test for starch with iodine solution

The reason of putting the leaf in alcohol before having the starch test is to make an easy observation in starch test since the green colour of chlorophyll in leaf will make the observation (If there is starch, iodine will change from brown to dark blue) more difficult.

Alcohol can dissolve and destroy the cell membrane, so that the chloroplast will be exposed to the alcohol and dissolved in it. Thus, after putting the leaf into a tube of alcohol in a hot water bath, you will see the solution in the tube become green.

The reason for putting the leaf into a tube of alcohol in a hot water bath is to speed up the destruction of the cell wall. Putting the leaf in a tube of alcohol without hot water bath to remove chloroplast in leaf is time-consuming...