In order for a reaction to begin there must be a certain amount of energy present. This amount of energy is called the activation energy. A catalyst is something used to lower the activation energy needed for a reaction to happen. A catalyst will affect the rate at which a reaction will happen. Catalysts speed up a reaction but are not used in the reaction (they are not reactants).
An example of a catalyst in your body would be an enzyme. Enzymes play several roles in your body and are necessary for many reactions in your body to take place at a faster speed. Enzymes are made from proteins which are synthesized by the ribosomes inside your cells.
Graph: A reaction needs less energy and happens faster in the presence of a catalyst.
