The energy to power the Calvin Cycle comes from adenosine triphosphate, or ATP, which is produced during the light reaction of photosynthesis. According to the University of Massachusetts, the first stage of photosynthesis, also known as the light-dependent reaction, converts sunlight into chemical energy in the form of ATP and NADPH.
According to the University of Cincinnati Clermont College, the light-dependent reaction occurs in the thylakoid membrane of chloroplasts in the plant cell. Chlorophyll, the green pigment within the membrane, and other colored pigments each absorb different wavelengths of the sunlight into their molecules. The energy is then transferred from each antenna pigment molecule to the central chlorophyll molecule, or reaction center, where photosynthesis begins. Once the energy reaches the reaction center, a specialized molecule called the primary acceptor captures an excited electron, which drives the synthesis of NADPH and ATP.
Next, the Calvin Cycle, or the dark reaction, begins in the stroma, the area surrounding the thylakoid membrane. Using the ATP produced from the light reaction, a pair of 3- phosphoglycerates are moved through a series of reactions until they are converted into two molecules of glyceraldehyde-3-phosphate. Eventually, after several molecules of glyceraldehyde-3-phosphate are produced, they combine to form glucose.