Chloroplasts are double membrane bound cell organells which help in photosynthesis in green plants. It has two distinct regions small disc like structures called grana which are the site for the light reaction of photosynthesis and colourless matrix called stroma which is the site for dark reactions of photosynthesis. Each granum is formed by a stack of closed compartments called thylakoids i.e., the thvlakoid in chloroplast are arranged as stacked discs. Thylakoid membranes have particles embedded on them called quantasomes. They are referred as photosynthetic units.