Answer:
The endosymbiotic theory is an evolutionary theory states the evolution of eukaryotic cell from the prokaryotic cells.
It was stated 1905 and 1910 by the Russian botanist. It holds mitochondrial plastids such as chloroplast and possibly the other organelles of the eukaryotic cells represents formerly free-living prokaryotes living one inside the other inside the body of prokaryotes.
The formation of eukaryotic organelles took place when the organelles of the prokaryotic cells combined together.