Apentix/AP Biology/Unit 3: Cellular Energetics/Question
AP Biologymediummcq1 pt

Yeast deprived of oxygen reduce pyruvate to ethanol and CO2, while hard-working human muscles reduce pyruvate to lactate. What do these two pathways have in common?

A.Each converts pyruvate into a useful industrial solvent.
B.Each reoxidizes NADH to NAD+, allowing glycolysis to continue generating ATP without the electron transport chain.
C.Each generates extra ATP directly during the pyruvate conversion step.
D.Each produces FADH2 that later feeds electrons into Complex II.

Explanation

Core Concept

Glycolysis consumes NAD+ when glyceraldehyde 3-phosphate is oxidized, and a blocked electron transport chain offers no way to recycle NADH. Yeast reduce acetaldehyde to ethanol and muscle reduces pyruvate to lactate, but both steps strip electrons from NADH, restoring NAD+. The shared achievement is bookkeeping: keep glycolysis funded even though fermentation itself nets zero ATP.

Correct Answer

BEach reoxidizes NADH to NAD+, allowing glycolysis to continue generating ATP without the electron transport chain.

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