Light and Carbon Reactions

Incorporating carbon from an inorganic source like carbon dioxide into organic compounds like glucose is called carbon fixation, an extremely important function of photosynthesis. Carbon fixation results in products (organic compounds) that contain more chemical energy than the reactants (carbon dioxide molecules). Doing so requires an input of energy. The input of energy for the carbon fixation that occurs during photosynthesis is energy in the form of sunlight. Powered by that light energy, water molecules are split into oxygen and hydrogen atoms, and the hydrogen atoms from the water end up bonded to carbon atoms from carbon dioxide molecules to form high-energy carbohydrates. This occurs in two major pathways that comprise photosynthesis. Notice that the speaker explains why he also calls light-independent reactions 'carbon reactions'. The light reactions take energy from light and convert it into the chemical form of ATP and NADPH. They also produce oxygen. The carbon reactions are powered by the ATP and NADPH to do the work of photosynthesis. Watch this video, which reviews the chemical processes that occur during the light-dependent and light-independent reactions of photosynthesis. Make sure you can describe how photosynthesis converts low-energy molecules into energy-rich carbohydrates. You should be able to explain how energy is transformed and transferred during photosynthesis.