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mad17743_ch07.qxd 3/9/06 3:44 PM Page 53 7 ENERGY FOR CELLS CHAPTER REVIEW Cellular respiration is the breakdown of glucose and other metabolites, along with the capture of energy for the buildup of ATP molecules. Of four phases, only one occurs outside the mitochondria. This chapter considers each phase of cellular respiration in some detail. It also considers fermentation, which provides a burst of ATP when oxygen is not available. Fermentation cannot occur long term because it leads to cramping and a lower pH than normal. CHAPTER KEY TERMS After studying the key terms of this chapter, match the phrases below with the alphabetized list of terms. acetyl-CoA glycolysis citric acid cycle intermembrane space electron transport chain oxygen deficit fermentation preparatory (prep) reaction a. space between the outer and inner membrane of a mitochondrion _______________________ b. passage of electrons from one carrier to the next with the capture of energy for ATP production _______________________ c. produces acetyl groups, which enter the citric acid cycle _______________________ d. series of reactions that begin and end with the same molecule; releases carbon dioxide _______________________ e. breakdown of glucose to two pyruvic acid molecules _______________________ f. molecule that transports acetyl groups to the citric acid cycle _______________________ g. breakdown of glucose to lactic acid (or alcohol and CO 2 ) _______________________ h. metabolic state in need of oxygen to restore homeostatic conditions in cells _______________________ 53 mad17743_ch07.qxd 3/16/06 8:26 AM Page 54 S T U DY E X E R C I S E S Study the text section by section as you answer the questions that follow. 7.1 CELLULAR RESPIRATION (PP. 98–99) • The breakdown of glucose to CO 2 and H 2 O during cellular respiration drives the synthesis of ATP. • The complete breakdown of glucose requires four phases: three metabolic pathways and one individual enzymatic reaction. 1. Study the overall equation for cellular respiration and then answer the questions: C6H12O6 glucose + 6 O2 6 CO2 + 6 H2O + energy a. What are the reactants for cellular respiration? _____________________________________________________ b. How do your cells acquire these reactants? ________________________________________________________ c. How does your body rid itself of the end products of cellular respiration? _____________________________ d. What is the purpose of cellular respiration? ________________________________________________________ e. What form of energy do cells use? ________________________________________________________________ 2. From the list of terms on page 53, list the four phases of cellular respiration which are a-d in the diagram: a. _______________________________________________________________________________________________ b. _______________________________________________________________________________________________ c. _______________________________________________________________________________________________ d. _______________________________________________________________________________________________ Cytoplasm e– glucose pyruvate b. a. c. ATP d. ATP ATP 3. Cellular respiration results in 38 ATP. Glycolysis and the citric acid cycle produce 2 ATP per glucose molecule: a. Write the number of ATP produced next to the ATP bursts in the diagram above. b. Which phase of cellular respiration accounts for most of the ATP produced? __________________________ 7.2 OUTSIDE THE MITOCHONDRIA: GLYCOLYSIS(P. 101) • Glycolysis is a metabolic pathway that partially breaks down glucose outside the mitochondria. 4. a. Where does glycolysis occur? ______________ b. Does it require oxygen? ______________ c. Glycolysis begins with ______________. d. Glycolysis ends with ______________. 54 mad17743_ch07.qxd 3/9/06 3:44 PM Page 55 e. How many ATP are produced per glucose molecule as a direct result of glycolysis? ______________ f. What coenzyme carries out oxidation of substrates during glycolysis? ______________ g. Considering your answers to these questions, what is the output of glycolysis? ______________, ______________, and ______________. 