Question

Rate of transpiration is measured by
A. Ganong’s potometer
B. Porometer
C. Auxanometer
D. Respirometer

Answer 1

Hint:- Transpiration is a phenomenon by which water is lost from the plants through evaporation. It mostly occurs through the stomata present in the leaves. It also helps the plants to exchange gases.

Complete Answer:-
The opening and closing of the stomata are dependent upon the guard cells. The inner wall of these cells is thick and elastic while the outer wall is thinner. When the cells are turgid, they bulge out forming a crescent shape, whereas when the cells lose turgidity due to water loss, the walls of the cells regain their original shape thus opening the stomata.
The rate of transpiration is measured by a device known as a potometer. It measures the uptake of water that occurs during the process of transpiration. In a laboratory setup, a potometer known as Ganong’s potometer is used to measure the rate of transpiration. This device consists of a glass tube and a glass cylinder with a wide mouth. A capillary is fitted in the glass bar kept horizontally which is connected to a reservoir. A rubber cork having a hole is inserted into the wide mouth of the glass cylinder. A freshly cut twig is kept in this hole to measure its rate of transpiration.

Thus the correct option is (A) Ganong’s potometer.

Note:- The lower surface of the dicotyledonous leaves have more stomatal opening as compared to the upper surface. On the other hand, both the upper and lower surfaces of a monocotyledonous leaf have an equal number of stomatal openings.
The rate of transpiration depends upon many factors (both external and internal), such as temperature, light, wind speed, humidity, number and distribution of stomata, amount of available water, canopy structure, etc.