Biology · BIOMOLECULES

Starch gives a blue colour with iodine (\( \text{I}_2 \)), but cellulose does not give this test. What is the precise structural basis for this difference?

1. A
   Starch forms helical secondary structures that can trap \( \text{I}_2 \) molecules in the helical portion, whereas cellulose does not contain complex helices.
2. B
   Cellulose is an unbranched polymer of galactose which chemically degrades \( \text{I}_2 \).
3. C
   Starch has free carboxylic groups that react covalently with iodine to form a blue pigment.
4. D
   Cellulose is a heteropolymer with charged subunits that repel electronegative iodide ions.