Problem:

Mitochondria and plastids have their own DNA, their own membranes, and their reproduction is not tied to the reproductive cycle of the host cell. However, they are considered to be organelles rather than a separate species in symbiosis with eukaryotes. Granted, mitochondria and plastids are incapable of living outside their parent cells, and likewise eukaryotes are incapable of surviving without the help of mitochondria and plastids. But this is also true of many other symbiotic pairs in Eukarya. So where does the distinction lie?

Question: What makes mitochondria and plastids organelles rather than separate organisms?

Explain your answer.