The Food-Making Plant Process

               

 This week in AP Bio we went over Photosynthesis. Photosynthesis is an anabolic and endergonic process that plants use to produce food (glucose). The process is done in two reactions, the light reaction and the Calvin Cycle. The chemical equation of this process is:

6 CO₂ + 6 H₂O à C₆H₁₂O₆ + 6O₂

                The first reaction in Photosynthesis is the light reactions. In this reaction solar energy is converted into chemical energy in the thylakoid membrane. This starts with water being split, and because of this it provides a source of electrons and protons and gives off O₂ as a by-product. Light is then absorbed by chlorophyll which excites the electrons in a domino effect until finally the electrons are accepted by the primary electron acceptor. All of this takes place in photosystem two. The electrons are then passed via electron transport chain to photosystem one. The fall of the electrons to a lower energy level provides enough energy for the synthesis of ATP. As the electrons do through part of the electron transport chain a proton gradient of H⁺ is produced and which is often used in chemiosmosis. Light energy meanwhile is transferred by light harvesting complexes and is used to excite electrons in photosystem one until they are accepted by the primary electron transport. The electrons in photosystem’s one primary electron acceptor are then transferred through redox reactions to another electron transport chain, although this one does not produce a proton gradient. The electrons are then transferred to NADPH.

                The second reaction in Photosynthesis is the Calvin Cycle. The Calvin Cycle performs carbon fixation where it takes CO₂ from the air and it to the enzyme RuBP. Then through a series of reactions the ATP and NADPH produced by the light reactions are used up and recycled back. After all these reactions a sugar called G3P is produced which eventually is used to make glucose.