Catalase is a name of a enzyme.This enzyme is nearly present in all living plants and animals which are always exposed to oxygen.Catalase enzyme is also present in aerobic and facultative anaerobic micro-organisms.Generally this micro-organisms utilise oxygen and produce hydrogen peroxide and this hydrogen peroxide is toxic to the cells and it effects the cells enzyme system so to avoid this toxic effect micro-organism produces catalase enzyme. The role of catalase enzyme is to convert hydrogen peroxide molecule to water and oxygen and this reaction is a irreversible reaction.