Cellular Respiration: Harvesting Chemical Energy CHAPTER 4 Cellular Respiration: Harvesting Chemical Energy

What if we do not have oxygen? Without trees and bacteria to make oxygen, we would still be able to make ATP from sugar (just not as much) Modifications of glycolysis called fermentation reactions are used to release energy

Fermentation Reactions These reactions produce only 2 ATP per glucose molecule and must regenerate NAD+ resulting in the formation of either: Ethanol and CO2 Lactic Acid

In Human Muscle Cells: Lactic Acid Fermentation Some of your cells can actually work for short periods without oxygen Pyruvate is converted to lactate. Pyruvic acid is reduced by NADH, producing NAD+, which keeps glycolysis going In human muscle cells, lactic acid is a by-product Human muscle cells can make ATP with and without oxygen They have enough ATP to support activities such as quick sprinting for about 5 seconds A secondary supply of energy (creatine phosphate) can keep muscle cells going for another 10 seconds To keep running, your muscles must generate ATP by the anaerobic process of fermentation

In Human Muscle Cells: Lactic Acid Fermentation Lactic acid is associated with the “burn” you get with heavy exercise. If too much lactic acid builds up, your muscles give out. Physical conditioning allows your body to adapt to increased activity. The muscle cells become more efficient (How?) The body can increase its ability to deliver oxygen to muscles (How?) Long-distance runners wait until the final sprint to exceed their aerobic capacity. Figure 6.1

In Microorganisms: Alcohol Fermentation Various types of microorganisms perform fermentation The food industry uses yeast to produce various food products Yeast cells carry out a slightly different type of fermentation pathway This pathway produces CO2 and ethyl alcohol

Alcohol fermentation: A two-step process where CO2 is lost… Lactic acid fermentation: A single step with no loss of CO2