Origins - Endosymbiosis
Biology: IB Diploma Higher Level, topic 2.1.1
Endosymbiosis
We have mentioned that both mitochondria and chloroplasts contain DNA and ribosomes. Have you wondered why? Strong evidence points to endosymbiosis as the explanation.
Symbiosis
- Symbiosis is a relationship in which organisms from two separate species depend on each other for their survival.
- Endosymbiosis (endo- = “within”) is a mutually beneficial relationship in which one organism lives inside the other.
Endosymbiosis - background
- Scientists have long noticed that bacteria, mitochondria, and chloroplasts are similar in size.
- We also know that bacteria have DNA and ribosomes, just as mitochondria and chloroplasts do.
Endosymbiosis - process
- Scientists believe that host cells and bacteria formed an endosymbiotic relationship when the host cells ingested both aerobic and autotrophic bacteria (cyanobacteria) but did not destroy them.
- Through many millions of years of evolution, these ingested bacteria became more specialized in their functions,
Animal and plant cells
- Scientists believe plant and animals cells most likely evolved through a process whereby:
- A host cell ingested aerobic bacteria gave rise to modern animals.
- An ancestor of that cell that also ingested photoautotrophic bacteria that gave rise to modern plants.
Test yourself on Origins - Endosymbiosis
Which of the following does NOT contain DNA and ribosomes?
What does "endo-" mean?