Question

When the relative humidity of atmosphere is 100% in day time, the stomata shall
A. Continue to remain open
B. Become closed to stop transpiration
C. Remain partially opened
D. Become partially opened

Answer 1

Hint: At a particular temperature, the quantity of water vapor present in the air to the quantity of water vapor present in the cloud is called Relative humidity.

Complete Answer:
- A process by which the water evaporates from the tiny pores of the aerial part of plants called stomata into the atmosphere is called transpiration.
- The water from leaves of plants moves to the atmosphere due to the gradient that is created when the amount of water in the atmosphere is reduced.
- Therefore, when there is decrease in the moisture content in the atmosphere, there will be low relative humidity, and hence there is an increase in the driving force for transpiration.
- But when the water content in the atmosphere reaches the saturation level, and the relative humidity is high, there will be less driving force for transpiration.
- Hence the rate of transpiration decreases as it is difficult for water to move to the saturated atmosphere than the dry atmosphere.
- Therefore the stomata tends to close when there is a decrease in transpiration rate.

Hence the correct answer is (b) Become closed to stop transpiration.

Note: When there is a high transpiration rate, there is excessive water loss from the plant which leads to wilting and stunted growth of the plant and eventually the plant dies. In extreme hot regions like deserts, the plants receive very less amount of water. So they modify their leaves into spines and thorns orchid their leaves to avoid transpiration.