Apentix/AP Biology/Unit 3: Cellular Energetics/Question
AP Biologyhardmcq1 pt

As electrons travel through the mitochondrial electron transport chain, complexes I, III, and IV use the released free energy to accomplish which task?

A.Pumping protons from the matrix into the intermembrane space, storing energy in an electrochemical gradient
B.Splitting water into electrons, protons, and oxygen gas
C.Passing electrons directly to ADP so that phosphate groups can attach
D.Moving protons from the intermembrane space back into the matrix to reduce NAD+

Explanation

Core Concept

Electron transfer through complexes I, III, and IV releases free energy that each complex spends translocating H+ against its gradient, out of the matrix and into the intermembrane space. The resulting proton motive force then drives ATP synthase as protons diffuse back toward the matrix through the F0 channel. Only complex IV hands the electrons to oxygen, joining them with protons to form water.

Correct Answer

APumping protons from the matrix into the intermembrane space, storing energy in an electrochemical gradient

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