Mitochondrion(pl. mitochondria)

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The mitochondrion is a double membraned organelle involved in the synthesis of ATP, the main substance used by cells to supply immediate energy to do work. Sometimes ATP is called the energy currency of the cell.

The diagram shows an enlargement of the mitochondrion with part of the outer membrane(purple) cut away to show the the inner membrane divides the mitochondrion into separate compartments. This arrangement is important for the method used by the organelle to make ATP by a process called chemiosmosis or electron transport phosphorylation. By the way, the oxygen that we breathe is plays a key role in this particular process inside the mitochondrion.

Mitochondria are interesting because they have their own DNA very much like that found in bacteria. Also the mitochodria replicate themselves rather than being replicated by the cell. For these and for other reasons scientists today suspect that mitochondria may have evolved from free living cells that developed a symbiotic relationship with the ancestors of modern eukaryotic cells.