Question

Describe how some cells came to have chloroplasts, according to the theory of endosymbiosis.

Answer 1

@Goku-Kai

Answer 2

According to the theory of endosymbiosis, chloroplasts (and mitochondria in animal cells) were once free living prokaryotes. These were 'eaten' or 'engulfed' by eukaryotic cells but, instead of being digested, came to serve specialized functions within the eukaryotic cell and replicate with it.

People who like this theory - most do - point to the fact that both chloroplasts and mitochondria still have some of their own DNA, possibly left from the days when they lived outside eukaryotic cells.