Prokaryotes are single-celled organisms that are composed of the bacteria. Unlike eukaryotic cells, they are less structured, contain no nucleus
In fact, in a loose sense, they serve as the “mitochondria ” of themselves. To put it another way, mitochondria are part of eukaryotic cells, which according to scientific studies evolved from ancestral bacteria.
Endosymbiosis Theory (Source: Wikimedia) Lynn Margulis (Source: Wikimedia) The mitochondria and chloroplasts (photosynthetic organelle) in eukaryotes are the known descendants of aerobic prokaryotes. In 1967, scientist
Lynn Margulis published her
Endosymbiosis theory about the formation of eukaryotic cells as well as the origin of the organelles contained inside them.
To explain the origin of the mitochondria and chloroplasts, she suggested that they were once free-living prokaryotes that were engulfed by a larger eukaryotic cell.
Through time, the organelles became one with those cells, yet remained to be genetically distinct from their host. One important evidence for this claim is the presence of unique genetic material in the eukaryotes’ mitochondria and chloroplasts. Margulis added that life itself, therefore, prevailed over the world not by combat, but rather by networking. 
