store of potential energy H+ concentrated on one side of the membrane (create disequilibrium) rushes back ‘downhill’ through ATP synthase (just as water turns the turbines in the dam) The rotation activates parts of the ATP synthase that attach phosphate group to ADP molecules to generate ATP

Figure 6.9-1 Figure The role of oxygen in harvesting food energy (part 1: lifeguard)

Mitochondria The molecules of electron transport chains are built into the inner membranes of mitochondria. Because these membranes are highly folded (inner membrane), their large surface area can accommodate thousands of copies of the electron transport chain, another good example of how biological structure fits function. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism fail to see “the forest for the trees.” Students often focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products, locations, and energy yields associated with glycolysis, the citric acid cycle, and electron transport before detailing the specifics of each reaction. Figure 6.4 can be especially helpful in providing physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37°C (98–99°F). This is about the same amount of heat generated by a 75-watt incandescent light bulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). Shouldn’t they feel cold? The answer is that 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 help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 200 Calories raises 2 L of water 100°C. (Note: It takes much more energy to melt ice or evaporate water as steam.) 2. 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. 3. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding water back. 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. 4. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under the best conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. Active Lecture Tips 1. As you relate the structure of the inner mitochondrial membrane to its functions, challenge students to explain the adaptive advantage of the many folds of this inner membrane. (These folds greatly increase the surface area available for the associated reactions.) 2. See the activity Cell Respiration: Pair and Share on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. See the activity Demonstration of Electron Transport and ATP Production in Aerobic Respiration Using Students and Balloons on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. Challenge your students to explain why most extra energy in the human body is stored as fat and not sugars or proteins. Have students work with others seated nearby. The general answer is this. The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) as an equivalent mass of protein or carbohydrates (about 4.5 kcal per gram). Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 lb overweight, you would be nearly 40 lb overweight if the same energy were stored as carbohydrates or proteins instead of fat.) 47

Mitochondria Outer membrane Inner membrane Cristae Matrix
TEM Inner membrane Cristae Matrix Space between membranes Figure 4.18 Figure 4.18 The mitochondrion: site of cellular respiration

The energy stored by electron transport behaves something like the water behind a dam. There is a tendency for hydrogen ions to gush back to where they are less concentrated, just as there is a tendency for water to flow downhill. The inner membrane temporarily “dams” hydrogen ions. Your mitochondria have structures that act like turbines. Each of these miniature machines, called an ATP synthase, is constructed from proteins built into the inner mitochondrial membrane, next to the proteins of the electron transport chains. Figure 6.10 shows a simplified view of how the energy previously stored in NADH and FADH2 can now be used to generate 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. Figure 6.4 can be especially helpful in providing physical orientation to these cellular processes. 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood in a fireplace or campfire. Pointing out the general similarities can help students comprehend the overall reaction and heat generation associated with both processes. 3. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel can be wasteful, reducing the efficiencies of the systems. Teaching Tips 1. During cellular respiration, our cells convert about 40% of our food energy to useful work. The other 60% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37°C (98–99°F). This is about the same amount of heat generated by a 75-watt incandescent light bulb (depending upon the size of the person). If you choose to include a discussion of heat generated by aerobic metabolism, consider the following: a. Ask your students why they feel warm when it is 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). Shouldn’t they feel cold? The answer is that 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 help us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0 to 100°C. This is something to think about the next time you heat water on the stove! Consider bringing a 2-L bottle as a visual aid, or ten 2-L bottles to make the point above; 200 Calories raises 2 L of water 100°C. (Note: It takes much more energy to melt ice or evaporate water as steam.) 2. 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. 3. The authors developed an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the mitochondrial membranes, like a dam holding water back. 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. 4. Students should be reminded that the ATP yield per glucose molecule of up to 32 ATP is only a potential. The complex chemistry of aerobic metabolism can only yield this amount under the best conditions, when every substrate and enzyme is immediately available. Such circumstances may only rarely occur in a working cell. Active Lecture Tips 1. As you relate the structure of the inner mitochondrial membrane to its functions, challenge students to explain the adaptive advantage of the many folds of this inner membrane. (These folds greatly increase the surface area available for the associated reactions.) 2. See the activity Cell Respiration: Pair and Share on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. See the activity Demonstration of Electron Transport and ATP Production in Aerobic Respiration Using Students and Balloons on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. Challenge your students to explain why most extra energy in the human body is stored as fat and not sugars or proteins. Have students work with others seated nearby. The general answer is this. The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) as an equivalent mass of protein or carbohydrates (about 4.5 kcal per gram). Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 lb overweight, you would be nearly 40 lb overweight if the same energy were stored as carbohydrates or proteins instead of fat.) 49

