You're right: I probably confounded "cells" with eucaryotic cells. My understanding (from school biology half a century ago) is that a strong candidate for the

You're right: I probably confounded "cells" with eucaryotic cells. My understanding (from school biology half a century ago) is that a strong candidate for the origin of chloroplasts is cyanobacteria, incorporated as guests. I'm not sure that eucaryotic cells are the only kind of "big" cells that could adopt cyanobcteria as organelles. Anyway, I wasn't considering bacteria as "cells".