Which statement is not true about the non-cyclic electron pathway?
Correct answer: C. Electrons return to Photosystem I after reaching NADP⁺
- A. Electrons originate from water molecules
- B. Both ATP and NADPH are produced
- C. Electrons return to Photosystem I after reaching NADP⁺
- D. Oxygen is released as a by-product of water splitting
Explanation
Non-cyclic photophosphorylation, or the non-cyclic electron pathway, is the linear flow of electrons from water to NADP⁺ in the thylakoid membranes of chloroplasts. Water is split at Photosystem II (P680), releasing electrons, protons, and oxygen. Electrons pass through plastoquinone (PQ), cytochrome b6f, plastocyanin (PC), and Photosystem I (P700), eventually reducing NADP⁺ to NADPH. ATP is simultaneously synthesized via chemiosmosis due to the proton gradient created during electron transport. Oxygen is released as a by-product, making Options A, B, and D true. However, electrons do not return to Photosystem I after reducing NADP⁺; this is characteristic of cyclic photophosphorylation, not the non-cyclic pathway.
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