AP Retrieval Practice Test

In anaerobic conditions, what accumulates in muscle cells due to fermentation?

Lactic acid Oxygen Glucose Water

Correct Answer:

Lactic acid

Explanation:

When oxygen is scarce, muscle cells rely on fermentation to keep making ATP. Pyruvate from glycolysis is converted into lactate by lactate dehydrogenase, and this reaction regenerates NAD+ so glycolysis can continue. The buildup of lactate (lactic acid) in the cytoplasm follows, and the associated hydrogen ions contribute to the acidic environment that leads to fatigue. Oxygen isn’t accumulating in this situation—it’s the lack of it that halts mitochondrial respiration, forcing fermentation to take over. Glucose is being consumed to fuel glycolysis, not accumulating, and water isn’t a primary product of this fermentation pathway.

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