Mitochondria

 Were Cellular Powerhouses Once Parasites?Thomas Fuchs

Mitochondria may have started out stealing energy rather than producing it

Jan 20, 2015 |By Annie Sneed

Mitochondria, the organelles known to every junior high school student as “the powerhouses of the cell,” go back some two billion years. Although these energy producers were identified in the 1800s, how they became fixtures in cells is still under debate.

Mitochondria's ancestor was a free-living bacterium that another single-celled organism ingested. Most biologists think that the bacterium benefited the host: in one hypothesis, these premitochondria supplied hydrogen to make energy. Other researchers think that when atmospheric oxygen rose sharply in that era, anaerobic cells needed the bacteria to clear out the gas, which is toxic to them. However the match was made, the two lived so harmoniously that they eventually became mutually dependent and formed a long-term relationship./.../