The origin of mitochondria and chloroplast are explained by endosymbiotic theory. This theory first postulated by Lynn Margulis in 1967. Mitochondria and chloroplast are eukaryotic cell organelles with bacterial characteristics. According to this theory eukaryotic mitochondria evolved from a small, prokaryotic autotrophic bacterium that was engulfed by large primitive heterotrophic eukaryotic cell. Endosymbiosis of chloroplast occurs when a cell engulfed a photosynthetic cyanobacterium.