According to endosymbiotic theory, the chloroplast evolved as a result of engulfment and assimilation of a Cyanobacteria by an eukaryotic cell.
Explanation:
Endosymbiotic theory supports the view that ceratain organelles of the eukaryotic cell evolved as a result of engulfment of single celled organism.
Evidences that support this theory is the presence of organellar DNA.
It is assumed that Mitochondria evolved as a result of engulfment and assimilation of an aerobic prokaryote while Chloroplast evolved due to engulfment and assimilation of a photosythetic prokaryote by an Eukaryote.
After the engulfment ,these organisms however escaped the phagocytosis and began to benefit the eukaryotic Host.
Soon it lost many of its Genes to the eukaryotic nucleus and became dependent on the Host.
Thus a symbiotic association was established between the prokaryote and the host.Giving rise to cell organelles.
