Examples of protists that possibly evolving form endosymbiosis are Paramecium and amoeba.
As per the theory of endosymbiosis, it is likely that some non-photosynthetic organisms formed a symbiotic relationship with organisms that had the ability to photosynthesize using chloroplasts. These organisms then got the ability to photosynthesize due to the addition of chloroplasts into their cells, and this resulted in eukaryotic organisms with chloroplasts.