Question

The apparatus shown here is Girreau’s poto-meter designed to demonstrate unequal transpiration from the two surfaces of a dorsiventral leaf. Before keeping the leaf in between the cups, anhydrous calcium chloride (CaCl₂) contained in two small vials were weighed and placed in both the cups. The ends of the cups were closed with corks through which two mercury manometers were connected. After a few hours, CaCl₂ vials were taken out and weighed again.

(i) What is the purpose of keeping CaCl₂ vials inside the cup?
(ii) After a few hours, the CaCl₂ vials were taken out and weighed again. Will you expect any difference in weight? If so, give reasons.
(iii) What was the purpose of using a mano-meter?
(iv) What do you mean by transpiration?

Answer 1

(i) The CaCl₂ vials are kept inside the cup to absorb water.
(ii) After few hours, the weight of the CaCl₂ vials will increase because they will absorb the water which is transpired by the leaf of the plant.
(iii) Manometers are used to indicate the unequal transpiration from two surfaces of a dorsiveritral leaf by showing difference in rise in their mercury levels.
(iv) Transpiration is the loss of water in the form of water vapour from the aerial parts of the living plants.