Aim : To prove that carbon dioxide is essential for photosynthesis by Mohl's half leaf experiment.
Apparatus : Wide mouthed bottle, KOH solution, potted plant, vertically split cork, Iodine solution, wax.
Procedure : Arrange the apparatus as shown in the figure.
(1) Take a potted plant and keep it in the dark for nearly 3 – 4 days for the removal of starch from the leaves.
(2) Take a wide mouthed transparent bottle.
(3) Pour potassium hydroxide solution in the bottle.
(4) Potassium hydroxide absorbs carbon dioxide 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 containing potassium hydroxide pellets or potassium hydroxide solution.
(7) Apply wax or grease to split cork so that, CO2 will not enter into the bottle.
(8) Leave the plant in sunlight.
(9) After a few hours, test this leaf and other leaf of this plant for starch.
Observation :
(1) The part of the leaf which is exposed to the air becomes bluish - black.
(2) The remaining part which is inside the flask containing KOH does not turn to bluishblack.
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.
