Q. How is the finding of ribosomes inside mitochondria and chloroplasts explained?
It is a strong hypothesis that chloroplasts and mitochondria were prokaryotes that associated to primitive eukaryotic cells under mutualism gaining protection and offering energy. This explains why within those organelles there are protein and DNA synthesis machinery including ribosomes. This hypothesis is called as the endosymbiotic hypothesis on the origin of chloroplasts and mitochondria.