Question

Water reaches to the top of trees of more than 100 feet against gravity, which one of the following is the main phenomenon responsible for this?

• A. Exudation
• B. Guttation
• C. Root pressure
• D. Transpiration pull

Hint:

Cohesion–tension theory explains ascent of sap due to transpiration pull.

Answer 1

The Correct Option is D

Step 1: Understanding ascent of sap.
The upward movement of water from roots to the top of tall trees against gravity is known as ascent of sap. This process requires a strong and continuous pulling force.
Step 2: Role of transpiration pull.
Transpiration from the leaves creates a negative pressure (tension) in the xylem vessels. Due to cohesion between water molecules and adhesion to xylem walls, this tension pulls the water column upward continuously.
Step 3: Why other options are incorrect.
(A) Exudation: Refers to oozing of sap, not long-distance water transport.
(B) Guttation: Involves loss of water droplets from leaf margins under high root pressure, not ascent to great heights.
(C) Root pressure: Insufficient to raise water to heights of more than a few meters.
Step 4: Conclusion.
Transpiration pull is the main force responsible for lifting water to the tops of tall trees.