Glucose is a monosaccharide containing six carbon atoms and an aldehyde group. It is referred to as an aldohexose. The glucose molecule can exist in an open-chain (acyclic) and ring (cyclic) form, the latter being the result of an intramolecular reaction between the aldehyde C atom and the C-5 hydroxyl group to form an intramolecular hemiacetal. In aqueous solution, both forms are in equilibrium and at pH 7 the cyclic one is predominant. Glucose is a primary source of energy for all living organisms. It is a fundamental metabolite found in all organisms, ranging from bacteria to plants to humans. Most of the world‚Äôs glucose is made by plants and algae during photosynthesis from water and carbon dioxide, where it is used to make cellulose (and other polymeric forms of glucose called polysaccharides) that stabilize plant cell walls. Glucose is also found in fruits and other parts of plants in its free state. In animals, glucose can be generated from the breakdown of glycogen in a process known as glycogenolysis. Glucose can also be synthesized de novo in animals. In particular it can be synthesized in the liver and kidneys from non-carbohydrate intermediates, such as pyruvate and glycerol, by a process known as gluconeogenesis. Humans also consume large amounts of glucose as part of their regular diet. Ingested glucose initially binds to the receptor for sweet taste on the tongue in humans. This complex of the proteins T1R2 and T1R3 makes it possible to identify glucose-containing food sources. Glucose in the body mainly comes from food - about 300 g per day for the average adult. In humans, the breakdown of glucose-containing polysaccharides happens partly during chewing by means of the enzyme known as amylase, which is contained in saliva, as well as by other enzymes such as maltase, lactase and sucrase on the brush border of the small intestine. The blood sugar content of a healthy person in the short-time fasting state, e.g. after overnight fasting, is about 70 to 100 mg/dL of blood (4 to 5.5 mM). In blood plasma, the measured values are about 10‚Äì15% higher.  Dysregulated metabolism of glucose can lead to a number of diseases including diabetes. Diabetes is a metabolic disorder where the body is unable to regulate levels of glucose in the blood either because of a lack of insulin in the body or the failure, by cells in the body, to respond properly to insulin. Each of these situations can be caused by persistently high elevations of blood glucose levels, through pancreatic burnout and insulin resistance.