5a: Plant nutrition (Test starch in leaf) [2005, 2013]***

Note:

Step 1: Boiling of the leaf initially is to denature all the enzymes in leaf. This prevents conversion of starch to glucose in the leaf during experiment.

Step 2: Alcohol is to decolourise the leaf by leaching the chlorophyll pigment out of the leaf. This will allow any colour change in the leaf to be observed when iodine solution is added to the leaf eventually.

Step 3: Put decolourised leaf back into the hot water is to soften the leaf and makes it more permeable to iodine.

Decolourised leaf

From 2013 Practical, test of starch in variegated leaf

Test of starch in normal leaf