1. Cellular Respiration (Chapter 9) 1

2. When you are hungry, how do you feel? If you are like most people, your stomach may seem empty, you might feel a little dizzy, and above all, you feel weak. The sensations produced by hunger may vary, but the bottom line is always the same. Our bodies have a way of telling us when we need food. 2

3. Food provides living things with the chemical building blocks they need to grow and reproduce. Food serves as a source of raw materials for the cells of the body. Most of all, food serves as a source of energy. 3

4. 9-1 Chemical Pathways p221 Food is the energy source for cells. They energy in food is measured in calories. A calorie is the amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius. Cells do not burn glucose or other food compounds. They gradually release the energy. The process begins with a pathway called glycolysis. 4

5. Cellular Respiration 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. (glycolysis -> Krebs cycle -> electron transport) 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: 5

6. Glycolysis Glycolysis takes place in the cytoplasm of a cell. Glycolysis is the process in which a glucose molecule is split in half. This forms two molecules of pyruvic acid, a 3-carbon compound. Through glycolysis, the cell gains 2 APT molecules. 6

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8. Fermentation When oxygen is not present, glycolysis is followed by another pathway called fermentation. Fermentation releases energy from food molecules by producing ATP in the absence of oxygen. Because fermentation does not require oxygen, it is said to be anaerobic which means “not in air”. The two main types of fermentation are: 1.Alcoholic fermentation 2.Lactic acid fermentation 8

9. Alcoholic Fermentation Yeast and few other microorganisms use alcoholic fermentation (causes bread dough to rise) Forms ethyl alcohol and carbon dioxide as wastes. The equation after glycolysis is: Pyruvic acid + NADH -> alcohol + CO2 + NAD + 9

10. Lactic Acid Fermentation Lactic acid fermentation occurs in your muscles during rapid exercise when the body cannot supply enough oxygen to the tissues. Your muscle cells rapidly begin to produce ATP by lactic acid fermentation. The buildup of lactic acid causes a painful, burning sensation. 10

11. Lactic Acid Fermentation The equation after glycolysis is: Pyruvic acid + NADH -> lactic acid + NAD+ Unicellular organisms produce lactic acid as a waste product during fermentation and are used in the production of a wide variety of foods. 11

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13. 9-2 The Krebs Cycle and Electron Transport At the end of glycolysis, about 90 percent of the chemical energy that was available in glucose is still unused. The rest of that energy is extracted in the presence of oxygen through the Krebs cycle; the second stage of cellular respiration. Because the pathways of cellular respiration require oxygen, they are said to be aerobic, Pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions. 13

14. The Krebs cycle The Krebs cycle starts when pyruvic acid formed by glycolysis enters the mitochondrion. The pyruvic acid is broken down into carbon dioxide and a 2-carbon acetyl group. The two carbons of the acetyl group join a 4-carbon compound to produce citric acid. In a series of reactions, two energy carriers accept high-energy electrons. NAD+ is changed to NADH, and FAD is changed to FADH 2. These molecules carry the high-energy electrons to the electron transport chain. 14

15. Electron Transport The electron transport uses high-energy electrons to change ADP into ATP. In the electron transport chain, high-energy electrons move from one carrier protein to the next. At the end of the chain, oxygen pulls electrons from the final carrier molecule. These electrons join with hydrogen ions, forming water. Each transfer along the chain releases a small amount of energy. ATP synthase uses the energy to produce ATP. 15

16. The Totals Glycolysis produces 2 APT molecules from one molecule of glucose. The Krebs cycle and the electron transport chain let the cell form 34 ATP molecules per glucose molecule. The total, then, for cellular respiration is 36 APT molecules per glucose molecule. 16