What are endosymbiosis and secondary endosymbiosis?
1 Answer
Endosymbiosis : The engulfing of prokaryotic cells by hetretrophic eukaryotic cells.
Secondary endosybiosis : The engulfing of an cell that has undergone endosymbiosis by a heterotrophic eukaryotic cell.
Explanation:
Endosymbiosis is the theory that attempts to explain how the prokaryotic cells gave rise to the first eukaryotic cell organelles.
In this theory, a heterotrophic (gains energy from outside sources) eukaryotic cell engulfs an autotrophic (creates its own energy) prokaryotic cell which is too big to be digested. The prokaryote is at first able to leave the eukaryotic cell, but if it doesn't then over time, the prokaryote loses the ability to function independently, and becomes reliant on the eukaryote for energy. At the same time, the eukaryote becomes more efficent at processing energy or gained additional energy because of the prokaryote.
Eventually, the prokaryote loses the genes necessary for independence and gives them to the eukaryotes nucleus, thus making the relationship truly symbitoic. The eukaryote now replicates itself with the prokaryote inside, which has now transformed into a chloroplast, or mitochondria, or other.
Secondary endosymbiosis is when a cell that has undergone endosymbiosis is engulfed by another, free living organism. The same process as endosymbiosis happens, except that the absorbed cell becomes completely dependent on the absorber cell almost immediately and cannot leave to return to its original state. Secondary endosymbiosis has happened enough times to create extreme genetic diversity amongst species on Earth.
This theory is an amalgamation of similar theories attempting to explain how organelles in eukaryotic cells formed, and is not complete or completely proven. Rather, it is the model that best fits the information at hand.
http://www.fossilmuseum.net/Evolution/Endosymbiosis.htm
I hope I helped!
