sugar
13.2.1 The Detailed Dark Reactions What the Dark Reactions Do: The dark reactions build sugar from carbon dioxide gas CO2 , water H2O , and energy from ATP molecules that were charged up during the light reactions. The dark reactions occur in the stroma of a chloroplast. Dark reactions usually occur in the light, but they don't have to. They'll occur in the dark until the chloroplast's supply of ATP runs out usually about 30 seconds . The Calvin Cycle: The Calvin Cycle is the fancy name for the metabolic pathway that builds sugar. This means that it involves a whole lot of chemical reactions, and it uses a lot of different enzymes to catalyze the reactions. Carbon dioxide gas is stable, therefore the bonds that hold the carbon and oxygen atoms are strong. Therefore it takes a lot of energy to break the bonds and separate the carbon atoms from the oxygen atoms. The energy needed to do this comes from ATP molecules. When inorganic carbon like from CO2 is being added to an organic molecule such as sugar , this is called carbon fixation. It takes 2 complete turns of the Calvin Cycle to make a glucose molecule. Some portions of this text is based on notes very generously donated by Paul Doerder, Ph. , of the Cleveland State University. The detailed portions are not provided by Dr. Doerder. How cells divide.