Transpiration is vital for water absorption because it creates the negative pressure (tension) that pulls water up from the roots through the plant.
The Cohesion-Tension Mechanism Explained
Transpiration, the process of water evaporating from the leaves of a plant, is the driving force behind water absorption and transport. This process relies on what is known as the Cohesion-Tension (C-T) mechanism. According to the provided reference, the bulk of water absorbed and transported through plants is moved by negative pressure generated by the evaporation of water from the leaves (i.e., transpiration).
How Transpiration Drives Water Absorption
Here's a breakdown of how transpiration leads to water absorption:
- Evaporation from Leaves: Water evaporates from the leaves through small pores called stomata.
- Negative Pressure (Tension): As water evaporates, it creates a negative pressure or tension within the leaves.
- Water Column Movement: This tension pulls water up the xylem (vascular tissue) from the roots to the leaves. The cohesive properties of water (water molecules sticking to each other) and the adhesive properties (water molecules sticking to the walls of the xylem) allow for the creation of an unbroken water column from the roots to the leaves.
- Absorption at Roots: As the water column is pulled upwards, water is drawn into the roots from the soil to replace the water being lost through transpiration.
In summary, transpiration acts like a pump, pulling water up from the roots by creating tension as water evaporates from the leaves. Without transpiration, this negative pressure wouldn't exist, and water absorption would be significantly reduced.
