Question

the endosymbiotic theory helps to explain the origin of which structures?
mitochondria
ribosomes
nuclei
cell membranes

Explanation:

The endosymbiotic theory posits that mitochondria and chloroplasts originated from prokaryotic cells that were engulfed by a host cell. Mitochondria are thought to have been aerobic bacteria. Ribosomes, nuclei, and cell - membranes are not explained by this theory.

Answer:

mitochondria