Question

Where does the oxygen liberated from the photosynthesis come from?

Answer 1

Hint: The photosynthesis is the process by which plants prepare carbohydrate and release oxygen by utilizing carbon dioxide and water vapour. The oxygen liberated is through photolysis. It is a light dependent reaction.

Complete answer:
During the process of photosynthesis, plants absorb carbon dioxide and water vapour from the atmosphere and liberate glucose and oxygen. The oxygen is liberated back to the atmosphere and the glucose is utilised by the plants.

During photosynthesis the light energy is converted into chemical energy. The light excites the chlorophyll. The light reaction takes place in the thylakoid. The photolysis of water molecules takes place. The photolysis is the splitting of the water molecule in the presence of light. The water is oxidised. This generates hydrogen ions, electrons and free oxygen species. The free oxygen combines with another free oxygen to form oxygen molecules. The hydrogen ion is further utilised by the plant in producing NADPH.
Thus, the oxygen evolved is produced by the photolysis of water.

The oxygen liberated during photosynthesis comes from water is proven experimentally. The experiment on green and purple bacteria by using hydrogen sulphide showed that the oxygen evolved during photosynthesis comes from water. If the oxygen comes from any other source then sulphur or sulphur compound would have been released.

Note: The plants release the oxygen during the day time which is further utilised in the respiration of other organisms. At night, the plants do not perform photosynthesis but the respiration takes place in plants. Thus, the plants liberate carbon dioxide during night.