Livings organisms survive due to the occurrence of chemical reactions that constantly take place in their bodies. This is known as metabolism and consists of two types of reactions, anabolic and catabolic.
Anabolism refers to the set of chemical reactions that have simple organic and inorganic molecules as reactants and complex organic molecules as the product. Anabolic reactions usually require energy for them to take place. The creation of new cells and reactions that lead to their growth and development are examples of anabolism.
Catabolism on the other hand refers to chemical reactions in which complex organic molecules are broken down and this leads to the formation of simpler organic and inorganic molecules. Catabolic reactions usually release energy, which is used by the body as a power source for anabolic reactions. Examples of catabolism are chemical reactions involved in the digestion of food, destruction of old cells, etc.