Question

Which is the evidence to show that $O_2$ released during photosynthesis comes from water?

• A. Synthesis of carbohydrates and formation of $H_{2}O$ and sulphur by photosynthetic bacteria when supplied with $H_{2}S$ and $C{O}_2$.
• B. Release of $O_2$ by isolated chloroplasts, when potassium ferrocyanide or some other reducing substance is supplied.
• C. Release of radioactive $O_2$ when water is supplied as $H_2{O}^{18}$.
• D. All of the above.

Answer 1

Answer: (D)

All of the above.

A. Van Neil in 1931 showed that photosynthetic bacteria fixed CO${}_2$ in the presence of H${}_2$S and postulated that plants evolve O${}_2$ by splitting H${}_2$O, not CO${}_2$.

B. Robin Hill in 1937 isolated chloroplast suspended in water in presence of a suitable hydrogen acceptor (for example, ferricyanide) which evolve oxygen in presence of light. He demonstrated that the source of O${}_2$ during photosynthesis is water and not CO${}_2$.

C. Ruben and Kamen in 1941 used radioactive oxygen ${}^{18}$O and supplied water as H${}_2$${}^{18}$O and proved that oxygen evolved was part of water.

Hence, all the statements are correct.

So, the correct answer is D.