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. Engelman
C. Van Niel
D. Blackman

Answer 1

Hint: Photosynthesis is the process of conversion of light energy into chemical energy by which plants have their food. They need $C{O_2}$ and ${H_2}O$ for their food production and give out ${O_2}$ which we breathe. This process is a complex and long process which was discovered by different scientists in small parts.

Complete answer:
What was the experiment? Van Niel studied the green and purple sulfur bacteria. He concluded that photosynthesis is a light-dependent reaction in which hydrogen will reduce $C{O_2}$ to form sugar.
As he did a set up in which sulphur hydroxide instead of ${H_2}O$ was used as hydrogen donor but the ${O_2}$ was not evolved. He deduced that the process is an oxidation-reduction process with the action of hydrogen of water to give carbon compounds. He also stated that oxygen is evolved from water.
Let us study the work of the given scientists.
Option A: Sachs: Julius Von Sachs was a supporter of Darwin. He gave the morphological and physiological explanation of germination. He developed the concept of photosynthesis in which he told that the starch in the chloroplast is dependent on sunlight.
Option B: Engelman: Theodor Engelman was a botanist who stated the conversion of solar light energy into chemical energy taking place in the chloroplast.
Option C: Van Niel: Van Niel told that ${H_2}O$ was the donor of oxygen not $C{O_2}$ in the photosynthesis process.
Option D: Blackman: Frederick Blackman stated that the $C{O_2}$ concentration is the limiting factor in the rate of oxygen produced during photosynthesis. He talked about the laws of limiting factors.

So the answer is option C: Van Niel.

Note: Green sulfur bacteria are the anaerobic bacteria which will absorb the longer wavelength of light. They do not need oxygen to make their food. Whereas purple sulfur bacteria are aerobes. They make carotenoids. They use sulfur compounds for the reduction of the $C{O_2}$.