What is the name of the structural polysaccharide that forms the primary component of plant cell walls, providing rigidity and tensile strength?

• A. Cellulose: Cellulose is a complex carbohydrate that is the main component of plant cell walls, providing structural support.
• B. Chitin: Chitin is a structural polysaccharide found in the cell walls of fungi and the exoskeletons of arthropods, not plants.
• C. Glycogen: Glycogen is a storage polysaccharide found in animals and fungi, not a structural component of plant cell walls.
• D. Starch: Starch is a storage polysaccharide found in plants, used for energy storage, not for structural support in cell walls.

Based on the functions, cellulose is the polysaccharide responsible for the structure, rigidity, and tensile strength of plant cell walls.

The correct answer is A.
$\boxed{\text{A. Cellulose}}$