7.3 INSIDE THE MITOCHONDRIA (PP. 102–106) • The preparatory reaction and the citric acid cycle, which occur inside the mitochondria, continue the breakdown of glucose products until carbon dioxide and water result. • The electron transport chain, which receives electrons from NADH and FADH 2 , produces most of the ATP during cellular respiration. • Other nutrients in addition to glucose can be broken down to drive ATP synthesis. 5. Label the following diagram of a mitochondrion using the terms: cristae inner membrane intermembrane space matrix outer membrane a. b. c. d. e. 6. Using three of your labels from question 5, where does each of the following processes occur? a. glycolysis ______________ b. citric acid cycle ______________ c. electron transport chain ______________ 7. a. The citric acid cycle begins and ends with what molecule? ______________ b. A two-carbon molecule acetyl group enters the citric acid cycle. What gas leaves the citric acid cycle? ______________ c. How many ATP are produced per glucose molecule as a direct result of the citric acid cycle? _____________ d. What coenzymes carry out oxidation of substrates in the citric acid cycle? ______________ e. Considering your answers to these questions, what are the outputs of the citric acid cycle? ______________, ______________, ______________, and ______________ The Electron Transport Chain ( PP . 104–105) 8. What coenzymes bring hydrogen atoms (H + + e – ) to the electron transport chain? a. ______________ What happens to the electrons? b. ______________ What happens to the hydrogen ions? c. ______________ What molecule is the final acceptor of electrons from the electron transport chain? d. ______________ Each pair of electrons carried by NADH from the citric acid cycle that passes down the electron transport chain accounts for the buildup of how many ATP? e. ______________ 55 mad17743_ch07.qxd 3/9/06 3:44 PM Page 56 9. As a result of electron transport chain activity, H + build up in the a. ______________ flow b. ______________ their concentration gradient into the matrix, ADP + P . space. When these H + c. ______________ is produced from Energy Yield from Glucose Metabolism ( P . 106) 10. After studying the following calculation of the ATP yield per glucose molecule, answer the questions: Phase NADH FADH2 ATP Yield Glycolysis 2 – 2 Prep reaction 2 – – Citric acid cycle 6 2 2 2 30 4 Electron transport chain 10 Total ATP 38 a. What is the only phase of cellular respiration that doesn’t produce some ATP directly? _________________ b. The formation of what reduced coenzyme accounts for most of the ATP production during cellular respiration? ____________________________________________________________________________________ Alternative Metabolic Pathways ( P . 106) Study the diagram and then answer these questions. 11. The carbon skeleton of amino acids can be respired if the amino acid first undergoes _________________________. 12. When fats are respired, glycerol enters a. ______________, fatty acids are converted to the molecule b. ______________, and the acetyl group enters the citric acid cycle. Proteins Carbohydrates amino acids glucose Fats and oils 13. Explain why the consumption of carbohydrates makes us fat. _________________________________ glycerol ______________________________________________ NH3 Glycolysis ATP pyruvate Acetyl-CoA Citric acid cycle ATP ATP Electron transport chain H 2O O2 56 fatty acids mad17743_ch07.qxd 3/9/06 3:44 PM Page 57 7.4 FERMENTATION (P. 107) • Fermentation is a metabolic pathway that partially breaks down glucose under anaerobic conditions. 14. a. What happens to pyruvate during fermentation in humans? _______________________________________________ b. Why is fermentation wasteful? __________________________________________________________________________ c. What is its advantage? __________________________________________________________________________________ d. What is oxygen deficit in humans? _______________________________________________________________________ glucose NAD+ I NADH DH II acetyl group III + D NA NA DH NA D+ pyruvate NA 15. Label the following processes I, II, and/or III, based on this diagram: a. occurs under anaerobic conditions b. fermentation c. glycolysis d. prep reaction e. occurs in cytoplasm f. occurs in mitochondria lactate Concerning microorganisms and fermentation, answer the following questions. 