Biology
The apparatus shown in the following diagram is Garreau's potometer designed to demonstrate unequal transpiration from the two surfaces of a dorsiventral leaf. Equal amounts of calcium chloride (CaCl2) was taken in two vials, which were placed in two cups. The leaf was placed between the cups. The ends of 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 is the purpose of using a manometer?
(d) What do you mean by transpiration?
Answer
(a) CaCl2 is a hygroscopic compound that absorbs moisture/water without changing its state. CaCl2 vials are placed inside the cup to absorb water.
(b) Yes, after few hours the weight of the CaCl2 vials will increase because they will absorb water lost by the leaf of the plant due to transpiration.
(c) Manometer is used to measure the pressure exerted by the water vapour that is released by the leaf through Transpiration. A change in vapour pressure within the cups shown by the manometers is indicative of the fact that either the connections are not air-tight or that all the vapour given out by the leaf surface is not being absorbed by the CaCl2 within the vials.
(d) Transpiration is the loss of water in the form of water vapour from the aerial parts (leaves and stem) of the plant.
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