2. A well-watered healthy plant with variegated leaves was kept in the dark for about 24 hours. It
was then set-up as shown in the diagram and exposed to light for about 12 hours. At the end of this
period, leaf X and leaf Y were tested for the presence of starch. Study the diagram and answer the
questions given below:
Leaf Y
Light proof
card attached
White part
of leaf
Brown
Blue-black
Sodium
hydroxide
solution
Leafx
Green part
of leaf
(1) Why was the plant initially kept in the dark?
11
12
Answers
Answer:
1)For carrying the starch test on the plants, it is important to place the potted plants in a dark room for 24 hours. The plant is particularly placed in the dark room to destarch it. When the plant is placed in the dark room, photosynthesis does not take place due to absence of light. And the stored food which was in the form of starch is used up by the plant and thus, the plant get's destarched and suitable for further experiments.
Answer:
The plant is kept in a dark room first before the starch test is carried out in order to to get good results as if the previously made extra starch would have been stored in the leaf and the leaf would show the starch test positive even if it is not prepared actually during the test.
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