How electron transport drives ATP synthase machines
Glucose CO2 ETC H2O Space between membranes H+ H+ H+ H+ H+ H+ H+ H+ H+ Electron carrier H+ H+ H+ 3 H+ 5 H+ Protein complex Inner mitochondrial membrane   FADH2 FAD H+ Electron flow 2 1 O2 2 H+ H2O 6 2   4 NADH NAD+ ADP + P ATP 1 H+ H+ H+ H+ H+ Matrix Electron transport chain ATP synthase Figure 6.10 Figure 6.10 How electron transport drives ATP synthase machines

Electron transport chain
Figure a Space between membranes H H+ H+ H+ H+ H+ H+ Electron carrier H+ H+ H+ 3 H+ Protein complex Inner mitochondrial membrane   FADH2 FAD H+ Electron flow 2 1 O2 + 2 H+ 2   4 NADH NAD+ 1 H+ H+ H+ H+ Matrix Electron transport chain Figure a How electron transport drives ATP synthase machines (part 1a: detail, electron transport chain)

5 + 6 4 ATP synthase H+ H+ + H+ H+ H+ H+ O2 2 H+ H2O ADP + P ATP H+ H+
Figure b H+ H+ + H+ H+ H+ 5 H+ 1 O2 + 2 H+ H2O 6 2 4 ADP + P ATP H+ H+ ATP synthase Figure b How electron transport drives ATP synthase machines (part 1b: detail, ATP synthase)

Cyanide is a deadly poison that: binds to one of the protein complexes in the electron transport chain prevents/blocks the passage of electrons to oxygen stops the production of ATP cell stops working and organisms dies

A summary of ATP yield during cellular respiration
Cellular respiration can generate up to 32 molecules of ATP per molecule of glucose. Cytoplasm Mitochondrion       6 NADH 2 NADH 2 NADH   2 FADH2  Glycolysis  2 Acetyl CoA 2 Pyruvic acid Citric Acid Cycle  Glucose Electron Transport Chain Maximum per glucose: 2 ATP 2 ATP About 28 ATP About 32 ATP by direct synthesis by direct synthesis by ATP synthase Figure 6.11 Figure 6.11 A summary of ATP yield during cellular respiration

A summary of ATP yield during cellular respiration
 Glycolysis  2 Acetyl CoA 2 Pyruvic acid Citric Acid Cycle  Glucose Electron Transport Chain 2 ATP 2 ATP About 28 ATP by direct synthesis by direct synthesis by ATP synthase Figure Figure A summary of ATP yield during cellular respiration (part 1: detail)

Practice The final electron acceptor of cellular respiration is _____. water / oxygen / FADH2 / CO2 / NADH A total of _____ ATP molecules are produced per glucose molecule in cellular respiration. A) B) 2 C) 4 D) The preparatory reaction and citric acid cycle are located in the _____ of the mitochondria. A) intramembrane space B) matrix C) cristae D) outer membrane

The Versatility of Cellular Respiration
In addition to glucose, Respiration is a versatile metabolic furnace that can “burn” many other kinds of food molecules such as carbohydrates, fats, and proteins Food Carbohydrates Fats Proteins Sugars Glycerol Fatty acids Amino acids  Citric Acid Cycle Glycolysis Acetyl CoA   Electron Transport Chain ATP Figure 6.12 Figure 6.12 Energy from food

