Pyrenoids are spherical protein body found in the chloroplasts of many algae and the homwons. These contain Rubisco, an enzyme that catalyzes the incorporation of inorganic CO2 into carbohydrate. In some algae, pyrenoids are the sites of carbohydrate (starch mainly) storage. Staining a thin algal preparation with iodine produces blue-black color which confirms the presence of pyrenoids.