Photosynthetic Pigments

A photosynthetic pigment is any light-absorbing molecule housed in a chloroplast (or, in bacteria, in an equivalent photosynthetic structure) that captures the light energy photosynthesis runs on. These pigments fall into three chemically distinct families, summarised in Table 13.1: the chlorophylls (the primary, magnesium-centred pigments, covered in 13.3.1), the carotenoids (accessory, protective tetraterpenoid pigments, covered in 13.3.2), and the phycobilins (water-soluble accessory pigments found in cyanobacteria and red algae, covered in 13.3.3). All of these pigments except chlorophyll a itself function as accessory pigments - they absorb light at wavelengths chlorophyll a absorbs only weakly, and then transfer that captured energy on to chlorophyll a at the reaction centre, effectively widening the range of light a plant can usefully capture. Because the different pigments differ in molecular size and in how strongly they bind to chromatography paper, they can be physically separated and visualised by paper chromatography, …