Final answer:
Mitochondria and chloroplasts are thought to have arisen from an early form of bacteria through endosymbiosis. They have their own genetic system and synthesize some of their own proteins.
Step-by-step explanation:
Scientists believe that mitochondria and chloroplasts originated from separate organisms through endosymbiosis. Host cells ingested bacteria, including aerobic bacteria which became mitochondria, and autotrophic bacteria which became chloroplasts. These organelles have their own DNA and ribosomes, similar to bacteria. They also have specialized functions and are surrounded by membranes. Therefore, the correct answer is b. they have their own genetic system and synthesize some of their own proteins.