Which statement correctly distinguishes starch, glycogen, and cellulose?

• A. Glycogen is a protein; starch is a lipid.
• B. Starch and glycogen are storage polysaccharides with α-linkages; cellulose is a structural β-1,4 polysaccharide forming plant cell walls.
• C. Cellulose is a storage polysaccharide with α-linkages.
• D. Starch is a structural polymer, while cellulose is storage.

Answer: (B)

The main idea is that the way glucose units are linked (α vs β) and the biological role—storage versus structure—drive why these polymers behave differently. Starch and glycogen store glucose for energy, and they use α-glycosidic bonds. Starch is mainly unbranched or moderately branched with α-1,4 linkages and some α-1,6 branches, while glycogen is highly branched, all built from α-1,4 chains with many α-1,6 branches. In contrast, cellulose is a structural polymer in plants made from β-D-glucose with β-1,4 linkages, producing straight chains that crystallize into strong fibers for cell walls. Humans can’t digest cellulose because we lack the enzymes to break β-1,4 bonds, which is consistent with its structural role rather than energy storage. Therefore, the statement that glycogen and starch are storage polysaccharides with α-linkages, and cellulose is a structural β-1,4 polysaccharide forming plant cell walls, is the accurate distinction. The other options misstate either the nature of glycogen or starch, or the role and linkage type of cellulose.