An organic compound present in the cells of all living organisms and a major organic nutrient for human beings; it consists of carbon, hydrogen, and oxygen, and makes up sugar, starch, and cellulose.

Carbohydrates are made up of carbon, hydrogen, and oxygen in a ratio of approximately one carbon, two hydrogen, and one oxygen.

Sugar, starch, and cellulose constitute the carbohydrates. Sugars are classified according to whether or not they can be decomposed in a water solution.

Simple sugars or monosaccarides cannot be so decomposed; complex sugars or polysaccarides can be broken down by water or hydrolysis. The most common simple sugars are glucose and fructose. See saccharo- for more details.

Glucose is also called dextrose, and fructose is also known as levulose. The common white commercial sugar is sucrose, which is a disaccharide or double sugar; a combination, actually, of a glucose and a fructose molecule.