A leaf was plucked from a plant on a sunny day and kept for 2 minutes

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A leaf was plucked from a plant on a sunny day and kept for 2 minutes in boiling water. It was subsequently immersed in boiling alcohol and treated with iodine solution. What will be the final colour of the leaf after the test?

Colourless
Green
Blue
White
This question was previously asked in
UPSC CDS-1 – 2023
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After treating the leaf with iodine solution following de-colourisation, the final colour will be blue (specifically blue-black).
This experiment is a standard test for the presence of starch in a leaf, which is a product of photosynthesis. Keeping the leaf on a sunny day ensures starch production. Boiling water kills the cells. Boiling alcohol removes the chlorophyll, making the leaf pale so the colour change with iodine is visible. Iodine solution turns blue-black in the presence of starch.
The steps are designed to isolate the starch and make its detection by iodine possible. Removing chlorophyll is crucial because it would mask the colour change. A leaf from a plant kept in darkness for a day or two would show no starch and would remain brown/yellow with iodine.

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