Question

Oxygen released during photosynthesis comes from 
A. Water 
B. Carbon dioxide 
C. Chloroplast
D. Chlorophyll 
 

Answer 1

 Hint: The photolysis step in photosynthesis generates oxygen and it is a light-dependent reaction. The substance utilized by the photolysis step constitutes 70% of the human body.

Complete answer
The oxygen released during photosynthesis is from the water. The plants will absorb water as well as carbon dioxide during photosynthesis. Later these water molecules are converted into oxygen and sugar. The oxygen is then released into the atmosphere whereas the sugar molecules are stored for energy.

Additional information
- During the process of photosynthesis, the plant absorbs carbon dioxide and water and in the presence of sunlight releases oxygen as a by-product.
- In the initial phase of photosynthesis, sunlight excites the chlorophyll in the plant, in the presence of this excited chlorophyll, water undergoes photolytic oxidation (splitting of the water molecule in the presence of sunlight) to generate H+ ions, electrons, and free oxygen species.
- The H⁺ ions and electrons are required for further steps to produce ATP and reduce NADP+ to NADPH, while the oxygen is released into the surrounding.


Note: Various experiments were done to identify the procedure of photosynthesis, but the experiments established that water is the source for the oxygen released during photosynthesis was conducted by Samuel Ruben and Martin Kamen. The experiment involved the use of radioactive isotopes to label the water and carbon dioxide absorbed by the plant and match the radioactivity of the oxygen released by the plant to identify its origin.