Question

Given below is the diagram of an apparatus used to study a particular phenomenon in plants:

1. Name the apparatus.
2. What is it used for?
3. What is the role played by the air-bubble in this experiment?
4. What is the use of the reservoir?
5. What happens to the movement of the air-bubble if the apparatus is kept:
   1. in the dark
   2. in sunlight
   3. in front of a fan?
      Give a reason in each case.

Answer 1

1. Ganong’s potometer
2. The rate of transpiration from a leafy shoot is measured using a potometer.
3. As transpiration occurs, the air bubble added to the horizontally graded capillary tube goes along. A suction force is created as the water from the twig is lost from the beaker and the bubble in the capillary tube goes along.
4. Opening the stopcock releases the water into the capillary tube from the reservoir.
5. The movement of air bubbles is affected as follows:
   1. The stomata, tiny openings on leaves, will close in the absence of light, sometimes known as the dark, therefore preventing transpiration. Thus, the air bubble will remain stationary in one location.
   2. More transpiration results during the day when the stomata are open to let carbon dioxide enter for photosynthesis. Transpiration lessens at night as the stomata close. As a result of the higher water loss throughout the day, the air bubble travels more.
   3. Placing the equipment before the fan speeds up transpiration. This causes the air bubble to migrate more since the quicker air from the fan removes more water vapour, promoting more transpiration.