16. a. What happens to pyruvate during fermentation in yeast? __________________________________________________ b. When yeast is used to leaven bread, what makes the bread rise? __________________________________________ c. When yeast is used to ferment grapes, which end product of fermentation is desired? _____________________ 17. Considering your answers to the questions about fermentation, what are the outputs of fermentation? In humans, a. ________________________, and b. ________________________ . In yeasts, c. ________________________, and d. ________________________. 57 mad17743_ch07.qxd 3/9/06 3:44 PM Page 58 K E Y WO R D C RO S S WO R D Review key terms by completing this crossword puzzle using the following alphabetized list of terms: 1 2 3 4 5 6 acetyl-CoA citric acid cycle coenzyme A electron transport fermentation glycolysis intermembrane space oxygen deficit 7 8 – Across 1 occurs between the outer and inner membrane of a mitochondrion (two words) 4 molecule that carries acetyl group to the citric acid cycle 5 anaerobic breakdown of glucose that results in two ATP and products such as alcohol and lactate 8 pathway of metabolism converting glucose to pyruvate; resulting in a net gain of two ATP and two NADH molecules 58 Down 2 type of chain whereby electrons are passed along a series of carrier molecules, storing energy for the synthesis of ATP (two words) 3 reactions in mitochondria that connect acetyl groups to carbon dioxide (three words) 6 molecule made up of an acetyl group attached to coenzyme A (two words) 7 occurs due to fermentation that results in lactate buildup (two words) mad17743_ch07.qxd 3/9/06 3:44 PM Page 59 CHAPTER TEST OBJECTIVE QUESTIONS Do not refer to the text when taking this test. 1. Fermentation is a. glycolysis and the citric acid cycle. b. glycolysis and the reduction of pyruvate. c. glycolysis only. d. the reduction of pyruvate only. 2. Each of the following is a product of cellular respiration EXCEPT a. ATP. b. carbon dioxide. c. oxygen. d. water. 3. Per glucose molecule, the net gain of ATP molecules from glycolysis per substrate phosphor– ylation is a. two. b. four. c. six. d. eight. 4. Fermentation supplies a. glycolysis with free NAD + . b. hydrogen to the prep reaction. c. oxygen as an electron acceptor. d. the citric acid cycle with oxygen. 5. Which is NOT an event of the prep reaction? a. breaks down pyruvate b. converts a citric acid molecule c. oxidizes pyruvate d. transfers an acetyl group 6. Select the incorrect association. a. electron transport chain—cristae b. fermentation—plasma membrane c. glycolysis—cytoplasm d. citric acid cycle—matrix 7. Select the process with the greatest yield of NADH per glucose molecule. a. glycolysis b. citric acid cycle c. substrate-level phosphorylation d. prep reaction 8. Which of the following do not result in NADH? a. glycolysis b. citric acid cycle c. electron transport chain d. prep reaction e. fermentation 9. The coenzyme that carries acetyl groups is a. ATP. b. NAD + . c. NADH. d. coenzyme A. e. RuBP. 10. The carbon dioxide given off by cellular respiration is produced by a. glycolysis. b. the prep reaction. c. the citric acid cycle. d. the electron transport chain. e. Both b and c are correct. 11. The final acceptor for electrons in cellular respiration is a. ATP. b. NAD + . c. FAD. d. oxygen. e. carbon dioxide. 12. Which of the following reactions occurs in the cristae of the mitochondria? a. the citric acid cycle b. the prep reaction c. the electron transport chain d. glycolysis e. the Calvin cycle 13. The coenzymes NAD + and FAD carry hydrogen atoms (H + + e – ) to the a. glycolysis reactions. b. prep reaction. c. citric acid cycle. d. Calvin cycle. e. electron transport chain. 