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Question

In an experiment to test the presence of starch in a leaf, the leaf is boiled in alcohol for a few minutes using a water bath. This is an essential step in the experiment because:

A
Alcohol is highly volatile.
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B
Alcohol decolourises the leaf.
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C
Alcohol cleans the leaf.
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D
Alcohol gives nutrients to the leaf.
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Solution

The correct option is B Alcohol decolourises the leaf.
The presence of starch in the leaves proves the process of photosynthesis in the plants. Now, in order to check the presence of starch, iodine solution is used. In the presence of starch, iodine changes its colour from yellow to blue-black colour. This change in colour cannot be seen in green leaves. Hence, to remove the green pigment present in the leaf, the leaf is boiled in alcohol using a water bath. The green pigments get dissolved in the alcohol and the leaf gets decolourised. The colour change of iodine is properly visible in the decolourised leaf.

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