The process in which leaves use energy of sunlight to synthesis food from carbon dioxide and water is called photosynthesis. The photosynthesis is derived from two Latin Words photo means light and synthesis means to combine. During the photosynthesis oxygen is released by leaves. The carbohydrates get converted into starch.The presence of starch in leaves indicates the occurrence of photosynthesis.
Experiment—Take two same plants. Keep one of them in sunlight and other one in dark room. Check them after 72 hours. Take one leaf form each of them and pour few drops of Iodine solution on both leaves. The leaf which is taken from plant kept in sunlight turns blue-black but the leaf taken from plant kept in dark room turns red or shows no change in colour. It shows presence of starch indicates occurrence of photosynthesis.