The endosymbiosis hypothesis proposes that some organelles which occur in eukaryotes occurred as prokaryotic cells in the past.
Some of the evidence which supports this theory is:
The size of the organelles, chloroplast and mitochondria, is similar to that of the bacterial cell.
Organelles like mitochondria and chloroplast posses their own DNA which is capable to make proteins.
The function of mitochondria is similar to purple- aerobic bacteria. They use oxygen for the synthesis of ATP. The process of Kreb's cycle and oxidative phosphorylation re similar in both.
Chloroplast is similar to photosynthetic bacteria. Both posses chlorophyll.
