Evolution of Photosynthesis

Photosynthesis is the conversion of radiant energy, as light, into stored chemical energy. The central process is a light-driven separation of electrical charge across a biological membrane. Photochemical reaction centres carry out this process, and their three-dimensional protein structures now indicate that all modern reaction centres are homologous. Reaction centres with light-harvesting complexes comprise photosynthetic units, two of which are required for the oxygenic photosynthesis that now dominates biological energy flow in the biosphere. The evolutionary origin of oxygenic photosynthesis in cyanobacteria had a profound effect on the chemistry of the Earth’s atmosphere, on geology and on biology, paving the way for the evolution of complex, multicellular life. Eukaryotic plants and algae maintain the descendents of cyanobacteria as specialised, subcellular, cytoplasmic organelles called chloroplasts. The genes that remain in chloroplasts may be retained to be subject to regulatory control by the photosynthetic electron transport chain.