According to the theory of endosymbiosis, early eukaryotes evolved by symbiotic association of prokaryotes. witch two protists evolved from a symbiotic relationship of organisms. which resulted in eukaryotic organisms containing chloroplasts

The protists that probably would have originated from endosymbiosis were amoeba and paramecium. On the basis of the theory of endosymbiosis, it is possible that some of the non-photosynthetic species produced a symbiotic association with organisms that possessed the tendency to perform photosynthesis with the help of chloroplasts. These species than would have gained the tendency to perform photosynthesis because of the supplementation of chloroplasts into their cells, and thus led to the formation of eukaryotic species comprising chloroplasts.