1. Do you find any colour change in both the leaves? 2. Why is there no change in colour of the leaf kept in dark?

Question

These plants are called symbiotic plants:

• Take two potted plants of the same genus.
• Keep one in the dark for 72 hours and the other in the sunlight.
• Take one leaf from both the pots.
• Now place both the leaves in a test tube and dip them in spirit.
• Now keep the test tube in a beaker half filled with water, and boil it till the leaves lose all chrophyll molecules.
• Wash the leaves with water and perform iodine test on them.

1. Do you find any colour change in both the leaves?

2. Why is there no change in colour of the leaf kept in dark?

Answer 1

1. Yes, we see that the colour, change occurs in the leaf of the plant kept in sunlight, but no colour change occurs in the leaf of the plant kept in dark.

2. Photosynthesis takes place in the presence of the sunlight. Due to which, starch is made in the leaves of the plant kept in sunlight and so the leaf turns blue – black in colour when iodine solution is dropped on it. Photosynthesis does not occur in the plant which was kept in the dark. Thus, starch is not present in its leaves. Hence, there is no colour change in its leaf. Starch reacts with iodine and imparts blue-black colour. This is called starch test.