During noncyclic electron flow, which component ultimately reduces NADP+ to NADPH?

During noncyclic electron flow, which component ultimately reduces NADP+ to NADPH?

• A. Photosystem II.
• B. The water-splitting complex.
• C. Photosystem I.
• D. Cyclic electron flow.

Answer: (C)

Noncyclic electron flow moves electrons from water through PSII and the electron transport chain to PSI, where light energy boosts them again and they are ultimately delivered to NADP+ to form NADPH. The key step is after electrons reach Photosystem I: the excited electrons are passed to ferredoxin and then to NADP+ via NADP+ reductase, producing NADPH. So Photosystem I is the component that ultimately reduces NADP+ to NADPH. The earlier components (the water-splitting complex and Photosystem II) supply electrons but do not directly reduce NADP+. Cyclic electron flow, on the other hand, recycles electrons to generate more ATP and does not produce NADPH.

Noncyclic electron flow moves electrons from water through PSII and the electron transport chain to PSI, where light energy boosts them again and they are ultimately delivered to NADP+ to form NADPH. The key step is after electrons reach Photosystem I: the excited electrons are passed to ferredoxin and then to NADP+ via NADP+ reductase, producing NADPH. So Photosystem I is the component that ultimately reduces NADP+ to NADPH. The earlier components (the water-splitting complex and Photosystem II) supply electrons but do not directly reduce NADP+. Cyclic electron flow, on the other hand, recycles electrons to generate more ATP and does not produce NADPH.