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The protons in the lumen of the thylakoid come partly from

  • (a) the breakdown of glucose Your answer
  • (b) the outer chloroplast membrane Your answer
  • (c) the splitting of water Correct
  • (d) the Calvin cycle Your answer
Your answer: Correct answer: (c)
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Explanation

Why (c) is correct

Protons accumulate in the thylakoid lumen partly from the splitting of water (on the lumen side) and partly from being pumped in by the electron transport chain.

Why the other options are wrong

  • (a) · your answer Glucose breakdown is respiration, not a source of lumen protons.
  • (b) · your answer The outer membrane does not supply these protons.
  • (d) · your answer The Calvin cycle is in the stroma and does not release protons into the lumen.
NCERT point: Three things build the gradient: water splitting, plastoquinone pumping, and NADPH formation in the stroma.
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