What structural difference accounts for the functional differences between starch and cellulose?

The primary structural difference that accounts for the functional differences between starch and cellulose lies in the types of glycosidic linkages between their glucose monomers.

1. **Glycosidic Linkages**: Starch is composed mostly of amylose and amylopectin, which have α(1→4) and α(1→6) glycosidic bonds. In contrast, cellulose consists of β(1→4) glycosidic bonds. The difference in these linkages significantly affects the three-dimensional structure of the polymers.

2. **Structural Implications**:
- **Starch**: The α-linked structure of starch leads to a helical shape, making it easier for enzymes in animals (like amylase) to break down the glucose units for energy. This is why starch is digestible by animal enzymes.
- **Cellulose**: The β-linked structure of cellulose results in straight, rigid chains that can form strong hydrogen bonds with neighboring chains, creating a stable and insoluble structure. This structure makes cellulose resistant to digestion by most animal enzymes, as they cannot easily break the β(1→4) bonds.

Therefore, the correct answer to highlight the structural difference that accounts for the functional differences is: **Starch and cellulose differ in the glycosidic linkages between their glucose monomers.**