Any of a class of yellow to red pigments found especially in plants, algae, and photosynthetic bacteria. Carotenoids generally consist of conjoined units of the hydrocarbon isoprene, with alternating single and double bonds. The carotenoids absorb light energy of certain frequencies and transfer it to chlorophyll for use in photosynthesis. They also act as antioxidants for chlorophyll, protecting it from damage by oxidation in the presence of sunlight. Carotenoids are nutritionally important for many animals, giving flamingoes their color, for example, and also have antioxidant properties. There are many types of carotenoids, including carotenes and xanthophylls.