How does the endosymbiotic theory (mitochondria and chloroplasts evolving from engulfed prokaryotes) explain the origin of certain viruses? A) Viruses originated from ancient bacterial endosymbiont B) Viruses originated from the host cell organelles C) Viruses originated from horizontal gene transfer D) None of the above

What the endosymbiotic theory is actually explaining

The endosymbiotic theory is about how some eukaryotic cell organelles formed. In particular, it describes how mitochondria and chloroplasts began as free-living prokaryotes that were engulfed by a larger host cell and then became permanent parts of the cell.

Compare each option to the theory’s central idea

• A) Viruses originated from ancient bacterial endosymbiont. The theory says bacteria became organelles (like mitochondria), not viruses.
• B) Viruses originated from the host cell organelles. The provided description does not claim viruses come from organelles; it claims organelles come from bacteria.
• C) Viruses originated from horizontal gene transfer. Horizontal gene transfer is a different idea and is not what the endosymbiotic theory describes.

Correct choice

Because none of A, B, or C matches what endosymbiotic theory explains, the best answer is D) None of the above.