Question

A leaf from a destarched plant is covered with a black paper strip as shown in the figure.
The starch test is done on the leaf after 8 hours of exposure to light.

The result will be shown in the diagram

Answer 1

Hint: The plants synthesise food by the process of photosynthesis using light and chlorophyll present in the leaves. The glucose synthesised is stored in the plants in the form of starch. The presence of starch is tested by iodine solution.

Complete answer:
Iodine is an indicator for starch. It turns blue-black in the presence of starch. The process of photosynthesis is generally indicated by the presence or absence of starch. The destarched leaf will be white due to the absence of starch.
Let us discuss the experiment given in the question. Here a destarched leaf with a black strip is exposed to sunlight for several hours. As the part of the leaf is covered with a black strip, it will not absorb any sunlight. In rest of the part of the leaf being exposed to the sunlight, will perform photosynthesis and therefore produce starch. After testing for starch using iodine solution, it will be observed that the part which is covered with black strip will not turn or change its colour that is remain green but the rest of the leaf will turn blue-black indicating starch produced as a result of photosynthesis. (option C).
In figure A, B, C the portion under the black strip will not turn black due to the absence of photosynthesis and consequently no starch.

Therefore the correct answer is option ‘C’.

Note: Photosynthesis is one of the essential processes which directly influences life on earth. The product obtained as a result of photosynthesis is directly and indirectly consumed by all the living forms. It converts solar energy into chemical energy.