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

A toxin irreversibly disables the pyruvate dehydrogenase complex in actively respiring animal cells. Which downstream consequence follows?

A.The citric acid cycle accelerates, compensating by oxidizing whatever acetyl-CoA remains faster
B.Acetyl-CoA production falls, starving the citric acid cycle and shrinking the NADH supply that feeds the electron transport chain
C.Oxygen consumption rises because cells burn extra glucose attempting to bypass the blockage
D.Glycolysis halts because its endpoint can no longer be processed

Explanation

Core Concept

Pyruvate dehydrogenase is the sole gateway converting pyruvate into acetyl-CoA in animal cells. With the complex disabled, carbon backs up as pyruvate and lactate while the cycle receives no fresh acetyl groups. Cycle throughput falls, so NADH and FADH2 generation dwindles and the electron transport chain runs short of electron donors. Aerobic ATP yield collapses even though the chain and ATP synthase remain structurally intact.

Correct Answer

BAcetyl-CoA production falls, starving the citric acid cycle and shrinking the NADH supply that feeds the electron transport chain

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