Chloroplasts play a major role in producing sugar or starch to photosynthetic plants, plants that can produce their own food. Granum (singular) or grana (plural) is generally a stack of thylakoids in the chloroplast, which is an organelle chiefly found in plants as well as in eukaryotic algae, wherein the production of starch (also known as photosynthesis) takes place. Grana are connected by the stroma thylakoids which is also called as either intergrana thylakoids or lamellae. Stroma thylakoids and grana thylakoids can be distinguished by their different protein composition. Since grana are vital in the formation of ATP (Adenosine triphosphate), chloroplasts have around 10 to 100 grana.
What is Granum Structure
The structure of granum, when seen under a light microscope, is normally in the formation of green granules and as a series of stacked disk-shaped membranes, under an electron microscope. Every granum contains the carotenoids and chlorophylls, which produces the color of the plant; and are the sites of the light reactions of photosynthesis.