Advanced Placement (AP) Biology Practice Exam

What is the defining characteristic of polysaccharides?

1. They are composed solely of glucose.

2. They are large polymers made up of many sugar monomers.

3. They are always insoluble in water.

4. They consist of only two sugar units.

The correct answer is: They are large polymers made up of many sugar monomers.

Polysaccharides are indeed characterized by being large polymers formed from numerous sugar monomers. These monomers are typically monosaccharides, like glucose, which can be linked together through glycosidic bonds during a dehydration reaction. The size of polysaccharides allows them to serve various biological functions, such as energy storage (e.g., starch in plants and glycogen in animals) and providing structural support (e.g., cellulose in plant cell walls and chitin in fungal cell walls). Other characteristics of polysaccharides include their variable solubility in water, which can depend on their structure and the types of monosaccharides they are composed of. For example, while some polysaccharides are soluble in water, others might be less soluble or even insoluble, which is influenced by their branching and organization. This context helps to maintain the understanding that while some soluble polysaccharides exist, it is not a definitive characteristic of all polysaccharides. Polysaccharides are not limited to glucose, nor do they consist only of two sugar units, which would define them as disaccharides instead of polysaccharides. Thus, the defining characteristic of their structure as being composed of many sugar units is what makes option B the most accurate description