Final answer:
Mitochondria were most likely descendants of aerobic bacteria according to the endosymbiotic hypothesis.
Step-by-step explanation:
The endosymbiotic hypothesis suggests that mitochondria were descendants of aerobic bacteria that were engulfed by primitive eukaryotic cells.
This theory was first proposed by Lynn Margulis.
The mitochondria and chloroplasts are believed to have originated from separate endosymbiotic events.