<unk>  describes the metabolic reactions and processes that take place in a cell or across the cell membrane to obtain biochemical energy from fuel molecules and the release of the cells' waste products. Energy is released by the oxidation of fuel molecules and is stored as "high-energy" carriers. The reactions involved in<unk>  are catabolic reactions in metabolism.
Fuel molecules commonly used by cells in<unk>  include glucose, amino acids and fatty acids, and a common oxidizing agent (electron acceptor) is molecular oxygen (O2).  There are organisms, however, that can respire using other organic molecules as electron acceptors instead of oxygen. Organisms that use oxygen as a final electron acceptor in<unk>  are described as aerobic, while those that do not are referred to as anaerobic.
The energy released in<unk>  is used to synthesize molecules that act as a chemical storage of this energy. One of the most widely used compounds in a cell is adenosine triphosphate (ATP) and its stored chemical energy can be used for many processes requiring energy, including biosynthesis, locomotion or transportation of molecules across cell membranes. Because of its ubiquitous nature, ATP is also known as the "universal energy currency", since the amount of it in a cell indicates how much energy is available for energy-consuming processes.
Cellular respiration
Fatty acid metabolism
Drug metabolism
Cell signaling
Oxidative phosphorylation
Carbohydrate metabolism
ATP hydrolysis
Chiral pool synthesis