Question

In hot summer day, plant cooling is due to
A. Loss of water vapours from leaf
B. Transport of water in plant
C. Loss of liquid water
D. Loss of water from entire plant

Answer 1

Plants are known for carrying out the process of photosynthesis which requires energy from the sun, making them hot. So, to cool the plants, the process of transpiration takes place from the aerial parts of the plant.

Complete answer:
-Option (A) is correct. During hot summer days, leaves absorb the energy from the sun to carry out photosynthesis which increases the temperature of the leaf. But, this temperature is brought down
through the rapid loss of water in the form of water vapors from the aerial parts of the plant through the process called transpiration, thereby, cooling the plant.
-Option (B) is incorrect. Transport of water in the plant helps in providing water that has been absorbed through the root to the other parts of the plant. This process has no role in providing a cooling effect on the
plants.
-Option (C) is incorrect. Loss of liquid water is also known as guttation. This water is lost mostly through the tips or edges of the leaves during the early morning when the weather is highly humid.
-Option (D) is incorrect. Loss of water from the entire plant can lead to the wilting process, thereby, damaging the plant.
Hence, the correct option is (A).

Note:
The transpiration process or loss of water vapors from aerial parts of the plant (leaf, stem) helps in bringing down the temperature of plants, thereby producing a cooling effect. This helps in protecting the plants from heat injury which takes place mostly when the temperature is high and the sunlight is more intense i.e., during hot summer days.