1. Chapter 9 - Chemical Pathways

2. Food serves as a source of raw materials for the cells in the body and as a source of energy. Animal Plant Animal Cells Plant Cells Mitochondrion

3. Both plant and animal cells carry out the final stages of cellular respiration in the mitochondria. Animal Cells Plant Cells Mitochondrion Outer membrane Intermembrane space Inner membrane Matrix

4. Chemical Energy and Food One gram of glucose (C 6 H 12 O 6 ), when burned, releases 3811 calories of heat energy. A calorie is the amount of heat energy needed to raise the temperature of 1 gram of water 1 degree Celsius.

5. What is cellular respiration?

6. Cytoplasm Pyruvic acid Mitochondrion Electrons carried in NADH Electrons carried in NADH and FADH 2 Glucose Glycolysis

7. Cellular respiration releases energy by breaking down glucose and other food molecules in the presence of oxygen.

8. The equation for cellular respiration is: 6O 2 + C 6 H 12 O 6 → 6CO 2 + 6H 2 O + Energy oxygen + glucose → carbon dioxide + water + Energy

9. Glycolysis takes place in the cytoplasm. The Krebs cycle and electron transport take place in the mitochondria. Cytoplasm Mitochondrion Glycolysis

10. What happens during the process of glycolysis?

11. ATP Production At the beginning of glycolysis, the cell uses up 2 molecules of ATP to start the reaction. 2 ADP 4 ADP 4 ATP 2 Pyruvic Acid 2 ATP Glucose

12. When glycolysis is complete, 4 ATP molecules have been produced. 2 ADP 4 ADP 4 ATP 2 ATP Glucose 2 Pyruvic acid

13. This gives the cell a net gain of 2 ATP molecules. 4 ADP 4 ATP Glucose 2 ADP 2 ATP 2 Pyruvic acid

14. NADH Production One reaction of glycolysis removes 4 high-energy electrons, passing them to an electron carrier called NAD +. Glucose 2 Pyruvic acid 4 ADP 4 ATP 2 ADP 2 ATP 2NAD +

15. Each NAD + accepts a pair of high-energy electrons and becomes an NADH molecule. Glucose 2 Pyruvic acid 4 ADP 4 ATP 2 ADP 2 ATP 2NAD + 2

16. The NADH molecule holds the electrons until they can be transferred to other molecules. To the electron transport chain 2NAD + 2 Pyruvic acid 4 ADP 4 ATP 2 ADP 2 ATP 2

17. The Advantages of Glycolysis The process of glycolysis is so fast that cells can produce thousands of ATP molecules in a few milliseconds. Glycolysis does not require oxygen.

18. Fermentation When oxygen is not present, glycolysis is followed by a different pathway. The combined process of this pathway and glycolysis is called fermentation. Fermentation releases energy from food molecules by producing ATP in the absence of oxygen.

19. During fermentation, cells convert NADH to NAD + by passing high-energy electrons back to pyruvic acid. This action converts NADH back into NAD +, and allows glycolysis to continue producing a steady supply of ATP. Fermentation does not require oxygen—it is an anaerobic process.

20. What are the two main types of fermentation?

21. Alcoholic Fermentation Yeasts and a few other microorganisms use alcoholic fermentation, forming ethyl alcohol and carbon dioxide as wastes. The equation for alcoholic fermentation after glycolysis is: pyruvic acid + NADH → alcohol + CO 2 + NAD +

22. Lactic Acid Fermentation In many cells, pyruvic acid that accumulates as a result of glycolysis can be converted to lactic acid. This type of fermentation is called lactic acid fermentation. It regenerates NAD + so that glycolysis can continue. The equation for lactic acid fermentation after glycolysis is: pyruvic acid + NADH → lactic acid + NAD +

23. The first part of the equation is glycolysis.

24. The second part shows the conversion of pyruvic acid to lactic acid.

25. Quiz 9-1

26. The raw materials required for cellular respiration are a.carbon dioxide and oxygen. b.glucose and water. c.glucose and oxygen. d.carbon dioxide and water.

