Chloroplasts are the site of photosynthesis. Chloroplasts are disc-shaped, 2-10 μm in diameter, about 1 μm thick and are surrounded by a double membrane.The light-dependent stage of photosynthesis takes place in the grana which are stacks of flattened discs called thylakoids. The thylakoids contain the photosynthetic pigment - chlorophyll and other photosynthetic pigments. Some thylakoids are joined to thylakoids in adjacent grana by inter-granal lamellae.The chloroplasts are filled with a fluid matrix called the stroma in which the light-independent reaction takes place. The chloroplast contains its own DNA and 70S ribosomes. The stroma may contain starch grains.