Photosystem-II consists of three parts. Light absorption organs, reaction centers (trapping centers) and electron transport systems. It consists of chlorophyll-ÔaÕ 673, chlorophyll-b and P-680. P-680 is a reaction dye. It absorbs red light the most at a wavelength of 680 nm. Hence it is called P-680. Photosystem-II resides mainly at the edges of the grana lamellae. Photosystem-II evolved in cyanobacteria only 3 billion years ago.