Question: 109 Given below are two statements :
Statement I : The forces generated by transpiration can lift a xylem-sized column of water over 130 meters height.
Statement II : Transpiration cools leaf surfaces sometimes 10 to 15 degrees, by evaporative cooling.
In the light of the above statements, choose the most appropriate answer from the options given below :
(1) Statement I is correct but Statement II is incorrect.
(2) Statement I is incorrect but Statement II is correct.
(3) Both Statement I and Statement II are correct.
(4) Both Statement I and Statement II are incorrect.
Answer: Option (3)
Explanation:
Transpiration creates a negative pressure or transpiration pull in the xylem.
This pull is strong enough to lift a continuous column of water to great heights,
even exceeding 130 meters, as seen in tall trees.
Therefore, Statement I is correct.
Transpiration also causes loss of water from leaf surfaces through evaporation.
Evaporation requires heat energy, which is taken from the leaf surface.
As a result, transpiration produces a cooling effect and can lower leaf temperature by about 10 to 15 degrees.
Thus, Statement II is also correct.
Hence, both Statement I and Statement II are correct.