Another class of pigments are the carotenoids. Carotenoids are typically yellow, orange, or red pigments. Carotenoids do not dissolve in water due to their two six carbon rings which are connected by a chain of carbon atoms. Carotenoids are accessory pigments, they cannot transfer the energy absorbed from the sun into photosynthetic pathways, instead they must give the energy to chlorophyll a. The third class of pigments are the phycobilins.
Phycobilins are water-soluble and are found in the stroma or cytoplasm of the chloroplast.
This last class of pigments is only found in the marine organisms Cyanobacteria and Rhodophyta. Phycobilins effectively absorb energy and are also used by scientists for cancer research. Scientists often use phycobilins to track tumor cells. Chromatography is a technique used to separate mixtures of compounds. This technique was discovered in 1906 but not widely used until the 1930's.