Endosymbiosis Theory

The endosymbiosis theory hypothesizes the origin of organelles within eukaryotic cells. It assumes that once all cells on Earth were prokaryotes. At some point, a larger bacteria ingested a smaller bacteria, keeping the membrane intact. The two bacteria began to work together as a unit, symbiotically, relying on each other and reproducing. If the larger cell ingested a cyanobacteria, that bacteria became a chloroplast and the cell a plant cell. In fact, chloroplast and mitochondria are the major evidence for the endosymbiotic theory because they both still act like prokaryotes. They have their own DNA compared to the rest of the cell and divide separately from the cell, using binary fission, typical to prokaryotes. However, the chloroplast and mitochondria still need the rest of the cell to live and thrive.