Hi their here is the Answer
During photosynthesis a plant absorbs light energy using the pigment chlorophyll. This allows it to convert carbon dioxide and water into glucose. This glucose is:
transported to the growing parts of the plant for use in respiration
transformed into cellulose, proteins and oils
turned into starch for storage
Therefore, to test if a plant has been photosynthesising, you can test the leaf to see if starch is present.
Iodine solution is used to test leaves for the presence of starch. You need to:
heat a plant leaf in boiling water for 30 seconds (this kills the leaf, stopping any chemical reactions)
add the leaf to boiling ethanol in a water bath for a few minutes (the boiling ethanol dissolves the chlorophyll and removes the green colour from the leaf - it turns white so it is easy to see the change in colour)
wash with water to rehydrate and soften the leaf and spread onto a white tile
add iodine solution from a dropping pipette
After a few minutes, the parts of the leaf that contain starch turn the iodine from brown to blue/black.
Hope this helps :)