Answer:
:
Experiment steps: 1 Mark each
Inference: 1 Mark
For proving the necessity of carbon dioxide for photosynthesis, the following steps are performed:
1) A potted plant is taken and placed in complete darkness for 24 to 72 hours to destarch it.
2) Take potassium hydroxide in a conical flask stoppered with a rubber cork. Insert one leaf (still attached to parent plant) through a hole in the rubber cork. Potassium hydroxide absorbs all the left-over carbon dioxide from the flask.
3) The entire arrangement is exposed to sunlight for 6 hours.
4) The leaf placed in the conical flask with potassium hydroxide solution is tested with iodine solution. This does not turn blue-black.
Inference: The leaf trapped inside the conical flask did not perform photosynthesis as it did not receive any carbon dioxide. This is the reason why it did not answer a positive test for starch.