Requirements: A potted plant, a wide-mouthed glass-bottle, a split cork, caustic potash (KOH) solution Alcohol, Iodine solution, and Vaseline.
Procedure: The potted plant should be kept. 48 hours in darkness so that the leaves do not have any starch. One-fourth of the wide-mouthed bottle should be filled with a caustic potash solution. Now take out the potted plant from darkness and insert half of a leaf in the bottle through a split cork, and fix tightly the cork to the bottle. Care should be made taking that a part of the leaf is placed inside the bottle. The bottle should be airtight with vaseline so that no air from outside can enter into the bottle. The CO2 present in the air inside the bottle will be absorbed by caustic potash (KOH) solution. Now the experimental set should be placed in Sunlight. After 24 hours take that leaf and after boiling in alcohol immerse it in the iodine solution.
Fig: Experiment: Photosynthesis cannot occur without CO2
Observation: On taking out of the iodine solution it will be seen that the portion of the leaf that was outside the bottle become blue (deep violet or black, and rest portion becomes yellow or brownish yellow.
Conclusion: The outside portion of the leaf absorbed CO2 and manufacture carbohydrate by photosynthesis. Carbohydrate turns blue in the iodine solution. The portion of the leaf kept inside the bottle did not manufacture carbohydrate, as there was no CO2. (CO2 present inside the bottle was absorbed by KOH solution). Thus it is proved that CO2 is essential for Photosynthesis. The portion of the leaf inside did not get both CO2 and Light so it could not take part in photosynthesis.