Which of the following describes the three kinds of carbohydrates?

• A. Monosaccharides, oligosaccharides, polysaccharides
• B. Monosaccharides, disaccharides, oligosaccharides
• C. Monosaccharides, oligosaccharides, lipids
• D. Monosaccharides, disaccharides, polysaccharides

Answer: (D)

Classifying carbohydrates by the number of sugar units is the idea being tested. The three main forms are monosaccharides, disaccharides, and polysaccharides. Monosaccharides are the simplest sugars, single-unit molecules like glucose and fructose that can’t be broken down into smaller sugars. Disaccharides are made of two monosaccharide units joined by a glycosidic bond, such as sucrose and lactose. Polysaccharides are long polymers of many monosaccharide units and include storage forms like starch and glycogen, and structural forms like cellulose. Oligosaccharides are shorter chains of sugars, but in introductory biology they’re usually discussed as a subset rather than a primary category, so the trio of monosaccharides, disaccharides, and polysaccharides best describes the three kinds of carbohydrates.