Q5 of 70 Page 73

Enumerate the steps involved in testing a green leaf for the presence of starch.

The leaf to be tested is first isolated for a period of 24-48 hours. This is done to destarch the leaf.


1) The destarched leaf is placed in boiling water to kill leaf cells.


2) It is the boiled in methylated sprit over a water bath to remove chlorophyll.


3) The leaf softens after placing it in hot water.


4) It is spread over a dish and iodine solution is poured on it.


The presence of starch will be indicated by region that turns bluish-black in colour. A leaf without starch will show brown colouration.


Explanation:


It is important to destarch the leaf so that the blueish-black colour obtained after the experiment will be the consequence of starch formed under experimental conditions. Iodine is used to test starch as it changes colour in the presence of starch.


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