The final product of the Calvin cycle, the second metabolic cycle of photosynthesis, is the sugar glucose. Carbon dioxide joins with organic molecules to produce glyceraldehyde-3-phosphate. After several glyceraldehyde-3-phosphates are produced from the cycle, they join together to form glucose.
The Calvin cycle is known as the dark reaction because it is the metabolic cycle of photosynthesis that does not require light. During the Calvin cycle carbon dioxide from the air is added to an organic molecule, RuBP, which is already present in the cell. RuBP becomes unstable and splits into two three-carbon chains known as 3-phosphoglycerate. The two molecules move through a series of reactions using the energies ATP and NADPH, which are produced from the light reactions of photosynthesis. Finally, the 3-phosphoglycerates are converted into two molecules of glyceraldehyde-3-phosphate. Then, some of the glcyeraldehyde-3-phosphates join together to form glucose. Several cycles of the Calvin cycle are required to produce one glucose chain because only one carbon atom is added to the chain from each molecule of carbon dioxide. However, once the glucose chain is formed, it is usually released to the plant to serve as energy for building new cells. Some of the glucose remains in the Calvin cycle to help facilitate the process.