Experiment to show that photosynthesis cannot occur without CO2 :
Requirements : A potted plant, a widemouthed glass-bottle, a splitted 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 caustic potash solution.
Now take out the potted plant from darkness and insert half of a leaf in the bottle through a splitted cork, and fix tightly the cork to the bottle. Care should be made taken that a part of the leaf is placed inside the bottle. The bottle should be air tight with vaseline so that no air from out side 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 34 hours take that leaf and after boiling in alcohol immerse it in iodine solution.
Observation: On taking out of the iodine solution it will be seen that theportion of the leaf that was out side the bottle become blue (deep violet or black, and rest portion becomes yellow or brownish yellow.
Conclusion: The outside portion of the leaf absorbed CO2and manufacturecarbohydrate by photoynthesis. Carbohydrate turns blue in iodine soulution. 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.