Iodine Test

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Leaf is most suitable for photosynthesis as it has a large surface area for harvesting sunlight, numerous stomata for exchange of gases and abundant water supply for bringing in water and taking out manufactured food materials. 

Most of the experiments of photosynthesis are based on the fact that starch is the end products of photosynthesis. It develops a blue black colour with iodine solution.

Test Steps: 

Destarch a potted plant of Croton or Pothos having variegated leaves by keeping it in complete darkness for two hours. Pluck a variegated leaf. Place a rice paper over it.Draw the outline of green and non-greenareas. The green areas contain chlorophyll. Thenon-green areas are pale in colour and devoid of chlorophyll. Place the leaf in boiling water for 5-10 minutes. Boiling kills the leaf. Dip the leaf in spirit or alcohol kept at 50 to 60 degree centigrade with the help of water bath. After 30-45 minutes the leaf will be decolorized completely. Take out the decolorizedleaf; dip in hot water for softening the same. Spread the leaf in a petridish. Pour dilute iodine solution over the leaf. After 4 to 5 minutes, rinse off excess iodine and observe.

The leaf has two types of patches, bluish black and yellowish. The bluish black areas are the ones which have starch. The yellow areas are the ones which have no starch. Compare the bluish black and pale areas with green and non-green areas sketched on rice paper. Bluish black areas are the ones which were green previously while non-green areas remain pale coloured.

Only chlorophyll containing areas produce starch which is the product of photosynthesis. Chlorophyll is necessary for photosynthesis.

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