Biology – 8.1 Transport in plants | e-Consult

The rate of transpiration, the loss of water vapour from a leaf, is significantly influenced by environmental conditions. Several factors play a key role in regulating this process:

Humidity: High humidity in the air surrounding the leaf reduces the rate of transpiration. This is because the water potential gradient between the leaf and the air is smaller, meaning there is less driving force for water to evaporate. When the air is already saturated with water vapour, transpiration slows down considerably.

Light Intensity: Increased light intensity generally increases the rate of transpiration. Light stimulates the opening of stomata, allowing for greater gas exchange, including water vapour loss. This is because photosynthesis requires carbon dioxide, and stomata must open to allow carbon dioxide to enter the leaf. The increased light also leads to a higher rate of photosynthesis, which requires more water.

Wind Speed: Wind increases the rate of transpiration. Wind removes the humid air layer that surrounds the leaf, maintaining a steeper water potential gradient and promoting faster water vapour diffusion. This is because the wind carries away the water vapour that has evaporated from the leaf surface, preventing the build-up of saturated air around the stomata.

In summary, transpiration is a complex process influenced by multiple environmental factors. Changes in humidity, light intensity, and wind speed all affect the rate at which water is lost from the leaf. These factors interact to maintain a balance between water uptake and water loss.