Question

The most important function of transpiration in plants is to cause
(a) Loss of surplus water
(b) Cooling of the plant
(c) The rapid ascent of sap
(d) The rapid rise of minerals

Answer 1

Hint: Plants lack a heart and a circulatory system. However, the upward flow of water through the xylem in plants is achieved by fairly high rates, up to 15 meters per hour. Most researchers believe that the main driving force for pulling fluid through the plant is transpiration from the leaves.

Complete answer:
The most important function of transpiration in plants is to cause rapid ascent of sap. Plants on the land take up a huge amount of water on a daily basis. However, most of this absorbed water is lost to the air through evaporation from the leaves by a process called ‘transpiration’. It takes place mainly through stomata. As we can guess transpiration is a pulling force so it pulls up water from the root to different parts of the plant. Now there has to be a balancing force to push an almost equal amount of water from the soil into the roots, otherwise, the plant may dry out. So this is caused by an anti- gravitational force which causes the ascent of sap. It has been measured that the forces generated by transpiration can create pressures enough to lift a xylem sized column of water over 130 meters high.

- Transpiration often causes enormous tension within the vascular bundles of the plant. This may lead to a break in the continuous chain of water molecules in the xylem. This chain is then re- established by a phenomenon called ‘root pressure.’
- Usually, stomata open in the daytime and close during the night.

So, the correct answer is ‘rapid ascent of sap.’

Note:
- Transpiration is affected by several external factors like temperature, light, wind speed, and humidity.
- Transpiration along with guttation also removes excess water from the plants.
- The phenomenon of transpiration also transports minerals from the soil to all parts of the plant.
- By the process of transpiration, the leaf surfaces cool down by about 10 to 15 degrees.