A mitochondrion produces energy for a cell. Mitochondria (the plural of mitochondrion) are small organelles found in most nucleated cells, including those of plants, animals and fungi.
The primary mechanism by which mitochondria generate energy is through the manufacture of ATP. Standing for adenosine triphosphate, ATP stores energy in its chemical bonds. When the molecule’s bonds are broken, energy is released. ATP is often called the energy currency of an organism, because it can be used to power a wide variety of systems, regardless of the task to be completed.
Mitochondria have their own DNA that is different from that in the cell’s nucleus. Most scientists agree that this is evidence that mitochondria used to be free-living creatures. At some point in evolutionary history, these mitochondria started living inside more advanced cells. This symbiotic relationship benefits both the cell, which derives the energy produced by the mitochondria, and the mitochondria, which has a safe, suitable habitat in which to live.
Mitochondria are also found in plant cells, but they are not the only source of energy for plants. Plants also have chloroplasts which engage in photosynthesis, which provides most of the plant’s energy. Some scientists suspect that chloroplasts were also free living organisms that now live symbiotically within plant cells.