14. Which of the following statements is NOT true about fermentation? a. It is an anaerobic process. b. The products are toxic to cells. c. It results in two ATPs per glucose molecule. d. In the absence of O 2 , muscle cells form CO 2 and alcohol. e. It can be used to make bread rise. 59 mad17743_ch07.qxd 3/9/06 3:44 PM Page 60 CRITICAL THINKING QUESTIONS The introduction to this chapter is about weight loss and cellular respiration. 15. Which section in the chapter discusses how you can gain weight regardless of the particular type of food you eat? ________________________________________________________________________________________________________ 16. Suppose your diet consisted of nothing but fruits, but at the end of the week, you consumed many more calories than usual. Would you gain weight? ________________________________________________________________ Explain. ____________________________________________________________________________________________________ 17. Why does exercise help you lose weight? ___________________________________________________________________ 18. Which organelle is working overtime when we exercise? ____________________________________________________ 19. What gas does mitochondria need to break down nutrient molecules and where does this gas come from? _____ ____________________________________________________________________________________________________________ 20. What do mitochondria specifically do with oxygen? _________________________________________________________ Test Results: ______ number correct ÷ 20 = ______ × 100 = ______ % EXPLORING THE INTERNET ARIS, the Essentials of Biology website: http://www.mhhe.com/maderessentials ARIS, the website for Essentials of Biology, offers access to a wide variety of tools to help students learn biological concepts and to reinforce their knowledge. Online study aids such as practice quizzes, interactive activities, animations, labeling exercises, flashcards, and much more are organized according to the major sections of each chapter. There is even an online tutorial service! ANSWER KEY CHAPTER KEY TERMS a. intermembrane space b. electron transport chain c. preparatory (prep) reaction d. citric acid cycle e. glycolysis f. acetyl-CoA g. fermentation h. oxygen deficit STUDY EXERCISES 1. a. glucose and oxygen b. Glucose is in the food we eat and oxygen is in the air we breathe. c. Breathing out CO 2 and urination rids the body of excess water. d. to acquire chemical energy in a form cells can use e. ATP molecules 2. a. glycolysis b. preparatory reaction c. citric acid cycle d. electron transport chain 3. a. 2, 2, 34 b. electron transport chain 4. a. cytoplasm b. no c. glucose d. pyruvate e. two ATP f. NAD g. pyruvate, NADPH, ATP 5. a. cristae b. matrix c. outer membrane d. intermembrane space e. inner membrane f. cytoplasm 6. a. cytoplasm b. matrix c. cristae 7. a. citrate b. CO 2 c. two ATP d. NAD and FAD e. NADH, FADH 2 , ATP, and CO 2 8. a. NADH and FADH 2 b. pass down the system c. pumped into intermembrane space d. O 2 e. three ATP 9. a. intermembrane b. down c. ATP 10. a. prep reaction b. NADH 11. removal of amino groups 12. a. glycolysis b. acetylCoA 13. Carbohydrates are metabolized to glycerol 60 and fatty acids, which join to form fat. 14. a. reduced to lactate b. produces only two ATP c. does not require oxygen d. O 2 needed to metabolize lactate 15. a. I and III b. I and III c. I d. II e. I and III f. II 16. a. reduced to alcohol and CO 2 b. release of CO 2 c. alcohol 17. a. two lactate b. two ATP net c. two alcohol d. two CO 2 and two ATP net KEYWORD CROSSWORD 1 I N T 2 E R M E M B R A N E S P L 4 C O E N Z Y M E E R R I M E N T 6 A O C N E T I O T 8 G L Y L C N 7 T R C T A T F 3 I C 5 A C O L O A X C Y G S I S I D A – E N C N C S O P A D C Y O E L R F E T I C I T E mad17743_ch07.qxd 3/9/06 3:44 PM Page 61 CHAPTER TEST 1. b 2. c 3. a 4. a 5. b 6. b 7. b 8. c 9. d 10. e 11. d 12. c 13. e 14. d 15. alternative metabolic pathways 16. yes, because all nutrient molecules in excess can be converted to fat 17. You need more ATP molecules to perform exercise, and your body breaks down many more nutrients to build up the number of ATP molecules needed. 18. mitochondrion 19. We breathe in oxygen from the atmosphere; oxygen was put there by plants. 20. Oxygen is the final acceptor for electrons at the end of the electron transport chain. 61