The Mitochondrion (mitochondria in plural) are very prominent in the cell, as they play a very important part in the creation of energy within the cell.   Mitochondria contain enzymes that help convert food material into adenosine triphosphate (ATP), which can be used directly by the cell as an energy source. Mitochondria tend to be concentrated near cellular structures that require large inputs of energy, such as the flagellum.

Mitochondria

Contributed By: John B. Ferguson, Sc.B., M.Phil., Ph.D.
Professor of Biology, Division of Natural Sciences and Mathematics, Bard College. Director,
Distinguished Scientist Lecture Series, Bard Center.
Biology, © Microsoft

A mitochondrion is typically long and slender, but it can appear bean-shaped or oval-shaped under the electron microscope. Ranging in size from 0.5 micrometer (0.00005 in) to 1 micrometer (0.0001 in) in length, a mitochondrion has a double membrane that forms a sacwithin a sac. The smooth outer membrane holds numerous transport proteins, which shuttle materials in and out of the mitochondrion. The region between the outer and inner membranes, which is filled with liquid, is known as the outer compartment. The inner membrane has numerous folds called cristae. Cristae are the sites of ATP synthesis, and their folded structure greatly increases the surface area where ATP synthesis occurs. Transport proteins, molecules called electron transport chains, and enzymes that synthesize ATP are among the molecules embedded in the cristae. The cristae enclose a liquid-filled region known as the inner compartment, or matrix, which contains a large number of enzymes that are used in the process of aerobic respiration.