. The apparatus shown in the following diagram is Garreaus potometer designed

The apparatus shown in the following 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, 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 few hours, CaCl vials were taken out and weighed again.

garreau potometer

  1. What is the purpose of keeping CaClvials inside the cup?
  2. After few hours CaCl2 vials were taken out and weighed again. Will you expect any difference in weight? If so, give reason.
  3. What is the purpose of using a manometer?
  4. What do you mean by transpiration?


Best Answer

  1. CaCl2 is a hygroscopic compound that absorbs moisture/water without changing its state. CaClvials inside the cup to absorb water.
  2. 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.
  3. Manometer is used to measure the pressure. In order to measure the pressure exerted by the fluid, the fluid is allowed to exert pressure on one of the closed ends of the tube. Under the effect of the pressure, the liquid inside the manometer tube gets displaced and the amount of displaced liquid is measured.
  4. 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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