What is one piece of evidence that some organelles like mitochondria and chloroplasts within eukaryotes used to be independent prokaryotes that were incorporated into eukaryotic cells?

organelles are very similar to present-day bacteria, suggesting a common ancestor.

Explanation:

Some evidence suggests that some organelles like mitochondria and chloroplasts within eukaryotes were once used to be independent eukaryotes.

Endosymbiosis theory says that ancestral prokaryotic cells engulfed bacteria like cyanobacteria which with time evolved into mitochondria and chloroplast. Molecular evidence also proves that these organelles were once prokaryotic organisms because they show similar genetic makeup and ribosome type.

So these organelles are similar to present-day bacteria showing that they have a common ancestor.