Testing leaves for starch

Leaves make their own food by the process of photosynthesis. This experiment
demonstrates the presence of starch in a leaf. It works particularly well
with variegated leaves because the starch will not show up on the white
parts of the leaf. This is because plants need chlorophyll to photosynthesise.

You will need

     iodine solution
     A leaf geranium is good
     A large test tube sometimes called a boiling tube
     A 250ml glass beaker
     ethanol (industrial methylated spirits)
     A pair of tweezers
     A white tile
     A teat pipette

Method

Half fill a beaker with boiling water and add a large test tube that is a
quarter full of ethanol. Allow the ethanol to come to the boil. Do not heat
the ethanol in a bunsen burner flame. This is not safe because ethanol is
highly flammable.

Take a leaf that has been sitting in good light for at least a few days, and
soften on the boiling water for ten seconds or so. Then add to the ethanol
and allow to boil for about a minute until all the colour disappears from
the leaf.

Remove the leaf from the ethanol. Put it back in the hot water to soften for
10 seconds.

Spread the leaf out on a white tile and use the iodine solution to test for
starch A blue-black colour indicates starch is present.

This experiment can be repeated with leaves that have been left in the dark.
or have been deprived of carbon dioxide.