Animation showing the transfer of light energy in a photosystem during photosynthesis, the process that plants use to convert energy from sunlight into food. At left is the Sun, which shines light onto a light_harvesting complex green in the photosystem. The energy is absorbed and is then passed by resonant energy transfer through other similar complexes, and eventually to the reaction centre red, called P680. At the reaction centre, the electron is passed on in the biochemical pathway, eventually forming crucial products for use in later reactions, and leading to the oxidation of water into oxygen gas. This latter process is the source of almost all of the oxygen in the atmosphere.