Water Molecules in Photosynthesis — NEET Biology

Correct answer: D — S1, S2 and S4

Let's evaluate each statement: S1: Correct. Van Niel's studies 'demonstrated that photosynthesis is essentially a light-dependent reaction in which hydrogen from a suitable oxidisable compound reduces carbon dioxide to carbohydrates.' S2: Correct. He observed that 'When H2S, instead is the hydrogen donor for purple and green sulphur bacteria, the ‘oxidation’ product is sulphur or sulphate depending on the organism and not O2.' S3: Incorrect. Van Niel inferred the opposite: 'the O2 evolved by the green plant comes from H2O, not from carbon dioxide.' S4: Correct. His generalized equation (2H2A + CO2 → 2A + CH2O + H2O) represents this, where H2A is the hydrogen donor. The text states 'photosynthesis is essentially a light-dependent reaction in which hydrogen from a suitable oxidisable compound reduces carbon dioxide to carbohydrates'. S5: Incorrect. While his inference about O2 from H2O was correct, his *experimental evidence* from sulfur bacteria didn't directly show water splitting in green plants; it was an *inference* based on analogy. Direct proof for water as the source of oxygen was 'later proved by using radioisotopic techniques', not directly by his bacterial work itself. His work provided the strong *hypothesis*. Therefore, statements S1, S2, and S4 are correct.