Photosynthetic pigment at 400-530 nm. However, none of the pigments absorbs well in the green-yellow region, which is responsible for the abundant green we see in nature. Like plants, the cyanobacteria use water as an electron donor for photosynthesis and therefore liberate oxygen; they also use chlorophyll as a pigment. In addition, most cyanobacteria use phycobiliproteins, water-soluble pigments which occur in the cytoplasm of the chloroplast, to capture light energy and pass it on to the chlorophylls. (Some cyanobacteria, the prochlorophytes, use chlorophyll b instead of phycobilin.) It is thought that the chloroplasts in plants and algae all evolved from cyanobacteria. Several
Carotene from their diets. Carotenes contribute to photosynthesis by transmitting the light energy they absorb to chlorophyll. They also protect plant tissues by helping to absorb the energy from singlet oxygen, an excited form of the oxygen molecule O which is formed during photosynthesis. β-Carotene is composed of two retinyl groups, and is broken down in the mucosa of the human small intestine by β-carotene 15,15'-monooxygenase to retinal, a form of vitamin A. β-Carotene can be stored in the liver and body fat and converted to retinal as needed, thus making it a form of vitamin A for humans and some