Question

The diagram below represents an experiment to demonstrate a certain phenomenon in a green plant:

1. Will the level of mercury in the glass tubing rise or fall?
2. Which conducting tissue of the plant does the glass-tubing represent?
3. Define transpiration.
4. How will the rate of the above process differ if the environment of the plant has
   1. Less humidity
   2. High temperature?

Answer 1

1. The level of mercury in the glass tubing will rise. This happens because as the leafy shoot loses water through transpiration, it creates a suction force called a transpiration pull that draws the water column—and consequently the mercury—upward into the tube.
2. The glass tubing represents the xylem tissue of the plant, which is responsible for the upward conduction of water and dissolved minerals from the roots to the leaves.
3. Transpiration is defined as the loss of water in the form of water vapor from the aerial parts (such as leaves and stems) of a living plant.
4. 1. Less humidity: The rate of transpiration will increase because dry air creates a steeper moisture gradient between the inside of the leaf and the outside atmosphere, allowing water vapor to diffuse out faster.
   2. High temperature: The rate of transpiration will increase because a higher temperature accelerates the rate of water evaporation from the mesophyll cells into the internal air spaces of the leaf.