What evidence is there to support the hypothesis that chloroplasts and mitochondria were primitive prokaryotes that developed a relationship of mutualism with primitive anaerobic eukaryotic cells?

Answer 1

Endosymbiotic hypothesis which proposes that mitochondria and plastids (in this case we're talking about chloroplasts, which are a type of plastid) were formerly small prokaryotes living within larger host cells. The prokaryotic ancestors of mitochondria and plastids probably gained entry to the host cell as undigested prey or internal parasites. In the process of becoming more interdependent, the host and endosymbionts would have become a single organism. Another concept known as Serial endosymbiosis supposes that mitochondria evolved before plastids through a sequence of endosymbiotic events is another way to think of it. When explaining mutualism in this example, it's due to the fact that mitochondria and chloroplasts offer energy and nutrients to the cell in exchange for protection. It's thought that these primitive organelles have their own DNA, RNA, and protein synthesis mechanisms, and can perform binary division like bacteria.