Question

The apparatus shown in the given diagram is Garreau's potometer designed to demonstrate unequal transpiration from the two surfaces of a dorsiventral leaf. Before keeping the leaf in between, the cups were closed with corks through which two mercury manometers were connected. After few hours, CaCl2 vials were taken out and weighed again.

(a) What is the purpose of keeping CaCl2 vials inside the cup?
(b) After few hours CaCl2 vials were taken out and weighed again. Will you expect any difference in weight? If so, give reason.
(c) What was the purpose of using a manometer?
(d) What do you mean by transpiration? [5 MARKS]

Answer 1

a) 1 Mark
b) 2 Marks
c) 1 Mark
d) 1 Mark
(a) The CaCl2 tubes are weighed and placed in both the cups and then weighed again because the difference in the two weighings is a measure of the amount of water lost from the leaf surfaces.
(b) Yes, the CaCl2 tube placed below the leaf will weigh less than the tube placed above the leaf. This is because as the ventral or the undersurface of the leaf has more stomatal openings, more transpiration will occur here.
(c) The manometer ensures the maintenance of constant vapour pressure within the cups.
(d) Transpiration is the loss of water from the aerial parts(leaves and stem) of a plant.