The elements carbon, hydrogen and oxygen make up carbohydrates. For instance, glucose, a monosaccharide, has six carbon atoms, 12 hydrogen atoms and six oxygen atoms.
One important characteristic that is common to carbohydrates is that there are always twice as many hydrogen atoms as oxygen atoms. For instance, maltose has 11 oxygen atoms and 22 hydrogen atoms.
Carbohydrates are types of sugars, but they come in many sizes and forms. Some, such as glucose and fructose, are simple sugars used as energy sources. Polysaccharides, or starches, are large combinations of carbohydrates. Some are also found in foods such as potatoes and pasta. Cellulose is a polysaccharide found in plants that helps support their structures. Another polysaccharide, chitin, is found in the shells of crustaceans.