Question

Explain the origins of organelles. (15MARKS) (200words)

Answer 1

There are many theories put forward fr endosymbiotic origin of eukaryotic organelles. Now-a-days scientists are under the opnion that the prokaryotic Archean seem to have acquired other prokaryootes as symbionts in their body which gradually evolved in ot organelle.s

Evolution of nucleus seems to have occured by endosymbiotic relation of Archaeon in eubacterial body. Some theories also explain about the invagination of the plasma membrane in to give rise to the membrane bound nucleus. But none of the theories do not have any molecular backing and also the nuclear structure does not resemble any prokaryotic cellular structure.

Mitochondria and plastids seem to have evolved by endosymbiosis. This is because we can see the similarities in these structures and the structure of the bacterial membranes, ribosomes and the bosy size of the prokaryotes.

Mitochondria seem to have originated by the phagocytosis of the aerobic bacterium which failed to get digested in side the cell and remained as the symbiont inside. Because of the bebifits the host and the symbiont have for each other, they must have remained as the symbionts and became organelles in the cells.

Plasids must have originated by endosymbiosis when a cyanobacteria which can photosynthesise is phagocytosed by a host eukaryotic cell. The host cell is getting benifitted by the food prepared by the symbiont and the symbiont is getting the raw materials and the shelter. This led to plastiids in plant cells. So all the two membrane bound organelles are hypothesized to ahve originated from phagocytosis and endosymbiotic relation.