When did chloroplasts evolve?
Why are chloroplasts green?
How did chloroplasts get inside cells?
But when other cells ate the blue-green prokaryotes, they found out that it was more useful to let the blue-green prokaryotes live inside them and keep making energy from sunlight, than it was to destroy them.
Gradually more and more cells began to have lots of blue-green prokaryotes living inside them, and by around two billion years ago some of the blue-green prokaryotes lost the ability to live on their own and evolved into chloroplasts (KLOR-oh-plasts) that could only live inside other cells (This is very much like what happened to mitochondria).
A video about chloroplasts
How many chloroplasts are there in a plant cell?
A project to use chromatography to see the colors in leaves