Respiration is a complex process, which includes :

 1. Absorption of O2.

2. Conversion of carbohydrate (complex) to CO2 and H2O and simpler substances (i.e. oxidation of food).

3. Release of energy -a part of which is utilized in various vital processes and the rest may be lost in the form of heat.

4. Formation of intermediate products playing different roles in metabolism.

5. Liberation of CO2 and H2O

6. Loss in weight in plants as a result of oxidation.

Therefore, respiration is a reverse process of photosynthesis.