Question

The apparatus shown here is Ganong's photometer 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 weighted and placed in both the cups. The ends of the cups were weighted and 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, CaCl₂ vials were taken out and weighed again.
will you except any difference in weight? If so, give reasons.
(iii) What was expect the purpose of using a manometer?
(iv) What do you mean by transpiration?

Answer 1

(i) To absorb the moisture formed by transpiration.
(ii) Yes, the weight of CaCl₂ vials kept on the lower side will be more because transpiration will be more on the lower surface and the moisture absorbed.
(iii) To check the outside and inside pressure.
(iv) Transpiration is the loss of water from the aerial parts of the plant in the form of water vapour.