Fermentation in Human muscles
Some of your cells can actually work for short periods without O2 After functioning anaerobically for about 15 seconds: Muscle cells will begin to generate ATP by the process of fermentation Fermentation is the anaerobic (without oxygen) harvest of food energy. It is an abbreviated respiratory process When energy uses outpaces the ability to replenish the oxygen used, fermentation becomes a matter of cellular survival Fermentation rely on glycolysis (anaerobic) to produces 2 ATP for each molecule of glucose broken down to pyruvic acid; then follow a reaction that regenerate NAD+ Although you must breath in O2 to stay alive, Some of your cells can actually work for short periods without oxygen When you walk, your leg muscles require a constant supply of ATP which is generated by cellular respiration. To keep this process going, your blood provide the muscle cells enough O2 . But when you run the cell uses ATP at a rate that outpaces your bloodstream’s delivery of oxygen from the lung to muscle

Animation: Fermentation Overview
© 2016 Pearson Education, Inc.

Fermentation in Human Muscle Cells
To harvest food energy during glycolysis, NAD+ must be present to receive electrons. This is no problem under aerobic conditions, because the cell regenerates NAD+ when NADH drops its electron cargo down electron transport chains to O2. This recycling of NAD+ cannot occur under anaerobic conditions because there is no O2 to accept the electrons. Instead, NADH disposes of electrons by adding them to the pyruvic acid produced by glycolysis (Figure 6.13). This restores NAD+ and keeps glycolysis working. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and perhaps carbon dioxide. Care should be taken to clarify the different possible products of fermentation in lactic acid 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 in which you mix about equal portions of milk (skim or 2%) and 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. Active Lecture Tips 1. See the activity Aerobic Respiration Gives a Cell More “Spending Power” on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 60

FERMENTATION: ANAEROBIC HARVEST OF FOOD ENERGY
Remember Glycolysis (a) does not require oxygen, (b) produces 2 ATP molecules for each glucose broken down to pyruvic acid Pyruvic acid is reduced by NADH, producing NAD+ and a continual supply of NAD+ is required for glycolysis to continue NAD+ accepts electrons from glucose as it is being broken down and is converted to NADH Under aerobic conditions, NAD+ can be recycled when NADH delivers the electrons to the electron transport chain (ETC) But what happens when there is no oxygen (anaerobic), hence no ETC? Although you must breath in O2 to stay alive, Some of your cells can actually work for short periods without oxygen When you walk, your leg muscles require a constant supply of ATP which is generated by cellular respiration. To keep this process going, your blood provide the muscle cells enough O2 . But when you run the cell uses ATP at a rate that outpaces your bloodstream’s delivery of oxygen from the lung to muscle

Fermentation: Producing lactic acid
Under anaerobic conditions, the NAD+ is regenerated when NADH transfers the electrons it removed from glucose to pyruvic acid, producing a waste product, lactic acid and regenerating NAD+ INPUT OUTPUT INPUT 2 ADP 2 ATP  2 P Glycolysis     2 NAD+ 2 NADH 2 NADH 2 NAD+ 2 pyruvic acid  2 H+ 2 lactic acid Glucose Figure 6.13 Figure 6.13 Fermentation: producing lactic acid

Fermentation in Human Muscle Cells
The addition of electrons to pyruvic acid produces a waste product called lactic acid. The lactic acid by-product is eventually transported to the liver, where liver cells convert it back to pyruvic acid. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and perhaps carbon dioxide. Care should be taken to clarify the different possible products of fermentation in lactic acid 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 in which you mix about equal portions of milk (skim or 2%) and 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. Active Lecture Tips 1. See the activity Aerobic Respiration Gives a Cell More “Spending Power” on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 63

