pply of adenosine triphosphate (ATP), which is subsequently used throughout the cell as a source of chemical energy.[2] They were discovered by Albert von Kölliker in 1857[3] in the voluntary muscles of insects. The term mitochondrion was coined by Carl Benda in 1898. The mitochondrion is popularly nicknamed the "powerhouse of the cell", a phrase coined by Philip Siekevitz in a 1957 article of the same name.[4] Some cells in some multicellular organisms lack mitochondria (for example, mature mammalian red blood cells). A large number of unicellular organisms, such as microsporidia, parabasalids and diplomonads, have reduced or transformed their mitochondria into other structures.[5] One eukaryote, Monocercomonoides, is known to have completely lost its mitochondria,[6] and one multicellular organism, Henneguya salminicola, is known to have retained mitochondrion-related organelles in association with a complete loss of their mitochondrial genome.[6][7][8] Mitochondria are commonly between 0.75 and 3 μm2 in area,[9] but vary considerably in size and structure. Unless specifically stained, they are not visible. In addition to supplying cellular energy, mitochondria are involved in other tasks, such as signaling, cellular differentiation, and cell death, as well as maintaining control of the cell cycle and cell growth.[10] Mitochondrial biogenesis is in turn temporally coordinated with these cellular processes.[11][12] Mitochondria have been implicated in several human disorders and conditions, such as mitochondrial diseases,[13] cardiac dysfunction,[14] heart failure[15] and autism.[16]