Cellulose is a complex carbohydrate, specifically a polysaccharide, that is a major component of the plant cell wall. It provides structural support and rigidity to plants, allowing them to maintain their shape. Unlike starch and glycogen, which are primarily used for energy storage in plants and animals respectively, cellulose is not digestible by humans and serves a different function. Chitin, on the other hand, is found in the exoskeletons of insects and fungi, providing structural support. Therefore, in the context of the statements provided, cellulose is the correct answer for the statement about the structure of plant cell walls.