What is glycogen? How is it different from starch?
Glycogen is a polysaccharide found in animals. It is a long chain of sugars that serves as a storage form of energy. Glycogen has branches in its structure.
Glycogen differs from starch in the following ways: (i) Glycogen is present in animal tissues, whereas starch is found in plant tissues as a store house of energy. (ii) Starch forms helical secondary structures and can hold I₂ molecules in the helical portion, giving a blue colour with iodine. Glycogen has branches in its structure, which is a distinguishing feature from starch.
Explanation
The textbook context clearly states that glycogen is the animal variant of polysaccharides, while starch is present in plant tissues. Both serve as storage forms of energy. The key structural difference mentioned is that starch forms helical secondary structures that can hold I₂ molecules (giving blue colour), while glycogen has branches. This is a 2-mark question, so students need to define glycogen and state two differences.