Canada History

Photosynthesis ( /foʊtoʊˈsɪnθəsɪs/; from the Greek φώτο- [photo-], "light," and σύνθεσις [synthesis], "putting together", "composition") is a process used by plants and other organisms to convert thelight energy captured from the sun into chemical energy that can be used to fuel the organism's activities. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea.Photosynthetic organisms are called photoautotrophs, since they can create their own food. In plants, algae, and cyanobacteria, photosynthesis uses carbon dioxide and water, releasing oxygen as a wasteproduct. Photosynthesis is vital for all aerobic life on Earth. In addition to maintaining normal levels of oxygen in the atmosphere, photosynthesis is the source of energy for nearly all life onearth, either directly, through primary production, or indirectly, as the ultimate source of the energy in their food,[1] the exceptions being chemoautotrophs that live in rocks or around deep seahydrothermal vents. The average rate of energy capture by photosynthesis globally is immense, approximately 130 terawatts,[2][3][4] which is about six times larger than the power consumption of humancivilization.[5] As well as energy, photosynthesis is also the source of the carbon in all the organic compounds within organisms' bodies. In all, photosynthetic organisms convert around 100-115 thousandmillion metric tons (i.e., 100–115 petagrams) of carbon into biomass per year.[6][7]

Although photosynthesis can happen in different ways in different species, some features are always the same. Forexample, the process always begins when energy from light is absorbed by proteins called photosynthetic reaction centers that contain chlorophylls. In plants, these proteins are held inside organellescalled chloroplasts, while in bacteria they are embedded in the plasma membrane. Some of the light energy gathered by chlorophylls is stored in the form of adenosine triphosphate (ATP). The rest of...