Fundamentholfundamenthol
NEET2023Biology
Q.

Cellulose does not form blue colour with Iodine because:

  1. A

    It is a disaccharide

  2. B

    It is a helical molecule

  3. C

    It does not contain complex helices and hence cannot hold iodine molecules

  4. D

    It breaks down when iodine reacts with it

Solution

Starch gives the blue-black iodine test because its amylose component forms a helical coil whose interior hydrophobic cavity can trap I ions. Cellulose, although also a glucan, has straight -1,4 linked chains that pack flatly into microfibrils without helical pockets, so iodine cannot be sequestered and no colour develops.

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