Fermentation in Microorganisms
Fermentation alone is enough to sustain many microorganisms. The lactic acid produced by yeast using lactic acid fermentation is used to produce cheese, sour cream, and yogurt, soy sauce, pickles, cabbage, and olives, and sausage meat products. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and perhaps carbon dioxide. Care should be taken to clarify the different possible products of fermentation in lactic acid 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 in which you mix about equal portions of milk (skim or 2%) and 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. Active Lecture Tips 1. See the activity Aerobic Respiration Gives a Cell More “Spending Power” on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 64

Fermentation in Microorganisms
Yeast is capable of cellular respiration and fermentation and can perform alcoholic fermentation to produce CO2 and ethyl alcohol instead of lactic acid. For thousands of years, people have put yeast to work producing alcoholic beverages such as beer and wine. As every baker knows, the CO2 bubbles from fermenting yeast also cause bread dough to rise. Alcoholic fermentation is used to produce: Beer, Wine, Breads © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and perhaps carbon dioxide. Care should be taken to clarify the different possible products of fermentation in lactic acid 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 in which you mix about equal portions of milk (skim or 2%) and 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. Active Lecture Tips 1. See the activity Aerobic Respiration Gives a Cell More “Spending Power” on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 65

Fermentation: Producing ethyl alcohol
INPUT OUTPUT 2 ADP 2 ATP  2 P P 2 CO2 released Glycolysis     2 NAD+ 2 NADH 2 NADH 2 NAD+ 2 Ethyl alcohol 2 pyruvic acid  2 H+ Glucose Figure 6.15 Figure 6.15 Fermentation: producing ethyl alcohol

INPUT OUTPUT 2 Ethyl alcohol Glucose Figure 6.15-1
Figure Fermentation: producing ethyl alcohol (part 1: input and output)

Evolution Connection: The Importance of Oxygen
Aerobic and anaerobic respiration start with glycolysis, the splitting of glucose to form pyruvic acid. Glycolysis is thus the universal energy-harvesting process of life. The role of glycolysis in both respiration and fermentation has an evolutionary basis. Between 3.5 and 2.7 billion years ago, before significant levels of oxygen were present in Earth’s atmosphere, ancient prokaryotes probably used glycolysis to make ATP and generated ATP exclusively from glycolysis. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and perhaps carbon dioxide. Care should be taken to clarify the different possible products of fermentation in lactic acid 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 in which you mix about equal portions of milk (skim or 2%) and 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. Active Lecture Tips 1. See the activity Aerobic Respiration Gives a Cell More “Spending Power” on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 68

First eukaryotic organisms 2.2
Figure 6.16 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 6.16 A time line of oxygen and life on Earth

Evolution Connection: The Importance of Oxygen
The fact that glycolysis occurs in almost all organisms suggests that it evolved very early in ancestors common to all the domains of life. The location of glycolysis within the cell also implies great antiquity. The pathway does not require any of the membrane-enclosed organelles of the eukaryotic cell, which evolved more than a billion years after the prokaryotic cell. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and perhaps carbon dioxide. Care should be taken to clarify the different possible products of fermentation in lactic acid 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 in which you mix about equal portions of milk (skim or 2%) and 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. Active Lecture Tips 1. See the activity Aerobic Respiration Gives a Cell More “Spending Power” on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 70

 Citric Acid  Glycolysis Cycle     ATP ATP ATP Electron
Figure 6.UN01  Citric Acid Cycle  Glycolysis     Electron Transport Chain ATP ATP ATP Figure 6.UN01 In-text figure, glycolysis, p. 96

Summary of cellular respiration
C6H12O6 6O2 6CO2 6H2O ~36 ATP  + Where did the glucose come from? Where did the O2 come from? Where did the CO2 come from? Where did the H2O come from? Where did the ATP come from? What else is produced that is not listed in this equation? Why do we breathe? Where did the glucose come from? from food eaten Where did the O2 come from? breathed in Where did the CO2 come from? oxidized carbons cleaved off of the sugars Where did the H2O come from? from O2 after it accepts electrons in ETC Where did the ATP come from? mostly from ETC What else is produced that is not listed in this equation? NAD, FAD, heat!

