The answer is the Ribosomes of mitochondria and plastids are very similar in their structure and function to bacterial ribosomes.Mitochondria, chloroplasts, and bacteria are alike in size. Bacteria also have DNA and ribosomes alike to those of mitochondria and chloroplasts. Based on this and other proof, experts ponder host cells and bacteria shaped endosymbiotic relationships precedent, when separate host cells took in oxygen-using and photosynthetic bacteria but did not put an end to them.