Plants: Testing leaves for starch

 Just sharing a little from my Sci Bio class, we did a test on starch present in the leaves. We were given the following instructions:
1. Heat half a beaker of water over the Bunsen flame until the water boils.
2. Turn off the Bunsen burner.
3. Put the leaf into the hot water. (This is to make the leaf more permeable by softening it)
4. Put the boiled leaf in a test tube containing some alcohol. Then, place the test tube in the beaker of hot water.(The alcohol would remove the green pigment, chlorophyll from the leaf.)

5.Gently remove the leaf with a pair of forceps then
put it back into the hot water.
6.Remove the leaf and place it in a petri dish. Add a few drops of iodine solution until the leaf is just covered.
7. The leaf should appear blue-black(starch present)


If you see carefully, my leaf did not turn blue-black. Instead, it remained brown. Why? Reason was that the leaf cut from the plant was not fully exposed to the sunlight, which means that the leaf may not have photosynthesized.