SQA National 5 Biology Practice Exam

Humans primarily store carbohydrates in the form of glycogen. Glycogen is a polysaccharide that is composed of many glucose units linked together. This storage form is crucial for maintaining blood sugar levels and providing energy during periods of fasting or intense physical activity.

When glucose is abundant, such as after a meal, the body converts excess glucose into glycogen, primarily in the liver and muscle tissues. During times when energy is needed quickly, glycogen can be broken down back into glucose to be used by the body's cells for fuel. This process helps to ensure that the body has a readily available energy source regardless of food intake.

In contrast, fructose and sucrose are not primarily stored forms of carbohydrates in humans. Fructose is a simple sugar found in fruits, while sucrose, or table sugar, is a disaccharide made up of glucose and fructose. Starch is primarily a storage form of carbohydrate in plants, not animals, and therefore is not stored in human bodies like glycogen is.