Metabolism is the sum of all the chemical reactions that occur in the cells of living organisms, which allow them to maintain life. These reactions involve transforming energy and matter from one form to another. Metabolism can be divided into two main processes: catabolism, in which larger molecules are broken down into smaller ones, releasing energy; and anabolism, in which smaller molecules are combined to form larger ones, consuming energy. The rate and efficiency of metabolism are determined by various factors, including genetics, age, sex, and lifestyle.