7.6 some cells can harvest energy without oxygen

1. 7.6 some cells can harvest energy without oxygen

2. Objectives • Explain how fermentation in muscle cells is different from cellular respiration. • Give examples of products that depend on fermentation in microorganisms. • Key Terms • fermentation • anaerobic

3. When you walk down the street, your lungs supply your cells with oxygen at a rate that keeps pace with ATP demand. But what happens when you sprint to catch a bus? Your leg muscles are forced to work without enough oxygen because you are spending ATP more quickly than your lungs and bloodstream can deliver oxygen to your muscles for cellular respiration. Fortunately, some of your cells can produce ATP and continue working for short periods without oxygen.

4. Fermentation in Human Muscle CellsIf you exercise for a certain amount of time, your muscles must regenerate ATP. Normally, the cells can produce ATP through cellular respiration. But when you sprint, your lungs and bloodstream can't supply oxygen fast enough to meet your muscles' need for ATP. In such situations, your muscle cells use another process, called fermentation, that makes ATP without using oxygen. Cellular respiration still continues, but it is not the main source of ATP while fermentation is occurring

5. Fermentation makes ATP entirely from glycolysis, the same process that is the first stage of cellular respiration. Note that glycolysis does not use oxygen

7. Remember that glycolysis produces 4 ATP but that 2 ATP molecules are required to power this stage, yielding a net of 2 ATP. This may not seem very efficient compared to the 38 molecules of ATP generated during all of cellular respiration. However, by burning enough glucose, fermentation can regenerate enough ATP molecules for short bursts of activity such as a sprint to catch the bus.

8. Fermentation in muscle cells produces a waste product called lactic acid. The temporary buildup of lactic acid in muscle cells contributes to the fatigue you feel during and after a long run or a set of push-ups. Your body consumes oxygen as it converts the lactic acid back to pyruvic acid. You restore your oxygen supply by breathing heavily for several minutes after you stop exercising

9. Fermentation in MicroorganismsLike your muscle cells, yeast (a microscopic fungus) is capable of both cellular respiration and fermentation. When yeast cells are kept in an anaerobic environment—an environment without oxygen—they are forced to ferment sugar and other foods.

10. In contrast to fermentation in your muscle cells, fermentation in yeast produces alcohol, instead of lactic acid, as a waste product • This fermentation reaction, called alcoholic fermentation, also releases carbon dioxide.

11. For thousands of years, humans have put yeast to work producing alcoholic beverages such as beer and wine. The carbon dioxide is what makes champagne and beer bubbly. In another example of "taming" microbes, the carbon dioxide bubbles from baker's yeast make bread rise.