The Glycemic Index (GI) is a system for rating carbohydrates, or saccharides, based on their immediate effect on the blood glucose level. An organic compound, glucose is a simple sugar or monosaccharide. Glucose is the principle sugar circulating in the blood; all cells use glucose as a source of energy and as a metabolic intermediate. Found in plants, glucose is the product of photosynthesis (the process of converting light energy to chemical energy and storing it in the bonds of a glucose molecule). Biologically active glucose is often referred to as dextrose. Glucose is often incorrectly referred to as table sugar – table sugar is a disaccharide composed of glucose and fructose.