BIO Discussion 4 PDF

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BIO 202 Discussion HW 4...

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Some friends are trying to make wine in their basement. They've added yeast to a sweet grape juice mixture and have allowed the yeast to grow. After several days they find that sugar levels in the grape juice have dropped, but there's no alcohol in the mixture. The most likely explanation is that ______. A. the mixture needs less oxygen; yeast only produce alcohol in the absence of oxygen B. the mixture needs more sugar; yeast need a lot of energy before they can begin to produce alcohol C. the mixture needs more oxygen; yeast need oxygen to break down sugar to produce alcohol D. the mixture needs less sugar; high sugar concentrations stimulate cellular respiration, and alcohol is not a by-product of cellular respiration

Choice A - Best Answer. Fermentation is the process in which yeast breaks down sugar into alcohol and carbon dioxide. Yeast is able to create energy without the presence of oxygen, but it produces ethanol as a result of fermentation. Fermentation does not require oxygen and is therefore anaerobic. Fermentation will replenish NAD+ from the NADH + H+ produced in glycolysis. One type of fermentation is alcohol fermentation. First, pyruvate is decarboxylated (CO 2 leaves) to form acetaldehyde. Hydrogen atoms from NADH + H+ are then used to help convert acetaldehyde to ethanol. NAD+ results.

Choice B - Falsification. Sugar is not needed in order to make alcohol. Because fermentation is just an extension of glycolysis, there is no more energy needed because it is already produced during glycolysis. The substrate level phosphorylation stage of glycolysis generates a sufficient amount of energy, or ATP. Oxygen does not need to be present in order for the 2 ATP to be produced during the process.

Choice C - Falsification. As stated in the explanation for part A, the process of fermentation does not require any oxygen. This means that alcohol can be produced without oxygen. During the anaerobic process, the first part would be the carbon dioxide leaving the pyruvate and forming acetaldehyde. The next step would be the acetaldehyde would be converted to ethanol with the assistance of NADH + and H+. Nowhere in this process is oxygen a necessity.

Choice D - Falsification. This statement is false because fermentation is a byproduct of glycolysis. Glycolysis is the first stage of cellular respiration. In the absence of oxygen, glycolysis allows cells to produce ATP through fermentation. Therefore, it is incorrect to say that

alcohol is not a byproduct of cellular respiration when fermentation occurs in the very first step of cellular respiration....