Question

How does rate of transpiration get affected by:

1. Wind velocity
2. Intensity of light
3. Humidity.

Answer 1

Transpiration:

1. The loss of water vapour from the aerial parts of the plant is called transpiration.
2. Transpiration may take place from stomata, cuticles and lenticels.

Rate of transpiration:

1. It is the ratio of the mass of water transpired to the mass of dry matter of the plant.
2. The rate of transpiration is also known as the transpiration ratio.
3. For most crop plants, the transpiration ratio or the rate of transpiration is between 200-1000.
4. This means that for every 1 kg mass of dry matter of plant the amount of water transpired is about 200-1000 kg of water.

Factors affecting the rate of transpiration:

1. External factors: wind velocity, the intensity of light, temperature, humidity, carbon dioxide percentage, soil condition, and atmospheric pressure.
2. Internal factors: thick cuticle, number of stomata, sunken stomata, epidermal hairs, stomata opening at night only.

Wind velocity:

1. The wind blows away the small pockets of humid air that are formed when the air is still.
2. Humid air gets replaced by drier air.
3. Drier air will cause more transpiration.

The intensity of light:

1. Light intensity triggers the opening of stomata for more exchange of gases for increased photosynthesis.
2. As stomata are also involved in transpiration along with gaseous exchange, the light intensity will increase the rate of transpiration.

Humidity:

1. The amount of water vapour in the air is called humidity.
2. For transpiration, there must be a water potential gradient between air and moisture content inside the leaves.
3. The more moisture in the air, the lower the water potential gradient.
4. A low water potential gradient will decrease the rate of transpiration.