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

How do leaves facilitate the diffusion of gases?

1. By being thick and waxy

2. By having a large surface area and stomata

3. By containing chlorophyll

4. By having root hairs

The correct answer is: By having a large surface area and stomata

Leaves facilitate the diffusion of gases primarily through having a large surface area and stomata. The large surface area of leaves allows them to capture maximum light for photosynthesis and provides ample area for gas exchange. Stomata are tiny openings found mainly on the underside of leaves that regulate the exchange of gases (such as oxygen and carbon dioxide) between the leaf and the atmosphere. These openings can open and close to control gas exchange and minimize water loss, which is crucial for plant health and efficiency in photosynthesis. In contrast, options that mention thickness and waxiness refer to the cuticle, which may reduce water loss but does not facilitate gas diffusion. Chlorophyll is essential for capturing light energy in photosynthesis but does not directly influence gas diffusion. Root hairs are specialized structures for water and nutrient uptake from the soil and have no connection to the function of leaves in gas exchange. Thus, the combination of a large surface area and the presence of stomata is key to effective gas diffusion in leaves.