Question

Leaf from the plant with the watch-glass in the experimental set up will not show blue black colour with iodine because (i) Photosynthesis doesn’t take place (ii) Carbon dioxide is not available (iii) Oxygen is not available (iv) Sunlight is not available​

Answer 1

Answer:

Experiment to prove the necessity of carbon dioxide in photosynthesis - definition

1. Insert a part of the leaf of a destarched plant into a conical flask containing potassium hydroxide.
2. Potassium hydroxide solution absorbs the carbon dioxide gas from the air present in the glass bottle.
3. Leave the plant sunlight.

Explanation:

The leaf of the potted plant was covered with a piece of black cloth to destarch it. Potassium hydroxide solution is to absorb the carbon dioxide gas from the air present in the glass bottle so that no carbon dioxide is left in the air inside the glass bottle. He will find that the leaf which was inside the glass bottle having no carbon dioxide around it, does not turn blue on adding iodine solution showing that no starch is present in this leaf. From this observation, we conclude that the photosynthesis to make starch in the leaf does not take place without carbon dioxide. And by covering the flask containing leaf B with black cloth, the leaf wont get exposure of sun light and photosynthesis won't happen. From this observation, we conclude that photosynthesis (to make starch) takes place in the presence of sunlight. Hence both the leaves do not have starch.