Question

Describe the theory of endosymbiosis

Answer 1

Theory of Endosymbiosis:

The theory of endosymbiosis is an attempt to explain the origin of modern day eukaryotic cells from ancestral prokaryotic cell. It explains the formation of various organelles, like the nucleus, endomembrane system, mitochondria and chloroplast. The process can be split into three stages-

1. Plasma membrane infolding: Initially, a large ancestral prokaryotic cell would have undergone infoldings in the plasma membrane. This gave rise to the nucleus, endoplasmic reticulum, and golgi apparatus (endomembrane system).
2. Primary endosymbiosis: In the next stage, the cell engulfed a smaller heterotrophic aerobic bacteria. It evolved into mitochondria of the eukaryotic cell and completed the formation of animal cells.
3. Secondary endosymbiosis: Finally, one lineage of these cells underwent another round of endosymbiosis, in which a photosynthetic bacteria was incorporated into the cell. This bacteria evolved into chloroplast, and this is how plant cells came into existence.