To prove-that carbon dioxide is essential for photosynthesis by Mohl’s half leaf experiment.
Apparatus:
Wide mouthed transparent bottle, KOH solution, potted plant, vertically split cork, Iodine solution. Procedure: Arrange the apparatus as shown in the figure.
1. Take a healthy potted plant and keep it in the dark for nearly a week for the removal of starch from the leaves
2. A wide mouthed transparent bottle is taken.
3. Put potassium hydroxide pellets or potassium hydroxide solution (KOH) in the bottle.
4. This KOH absorbs CO2 present in the bottle.
5. Insert splitted cork in the mouth of the bottle.
6. Insert one of the leaves of destarched plant through a split cork into transparent bottle.
7. Arrange half of the leaf is inside bottle and the remaining half outside.
8. Leave the plant in the sunlight for 2-3 hours. 9. After a few hours, test this leaf and other leaf of this plant for starch.
Observation :
1. The part of the leaf outside the bottle turns blue-black because starch is formed in this part due to photosynthesis.
2. The part of the leaf inside the bottle does not turn blue-black because the carbon dioxide present inside the bottle is absorbed by potassium hydroxide solution.
3. All the other factors water, sunlight and chlorophyll are available but not CO2. Hence starch is not formed in the leaf part which is inside the bottle.
Result: This experiment proves that CO2 is necessary for photosynthesis. Precautions:
1. The part of the leaf kept inside the bottle should not touch potassium hydroxide solution.
2. The apparatus should be kept air tight by applying grease or vaseline.
