Under anaerobic conditions, cells can continue to produce ATP through glycolysis, but this process requires a continuous supply of NAD+. Which of the following statements best describes the primary role of fermentation in maintaining ATP production during these conditions?
Show answer and explanation
The answer
Correct answer: B. Fermentation regenerates NAD+ from NADH, which is essential for glycolysis to continue producing a net gain of two ATP molecules.
Tested concept: Fermentation and anaerobic respiration
Explanation
The primary role of fermentation under anaerobic conditions is to regenerate NAD+ from NADH. Glycolysis requires NAD+ as an electron acceptor to oxidize glucose. Without oxygen, the electron transport chain cannot reoxidize NADH to NAD+. Fermentation pathways (like lactic acid fermentation or alcoholic fermentation) consume NADH, producing NAD+ that can then be reused by glyceraldehyde-3-phosphate dehydrogenase in glycolysis, allowing glycolysis to continue producing a small net amount of ATP (2 ATP per glucose molecule). The option stating that fermentation directly produces a significant amount of ATP is incorrect because fermentation itself does not produce ATP; glycolysis is the ATP-producing step. The option stating that fermentation completely oxidizes glucose to carbon dioxide and water is incorrect because fermentation is an incomplete oxidation of glucose and does not involve the electron transport chain, thus yielding far less ATP than complete oxidation. The option stating that fermentation serves to detoxify the cell describes a consequence of fermentation but not its primary role in sustaining ATP production; the detoxification is secondary to the NAD+ regeneration.
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