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I, Name tE. Class Date ha~pter~Lc~iiiiiariespiration I Summary 9—i Chemical Pathways Food serves as the source ofenergy for cells. Quite a lot of energy is stored in food. For instance, I gram of the sugar glucose releases 3811 calories ofheat energy when burned in the presence of oxygen. A calorie is the amount of energy needed to raise the temperature of I gram ofwater 1 degree Celsius. Cells don’t burn glucose and other food compounds. They gradually release the energy. The process begins with a pathway called glycolysis. In the presence of oxygen, glycolysis is followed by the Krebs cycle and the electron transport chain. Together, these three pathways make up cellular respiration. Cellular respiration is the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen. The equation for cellular respiration is: :11: p 13:E S. I S. I I, I. During fermentation, cells convert NADH back into the electron carrier NAD~,which is needed for glycolysis. This action allows glycolysis to continue producing a steady supply ofATE The two main types of fermentation are alcoholic fermentation and lactic acid fermentation. Yeasts and a few other microorganisms carry out alcoholic fermentation. The equation for alcoholic fermentation after glycolysis is: pyrnvic + NADH acid .~ alcohol + CO2 + NAD~ Lactic acid fermentation occurs in your muscles during rapid exercise. The equation for lactic acid fermentation after glycolysis is: pyruvic acid + NADH —‘ lactic acid + NAD~ C6H1,06 —‘ 6W2 + 6H20 + Energy oxygen + glucose carbon + water + energy dioxide 602 + C ~2 bt ‘C There are three main stages of cellular respiration: (1) glycolysis, (2) the Krebs cycle, and (3) electron transport. Clycolysis is the process in which one molecule of glucose is broken in half, producing two molecules of pyruvic acid, a 3carbon compound. Through glycolysis, the cell gains 2 ATP molecules. In one of the reactions of glycolysis, the electron carrier NAD4 accepts a pair of high-energy electrons, producing NADH. By doing this, NAD~helps pass energy from glucose to other pathways in the cell. When oxygen is not present, glycolysis is followed by another pathway. This pathway is called fermentation. Fermentation releases energy from food molecules by producing ATP. Because fermentation does not require oxygen, it is said to be anaerobic. 9-2 The Krebs Cycle and Electron Transport When oxygen is available, glycolysis is followed by the Krebs cycle and the electron transport chain. The three pathways together make up the process ofcellular respiration. Because the pathways of cellular respiration require oxygen, they are said to be aerobic. The Krebs cycle is the second stage of cellular respiration. In eukaryotes, the Krebs cycle takes place in the mitochondrion. During the Krebs cycle, pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions. The Krebs cycle is also known as the citric acid cycle, because citric acid is one of the first products. Reading and Study Workbook 95 Name Class The ICrebs cycle begins when pyruvic acid produced by glycolysis enters the mitochondrion. One carbon atom from pyruvic acid becomes part of a molecule of carbon dioxide, which is eventually released into the air. The carbon dioxide released during the Krebs cycle is the source of much of the carbon dioxide in air. The other two carbon atoms from pyruvic acid are used in a series of reactions. During these reactions, two energy carriers accept high-energy electrons. NAD~is changed to NADH, and FAD is changed to FADH2. These molecules carry the high-energy electrons to the electron transport chain. Electron transport is the third stage of cellular respiration. The electron transport chain uses the high-energy electrons from the Krebs cycle to convert ADP into ATE In eukaryotes, the electron transport chain is composed of a series of carrier proteins located in the inner membrane ofthe mitochondrion. In prokaryotes, the same chain is in the cell membrane. In this pathway, high-energy electrons move from one carrier protein to the next. Their energy is used to move hydrogen ions across the membrane through a protein sphere called ATP synthase. Each time an ATP synthase spins, a phosphate group is added to an ADP molecule, producing an ATP molecule. Date In the absence ofoxygen, all the energy that a cell can extract from a single molecule of glucose is 2 ATP molecules—the product of glycolysis. In the presence of oxygen, though, the cell can extract many more ATP molecules. The Krebs cycle and the electron transport chain enable the cell to produce 34 more ATP molecules per glucose molecule. The total, then, for cellular respiration (glycolysis plus the Krebs cycle plus electron transport) is 36 ATP molecules per glucose molecule. Human body cells normally contain small amounts of ATP produced during cellular respiration. When the body needs energy in a hurry, muscle cells produce ATP by lactic acid fermentation. For long-term energy needs, the body must use cellular respiration. The energy flows in photosynthesis and cellular respiration take place in opposite directions. On a global level, photosynthesis and cellular respiration are also opposites. Photosynthesis removes carbon dioxide from the atmosphere and puts back oxygen. Cellular respiration removes oxygen from the atmosphere and puts back carbon dioxide. 