The 1 st Law of Thermodynamics is the law of energy conservation. This means that the total amount of energy in the universe is constant. In an isolated system, energy can be changed from one form to another and transferred from one molecule to another, but energy cannot be created or destroyed . The 2 nd Law of Thermodynamics states that energy conversions reduce the order in the universe. That reduced order is called entropy .
Heat is one form of disorder or entropy.
They regulate chemical reactions, through metabolism. Metabolism is the sum total of all chemical reactions in a cell. These reactions have a net release of energy so they are called exergonic reactions. Examples of catabolic reactions would be hydrolysis and the reactions involved in cellular respiration. There is a net input of energy so these reactions are called endergonic .