Also found in: Dictionary, Medical.
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.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.