Respiration : Respiration is a catabolic. oxidising and energy liberating process. During this process, exchange of gases takes place, i.e. oxygen is taken into tissue cells and carbon dioxide produced as metabolic waste matter is given out. The energy released by oxidation of food substances such as carbohydrates, fats and proteins is stored in the form of ATP molecules. 

Respiration serves the following purposes :

(1) It helps in keeping the functions of blood normal by adjusting changes in the pH of blood.

(2) It helps in maintaining proper oxygen concentration in the body.

(3) It helps in maintaining normal body temperature.

(4) It provides energy for the activities of the body.