The biochemical processes by which all living organisms sustain life. Metabolism is the sum of all chemical processes occurring within living cells and organisms. Although most living organisms on earth share common pathways to sustain life they do so with the use of different sources of energy and carbon. Metabolism consists of two main types of reactions, catabolic and anabolic. Catabolic processes are ones in which biomolecules are being degraded or oxidized. Anabolic processes are ones in which biomolecules are built via biosynthesis and reduction.