Final answer:
Starch and cellulose differ in their glycosidic linkages; starch has α-1,4 and α-1,6 linkages, resulting in digestible structures, while cellulose has β-1,4 linkages leading to a rigid, indigestible structure.
Step-by-step explanation:
The structural difference between starch and cellulose lies in the type of glycosidic linkages that connect the glucose monomers. Starch consists of α-glucopyranose units linked by α-1,4 and α-1,6 glycosidic linkages, while cellulose consists of β-glucopyranose units that form straight chains connected by β-1,4 glycosidic linkages. The β-1,4 linkages in cellulose cause the glucose monomers to flip relative to one another, resulting in a linear, fibrous structure that is conducive to extensive hydrogen bonding between chains which gives cellulose its rigidity. In contrast, the α linkages in starch result in a structure that can be more easily digested to release glucose for energy.