Function. The function of glucose in the body is an energy molecule. Cells take up glucose absorbed by the digestive tract and either use the glucose or store it for later.While proteins and fat also provide cells with energy, some body cells -- the cells of the brain in particular -- preferentially rely upon glucose, notes Dr. Lauralee Sherwood in her book, Human Physiology..Further, glucose breaks down into smaller molecules that provide building blocks for many cellular products.ources of Glucose. Any food that contains carbohydrates serves as a source of glucose. Even if the food itself doesn't contain glucose, your body can break down sugar and starch in the foods you eat into glucose and other simple sugars, and can then convert the other simple sugars into glucose.