1) Heat some water to boiling point in a beaker and the turn out the Bunsen Flame.
2) Use forceps to dip a leaf in the hot waterfor about 30 seconds. This kills the cytoplasm, denatures the enzymes and makes the leaf more permeable to iodine solution.
3) Push the leafto the bottom of a test -tube, and cover it with alcohol (ethanol). Place the tube in the hot water. The alcohol will boil and dissolve out most ofthe chlorophyll. This makes color changes with iodine easier to see.
4) Pour the green alcohol into a spare beaker, remove the leaf and dipit once more into the hot water to soften it.
5) Spread the decolorized leaf flat on a white tile and drop iodine solution on to it. The partscontaining starch will turn blue; parts without starch will stain brown or yellow with iodine.
-The leaf that wasexposed to darkness after , didn´t turn blue when dropped iodine on it.
This was because the leaf didn’t have starch.
-In theleaf that was exposed to light, as soon as we poured the iodine on it, it formed a clear blue stain in that part.
Conclusion: plants need lightto produce their own food. If you don´t allow this, it would reduce or even stop producing starch.
The leaf that was not exposed to light had ayellowish stain in the part where we dropped the iodine. This showed that this leaf had stopped producing starch during that period of time.