Answer/Explanation:
The endosymbiotic theory is the idea that eukaryotic cells evolved from the fusion of two prokaryotic cells that formed a symbiotic relationship, with one living inside the other.
An endosymbiont is one organism that lives inside another one.
The existence of mitochondria and chloroplasts, which contain their own DNA and ribosomes, supports this theory. Mitochondria are chloroplasts were once free-living organisms, they were prokaryotes that ended up inside of other cells.
Mitochondria and chloroplasts have genes that are very similar to the genes of prokaryotes. Their membranes look like the prokaryotic cell membrane, and they divide in similar ways.