Practice Most of the carbon dioxide you exhale is released during
1. the Krebs cycle. 2. lactate fermentation. 3. glycolysis. 4. electron transfer phosphorylation. 5. alcoholic fermentation.

Practice In cellular respiration, most ATP molecules are produced by _____. A. photophosphorylation B. substrate-level phosphorylation C. cellular respiration D. oxidative phosphorylation E. Photosynthesis Which pathway for aerobic cellular respiration is located in the cytoplasm of the cell? A) glycolysis B) citric cycle C) electron transport system D) preparatory reaction E) Calvin cycle

Practice The carriers for the electron transport system are located ______. A) within the cytoplasm of a cell B) on the cristae of mitochondria C) within the matrix of mitochondria D) within the Golgi apparatus E) within the stroma of chloroplasts Which pathway will result in the production of four carbon dioxide molecules, two ATP molecules, NADH2 and FADH2? A) glycolysis B) preparatory reaction C) citric acid cycle D) Calvin cycle E) electron transport system

Practice Which molecule is the final acceptor of electrons at the end of the electron transport system in aerobic cellular respiration? A) oxygen B) carbon dioxide C) lactate D) citrate E) pyruvate Which of the following overall equations represents aerobic cellular respiration? A) C6H12O > 2 pyruvate + 2 ATP B) 6 CO2 + 6 H2O + energy -----> C6H12O6 + 6 O2 C) C6H12O6 + 6 O > 6 CO2 + 6 H2O + energy D) C6H12O > 2 lactate + 2 ATP E) C6H12O > 2 alcohol + 2 CO2 + 2 ATP

Practice Which of the following pathways and reactions will result in the production of the most ATP molecules during aerobic cellular respiration of one glucose molecule? A) glycolysis B) preparatory reaction C) citric acid cycle D) electron transport system E) fermentation Where do the final steps of aerobic cellular respiration occur? 1. along the endoplasmic reticulum 2. inside the mitochondria 3. throughout the cytoplasm 4. on the surface of the ribosomes

Practice Which end product of respiration is of the greatest benefit to organism? 1. carbon dioxide 2. glucose 3. ATP molecules 4. water molecules

Practice ATP is 1. a short-term energy-storage compound.
2. All of these 3. the molecule all living cells rely on to do work. 4. synthesized within mitochondria. 5. the cell’s principal compound for energy transfers.

Practice Which of the following describes the fate of oxygen utilized directly during cellular respiration? 1. the citric acid cycle 2. glycolysis 3. accepting electrons at the end of the electron transport chain 4. the oxidation of pyruvate to acetyl CoA 5. the phosphorylation of ADP

Practice The oxygen utilized in cellular respiration finally shows up as 1. new O2. 2. H2O. 3. part of a sugar. 4. CO2. 5. ATP.

Practice The outputs of oxidative phosphorylation include ATP, , and
1. water, NADH and FADH2 2. water, NAD+ and FAD 3. O2, ADP, Pi 4. free electrons and protons 5. carbon dioxide, NAD+ and FAD

Practice When you inhale, you are taking in oxygen for aerobic respiration. During which stage of aerobic respiration is oxygen necessary? 1. Krebs cycle and electron transport phosphorylation 2. electron transport phosphorylation 3. Glycolysis and electron transport phosphorylation 4. Krebs cycle 5. glycolysis

Challenge Question 1. If the Citric acid cycle does not require oxygen, why does cellular respiration stop after glycolysis when no oxygen is present? 2. Where is each of the reactants used in the overall process? Where do the reactants come from? Where is each of the products produced in the overall process? d. What is the fate if each of the products? C6H12O O ® CO H2O Energy

Citric Acid Cycle  Glycolysis   ATP ATP ATP Electron
Figure 6.UN02 Citric Acid Cycle  Glycolysis   Electron Transport Chain ATP ATP ATP Figure 6.UN02 In-text figure, citric acid cycle, p. 97

