Ace the AP Biology Challenge 2025 – Unleash Your Inner Scientist and Conquer the Course!

Glycogen serves as a primary storage form of glucose in the body. It is a polysaccharide made up of long chains of glucose molecules and is predominantly found in the liver and muscle tissues. When the body requires energy, particularly during periods of fasting or intense physical activity, glycogen is broken down through a process called glycogenolysis to release glucose. This glucose can then be used for energy production in cellular respiration, providing a quick and accessible source of fuel for the body's needs.

In contrast, other options relate to different functions and components of cells and tissues. For instance, while cellular membranes are constructed from phospholipids and proteins, signal transduction involves various signaling molecules and receptors, and muscle proteins consist of actin and myosin, rather than glycogen. Thus, glycogen's primary role is specifically as a storage form of glucose, crucial for maintaining energy homeostasis in the body.