Question

which of the following organelles is believed to have been its own prokaryotic cell (with its own dna), and then, was engulfed by a larger prokaryotic cell, forming a symbiotic relationship?
nucleus
mitochondrion
ribosomes
golgi

Explanation:

The endosymbiotic theory posits that mitochondria were once free - living prokaryotic cells with their own DNA. They were engulfed by larger prokaryotic cells, establishing a symbiotic relationship. Nucleus, ribosomes, and Golgi do not have this origin story.

Answer:

B. Mitochondrion