Evidence supporting the idea that mitochondria and chloroplasts in present-day cells originated as independent organisms includes:

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All of these options provide evidence supporting endosymbiotic theory, which suggests that mitochondria and chloroplasts were once independent bacterial organisms that were engulfed by another cell and formed a symbiotic relationship. The similarities in DNA sequences between mitochondrial and bacterial genomes, as well as similarities in size and shape between mitochondria and some prokaryotes, support the idea that they originated from bacteria. The similarity between photosynthetic pigments in chloroplasts and cyanobacteria further supports the idea that chloroplasts originated from cyanobacteria. Finally, the similarity in the way mitochondria, chloroplasts, and prokaryotes reproduce also supports the idea that they share a common ancestor.

Evidence Supporting the Idea That Mitochondria and Chloroplasts in Present-Day