Glucose (/ˈɡluːkoʊs/ or /-koʊz/; C6H12O6, also known as -glucose, dextrose, or grape sugar) is a simple monosaccharide found in plants. It is one of the three dietary monosaccharides, along with fructose and galactose, that are absorbed directly into the bloodstream during digestion. An important carbohydrate in biology, cells use it as the primary source of energy and a metabolic intermediate. Glucose is one of the main products of photosynthesis and fuels for cellular respiration. Glucose exists in several different molecular structures, but all of these structures can be divided into two families of mirror-images (stereoisomers). Only one set of these isomers exists in nature, those derived from the "right-handed form" of glucose, denoted -glucose. -glucose is sometimes referred to as dextrose, although the use of this name is strongly discouraged. The term dextrose is derived from dextrorotatory glucose. This name is therefore confusing when applied to the enantiomer, which rotates light in the opposite direction. Starch and cellulose are polymers derived from the dehydration of -glucose. The other stereoisomer, called -glucose, is hardly ever found in nature.
The name "glucose" comes from the Greek word glukus (γλυκύς), meaning "sweet". The suffix "-ose" denotes a sugar.