A Level Biology Practice Exam

Which of the following best describes sucrose?

1. A disaccharide made of glucose and galactose

2. A polysaccharide used for energy storage

3. A disaccharide made of fructose and glucose

4. An oligomer of several glucose molecules

The correct answer is: A disaccharide made of fructose and glucose

Sucrose is best described as a disaccharide composed of fructose and glucose. This specific structure allows it to be an important carbohydrate that serves as an energy source in many plants and is commonly found in sugar cane and sugar beets. In terms of carbohydrate classification, a disaccharide consists of two monosaccharides linked together through a glycosidic bond. In the case of sucrose, the bond is formed between the anomeric carbon of glucose and the fructose molecule. This makes sucrose different from other carbohydrates, such as polysaccharides, which are made up of many monosaccharide units linked together. Recognizing the composition of sucrose is key in understanding its metabolic pathway and its role in nutrition, as it breaks down into glucose and fructose upon hydrolysis, contributing to energy metabolism in organisms.