Through an experiment show how $C{O}_2$ is essential for photosynthesis.

Part 1: Introduction
An experiment that can prove carbon dioxide is essential for photosynthesis is Mohl’s half leaf experiment.
Part 2: Procedure

• The plant is left in a dark room for two to three days. Due to the unavailability of sunlight, all the reserved starch gets used up.

• Place a single leaf between a split cork.

• Now insert the leaf into a bottle containing KOH in such a way that only a part of the leaf is dipped into the solution.

• Expose this whole setup to sunlight for three to four hours.

• After three to four hours the leaf has to be removed and a test for starch is to be performed by adding a few drops of iodine solution on the leaf.

Part 3:
Observation It was observed that the color of the leaf which was dipped into the solution did not not turn blue black but the part which was exposed to the atmosphere gave a positive result and indicated the presence of starch.
Part 4:
Inference KOH solution absorbs the carbon dioxide present within the conical flask. Starch is produced as a result of photosynthesis. But the leaf which was dipped into the solution showed negative results for the presence of starch, this indicates that photosynthesis did not take place in this part of the leaf. Even though there was enough sunlight and water still photosynthesis did not occur in the leaf dipped in the solution This proves that carbon dioxide is an essential ingredient for photosynthesis