Citric Acid  Glycolysis Cycle   ATP ATP ATP Electron
Figure 6.UN03 Citric Acid Cycle Glycolysis    Electron Transport Chain ATP ATP ATP Figure 6.UN03 In-text figure, electron transport chain, p. 98

Heat C6H12O6 Sunlight O2 ATP Cellular Photosynthesis respiration H2O
Figure 6.UN04 Heat C6H12O6 Sunlight O2 ATP Cellular respiration Photosynthesis CO2 H2O Figure 6.UN04 Summary of key concepts: chemical cycling

Mitochondrion O2       6 NADH 2 NADH 2 NADH   2 FADH2
Figure 6.UN06 Mitochondrion O2       6 NADH 2 NADH 2 NADH   2 FADH2 Glycolysis2 2 Acetyl CoA Citric Acid Cycle  Glucose Pyruvic acid   Electron Transport Chain 2 CO2 4 CO2 H2O 2 ATP 2 ATP by direct synthesis by direct synthesis by ATP synthase About 28 ATP About 32 ATP Figure 6.UN06 Summary of key concepts: cellular respiration results

BMR by weight 2100 2050 2000 1950 1900 BMR (calories) 1850 1800 1750
Figure 6.UN07 BMR by weight 2100 2050 2000 1950 1900 BMR (calories) 1850 1800 1750 1700 1650 1600 150 160 170 180 190 200 210 220 230 240 250 Pounds Figure 6.UN07 Process of science, question 12 (BMR)

The Process of Science: What Causes 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: Researchers tested frog muscles under conditions when lactic acid could and could not diffuse away from the muscle tissue. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and perhaps carbon dioxide. Care should be taken to clarify the different possible products of fermentation in lactic acid 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 in which you mix about equal portions of milk (skim or 2%) and 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. Active Lecture Tips 1. See the activity Aerobic Respiration Gives a Cell More “Spending Power” on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 90

Results: When lactic acid was allowed to diffuse away, performance improved significantly. Conclusion: The buildup of lactic acid is the primary cause of muscle failure under anaerobic conditions. However, recent evidence suggests that the role of lactic acid in muscle function remains unclear. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and perhaps carbon dioxide. Care should be taken to clarify the different possible products of fermentation in lactic acid 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 in which you mix about equal portions of milk (skim or 2%) and 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. Active Lecture Tips 1. See the activity Aerobic Respiration Gives a Cell More “Spending Power” on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 91

diffusion of lactic acid diffusion of lactic acid;
Figure 6.14 Battery Battery     Force measured Force measured Frog muscle stimulated by electric current Solution prevents diffusion of lactic acid Solution allows diffusion of lactic acid; muscle can work for twice as long Figure 6.14 A. V. Hill’s 1929 apparatus for measuring muscle fatigue

Evidence began to accumulate that contradicted Hill’s results. The effect that Hill demonstrated did not appear to occur at human body temperature. Further, certain individuals who are unable to accumulate lactic acid have muscles that fatigue more rapidly, the opposite of what is expected. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and perhaps carbon dioxide. Care should be taken to clarify the different possible products of fermentation in lactic acid 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 in which you mix about equal portions of milk (skim or 2%) and 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. Active Lecture Tips 1. See the activity Aerobic Respiration Gives a Cell More “Spending Power” on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 93

Recent research indicates that increased levels of other ions may be to blame. The role of lactic acid in muscle fatigue remains a hotly debated topic. Science is dynamic and subject to constant adjustment as new evidence is uncovered. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Some students might expect that fermentation produces alcohol and perhaps carbon dioxide. Care should be taken to clarify the different possible products of fermentation in lactic acid 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 in which you mix about equal portions of milk (skim or 2%) and 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. Active Lecture Tips 1. See the activity Aerobic Respiration Gives a Cell More “Spending Power” on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 94

Cellular Respiration: Obtaining Energy from Food

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