Final answer:
Chloroplasts and mitochondria are believed to have evolved from bacterial cells through endosymbiosis. They have their own DNA and are surrounded by two membranes.
Step-by-step explanation:
Chloroplasts and mitochondria are believed to have evolved from bacterial cells through a process called endosymbiosis. This theory suggests that a primitive eukaryotic cell engulfed a complete aerobic bacterium (or proto-bacterium) and formed a symbiotic relationship with it. The bacterium eventually became an organelle within the host cell cytoplasm, giving rise to mitochondria. Similarly, chloroplasts may have originated from cyanobacteria engulfed by primitive eukaryotic cells. These organelles have their own DNA, similar to bacteria, and are surrounded by two membranes.