How would you define endosymbiotic theory?

1 Answer
Jul 4, 2017

The endosymbiotic theory describes how mitochondria and chloroplasts (cell organelles) came to exist in eukaryotic organisms.


The endosymbiotic theory explains the evolution of mitochondria and chloroplasts. Before mitochondria and chloroplasts were organelles in a cell, they were free prokaryotic cells that were absorbed by eukaryotic cells.

The mitochondrion was originally a prokaryotic cell that could undergo aerobic respiration. After being absorbed by a eukaryotic cell, it developed a symbiotic relationship with its host cell.

The chloroplast was originally a prokaryotic cell that could undergo photosynthesis (eg. cyanobacteria). Like the mitochondria, the photosynthesizing bacteria became dependent on the host cell after being engulfed.

There is much evidence to support the endosymbiotic theory.

  • Both prokaryotes and chloroplasts/mitochondria have circular DNA
  • Both have their own ribosomes
  • Both divide through binary fission (splitting into two)
  • Both have their own cell membranes