OCR GCSE Biology 2026 – 400 Free Practice Questions to Pass the Exam

Transpiration is the process where plants lose water vapor through small openings called stomata. For transpiration to occur efficiently, a combination of low humidity and breezy conditions is ideal. When humidity is low, the concentration gradient between the moisture inside the leaf and the drier outside air increases, promoting faster water vapor diffusion from the leaf to the atmosphere.

Breezy conditions facilitate this process by moving the saturated air (air that has absorbed moisture) away from the leaf surface quickly. This action keeps the concentration gradient steep, which enhances the rate at which water vapor can escape the leaf.

The other scenarios provide conditions that are less conducive to efficient transpiration. High humidity slows down the diffusion of water vapor because the air is already holding a significant amount of moisture, reducing the gradient. Still air can lead to a build-up of moisture around the leaf, again decreasing the effectiveness of transpiration. Warm temperatures can increase water uptake, but without proper humidity and airflow, transpiration may be less efficient. Cool temperatures may reduce the rate of water loss, while high carbon dioxide typically lowers the opening of stomata to conserve water, which can further inhibit transpiration.