Facilitated diffusion, a form of passive transport, is the process that allows sugars to enter cells. Scientists also refer to this process as facilitated transport. During the process, glucose crosses the cell membrane.
About.com says that glucose is unable to pass through the lipid layer of the cell wall, due to the hydrophobic nature of the lipids, although small molecules such as oxygen are able to pass easily. Sugar molecules pass through proteins that form transmembrane channels. These channels have gates that open and close, allowing selected molecules through the cell walls. Carrier proteins transport the larger molecules, including glucose and amino acids. Closing these gates protects the cell from disease and potential danger.
According to HowStuffWorks, all the processes the cell carries out require energy. Generating energy is a basic process of all cells. It is generated by rearranging glucose molecules by controlled oxidation or cellular respiration. Plants, bacteria and algae create the carbohydrates they need for cellular respiration through photosynthesis, transport them to the cells and oxidize them for energy. Animals, as well as some bacteria and certain protists, are unable to produce carbohydrates and depend on their environment for this energy supply. Once the cell releases the energy from glucose, it stores it in the bonds of ATP.