Photosynthesis

Abstract

Photosynthesis is the most important biological phenomenon on earth, and it is a multistep process utilizing three substrates (light, water, and carbon dioxide) to yield two primary products (oxygen and reduced carbohydrates) upon which all life in the biosphere is dependent. The term photosynthesis means literally “synthesis using light.” Photosynthetic organisms use solar energy to synthesize carbon compounds that cannot be formed without the input of energy. More specifically, light energy drives the synthesis of carbohydrates from carbon dioxide and water with the generation of oxygen.Energy stored in these molecules can be used later to power cellular processes in the plant and can serve as the energy source for all forms of life. Photosynthesis takes place in three stages: 1. Capturing radiant energy of sunlight by the chloroplast 2.Using the energy to make ATP and NADPH in the light reaction or photochemical reaction 3.Using the ATP and NADPH to power the synthesis of organic molecules from atmospheric carbon dioxide during the dark reaction or biochemical reaction The most active photosynthetic tissue in higher plants is the mesophyll of leaves. Mesophyll cells have many chloroplasts, which contain the specialized light-absorbing green pigments, the chlorophylls. In photosynthesis, the plant uses solar energy to oxidize water, thereby forming large carbon compounds, primarily sugars. The complex series of reactions that culminate in the reduction of CO2 include the thylakoid reactions and the carbon-fixation reactions. The thylakoid reactions of photosynthesis takes place in the specialized internal membranes of the chloroplast called thylakoids. The end products of these thylakoid reactions are the high-energy compounds ATP and NADPH, which are used for the synthesis of sugars in the carbon-fixation reactions. These synthetic processes take place in the stroma of the chloroplasts, the aqueous region that surrounds the thylakoids. In the chloroplast, light energy is converted into chemical energy by two different functional units called photosystems. The absorbed light energy is used to power the transfer of electrons through a series of compounds that act as electron donors and electron acceptors. The majority of electrons ultimately reduce NADP+ to NADPH and oxidize H2O to O2. Light energy is also used to generate a proton motive force across the thylakoid membrane, which is used to synthesis ATP.