Question

Guttation is release of liquid water from veins of the leaf margins. It is caused by:

• A. Transpiration
• B. High Root Pressure
• C. High Leaf Pressure
• D. Clogged tracheids or vessel elements

Hint:

- Transpiration: Loss of water as vapor through stomata (daytime). - Guttation: Exudation of liquid water through hydathodes due to high positive root pressure (night/early morning when humidity is high).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Guttation is the exudation of liquid water droplets from specialized pores called hydathodes located along the leaf margins of certain vascular plants.
Understanding the water transport mechanisms in plants helps explain the physical forces behind this process.

Step 2: Detailed Explanation:
Water moves through plants primarily via transpiration pull during the day.
However, at night or early in the morning under conditions of high soil moisture and high relative humidity, the rate of transpiration is extremely low.
Despite this low transpiration rate, plant roots continue to actively absorb water and minerals from the soil.
This active absorption generates a positive hydrostatic pressure within the xylem vessel elements, known as root pressure.
As this root pressure builds, it pushes water upward through the stem.
Because the water cannot escape as vapor through transpiration, it is forced out in liquid form through specialized pores called hydathodes located at the vein endings along the leaf margins.
Therefore, guttation is directly caused by high root pressure.

Step 3: Final Answer
The correct option is (B).