Question

Which of the following statement is correct with respect to non-cyclic photophosphorylation?

• A. Light cause the splitting of water at stroma side of thylakoid membrane
• B. e- from first acceptor of PS-II to NADP+ involve uphill movement in terms of redox potential scale
• C. NADP+ recieve e- from donor which is having redox potential lower than NADP+.
• D. Splitting of water lead to release of e- from PS-II

Answer 1

Answer: (B), (C)

(2) e- from first acceptor of PS-II to NADP+ involve uphill movement in terms of redox potential scale (3) NADP+ recieve e- from donor which is having redox potential lower than NADP+.

Answer 2

1. Statement (1): Water splitting (photolysis) occurs on the lumen side of the thylakoid membrane, not the stroma side. Thus, this statement is incorrect.
2. Statement (2): The electron path from the first acceptor of PSII (pheophytin, +0.5 V) to NADP$^+$ (-0.32 V) involves several steps. For example, electrons move from plastocyanin (+0.37 V) to PSI (ground state +0.45 V), and from ferredoxin (-0.4 V) to NADP$^+$ (-0.32 V). Both of these are uphill movements in terms of redox potential. Therefore, this statement is correct.
3. Statement (3): NADP$^+$ is reduced to NADPH by electrons donated from ferredoxin. The redox potential of ferredoxin is approximately -0.4 V, which is lower (more negative) than the redox potential of NADP$^+$ (~-0.32 V). Electrons flow from a lower redox potential to a higher redox potential, which is an uphill movement. Thus, NADP$^+$ receives electrons from a donor with a lower redox potential, making this statement correct.
4. Statement (4): Water splitting occurs on the lumen side of the thylakoid membrane and provides electrons to PSII. It does not release electrons from PSII; rather, it replenishes the electrons lost by PSII's reaction center (P680) when it gets excited. Thus, this statement is incorrect.

Since statements (2) and (3) are both correct, and the question asks for correct statements, both should be selected.