Potometer works on the principle of:

Explanation

Potometer is an instrument or apparatus with the help of which, rate of transpiration can be measured. Main types of potometers are as under: Simple potometer, Farmer's potometer and Ganong's potometer. The whole instrument is made of glass and is consisted of a long tube, having a side tube, bent at right angles. A fresh plant shoot is cut underwater and is inserted into the side tube through a cork, fitted into the mouth of this tube. The whole apparatus is filled with water and the joints are made air tight. The apparatus is placed in the sunlight. Air bubble enters the tube and after this lower end of the tube is placed in the beaker, containing water. Water is absorbed by the shoot and is transpired through the leaves. Transpiration pull is created and the air bubble begins to move along with the transpiration pull. Readings are taken for the air bubble and thus amount of water absorbed and transpired is calculated. So option B is correct.