Thus, the Calvin cycle has to run 6 times to produce one molecule of glucose. These molecules can remove their phosphate and add fructose to form sucrose, the molecule plants use to transport carbohydrates throughout their system. Glucose phosphate is also the starting molecule for the synthesis of starch and cellulose. Plants produce sugars to use as storage molecules and structural components for their own benefit. By utilizing the energy of the sun, along with inputs of water and carbon dioxide, plants act as glucose factories. Photosynthetic organisms are the primary producers of glucose on the planet. They also produce oxygen gas as a byproduct and thus serve as the foundation of life, providing food and oxygen for the complex food webs on both land and in the oceans.