Photosynthesis

Photosynthesis is a two step process that takes carbon dioxide, water, and sunlight and converts carbon dioxide into glucose with the help of ATP, NADPH, RuBP, and the enzyme that puts it all together, RuBisCO.  Photosynthesis is divided into the light dependent and light independent reactions.  The light dependent reactions come first, and take place in the lumen, or inside, of the thylakoid.  There are two ways in which the light dependent reactions can occur: non-cyclic or cyclic electron flow.  In the case of non-cyclic electron flow, both Photsystems I and II are used, creating products ATP and NADPH with the use of a proton concentration gradient and sunlight.  In cyclic electron flow, only Photosystem I is used, and only ATP is synthesized.  ATP and NADPH are sent to the stroma, the outside fluid surrounding the thylakoids in the chloroplast to assist with the light independent reactions.  ATP and NADPH reduce the molecule that is synthesized using carbon dioxide and RuBP.  RuBisCO is the enzyme responsible for attaching carbon dioxide to RuBP.  There are three different variants of the light independent reaction that different plants use.  C3 is the fastest and most efficient, but it loses the most water due to mistakes in the Calvin Cylce.  C4 is less prone to error, but uses more energy and is less efficient.  CAM is designed for plants in very dry conditions, where carbon fixation only occurs at night.  It also is less efficient, but loses very little water and is a great adaptation for plants in arid conditions.