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

What role do stomata play in a leaf?

1. They store water and nutrients

2. They facilitate gas exchange

3. They provide structural integrity to leaves

4. They conduct photosynthesis

The correct answer is: They facilitate gas exchange

Stomata are small openings located primarily on the underside of leaves that play a crucial role in facilitating gas exchange. They allow for the exchange of gases between the internal tissues of the leaf and the external environment. When stomata open, carbon dioxide from the atmosphere can enter the leaf, which is essential for the process of photosynthesis, where plants convert carbon dioxide and sunlight into glucose and oxygen. At the same time, oxygen produced during photosynthesis can exit through the stomata, along with water vapor in a process known as transpiration. By regulating the extent to which they open and close, stomata help maintain a balance between gas exchange and water loss, allowing plants to adapt to varying environmental conditions and thus playing a fundamental role in their overall physiology and health. The other options do not accurately describe the function of stomata. While stomata do not store water and nutrients, they do help manage water vapor loss. They do not provide structural integrity to leaves, which is primarily due to cell wall materials. Additionally, stomata themselves do not conduct photosynthesis but allow for the necessary gas exchange that supports this process within the leaf’s chloroplasts.