Carbohydrates

There are three principal kinds of carbohydrates and each are classified according to the number of sugar molecules they contain. Monosaccharides, such as ribose, glucose, and fructose, contain only one sugar molecule. Disaccharides consist of two sugar molecules linked covalently. Familiar examples are sucrose (table sugar), maltose (malt sugar), and lactose (milk sugar). Polysaccharides, such as cellulose and starch, contain many sugar molecules linked together. Monosaccharides are organic compounds composed of carbon, hydrogen, and oxygen. …

…Starch is the principal food storage form in most plants. Starch occurs in two forms, amylose and amylopectin. Both consist of glucose units linked together. Glycogen is the principal storage form for sugar in higher animals. Glycogen has a structure similar to that of amylopectin except that it is more highly branched. The principal structural molecule in plants is cellulose. Cellulose is a polymer composed of monomers of glucose, just as starch and glycogen are.