* Mitochondria: These organelles are responsible for cellular respiration and energy production. They have their own DNA, separate from the cell's nuclear DNA, and ribosomes that resemble those found in bacteria. This suggests that mitochondria were once free-living bacteria that were engulfed by a larger cell.
* Chloroplasts: These organelles are responsible for photosynthesis in plants and algae. They also have their own DNA and ribosomes that are similar to those found in bacteria. This suggests that chloroplasts were once free-living cyanobacteria that were engulfed by a larger cell.
The endosymbiotic theory proposes that these organelles were once free-living prokaryotes that were engulfed by larger cells and eventually became integrated into the host cell. The similarities between these organelles and bacteria in terms of DNA, ribosomes, and their own membranes strongly support this theory.
