Which of the following is the correct sequence for the movement of electrons during non-cyclic photophosphorylation?
Correct answer: A. Water → Photosystem II (P680) → Plastoquinone (PQ) → Cytochrome b6f → Plastocyanin (PC) → Photosystem I (P700) → Ferredoxin (Fd) → NADP⁺
- A. Water → Photosystem II (P680) → Plastoquinone (PQ) → Cytochrome b6f → Plastocyanin (PC) → Photosystem I (P700) → Ferredoxin (Fd) → NADP⁺
- B. Water → Photosystem I (P700) → Plastoquinone (PQ) → Cytochrome b6f → Plastocyanin (PC) → Photosystem II (P680) → Ferredoxin (Fd) → NADP⁺
- C. NADP⁺ → Ferredoxin (Fd) → Photosystem I (P700) → Plastocyanin (PC) → Cytochrome b6f → Plastoquinone (PQ) → Photosystem II (P680) → Water
- D. Water → Photosystem II (P680) → Photosystem I (P700) → Ferredoxin (Fd) → Cytochrome b6f → NADP⁺
Explanation
In non-cyclic photophosphorylation, electrons originate from water molecules, which are split by Photosystem II (P680), releasing oxygen and protons. The electrons then move to plastoquinone (PQ), which carries them to the cytochrome b6f complex, helping pump protons into the thylakoid lumen to generate a proton gradient for ATP synthesis. From cytochrome b6f, electrons are transferred to plastocyanin (PC), a small protein that shuttles them to Photosystem I (P700). After light excitation in P700, electrons are passed to ferredoxin (Fd) and finally to NADP⁺, forming NADPH. This linear flow of electrons produces both ATP and NADPH, which are essential for the Calvin cycle and biosynthesis in plants.
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