A Level Biology Practice Exam

What type of carbohydrate is lactose?

1. Monosaccharide

2. Disaccharide

3. Polysaccharide

4. Oligosaccharide

The correct answer is: Disaccharide

Lactose is classified as a disaccharide because it is composed of two monosaccharide units: glucose and galactose. In the structure of lactose, these two simple sugars are joined together by a glycosidic bond, which is a typical characteristic of disaccharides. This classification is significant in understanding how carbohydrates are categorized based on their complexity and number of sugar units. Disaccharides like lactose are important in various biological processes, including digestion and metabolism, highlighting their role in nutrition. Monosaccharides, on the other hand, consist of single sugar units, while polysaccharides contain many monosaccharide units linked together. Oligosaccharides are slightly more complex than disaccharides but typically consist of 3 to about 10 monosaccharides. Thus, the structure and composition of lactose distinctly fit the definition of a disaccharide.