Why are mitochondria and chloroplasts believed to have entered early eukaryotic cells by endosymbiosis of bacteria?

Question

Quizplus · Accepted Answer

Mitochondria and chloroplasts are believed to have entered early eukaryotic cells by endosymbiosis of bacteria because they are the same size as bacteria, contain DNA, and are not derived from the endomembrane system as other organelles are. All of these characteristics support the endosymbiotic theory, which states that early eukaryotic cells engulfed bacteria that were able to provide a benefit to the host cell, and over time, the bacteria and host cell evolved together to form a symbiotic relationship.

Why Are Mitochondria and Chloroplasts Believed to Have Entered Early