The endosymbiotic theory explains that mitochondria and chloroplasts descended from the same type of bacteria. Symbiosis is an interaction between two organisms of different species, and <u>endo</u>symbiosis is a type of symbiosis in which one organism lives <u>inside </u>the other one. According to the endosymbiotic theory, a host cell ingested symbiotic bacteria, which specialized into mitochondria or chloroplasts. The evidence for this theory is that mitochondria and chloroplasts, like bacteria, have their own circular DNA. They also have their own transcriptional and translational machinery.
