Question

Which one of the following equations suggests that $O _{2}$ released during photosynthesis comes from water?

• A. $6CO_{2}\,^{18}+12H_{2} \to 6O_{2}\,^{18} +C_{6}H_{12}O_{6} + 6H_{2}O\,^{18}$
• B. $6CO_{2}+12H_{2} O\,^{18} \to 6O_{2} +C_{6}H_{12}O_{6} + 6H_{2}O\,^{18}$
• C. $6CO_{2}\,^{18}+12H_{2} \to 6O_{2}\,^{18} +C_{6}H_{12}O_{6} + 6H_{2}O$
• D. $6CO_{2}+12H_{2} O\,^{18} \to 6O_{2}\,^{18} +C_{6}H_{12}O_{6} + 6H_{2}O$

Answer 1

Answer: (D)

$6CO_{2}+12H_{2} O\,^{18} \to 6O_{2}\,^{18} +C_{6}H_{12}O_{6} + 6H_{2}O$

Answer 2

Ruben and Kamen $(1941)$, while working on Chlorella (unicellular green alga) found that oxygen liberated during photosynthesis comes from water. (i) When normal $H_{2}O$ and radioactive $CO_{2}$ (i.e., $CO^{18}\,_{2}$) were used, normal $O_{2}$ is evolved. $nCO_{2}^{18} + nH_{2}O$ ${->[{\text{Light}}][{\text{Chlorophyll}}]}$ $(CH_{2}O^{18})_n + nO_{2} ? (ii) When normal$CO_{2}$and radioactive$H_{2}O$(i.e.,$H_{2}O^{ 18}$) were used, radioactive$O_{2}$(i.e.,$O_{2}^{8}$) is evolved.$nCO_{2} +nH_{2}O^{18} \to (CH_{2}O)n+O^{18}{2}?