Answer & Explanation
B) biochemical reactions involved in building cell molecules or breaking down molecules for energy
Metabolism (from Greek: μεταβολή metabolē, "change") is the set of life-sustaining chemical transformations within the cells of organisms. The three main purposes of metabolism are the conversion of food/fuel to energy to run cellular processes, the conversion of food/fuel to building blocks for proteins, lipids, nucleic acids, and some carbohydrates, and the elimination of nitrogenous wastes.
In brief, the chemical processes that occur within a living organism in order to maintain life is called metabolism.