2.3 - Main Organ for Transpiration

The Necessity of Transpiration in Plants

Transpiration is the process of water loss through evaporation to the atmosphere. Most of the water (90%) is lost through the stomata of the leaves. In order to maintain the balance of water volume in plants, the roots will absorb water continuously from the soil to replace the water loss.

Figure 5 - The movement of water in plants. Water absorbed from the soil moves upwards (towards the leaves) through the xylem. The leaf veins carry water to the leaves. Transpiration happens through stomata in the leaves.

The Environmental Factors that Affect the Rate of Transpiration

1. Light intensity

Figure 6 - When the light intensity increases, the rate of transpiration also increases. However, the rate of transpiration becomes constant after a certain point of light intensity. The rate of transpiration becomes constant due to other existing limiting factors such as relative air humidity, temperature and air movement.

2. Relative air humidity

Figure 7 - The lower relative air humidity at the outer environment promotes the rate of transpiration in plants. More water vapor is lost through evaporation via the stomata.

3. Temperature

Figure 8 - Higher temperature will increase the rate of transpiration in plants. The high temperature increases the kinetic energy of water molecules dan the process of evaporation.

4. Air movement

Figure 9 - Faster air movement increases the rate of transpiration. The moving air carries the water molecules evaporated from the stomata of plants.