Biological energy: Whenever matter is broken down its chemical energy is released as heat. Non biological system can utilize this heat energy directly in the performance of work, or may easily convert it into mechanical electrical or other forms of energy. Because these system are an isothermal i.e. they do not maintain constant temperatures. Biological system on the other hand are isothermal they maintain either a fixed body temperature or an optimum range of temperature equal to that of the environment. A rise or fall in body temperature by a few degrees from the constant or optimum temperature has an adverse effect on the structure and function of living cells. Thus living systems cannot use heat energy directly to perform work. These therefore require an energy exchanges i.e. an intermediary compound capable of receiving energy of chemical oxidation directly from the oxidative or energy release processes, storing this energy in its molecules and supplying it directly to the energy consuming processes .Obviously, the energy stored by this compound is the energy used by living system ,and this is called Biological energy.