(i) Various organ systems are continuously performing their functions in human body.
(ii) Along with the various systems like digestive, respiratory, circulatory, excretory and control systems, different external and internal organs are performing their functions independently but through a complete co-ordination.
(iii) This overall system is in need of continuous source of energy.
(iv) Besides , it is co-ordinated byt he control system of the body i.e. each life process contributes in its own way in the process of energy production .
(v) Thus , all life processes contribute to the growth and development of the body.
