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In photosystem I, the first electron acceptor is

  • (a) an iron-sulphur protein Correct
  • (b) cytochrome Your answer
  • (c) plastocyanin Your answer
  • (d) ferredoxin Your answer
Your answer: Correct answer: (a)
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Explanation

Why (a) is correct

The excited electron from P700 is first accepted by bound iron-sulphur proteins in PS I. From them it passes to ferredoxin (a soluble iron-sulphur protein) and then to NADP+.

Why the other options are wrong

  • (b) · your answer Cytochromes come before PS I in the chain; they do not accept electrons from P700.
  • (c) · your answer Plastocyanin gives electrons to PS I; it is a donor, not the acceptor.
  • (d) · your answer Ferredoxin receives electrons after the bound iron-sulphur centres, so it is not the first acceptor.
NCERT point: After PS I, electrons go to ferredoxin and then NADP+ is reduced to NADPH.
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