It is define as the elimination or removal of waste product of metabolism which if allow to accumulate it will poisson the cells and prevent the functioning of the cells. It allows involve the elimination of useful substances that are in excess in the body e.g Water other substances that are excreted include carbon dioxide, urea, salts, bile pigment, faeces is not a metabolic waste product because it is undigested food material which has not been involved in cell metabolic activity.

OSMOREGULATION

             It is the maintenance of a relativelt stable water and salt balance I blood plasma or it is the maintenance of the water contain of and organism. This is done by regulating the osmotic pressure of blood and tissue fluid.

HOMEOSTASIS

            It is the maintenance of the constant internal environment i.e tissues fluid in other to creat a stable condition for proper functioning of the body cells. This is brought about by cell regulating of the body cells. This is brought about by cell regulating mechanism. The most important factors of the internal environment that must be kept constant are; Osmotic pressure, Chemical constituents, level of carbon dioxide and temperature.