Mitochondria

Mitochondria are organelles present in most eukaryotic cells that are responsible for electron transport, ie the utilization of oxygen in burning food. They contain DNA and are generally considered to be highly modified symbiotic bacteria, possibly related to the purple bacteria, and are believed to have been incorporated only once - compare chloroplasts. Each mitochondrion each have two membranes, the outer one corresponding roughly to a vacuole, and the inner one (of different composition) corresponding to the ancestral bacterial membrane. In order to increase surface area the inner membrane is full of folds called cristae. Mitochondria replicate by fission.