[Campbell Biology P.247] As photoexcited electrons move from Photosystem II to Photosystem I... | Practice Question

As photoexcited electrons move from Photosystem II to Photosystem I through the electron transport chain, which of the following is the correct sequence of electron carriers and their direct consequence?

  • A: Plastoquinone (Pq) → Cytochrome complex → Plastocyanin (Pc); this flow directly contributes to pumping protons (H+) into the thylakoid space.
  • B: Plastocyanin (Pc) → Plastoquinone (Pq) → Cytochrome complex; this flow directly produces ATP.
  • C: Ferredoxin (Fd) → NADP+ reductase; this chain contributes to the proton gradient for ATP synthesis.
  • D: Cytochrome complex → Plastocyanin (Pc) → Plastoquinone (Pq); this flow only reduces NADP+ to NADPH.

Explanation

Paragraph 4 clearly states that the electron transport chain between Photosystem II and Photosystem I is composed of plastoquinone Pq , a cytochrome complex, and plastocyanin Pc . As electrons flow through these carriers, free energy is released and used to pump protons H+ into the thylakoid space, which creates the proton gradient necessary for ATP synthesis via chemiosmosis.