27. Glycolysis occurs in the a.mitochondria. b.cytoplasm. c.nucleus. d.chloroplasts.

28. The net gain of ATP molecules after glycolysis is a.3 ATP molecules. b.2 ATP molecules. c.3 pyruvic acid molecules. d.4 pyruvic acid molecules

29. Fermentation releases energy from food molecules in the absence of a.oxygen. b.glucose. c.NADH. d.alcohol.

30. The first step in fermentation is always a.lactic acid production. b.the Krebs cycle. c.glycolysis. d.alcohol production.

31. Oxygen is required for the final steps of cellular respiration. Because the pathways of cellular respiration require oxygen, they are aerobic.

32. What happens during the Krebs cycle?

33. During the Krebs cycle, pyruvic acid is broken down into carbon dioxide in a series of energy- extracting reactions.

34. The Krebs cycle begins when pyruvic acid produced by glycolysis enters the mitochondrion.

35. One carbon molecule is removed, forming CO 2, and electrons are removed, changing NAD + to NADH.

36. Coenzyme A joins the 2-carbon molecule, forming acetyl-CoA.

37. Citric acid Acetyl-CoA then adds the 2-carbon acetyl group to a 4- carbon compound, forming citric acid.

38. Citric acid is broken down into a 5-carbon compound, then into a 4-carbon compound.

39. Two more molecules of CO 2 are released and electrons join NAD + and FAD, forming NADH and FADH 2

40. In addition, one molecule of ATP is generated.

41. The energy tally from 1 molecule of pyruvic acid is –4 NADH –1 FADH 2 –1 ATP

42. How are high-energy electrons used by the electron transport chain?

43. Electron Transport The electron transport chain uses the high- energy electrons from the Krebs cycle to convert ADP into ATP.

44. High-energy electrons from NADH and FADH 2 are passed along the electron transport chain from one carrier protein to the next.

45. At the end of the chain, an enzyme combines these electrons with hydrogen ions and oxygen to form water.

46. As the final electron acceptor of the electron transport chain, oxygen gets rid of the low-energy electrons and hydrogen ions.

47. When 2 high-energy electrons move down the electron transport chain, their energy is used to move hydrogen ions (H + ) across the membrane.

48. During electron transport, H + ions build up in the intermembrane space, so it is positively charged.

49. The other side of the membrane, from which those H + ions are taken, is now negatively charged.

50. ATP synthase The inner membranes of the mitochondria contain protein spheres called ATP synthases.

51. As H + ions escape through channels into these proteins, the ATP synthase spins. ATP synthase Channel

52. As it rotates, the enzyme grabs a low-energy ADP, attaching a phosphate, forming high-energy ATP. ADP ATP synthase Channel

53. The Totals Glycolysis produces just 2 ATP molecules per molecule of glucose. The complete breakdown of glucose through cellular respiration, including glycolysis, results in the production of 36 molecules of ATP.

55. Comparing Photosynthesis and Cellular Respiration The energy flows in photosynthesis and cellular respiration take place in opposite directions.

56. On a global level, photosynthesis and cellular respiration are also opposites. –Photosynthesis removes carbon dioxide from the atmosphere and cellular respiration puts it back. –Photosynthesis releases oxygen into the atmosphere and cellular respiration uses that oxygen to release energy from food.

57. Quiz 9-2

58. The Krebs cycle breaks pyruvic acid down into a.oxygen. b.NADH and FADH 2. c.carbon dioxide. d.alcohol.

59. What role does the Krebs cycle play in the cell? a.It breaks down glucose and releases its stored energy. b.It releases energy from molecules formed during glycolysis. c.It combines carbon dioxide and water into high-energy molecules. d.It breaks down ATP and NADH, releasing stored energy.

60. In respiration, the electron transport chain is located in the a.cell membrane. b.inner mitochondrial membrane. c.cytoplasm. d.outer mitochondrial membrane.

61. To generate energy over long periods, the body must use a.stored ATP. b.lactic acid fermentation. c.cellular respiration. d.glycolysis.

62. Which statement correctly describes photosynthesis and cellular respiration? a.Photosynthesis releases energy, while cellular respiration stores energy. b.Photosynthesis and cellular respiration use the same raw materials. c.Cellular respiration releases energy, while photosynthesis stores energy. d.Cellular respiration and photosynthesis produce the same products.