OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

How does air movement influence transpiration?

1. It decreases the transpiration rate

2. It has no effect on transpiration

3. It speeds up transpiration rate

4. It only affects transpiration in humid conditions

The correct answer is: It speeds up transpiration rate

Air movement plays a significant role in the process of transpiration, which is the loss of water vapor from plant surfaces, primarily through stomata in leaves. When there is increased air movement, such as with wind, it can enhance the rate of transpiration. Here's how this works: Wind or air movement can carry away the moisture that surrounds the leaf surface. When the air is still, moisture can accumulate around the stomata, creating a high humidity microclimate that can slow down the rate of water vapor loss. By moving this humid air away, the surrounding air tends to be drier, which maintains a steeper concentration gradient between the moisture inside the leaf and the drier air outside. This gradient facilitates the diffusion of water vapor out of the leaf more rapidly, thus speeding up the process of transpiration. In contrast, in conditions where air movement is minimal, moisture retention around the stomata can limit transpiration rates due to decreased concentration gradients. Overall, the correct answer highlights how increased air movement enhances transpiration, making it a crucial factor for plants, especially those in windy environments.