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
lead 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 chlo