Describe step by step, how the candidate proceeded to test the leaf for the presence of starch.

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Solution

(a) The candidate dipped the leaf in boiling water for a minute to kill the cells.
(b) Then boiled the leaf in methylated spirit over a water bath till it becomes pale-white due to the removal of chlorophyll. The leaf now becomes hard and brittle.
(c) Then place it again in hot water to soften it.
(d) Spread the leaf in a dish and pour iodine solution on it. The presence of starch will be indicated by a blue-black colour. A leaf without starch will show brown colouration.

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