Phytochrome has a light absorbing or light detecting portion (the chromophore) attached to small protein of about 1,24,000 daltons. Phytochrome occurs in 2 forms, i.e., P_R and P_FR (i.e., red light and far red light absorbing forms) and these 2 forms are interconvertible.

Cytochromes are electron transferring proteins. They contain iron porphyrin or copper porphyrin as prosthetic groups. Chlorophyll is the fundamental green pigment of photosynthesis. It is localised in the chloroplasts. Carotenoids are lipid compounds and they are yellow, orange, purple, etc. in colour. These are found in higher plants red algae, green algae, fungi and photosynthetic bacteria.