0 i) ~1 Ct C rt C n C C 0, 0) 0 -t C, C n 0 96 Chapter 9 Name Chapter 9 Class Date Cellular Respiration Section 9—1 Chemical Pathways 0 Key Concepts (pages 221-225) • What is cellular respiration? • What happens during the process of glycolysis? • What are the two main types of fermentation? Chemical Energy and Food 1. What is a calorie? (page 221) _______________ 2. How many calories make up 1 Calorie? 3. Cellular respiration begins with a pathway called 4. Is the following sentence true or false? Glycolysis releases a great amount of energy. ___________________ — Overview of Cellular (pageon 222) 7. Label the three main stagesRespiration of cellular respiration the illustration ofthe complete 5. What is cellular respiration? 6. What is the equation for cellular respiration, using chemical formulas? 0) U C C) process. C C Co ICt 0) ci) ‘U ‘C CO ‘C C) C C~ucose C i3 t Reading and Study Workbook 97 Name Class Date 8. What would be the problem if cellular respiration took place in just one step? 9. Where does glycolysis take place? 10. Where do the Krebs cycle and electron transport take place? Glycolysis (page 223) 11. What is glycolysis? 12. How does the cell get glycolysis going? 13. If the cell uses 2 ATP molecules at the beginning of glycolysis, how does it end up with a net gain of 2 ATP molecules? 0 14. What is NAD~? 15. ~— What is the function of NAD~in glycolysis? C- CE ~2 C SE 16. Why can glycolysis supply energy to cells when oxygen is not available? ____________ 17. What problem does a cell have when it generates large amounts of ATP from glycolysis? Fermentation (pages 224—225) 18. What is fermentation? 98 Chapter 9 iwu ))DflU)~1~t)C)SiC~C,-~se ~lrnqsqqnd CI P 1 ~t IS “Del ‘UO!iPDi1P~uosleaJ © nglsPcl onPrenticeHall. ‘<I CCMC- Ct~” C,Ct~~ ~ a C)-4•Ct = ~ C,0) ~ C- 0 CD 0) C- C ~ — ~ ?c. =~‘a C-CM~C) — C-CDCM ~ ~.1 Ct CtC ~ Ct C aQ C. s” C Ct C~C C ~QC~ ~ Ct ct_I CD CCS CS a CM C C- .CM Ct aqC) — CC ~Ct = C = Ct ~ Ct CC ~ C C, C-OIC C C, — — — — C I C- CM C, C- — C — Ct ~ Ct~ t C, .-r a~ C- ~ — C-G~ C “‘ C, CD C C, CM Ct 2-0-C ~‘ ~ C, C a C C) Ct ~ta 0-’~~Ct= ~ ~ — “’~C-C- CC) C CD — C — I — ~ — C ~ -~ rr = r’t’ —— Ct ~4OX CC~ Ct F C- ~ a~ E CM C-t C t C- —. Ct ~ C = C- C- CC-C-C) ~, C’ C- =cj C- C) C C = -u CM N —. C ~ C’, 9~ 1 2 SCD a C C— .,~ C- SC C = a n C, Ct C) C C C, C — C- “’“ —. ,~ — C C C CCt cc — 8 -. CM = 2. C) C- C— ~‘ CM Ct ~ 0- Ct CM CC C ECM ““Ct C, a C- Cl) Ct C- C- — aC’ —. C) Ct 0C C) CD a C, ECt C 2 C C C- ~ C C 0-CM a2. -~ s E. C — C— Ct — C- C, Ct C C —~ p C = C x cc a C) ~ fl ,-.“ C- 0 Ct C — C- C- — CD ~i SC, a CC- ~. CM a= C’C) 1 2 Z C- VP CM C -4, C It C, CM CM ‘.< a C—. C CD — C- CM Ct C C’ C — 0 ~. S Ct C — C- ~ r- C Ct Name Class Date Section 9-2 The Krebs Cycle and Electron Transport (pages 226-232) 0 Key Concepts • What happens during the Krebs cycle? • How are high-energy electrons used by the electron transport chain? Introduction (page 226) 1. At the end of glycolysis, how much of the chemical energy in glucose is still unused? 2. Because the final stages of cellular respiration require oxygen, they are said to be The Krebs Cycle (pages 226—227) 3. In the presence of oxygen, how is the pyruvic acid produced in glycolysis used? 4. What happens to pyruvic acid during the Krebs cycle? 5. Why is the Krebs cycle also known as the citric acid cycle? © 6. When does the Krebs cycle begin? 7. What happens to each of the 3 carbon atoms in pyruvic acid when it is broken down? S t’1 8. What happens to the carbon dioxide produced in breaking down pyruvic acid? CCO -t CD 9. How is citric acid produced? 10. During the energy extraction part of the Krebs cycle, how many molecules of CO, are released? 11. What is the energy tally from I molecule of pyruvic acid during the Krebs cycle? 