Cells that need to perform high amounts of work, such as muscle cells in the heart and legs, fat cells and liver cells. Mitochondria are organelles which contain their own DNA. Animal cells generally have approximately 1,000 to 2,000 mitochondria.
Mitochondria are organelles that are about 1 to 10 micrometers long. They produce adenosine triphosphate, or ATP, using the energy stored in food. The ATP molecules produced by mitochondria are used as the energy supply for the various cell metabolic processes. The process by which the mitochondria produce ATP is called aerobic respiration and this process allows cells to produce 15 times more ATP than they would without mitochondria.