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Which sequence correctly shows the movement of protons in chloroplast chemiosmosis?

  • (a) lumen → stroma by pumping, then stroma → lumen through ATP synthase Your answer
  • (b) lumen → cytoplasm through CF1 Your answer
  • (c) stroma → lumen by pumping, then lumen → stroma through ATP synthase Correct
  • (d) outer membrane space → stroma → lumen Your answer
Your answer: Correct answer: (c)
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Explanation

Why (c) is correct

Protons are pumped from the stroma into the lumen (by the electron transport chain), then flow back from the lumen to the stroma through ATP synthase, making ATP.

Why the other options are wrong

  • (a) · your answer This reverses both steps.
  • (b) · your answer Protons do not move into the cytoplasm.
  • (d) · your answer Protons do not come from the outer membrane space.
NCERT point: Lumen: high H+; stroma: low H+.
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