Answer: It is because glucose and oxygen which are formed during photosynthesis are used in respiration to produce carbon dioxide and water which are the reactants in photosynthesis.
Explanation: The reactants in respiration are the products of photosynthesis while the products of respiration are the reactants in photosynthesis. The equation for photosynthesis is 6CO2 + 6H2O + sunlight --> C6H12O6 + 6O2
The equation for respiration is C6H12O6 + 6O2 --> 6CO2 + 6H2O.
In photosynthesis one molecule of glucose and six molecules of oxygen are formed from six molecules of carbon dioxide and six molecules of water while in respiration six molecules of carbon dioxide and six molecules of water are formed from one molecule of glucose and six molecules of oxygen.
