Question

Who, after conducting experiments on purple and green sulfur bacteria, inferred that $O_2$ evolved during photosynthesis comes from $H_{2}O$ not from $C{O}_2$?

• A. Sachs
• B. Engelmann
• C. van Niel
• D. Blackmann

Answer 1

The correct option is C van Niel

Van Niel (1897-1885), on the basis of his studies with purple and green sulfur bacteria, demonstrated that photosynthesis is a light-dependent reaction in which hydrogen from an oxidizable compound reduces $C{O}_2$ to form sugar.

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

In green sulfur bacteria, when $H_{2}S$ instead of $H_{2}O$ was used as a hydrogen donor, no $O_2$ was evolved.

$6C{O}_2+12H_{2}S\to C_6{H}_{12}{O}_6+6H_2+12S$

From the above observation and conclusion, van Niel proposed that oxygenic photosynthesis of all organisms is actually an oxidation-reduction reaction involving the action of hydrogen of water over carbon dioxide to form organic compounds. He also propounded that oxygen is evolved from water.

So the correct action is 'van Niel'.