Question

Who demonstrated that in purple and green sulphur bacteria when $H_{2}S$ is used as hydrogen donor, sulphur is released instead of oxygen?

• A. Engelmann
• B. Julius von Sachs
• C. Van Niel
• D. Jan Ingenhousz

Answer 1

The correct option is C Van Niel

Van Niel proposed that oxygen released during photosynthesis comes from water and not from $C{O}_2$. He could arrive at this based on experiments conducted on purple and green sulphur bacteria. He observed that when these bacteria undergo photosynthesis, oxygen is not released and instead sulphur is released. He argued that if carbon dioxide was the source of oxygen released during photosynthesis, then the byproduct of bacterial photosynthesis should be oxygen but not sulphur. Hence, he concluded that oxygen released in green plants comes from water but not carbon dioxide. In purple and green sulphur bacteria, $H_{2}S$ is the hydrogen donor and hence the oxidation product is sulphur. In green plants, $H_{2}O$ is the hydrogen donor and hence the oxidation product is oxygen.

Julius von Sachs provided evidence for production of glucose when plants grow.

Jan Ingenhousz (1730-1799) showed that sunlight is essential for photosynthesis.

Engelmann did an experiment to describe the action spectrum of photosynthesis.