Question

Why do well-watered plants transpire more during sunny and windy days than in the cool and calm mornings? How is transpiration different from evaporation?

Answer 1

Hint: Transpiration is defined as the loss of water in the form of vapours from the aerial parts of the plant. The loss of water is so great and high that it reduces water level in the soil and can lead to the death of plants, but transpiration is said to be essential for water and mineral absorption, ascent of sap and lowering the temperature (cooling effect).

Complete Answer:
Transpiration takes place mainly through the stomata in the leaves. Transpiration is similar to evaporation in that water from the wet surface is converted into vapours form. It is different from evaporation in being controlled by structural and physiological adaptations of plants.

Factors affecting Transpiration:
External factors:
1. Light Blue light induces maximum opening of stomata: In its absence, stomata remain closed. Light is one of the factors that affects the rate of transpiration by increasing temperature. Blue and red light are effective for transpiration, constituting its action spectrum.
2. Relative humidity (vapour pressure gradient): In a humid atmosphere (when the relative humidity is high), the rate of transpiration decreases. In dry atmosphere, the relative humidity is low (low water vapour pressure), so the rate of transpiration increases.
3. Temperature: Higher the temperature means more is the rate of transpiration as it results in a higher vapour pressure gradient. Lowering of temperature leads to decreases the rate of transpiration.
4. Wind: If wind is not blowing, water vapours accumulate and get associated above the transpiring leaves which decrease the rate of transpiration. The blowing wind (slow breeze) removes the accumulated humidity and brings fresh air capable of absorbing water and thus, the rate of transpiration is enhanced. Breeze is wind with velocity 6 - 50 km/hour
5. Available soil water: If the available water in the soil is not sufficient, the rate of transpiration is decreased. A high concentration of salts in the soil water also reduces the rate of transpiration due to less water absorption.
So, well-watered plants transpire more during sunny and windy days than in the cool and calm mornings.

Note: Transpiration Serves more than one purpose in plants It Creates or exerts transpiration pull for absorption and transport in plants and Supplies water needed for photosynthesis. It transports minerals along with water from the soil to various parts of the plant.