Mitochondria perform several functions within cells, including the production of energy, the generation of heat, the storage of calcium, and the regulation of cell death. Let's take a closer look at each of these.
Mitochondria are organelles (miniature organs) within cells. They have their own membranes (both inner and outer) as well as folds (cristae) and spaces within them that contribute to their function. That function includes the creation of ATP, adenosine triphosphate, which is an energy molecule that cells use to keep on functioning. The citric acid or Krebs cycle produces the chemical NADH, which in turn interacts with enzymes within the mitochondria to produce ATP. When the chemical bonds in the ATP are broken, the result is energy that our bodies use.
Mitochondria are also involved in producing heat to keep our bodies warm. The process is called "proton leak," and it occurs in body tissue known as "brown fat." Mitochondria provide storage for calcium as well, a mineral that our bodies need for many different functions. Mitochondria absorb calcium ions and hold them until our bodies require them.
Finally, mitochondria are key players in cell death. When cells break or get too old to function, our bodies clear them out. The mitochondria release chemicals that aid in this process (which is called apoptosis).