Noun
a unicellular organism having cells lacking membrane-bound nuclei; bacteria are the prime example but also included are blue-green algae and actinomycetes and mycoplasma
Source: WordNetIt used to be widely assumed that the inner membrane is the original membrane of the once independent prokaryote, while the outer one is the food vacuole (phagosomal membrane) it was enclosed in initially. Source: Internet
Is it a simplified version of a parasitic prokaryote, or did it originate as a simpler virus that acquired genes from its host? Source: Internet
Mitochondria are thought to have come from a similar event, where an aerobic prokaryote was engulfed. Source: Internet