Transmission electron micrograph (TEM) of mitochondria (see arrows). The mitochondrion (plural mitochondria) is a double membrane-bound organelle found in all eukaryotic organisms. 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. The number of mitochondria in a cell can vary widely by organism, tissue, and cell type. For instance, red blood cells have no mitochondria, whereas liver cells can have more than 2000. The organelle is composed of compartments that carry out specialized functions. These compartments or regions include the outer membrane, the intermembrane space, the inner membrane, and the cristae and matrix. Mitchondria have their own DNA (deoxyribonucleic acid) and replicate autonomously. Magnification unknown.