Question

To show that carbon dioxide is necessary for photosynthesis

Answer 1

Explanation:

Aim: To show that carbon dioxide is necessary for photosynthesis

Procedure:

Take a plant with destarched leaves.

Insert one of its leaves in a conical flask containing potassium hydroxide.

Leave the plant in sunlight.

After a few hours, test the particular leaf and some other leaf of the same plant for the presence of starch.

Observation:

The leaf which was inserted in the conical flask stains brown, and the other leaf which is exposed to sunlight turns blue-black.

Inference:

Potassium hydroxide in the flask absorbs carbon dioxide; thus, due to the absence of CO2, the leaf fails to produce starch which proves that carbon dioxide is necessary for photosynthesis.

Answer 2

MATERIAL AND APPARATUS:

Potted plant, 2 conical flasks, Soda lime, cork, Vaseline, water, iodine solution.  

PROCEDURES :

1. Destarch a plant (potted plant) by keeping it in darkness for two continuous days.

2. Pluck a leaf from the plant and test it for starch. If starch is present then keep the plant in darkness for some more days. If starch is absent continue with step 3.

 3. Enclose one leaf in a conical flask labelled A, containing sodium hydroxide. Enclose another leaf in another conical flask labelled B, without sodium hydroxide. Pass the leaf stalk through a split cork which has been vaselined to keep the flask air tight. The sodium hydroxide removes or absorbs all the carbon dioxide from the flask A.

4. Support each flask with a clamp. Place the potted plant in sunlight for 3-4 hours..

5. Remove the leaf from each flask and test each of them for starch.

OBSERVATION :

When iodine solution was added to the leaf from flask A, the brown colour of iodine solution remained unchanged.

For the leaf in flask B, the colour of the iodine solution changed into blue black.

CONCLUSION:

Carbon dioxide is necessary for photosynthesis.