Mitochondria are cellular organelles found in the cytoplasm in round and elongated shapes, that produce adenosine tri-phosphate (ATP) near intra-cellular sites where energy is needed. Shape, amount, and intra-cellular position of mitochondria are not fixed, and their movements inside cells are influenced by the cytoskeleton, usually in close relationship with the energetic demands of each cell type. For instance, cells that have a high consumption of energy, such as muscular, neural, retinal, and gonadic cells present much greater amounts of mitochondria than those with a lower energetic demand, such as fibroblasts and lymphocytes. Their position in cells also varies, with larger concentrations of mitochondria near the intra-cellular areas of higher energy consumption. In cells of the ciliated epithelium for instance, a greater number of mitochondria is found next to the cilia, whereas in spermatozoids they are found in greater amounts next to...