Apentix/AP Biology/Unit 3: Cellular Energetics/Question
AP Biologyeasymcq1 pt

Human muscle cells deprived of oxygen keep drawing ATP from glycolysis for some time. Which problem does lactic acid fermentation solve to permit this?

A.It manufactures extra ATP beyond what glycolysis already yields
B.It converts lactate directly into the oxygen the cells are missing
C.It removes surplus NAD+ that would otherwise poison the glycolytic enzymes
D.It regenerates the NAD+ that glycolysis must continually consume at its oxidation step

Explanation

Core Concept

The payoff phase of glycolysis reduces NAD+ to NADH whenever it oxidizes a G3P molecule. Starved of oxygen, the electron transport chain cannot reoxidize NADH, so the NAD+ pool would vanish and glycolysis would halt mid-pathway. Lactate dehydrogenase hands NADH's electrons to pyruvate, producing lactate and freeing NAD+. This single regeneration step lets the pathway keep collecting its small but vital ATP payment.

Correct Answer

DIt regenerates the NAD+ that glycolysis must continually consume at its oxidation step

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