Test For Starch

Steps:
1. Put one of the plants in the dark for 24 hours; leave the other one on a windowsill.
2. Put some ethyl alcohol in a beaker after 24 hours, and place that in a saucepan full of water. Heat the pan until the ethyl alcohol begins to boil. Remove from the heat.
3. Use tweezers to dip each of the leaves in the hot water for 60 seconds. Then place them in the beaker of ethyl alcohol for two minutes or until they turn almost white. Set them each in a shallow dish.
4. Cover the leaves with some iodine solution and see if the iodine solution turns blue-black or remains yellowish-brown.

Why must we boil the leaf before testing it for starch?
The hot water kills the leaf and opens the cells, allowing iodine to penetrate it. The hot alcohol breaks down the chlorophyll, taking the green color out of the leaf, making it yellowish