The diagram below represents an experiment to demonstrate a particular aspect of a physiological process in plants. Study the diagram and answer the questions that follows.

(a) What is the aim of the experiment?

(b) What is the chemical substance named X in the diagram? What will be the effect of treatment with the solution of substance X?

(c) Out of the parts mentioned A and B, which will show blue-black colour in the presence of X. Why?

(a) The aim of the experiment is to show that sunlight is necessary for photosynthesis.

(b) The chemical substance named X in the diagram is iodine. After treatment with iodine solution, the part of the leaf, which contains starch will show blue-black colour. The part having no starch will turn brown.

(c) The portion A will show blue black colour because it received sunlight and starch was formed as a result of photosynthesis.