Assertion: The higher concentration of O2 in the atmosphere is inhibitory to photosynthesis.
Reason: CO2 is the main substrate of photosynthesis.
If both assertion and reason are true and reason is the correct explanation of assertion
If both assertion and reason are true but reason is not the correct explanation of assertion
If assertion is true but reason is false
If both assertion and reason are false.
B.
If both assertion and reason are true but reason is not the correct explanation of assertion
Oxygen accumulation causes substantial inhibition of photosynthesis. Both oxygen evolution and CO2 assimilation were reduced in the presence of atmospheric oxygen. Oxygen causes a direct and indeed competitive inhibition of Ribulose diphosphate carboxylase. As a result glycolate synthesis is enhanced and leads to begin photorespiration. Carbon dioxide being one of the raw materials for photosynthesis, its concentration affects the rate of photosynthesis markedly. Because of its very low concentration in atmosphere (0.03 per cent only) it acts as a limiting factor in natural photosynthesis.
