Metabolism is the overall process through which living systems acquire and utilize the free energy they need to carry out their various functions. Metabolism is the essential for all types of living organisms and cells. The chemical changes that occur when animals consume plant or animal tissues as food, or when plants carry out photo synthesis are known as metabolism The free energy content of a substance play the role in the lives of organisms and cells. The metabolism is also essential in the course of study related to the biological sciences at various levels.