Question

A candidate in order to study the importance of certain factors in photosynthesis took a potted plant and kept it in the dark for over 24 hours. Then in the early hours of the morning, she covered one of the leaves with black paper in the center only. She placed the potted plant in the sunlight for a few hours, and then tested the leaf which was covered with black paper for starch.

1. What aspect of photosynthesis was being investigated?
2. Is there any control in this experiment? If so, state the same.
3. Why was the plant kept in the dark before the experiment?
4. Describe step by step how the candidate proceeded to test the leaf for the presence of starch.

Answer 1

(i) The student is investigating the necessity of sunlight for photosynthesis.
(ii) The leaf portion which is not covered with black paper is the control as it receives sunlight.
(iii) The plant is kept in the dark before the experiment to destarch the leaves.
(iv) The leaf is tested for the presence of starch as follows:

1. 1. The leaf is boiled with alcohol over a water bath till it becomes colourless.
   2. It is rinsed with hot water to remove alcohol and spread it on a white tile.
   3. Pour iodine solution on it. The portion covered with black paper remains colourless while the rest of the leaf turns blue-black.