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 endosymbiosis is a type of
symbiosis in which one organism lives inside 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.
