Answer:
During photosynthesis, to form 1 molecule of glucose, 6 molecules of CO2 is needed to be used as a reactant. 6 molecules of O2 is released as a by-product.
However, during aerobic respiration, to hydrolyse 1 molecule of glucose, you will need 6 molecules of O2 as a reactant, releasing 6 molecules of CO2 as by-product.
Essentially, the total amount of CO2 and O2 remains the same assuming the rate of aerobic respiration is the same as the rate of photosynthesis, resulting in no net gain or loss of both CO2 and O2 in the atmosphere.