endosymbiont theory(redirected from Endosymbiotic theory)
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endosymbiont theory[‚en·dō′sim·bē‚änt ‚thē·ə·rē]
(cell and molecular biology)
A theory that the mitochondria of eukaryotes and the chloroplasts of green plants and flagellates originated as free-living prokaryotes that invaded primitive eukaryotic cells and become established as permanent symbionts in the cytoplasm.