D-Glucose is an incredibly important molecule for many organisms including humans. It is a monosaccharide (a simple sugar). Glucose is a aldohexose, meaning it is a sugar consisting of 6 carbons and an aldehyde group. It is one of the 3 monosaccharides that can be absorbed directly into the bloodstream in digestion, the other two being fructose and galactose. It has 4 stereocenters within the molecule. Glucose is produced by plants through photosynthesis and serves as an important energy source in metabolism. It is broken down in both aerobic and anaerobic metabolic processes. Starch and cellulose are polymers of glucose. Glycogen is also a polymer of glucose and functions as an important energy storage molecule. The enantiomer of D-glucose is L-glucose; however, L-glucose is very rarely found in nature. Glucose levels in the blood are regulated by insulin and glucagon which are hormones of the endocrine system. In diabetics, insulin is either not produced or there is resistance to insulin effects which results in high levels of glucose in the blood.