Evolutionary Biology/Secondary endosymbiosis

A process in eukaryotic evolution in which a heterotrophic eukaryotic cell engulfed a photosynthetic eukaryotic cell which survived in a symbiotic relationship inside the heterotrophic cell from primary endosymbiosis.

Secondary endosymbiosis is when a living cell engulfs another eukaryote cell that has already undergone primary endosymbiosis. It has happened often enough that it has led to genetic diversity among the organisms on Earth. Though it undergoes the same process of primary endosymbiosis, the cell that becomes engulfed now becomes very dependent on the larger cell. Unlike primary endosymbiosis, the engulfed cell cannot leave the larger cell and return to its original state. The engulfed primary endosymbiosis cell now has a double phospholipid bilayer. The bilayer consists of its original outer membrane and the membrane of the cell it engulfed in primary endosymbiosis. This evidence of a phospholipid bilayer also encourages that both mitochondria and chloroplasts originated from endosymbiosis.