Carbohydrates, also known as sugars or saccharides, are molecules composed of carbon, hydrogen, and oxygen that contain multiple hydroxyl groups and at least one carbonyl group. They can be classified as monosaccharides, disaccharides, or polysaccharides. Monosaccharides are simple sugars, disaccharides are two monosaccharides joined by a glycosidic bond through a dehydration reaction, and polysaccharides are polymers of hundreds to thousands of monosaccharides joined by glycosidic bonds through dehydration reactions. Common examples of polysaccharides are amylose and amylopectin.