NEETBotanyBiomolecules (B)
Starch gives a characteristic blue colour when treated with iodine solution. Which of the following structural features of starch is responsible for this phenomenon?
Options
- AIt is a heteropolymer composed of multiple types of monosaccharides.
- BIt forms covalent bonds with iodine molecules upon reaction.
- CIt forms helical secondary structures that can hold iodine molecules.
- DIt consists of highly branched chains without any secondary structure.
Correct answer
C. It forms helical secondary structures that can hold iodine molecules.
Step-by-step solution
According to NCERT, starch forms helical secondary structures. These helices act as a trap, holding the iodine ( I₂ ) molecules inside the helical portion, which results in the characteristic blue colour. Starch does not form covalent bonds with iodine, nor is it a heteropolymer (it is a homopolymer of glucose). While amylopectin in starch is branched, it is the presence of helical secondary structures that allows it to hold iodine. Answer: It forms helical secondary structures that can hold iodine molecules.