Question

How would you prove that the lower surface of the leaf transpires more than the upper surface? [4 MARKS]

Answer 1

Experiment: 2 Marks
Observation: 2 Marks

To demonstrate unequal transpiration from the two surface of a dorsiventral leaf. (Hygrometric paper method)
Select a potted plant having dorsiventral leaves. Take two strips of filter paper and soak them in a concentrated solution of Cobalt chloride. Dry both the strips in the Sun. The strip of filter paper becomes deep blue coloured when dry. (it is pink when moist). Place the dried, blue strip of cobalt chloride paper on either side of a healthy leaf and immediately cover these with two glass slides which are fixed into position by rubber bands or clamps as shown in the diagram. Place the apparatus in sunlight.

Observation. You will observe that the cobalt chloride strip attached to the lower surface turns pink within a few minutes, while that placed on the upper surface remains blue for a longer time. This is because there are more stomata on the lower surface of leaf where the rate of transpiration is higher.