Transpiration is essentially a plant's way of "sweating," involving the loss of water vapor primarily through the stomata (tiny pores) on its leaves. A plant doesn't use most of the water it absorbs, as about 97-99% of it is lost through transpiration. Transpiration occurs mainly from the stomata in leaves, but also through evaporation from the surfaces of leaves, flowers, and stems.
Here's a breakdown of how it works:
The Transpiration Process Explained
| Step | Description |
|---|---|
| 1. Water Absorption | Plants absorb water from the soil through their roots. |
| 2. Water Transport | The water is transported upward through the xylem (vascular tissue) to the leaves. |
| 3. Evaporation | Inside the leaves, water evaporates from the mesophyll cells into the air spaces within the leaf. |
| 4. Diffusion | Water vapor diffuses from the air spaces within the leaf to the outside atmosphere through the stomata. |
| 5. Water Loss | The water vapor exits the plant, resulting in transpiration. |
Factors Affecting Transpiration
Several environmental factors influence the rate of transpiration:
- Temperature: Higher temperatures increase the rate of evaporation and diffusion.
- Humidity: Lower humidity creates a greater difference in water vapor concentration between the leaf and the air, increasing transpiration.
- Wind: Wind removes water vapor from the leaf surface, maintaining a concentration gradient that promotes transpiration.
- Light Intensity: Light stimulates the opening of stomata, which are generally closed in the dark, thereby increasing transpiration.
Why is Transpiration Important?
While seemingly wasteful, transpiration is crucial for plant survival:
- Water Transport: Transpiration creates a "pull" that helps draw water and minerals from the roots to the leaves. This is known as the transpiration stream.
- Nutrient Uptake: As water is transported, essential mineral nutrients are carried along, supplying the plant with the necessary building blocks for growth.
- Cooling: Evaporation of water cools the plant, preventing it from overheating, especially in hot environments.
- Turgor Pressure: Transpiration helps maintain turgor pressure within cells, which is essential for rigidity and support.
Example
Think of a hot summer day. Plants transpire more on hot, dry, and windy days than on cool, humid, and calm days. This is because the evaporation rate is higher in hot conditions, the concentration gradient of water vapor is steeper in dry conditions, and wind removes water vapor, maintaining the gradient.
