Explain how the presence of starch can be detected in plants.

Plants store glucose produced by photosynthesis in the form of starch. To test the presence of starch in plants, first heat a leaf in boiling water for 30 seconds followed by boiling it in ethanol for a few minutes. Ethanol allows the removal of the leaf's colour. Next, wash the leaf with some water and spread it out on a tile. Add a few drops of iodine solution onto the leaf. A colour change of the leaf to blue-black indicated the presence of starch in the leaf.