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Photosynthesis may simply be defined as the conversion of light energy into chemical energy by living organisms. In the Light-independent or dark reactions the enzyme RuBisCO captures CO 2 from the atmosphere and in a process that requires the newly-formed NADPH, called the Calvin-Benson cycle releases three-carbon sugars, which are later combined to form sucrose and starch. The chlorophyll molecule regains the lost electron by taking one from a water molecule through a process called photolysis, that releases oxygen gas. In addition, it serves to create a proton gradient across the chloroplast membrane its dissipation is used by ATP Synthase for the concomitant synthesis of ATP. This electron is passed to a modified form of chlorophyll called pheophytin, which passes the electron to a quinone molecule, allowing the start of a flow of electrons down an electron transport chain that leads to the ultimate reduction of NADP into NADPH. In the light reactions, one molecule of the pigment chlorophyll absorbs one photon and loses one electron. During the second phase, the light-independent reactions (also called the Calvin-Benson Cycle, and formerly known as the Dark Reactions) use the high-energy molecules to capture carbon dioxide (CO 2) and make the precursors of carbohydrates. In the first phase, light-dependent reactions or photosynthetic reactions (also called the Light reactions) capture the energy of light and use it to make high-energy molecules. The equation is often presented in introductory chemistry texts in an even more simplified form as: 6 CO 2(gas) + 6 H 2O (liquid) + photons → C 6H 12O 6(aqueous) + 6 O 2(gas) Here the monosaccharide glucose is shown as a product, although the actual processes in plants produce disaccarides. When written as a word equation the light energy appears above the arrow as it is required for photosynthesis but it is not actually a reactant. It can be used as an immediate food nutrient, or combined and rearranged to form disaccharide sugars, such as sucrose and fructose, which can be transported to other cells, or packaged for storage as insoluble polysaccharides such as starch.Ī commonly used but slightly simplified equation for photosynthesis is:Ħ CO 2(gas) + 12 H 2O (liquid) + photons → C 6H 12O 6(aqueous) + 6 O 2(gas) + 6 H 2O (liquid) carbon dioxide + water + light energy → glucose + oxygen + water G3P is generally considered the prime end-product of photosynthesis. Photosynthesis uses light energy and carbon dioxide to make triose phospates (G3P). 5.2 Carbon dioxide levels and photorespiration.5.1 Light intensity (Irradiance), wavelength and temperature.2.2 Cyanobacteria and the evolution of photosynthesis.
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