Question

Here is the diagram of an apparatus used to study a particular phenomenon in plants:
What is the role played by the air-bubble in this experiment?

Answer 1

As transpiration proceeds, that is, as the water is lost from the twig, a suction force is set up which pulls the water from the beaker and the bubble in the capillary tube moves along. The readings on the capillary tube would give the volume of water lost at a given time.