Question

During photosynthesis $O_2$ is liberated by oxidation of

• A. $H_{2}O$
• B. $C{O}_2$
• C. Phosphoglyceraldehyde
• D. None

Answer 1

The correct option is A $H_{2}O$

During photosynthesis, $O_2$ is liberated by oxidation of water. Van Niel was a microbiologist who on the basis of his studies of purple and green sulphur bacteria demonstrated that during photosynthesis, hydrogen released from a suitable oxidizable compound reduces carbon dioxide to carbohydrates. The first hypothesis that oxygen released during photosynthesis is derived from the water was proposed by Van Niel. This hypothesis was later proved by using radioisotopic techniques.

$2H_{2}A$ + $C{O}_2$ $\stackrel{light}{\to }$ $2A$ + $C{H}_{2}O$ + $H_{2}O$

where $H_{2}A$ is the oxidisable compound ($H_{2}O$ or $H_{2}S$)

The correct equation to represent the overall process of photosynthesis could thus be summed as:

$6H_{2}O$ + $12H_{2}O$ $\stackrel{light}{\to }$ $C_6{H}_{12}{O}_6$ + $6H_{2}O$ + $6O_2$

where $C_6{H}_{12}{O}_6$ is glucose and $O_2$ is released from water.