Metabolism + 3 laws of Thermodynamics

1-First Law of Thermodynamics: Energy can be changed from one form to another, but it cannot be created or destroyed.  The Total amount of energy and matter in the universe remains CONSTANT from one form to another
With respect to metabolism and the human body, when we say calories are being "burned" it does not mean that the calories are disappearing.  We know that since calories are unites of energy they cannot disappear, they are just being transformed from the chemical form stored whithin your body to either heat or mechanical form that is not stored whithin your body.

2-Second Law of Thermodynamics: states that "in all energy exchange, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state."
This is also reffered to as ENTROPY.

It is important to understand that it is the second law that drives chemical reactions.  The second law tells us whether a metabolic reaction will occur and what the relative distributions of the forms of the energy will be. To predict the tendency of the reaction to occur, we must employ the second law that says the entropy must increase. Thus living systems are not in equilibrium, but instead are dissipative systems that maintain their state of high complexity by causing a larger increase in the entropy of their environments. The metabolism of a cell achieves this by coupling the spontaneous processes of catabolism to the non-spontaneous processes of anabolism. In thermodynamic terms, metabolism maintains order by creating disorder.

3-Third Law of Thermodynamics: or Absolute Zero (-273C) explains that nothing in this temperature can have function because all the thermal kinetic energy ceases.
There would be no function in this temperature and no metabolism takes place because there would be no molecular motion.  Enzymes also cannot function in extremely high or low temperatures.