Biology Biomolecules SZABMU 2024
PMDC Verified Question 9 of 142
Which of the following carbohydrates gives dark brown colour with iodine solution?
A
Starch
B
Glycogen
C
Sucrose
D
Glucose
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Glycogen
Concept:

The iodine test is a classic qualitative biochemical assay used to distinguish complex polysaccharides based on their helical coiling.

Solution:

  • When \(I_2\) interacts with the highly branched structure of Glycogen, the iodine molecules slip into the coils, producing a characteristic red-brown / dark brown color.


  • This specifically differentiates it from plant starch.


Why other options are incorrect:

  • Starch: Produces a stark, intense blue-black color because its long amylose helices perfectly trap the iodine chains.


  • Sucrose & Glucose: Small, simple sugars that lack the complex helical structure to trap iodine. They yield no color change (the solution remains the yellowish-brown color of raw iodine).

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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