To test the presence of starch in leaves, follow these steps:
- Pluck a green leaf from the plant, preferably one that has been exposed to sunlight.
- Boil the leaf in water for about 2-5 minutes. This kills the leaf and stops chemical reactions.
- Remove the leaf and place it in boiling ethanol (placed in a boiling water bath) for several minutes to remove the chlorophyll, making the leaf pale or white.
- Rinse the leaf in warm water to soften it and spread it flat.
- Place the leaf on a white tile and add a few drops of iodine solution.
- Observe the leaf after a few minutes. If starch is present, the leaf will turn blue-black where starch exists.
The blue-black color change happens because iodine reacts with starch, indicating starch presence in the leaf, which usually means photosynthesis has occurred in that part of the leaf.
