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

During active photosynthesis, the thylakoid lumen becomes more acidic than the stroma mainly because...

A.carbon dioxide dissolving in the lumen generates carbonic acid
B.the electron transport chain pumps protons into the lumen and water splitting releases more there
C.protons are consumed faster inside the lumen than elsewhere
D.ATP synthase pushes protons inward against their gradient

Explanation

Core Concept

As electrons travel from photosystem II toward photosystem I, the cytochrome b6f complex moves protons from the stroma into the lumen. Photolysis of water at photosystem II deposits additional protons directly inside the lumen. Meanwhile NADP+ reduction consumes stromal protons, deepening the contrast. The accumulating acidity stores the gradient that ATP synthase later exploits as protons exit back to the stroma.

Correct Answer

Bthe electron transport chain pumps protons into the lumen and water splitting releases more there

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