Question

Two potted green plants of the same kind were taken to perform an experiment. One of them was kept in a dark room, while the other one was kept in sunlight for 3–4 days. A leaf from each of the plant was taken to perform the iodine test. Which of the leaves turned blue-black in colour and why? [5 MARKS]

Answer 1

Photosynthesis:

1. Plants prepare their food by a process called photosynthesis.
2. Photosynthesis, as the name says, requires sunlight.
3. In this process, plants take carbon dioxide and water to form sugar and release oxygen as a by-product.
4. The sugar thus formed is converted into starch. Starch gives a blue-black colour with iodine.

Inference of the experiment:

1. The leaf placed in a dark room could not photosynthesize as there was no light and hence starch was not produced.
2. Thus the leaves do not turn blue-black and remain brown with iodine.
3. The leaf that was placed in the light, produces starch and hence turns blue-black with iodine.

Only the leaf of the plant kept in sunlight turns blue black.