NEETBotanyBiomolecules (B)
Consider two plant polysaccharides, X and Y. Polysaccharide X is the main structural component of plant cell walls, whereas polysaccharide Y acts as a storehouse of energy in plant tissues. Which of the following correctly describes their secondary structures and their reaction with iodine?
Options
- AX: Helical structure, gives blue colour with iodine Y: Lacks complex helices, gives no colour with iodine
- BX: Lacks complex helices, gives no colour with iodine Y: Helical structure, gives blue colour with iodine
- CX: Helical structure, gives no colour with iodine Y: Helical structure, gives blue colour with iodine
- DX: Lacks complex helices, gives no colour with iodine Y: Lacks complex helices, gives blue colour with iodine
Correct answer
B. X: Lacks complex helices, gives no colour with iodine Y: Helical structure, gives blue colour with iodine
Step-by-step solution
Polysaccharide X is cellulose, which is the main structural component of plant cell walls. Cellulose does not contain complex helices and hence cannot hold iodine molecules, resulting in a negative iodine test (no colour). Polysaccharide Y is starch, which acts as a storehouse of energy in plant tissues. Starch forms helical secondary structures that can hold iodine molecules in the helical portion, producing a blue colour. Thus, X lacks complex helices and gives no colour, while Y has a helical structure and gives