Question

The source of ${ O }_{ 2 }$ liberated during photosynthesis is
(a) Photosynthetic enzyme
(b) Carbohydrate present in the leaf
(c) Water
(d) Carbon dioxide

Answer 1

Hint: Hydrogen donors such as ${ O }_{ 2 }$ or ${ H }_{ 2 }S$ are oxidized; they form either oxygen, sulfur, or sulfate depending on the hydrogen donor used.

Complete step by step answer:
For plants to perform photosynthesis the essential components are sunlight, water, carbon dioxide, and chlorophyll. In the middle of the 19th century a microbiologist, Cornelius Van Neil performed on purple sulfur bacteria and green sulfur bacteria and proved that the oxygen released during photosynthesis comes from water.
The equation that represents the entire process of photosynthesis is:
${ 6Co }_{ 2 }+{ 12H }_{ 2 }O\xrightarrow { sunlight } { C }_{ 6 }{ H }_{ 12 }{ O }_{ 6 }+{ 6H }_{ 2 }O+{ 6O }_{ 2 }$

Additional information:
- Green plants in the presence of sunlight by using water and carbon dioxide for the production of oxygen and carbohydrates is called photosynthesis.
- Several experiments are conducted on the release of oxygen during photosynthesis.
- It was Joseph Priestly who discovered oxygen in the year 1774.
- Sunlight is essential for photosynthesis, which is known from the experiments conducted by Jan Ingenhousz
- In 1854 the scientist named Julius Von Sachs discovered that glucose is produced by the plants during photosynthesis
- T.W.Engelmann showed that sunlight is essential for photosynthesis by using a prism on green algae
- In plants ${ O }_{ 2 }$ is the hydrogen donor which gets oxidized to ${ O }_{ 2 }$.
So, the correct answer is ‘water’.

Note: Some organisms do not release oxygen during photosynthesis. If ${ H }_{ 2 }S$ is a hydrogen donor the oxidation product will be sulfur or sulfate and not ${ O }_{ 2 }$. This can be seen in purple sulfur bacteria or green sulfur bacteria depending upon the organism.