Question

A student is performing an experiment to show that sunlight is necessary for photosynthesis. In the first stage, he keeps a potted plant with green leaves in a dark place for about 3 days. Towards the end of the experiment, he boils one leaf in alcohol before using iodine for testing starch.
(a) Why is the plant kept in a dark place for about 3 days?
(b) Why is the leaf boiled in alcohol before testing for starch with iodine?

Answer 1

(a) The plant is kept in dark so as to destarch it, so that in the beginning of the experiment itself, the leaves do not have any starch.
(b) After the plant is destarched by keeping it in dark, it is again placed in sunlight so that photosynthesis can occur. This would result in the synthesis of starch. The leaves are again destarched by boiling them in alcohol before testing them with iodine.