Summary
Proposes that mitochondria and chloroplasts arose from engulfed bacteria that became permanent cell residents.
In depth
Lynn Margulis championed the idea that an ancestral host cell engulfed an aerobic bacterium (mitochondria) and, later in some lineages, a cyanobacterium (chloroplasts). Evidence includes their double membranes, circular DNA, 70S ribosomes, binary fission-like division and genome similarity to bacteria.
Over time many genes moved to the host nucleus. The theory explains why organelles are semi-autonomous.
Frequently asked questions
What is Endosymbiotic Theory?
Proposes that mitochondria and chloroplasts arose from engulfed bacteria that became permanent cell residents.
Which area of biology covers Endosymbiotic Theory, and how advanced is it?
Endosymbiotic Theory is one of the 52 topics in Cell Biology. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Prokaryotic Cell, Chloroplast, Mitochondrion.
Why does Endosymbiotic Theory matter?
It is a major example of a cooperative step in evolution, complementing competition-based ideas.
What should I learn before Endosymbiotic Theory?
Work through the Beginner topics in Cell Biology first, such as Cell Theory, Prokaryotic Cell, Eukaryotic Cell, then return to Endosymbiotic Theory. Intermediate topics assume the Beginner vocabulary.
What topics are related to Endosymbiotic Theory?
The closest topics to Endosymbiotic Theory are Prokaryotic Cell, Chloroplast, Mitochondrion, Eukaryotic Cell. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Endosymbiotic Theory?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Endosymbiotic Theory. To practise the whole of Cell Biology, use the Cell Biology quiz.
How is Endosymbiotic Theory different from Prokaryotic Cell?
Endosymbiotic Theory: Proposes that mitochondria and chloroplasts arose from engulfed bacteria that became permanent cell residents. Prokaryotic Cell: A simple cell with no membrane-bound nucleus; its DNA lies in a nucleoid region, as in bacteria and archaea. Read both side by side and note what each one explains.
How should I study Endosymbiotic Theory step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Prokaryotic Cell and explain the difference aloud. Finally, take the Cell Biology quiz and come back to this page for any question you miss.