Chapter 9

1. Chapter 9 Cellular Respiration

2. 9-1 Cellular Respiration: An Overview • Chemical Energy and Food Food provides living things with the chemical building blocks they need to grow and reproduce. Food is the source of raw materials from which cells can synthesize new molecules Most importantly, food is a source of energy.

3. A calorie is the amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius. • Glucose is a source of energy. • Cells release the energy from glucose and other food compounds.

4. Cells don’t simply burn food and release energy as heat. • Instead, they break down food molecules gradually, capturing a little bit of chemical energy at key steps. • This begins with glycolysis. Glycolysis releases only a small amount of energy.

5. Mitochondrion Structure Living things get the energy they need from food. Both plant and animal cells carry out the final stages of cellular respiration in the mitochondria.

6. Overview of Cellular Respiration • Cellular Respiration is the process that releases energy by breaking down food molecules in the presence of oxygen. • 6O2 + C6H12O6 → 6CO2 + 6H2O + Energy (oxygen + glucose → carbon dioxide + water + energy)

7. This equation does not fully explain cellular respiration. • Cellular respiration takes place in 3 stages in order to control the energyreleased. • Energy has to be released a little at a time or it would be explosive. • The cell traps these little bits of energy by using them to make… ATP

8. Stages of Cellular Respiration Glycolysis Oxygen Present No Oxygen High Energy Limited Energy Release Release

9. Glycolysis: • Small energy yield • Fast process • Can produce 1,000’s of ATP molecules in a few milliseconds • Does not require oxygen

10. At the end of glycolysis about 90%of the energy that was available in the glucose is still unused • To extract the rest of that energy, the cell turns to one of the most powerful electron acceptors →oxygen • Oxygen is required for the final steps of respiration and because of this these steps are said to be aerobic.

11. The 3 main Stages of Cellular Respiration • Glycolysis takes place in the cytoplasm • Krebs Cycle and the Electron TransportChain take place inside the mitochondria

12. The 3 main Stages of Cellular Respiration

13. 9.2 The Process of Cellular Respiration • Glycolysis is the process in which one molecule of glucoseis broken in half, producing two molecules of pyruvic acid (a 3-carbon compound). Glycolysis

14. ATP Production • A little energy is needed to get the process of glycolysis going. • 2 ATP molecules are needed to produce 4 ATP molecules through glycolysis. • This gives the cell a net gain of 2 ATP molecules.

15. NADH Production • NAD+ is an electron carrier. • When NAD + accepts a pair of high-energy electrons, it is known as NADH. • NADHholds the electrons until they can be transferred to other molecules. • Therefore, NAD +helps to transfer the energy from glucose to other pathways in the cell.

16. The Krebs Cycle • In the presence of oxygen, pyruvic acid produced in glycolysis passes to the second stage of cellular respiration -The Krebs Cycle • During the Krebs cycle, pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions.

17. At the end of the Krebs Cycle, CO2 is released, ATP is produced and a number of high-energy electrons are captured by NAD+ making NADH and other electron carrier molecules.

18. Electron Transport Chain • The cell uses the high energy electrons from the Krebs cycle to convert ADP to ATP

19. Cellular Respiration Totals • Glycolysis = 2 ATP • Krebs Cycle = 2 ATP • Electron Transport Chain = 32 ATP • Total 36ATP/Glucosemolecule or about 38% of the total energy in the molecule. • The rest is released as Heat.

20. 9.3 Fermentation (Anaerobic Respiration) • Fermentation follows glycolysis when oxygen is not present. • Fermentation releases energy from food molecules in the absence ofoxygen.

21. During fermentation, NADH converts back to NAD+ by passing high-energy electrons to pyruvic acid. • This allows glycolysis to continue producing a steady supply of ATP.

22. Because fermentation does not require oxygen, it is anaerobic. • Anaerobic means “not in air” • The 2 main types of fermentation are alcoholic fermentation and lactic acid fermentation.

23. Alcoholic Fermentation • Produces carbon dioxide (CO2) as well as alcohol. pyruvic acid + NADH → alcohol + CO2 + NAD+ • Examples: • Yeasts (Breads, etc.) • Beverages

24. Lactic Acid Fermentation • In 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. • This process regenerates NAD+ so that glycolysis can continue pyruvic acid + NADH →lactic acid + NAD +

25. Lactic acid is produced in your muscles during rapid exercise when the body cannot supply enough oxygen to the muscle tissues. • The larger muscles (arms and legs) quickly run out of oxygen and ATP • Muscles rapidly produce ATP by lactic acid fermentation. • The build up of lactic acid causes a painful, burning sensation.

26. Energy and Exercise • Quick Energy • Cells normally contain a small amount of ATP produced from glycolysis (enough for a few seconds of activity) • After a few seconds, cells produce energy by lactic acid fermentation

27. Lactic acid requires extra oxygen to get rid of it. This is why you keep breathing heavily after the race is over. • For long term energy, the body uses a combination of both aerobic and anaerobic respiration. • That is why athletes pace themselves in a race.

28. Comparing Photosynthesis and Cellular Respiration • Photosynthesis is the process that depositsthe energy • Respiration is the process that withdrawsthe energy.

29. The equations of photosynthesis and respiration are the oppositeof each other. • Photosynthesis removes CO2 from the air and respiration puts it back. • The products of cellular respiration are the reactants of photosynthesis.

31. Comparing Photosynthesis and Cellular Respiration