100 Chapter 9 C) -C CM C S Class Name Date 12. When electrons join NAD~and FAD during the Krebs cycle, what do they form? 13. Why is the 4-carbon compound generated in the breakdown ofcitric acid the only permanent compound in the Krebs cycle? Electron Transport (pages 228—229) 14. What is the electron transport chain? ____________________________________ 15. What does the electron transport chain use the high-energy electrons from the Krebs cycle for? _______________________________________________ ______ _____ 16. How does the location of the electron transport chain differ in eukaryotes and prokaryotes? 17. Where does the electron transport chain get the high-energy electrons that are passed down the chain? © -t CD C) C) C S C U) I. C. C. C0 C CO U)I., CC S -t C, I C- lIE lEE~:E C, P C S. PE. DC P P C) C, _________ U) C, 2 __________________________________ C ~1 S ____ It E DO 18. Is the following sentence true or false? Hydrogen serves as the final electron acceptor of the electron transport chain. 19. What is the energy of the high-energy electrons used for every time 2 high-energy electrons move down the electron transport chain? ________________ _________ .il C. 20. What causes the H~ions in the intermembrane space to move through the channels in ci the membrane and out into the matrix? CD C) ~1 C, PEE:E S Sc IIEE.EE 13 ~E~E 0,) SEE:: IE~E.E. PIE jEE.:E p:EIE:EE 5 4) C. 21. On average, how many ATP molecules are produced as each pair of high-energy electrons moves down the electron transport chain? - I Reading and Study Workbook 101 Name Class Date 22. Complete the flowchart about electron transport. (Review Figure 9—7 on page 228 of your textbook.) High-energy electrons from NADH and FADH2 are passed into and along the r The energy from the electrons moving down the chain is used to move ft ions across the ft ions build up in the space, making it charged and making the matrix negatively charged. [~H+ions move through channels of in the inner membrane. j C~f The ATP synthase uses the energy from the moving ions to combine ADP and phosphate, forming high-energy -~ CD C) 5: S •0 15 The Totals (page 229) 23. How many ATP molecules are formed during cellular respiration? 24. Why is more AlP generated from glucose in the presence of oxygen? ~: S E’ 2 -C C If.~. gEE ~ lIE. P Z 0, S. 5 DC C) .~EE lEE.: CM 25. What happens to the energy of glucose that is not used to make ATP molecules? CD C~1 SE: ~S c~ 26. What are the final waste products of cellular respiration? Energy and Exercise (pages 230-231) 27. What are three sources ofATP a human body uses at the beginning ofa race? t I tiE 102 Chapter 9 P Name Class__________________ Date 28. When a runner needs quick energy for a short race, what source can supply enough ATP for about 90 seconds? _______________________________________________ 29. Why does a sprinter have an oxygen debt to repay after the race is over? __________ 30. A runner needs more energy for a longer race. How does the body generate the necessary ATP? 31. Why are aerobic forms of exercise so beneficial for weight control? Comparing Photosynthesis and Cellular Respiration ‘I (page 232) 32. If photosynthesis is the process that “deposits” energy in a “savings account,” then what is cellular respiration? 33. How are photosynthesis and cellular respiration opposite in terms of carbon dioxide? © 34. How are photosynthesis and cellular respiration opposite in terms ofoxygen? -3 N C, C S 13 C. C Cl C) C C C S C, S Cl ‘13 C C- DC / C -t CO Cl) S. S DC C) C) C C, -3 CD C) ~1 C EEC C, C S -3 S -C /0,3 S C) CD CC) © Reading and Study Workbook 103 EjE. Name _____ ____ Class _____ t1ii~téiE9 Ce1IüTaiRSj~iratiàn ‘ _____ I Date _____ - . . - Vocabulary Review Matching In the space provided, write the letter of the definition that best matches each term. 1. calorie a. electron carrier 2. glycolysis 3. cellular respiration 4. NAD~ b. pathway that releases energy from food in the absence of oxygen c. requires oxygen d. process in which one molecule of glucose is broken _____ 5. fermentation 6. anaerobic _____ 7. aerobic in half, producing two molecules of pyruvic acid e. does not require oxygen f. amount of energy needed to raise I gram of water I degree Celsius g. process that releases energy by breaking down food molecules in the presence of oxygen ______ _____ ______ _____ ______ C,: EIE Answering Questions In the space provided, write an answer to each question. 8. What is the first stage of cellular respiration? 9. What is the second stage of cellular respiration? 4: 10. What is the third stage of cellular respiration? ~ 4: Ii: 11. How many ATP molecules can the cell produce from a single molecule of glucose through glycolysis? 12. How many ATP molecules can the cell produce from a single molecule of glucose through the complete process of cellular respiration? — Completion T/Vrite an equation for each of the pathways bc/ow. 13. lactic acid fermentation after glycolysis 14. alcoholic fermentation after glycolysis 15. cellular respiration 104 Chapter 9