Water Splitting and Proton Release in PS II — NEET Biology

Correct answer: B — S2, S3 and S4 are correct

The core concept tested is the location, products, and role of water splitting (photolysis) in photosynthesis. S1 is incorrect: Oxygen evolution is specifically associated with Photosystem II (PSII), not PSI. The NCERT states, 'The splitting of water is associated with the PS II'. S2 is correct: The water-splitting complex is indeed located on the inner surface of the thylakoid membrane. The NCERT states, 'the water splitting complex is associated with the PS II, which itself is physically located on the inner side of the membrane of the thylakoid'. S3 is correct: Water splitting provides the electrons necessary to replace those that PSII donates to the electron transport chain, thus ensuring a continuous supply of electrons. The NCERT states, 'The electrons that were moved from photosystem II must be replaced. This is achieved by electrons available due to splitting of water'. S4 is correct: Protons (H+) released from water splitting accumulate within the thylakoid lumen, which is crucial for establishing the proton gradient that drives ATP synthesis. The NCERT states, 'the protons or hydrogen ions that are produced by the splitting of water accumulate within the lumen of the thylakoids'. S5 is incorrect: The oxygen released during photosynthesis comes from the splitting of water molecules, not from carbon dioxide. This was proven using radioisotopic techniques. The NCERT states, 'Hence, he inferred that the O2 evolved by the green plant comes from H2O, not from carbon dioxide'. Therefore, statements S2, S3, and S4 are correct.