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The chemiosmotic coupling hypothesis of oxidative phosphorylation proposes that ATP is formed because

  • (a) ADP is pumped out of the matrix into the intermembrane space Your answer
  • (b) a proton gradient forms across the inner membrane Correct
  • (c) the permeability of the inner mitochondrial membrane to ADP changes Your answer
  • (d) high-energy bonds are formed in mitochondrial proteins Your answer
Your answer: Correct answer: (b)
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Explanation

Why (b) is correct

According to the chemiosmotic hypothesis, electron transport pumps protons across the inner mitochondrial membrane. The proton gradient formed then drives ATP synthase as protons flow back.

Why the other options are wrong

  • (a) · your answer ATP synthesis is driven by protons, not by pumping ADP between compartments.
  • (c) · your answer A change in ADP permeability is not the basis of chemiosmosis.
  • (d) · your answer The theory does not depend on high-energy bonds in proteins; the energy is stored as a proton gradient.
NCERT point: The same chemiosmotic mechanism makes ATP in chloroplasts (across the thylakoid membrane) and mitochondria (across the inner membrane).
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