What Is Primary Endosymbiosis?


Quick Answer

Primary endosymbiosis is the hypothesis that the first eukaryotic cells began as a result of the coming together of different types of microbes. Animal cells all contain mitochondria, and these organelles show many signs of having once been free-living prokaryotes that were taken up by early nucleated cells.

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Full Answer

This hypothesis explains many features of mitochondria and chloroplasts. These structures have their own DNA, for example, that is organized in a ring shape common to bacteria but unknown among eukaryotes. A likely explanation for the partnership between cell types is that a nucleated cell absorbed a bacterial cell, without digesting it, and came to rely on the nutrients its "prey" secreted.

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