In the process of photosynthesis, plants use carbon dioxide (CO2), water (H2O), and light energy to produce a sugar (C6H12O6) and oxygen (O2). In the process of aerobic respiration, animals and plants release energy from sugar and oxygen and produce carbon dioxide and water. The chemical equations that describe these reactions look like this:

6CO2 + 6H2O + light C6H12O6 + 6O2 C6H12O6 + 6O2 6CO2 + 6H2O + energy

How do these equations explain why the total amount of O2 and CO2 remains the same?

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.

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