Carotene and xanthophyll are the two classes of carotenoids in plants that function as accessory pigments in photosynthesis by absorbing light energy at wavelengths inefficiently absorbed by chlorophyll. They also protect plants from overexposure to sunlight by absorbing the excess light energy as heat.
Carotenoids are fat-soluble pigments attached to the wall of chloroplasts in which they are synthesized and stored. Carotenes are reddish-orange pigments that contain only one carbon and hydrogen atom. Common carotenes are alpha-carotene, beta-carotene and lycopene. Xanthophylls are yellow pigments that are oxygenated carotenoids. The oxygen atom helps in accepting or donating electrons. Zeaxanthin and lutein are typical xanthophylls.