Carotenoids are tetraterpenes. They are present in both plants and animals. The isoprene derivatives of carotenoids are highly unsaturated. Due to the presence of many conjugated double bonds, they are red or yellow in colour. For example, the pigments of tomato (lycopene) and carrot (α- and β-carotene) are red, whereas oxygen-containing carotenoids are yellow (xanthophyll).