A Level Biology Practice Exam

Glycogen is primarily known for being what?

1. A type of amino acid

2. A chemical energy store in plant cells

3. A branched polysaccharide formed from alpha glucose molecules

4. A water-soluble vitamin

The correct answer is: A branched polysaccharide formed from alpha glucose molecules

The correct choice describes glycogen accurately as a branched polysaccharide formed from alpha-glucose molecules. Glycogen serves as a vital energy reserve in many living organisms, primarily animals, and is similar in structure to starch, which is found in plants. Its branched structure allows for rapid release of glucose when the body needs quick energy, making it an essential molecule for energy metabolism. Understanding the structure of glycogen is fundamental to its function; the branching points provide multiple sites for enzymes to act, facilitating faster mobilization of glucose compared to linear carbohydrates. This characteristic is especially important during periods of high energy demand, such as during exercise. The other options do not accurately characterize glycogen. Glycogen is neither an amino acid nor a vitamin, nor is it primarily associated with energy storage in plant cells – that role is predominantly fulfilled by starch. Thus, identifying glycogen as a branched polysaccharide of alpha glucose captures its biochemical nature and functional role effectively.