| endosymbiosis | A symbiotic relationship between two organisms in which one of the two organisms (the endosymbiont) lives inside the body of the other one (the host). Compare: ectosymbiosis. (09 Oct 1997) |
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| endosymbiosis theory | The scientific theory that the organelles of eukaryotic cells arose when free-living procaryotic cells began living within other, larger free-living procaryotic cells and formed mutualistic symbiotic relationships with them. (09 Oct 1997) |