1. Project .Take a potted plant with broad leaves. Take two strips of black paper and cut out a small square in the centres. Cover a part of two leaves with these papers and secure them with paper clips (Fig. 1.9). Keep the plant in sunlight for 2–5 days. Observe the difference in the colour of the covered and the uncovered portions on the leaf. Perform iodine test on this leaf. Did the two parts show different results? Now take second leaf. Remove the strip and expose the covered part to the sunlight for 2–3 days and do the iodine test again. Describe your observations.
Answer:
The above activity can be carried out in the following way:
Aim: To observe how the covered and uncovered portions on the leaf respond to the iodine test and make the necessary conclusions.
Materials Required: Potted plant, two strips of black paper, paper clips, iodine.
Procedure:
(i) Take a potted plant with broad enough leaves.
(ii) Cut out a small square from the centre of each of the two strips of black paper. Now cover a part of two leaves of the plant with these papers and secure them with paper clips.
(iii) Now keep the plant in sunlight for 2-5 days and observe the difference in the colour of the covered and the uncovered portions on the leaf.
(iv) Now perform iodine test on the covered and the uncovered portions on the first leaf. Using a dropper, apply a small amount of iodine solution directly onto both the covered and uncovered parts of the leaf. Note the results. (v) Now for the second leaf remove the strip and expose the covered part to the sunlight for 2–3 days and do the iodine test again. Note the results.
Observations:
You will observe that:
- For both leaves the portion of the leaf covered with the paper turns lighter in colour or even yellowish.
- For the first leaf iodine turns blue-black in contact with the uncovered middle portion of the leaf. However, it remains reddish-brown in contact with the covered portion of the leaf.
- When the second leaf is again exposed to sunlight for 2–3 days the previously yellowish portion of the leaf regains some of its original green colour. Iodine turns blue-black in contact with previously covered part of the leaf.
Conclusions:
We conclude that:
- The covered portion of the leaves could not produce the green pigment chlorophyll in the absence of sunlight. Hence, the colour turned yellowish.
- Due to the absence of chlorophyll in covered portion of the first leaf, photosynthesis did not occur and starch was not produced. Thus, the colour of iodine remained reddish-brown.
- After the second leaf was uncovered and exposed to sunlight, chlorophyll was produced and photosynthesis occurred in the previously covered portion. Hence, starch was produced and the colour of iodine solutions turned blue-black.
- Thus, we see that sunlight is essential for photosynthesis or occur.
“Project .Take a potted plant with broad leaves. Take two strips of black paper and cut out a small square in the centres. Cover a part of two leaves with these papers and secure them with paper clips (Fig. 1.9). Keep the plant in sunlight for 2–5 days. Observe the difference in the colour of the covered and the uncovered portions on the leaf. Perform iodine test on this leaf. Did the two parts show different results? Now take second leaf. Remove the strip and expose the covered part to the sunlight for 2–3 days and do the iodine test again. Describe your observations.” – Solved.
Related Links:
Solution to Extended Learning Problem 2
Solution to Extended Learning Problem 3
Solution to Activity 1.1
Solution to Activity 1.2
