Color enhanced illustration of a mitochondrion. In cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed organelle. Mitochondria are sometimes described as "cellular power plants" because they generate most of the cell's supply of adenosine triphosphate (ATP). As well as supplying cellular energy, mitochondria are involved in a range of other processes, such as signaling, cellular differentiation, cell death, as well as the control of the cell cycle and cell growth.