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

What is the function of the spongy layer in the leaf?

1. It absorbs sunlight

2. It helps in gas exchange

3. It stores water

4. It supports the leaf's structure

The correct answer is: It helps in gas exchange

The spongy layer in the leaf, also known as the spongy mesophyll, plays a crucial role in gas exchange, which is essential for photosynthesis and respiration. This layer consists of loosely packed cells and large air spaces, creating a surface area that facilitates the movement of gases, particularly carbon dioxide and oxygen, within the leaf. During photosynthesis, carbon dioxide diffuses from the atmosphere into the leaf through small openings called stomata, reaching the spongy layer where it can then move to the chloroplasts in the palisade layer for photosynthesis. Oxygen, a product of this process, will diffuse out of the leaf through the same spaces. While the other functions mentioned are important in plants, they do not accurately describe the primary role of the spongy layer. For instance, the absorption of sunlight occurs mainly in the palisade mesophyll where chloroplasts are densely packed, water storage is primarily the function of specialized tissues in various parts of the plant, and structural support is mainly provided by cell walls and the leaf's overall anatomy rather than the spongy layer itself.