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

How does the spongy layer facilitate gas exchange?

1. By producing glucose

2. By providing a large surface area

3. By allowing gases to diffuse through stomata

4. By secreting moisture

The correct answer is: By allowing gases to diffuse through stomata

The spongy layer of a leaf plays a crucial role in gas exchange primarily by allowing gases, such as carbon dioxide and oxygen, to diffuse throughout the leaf structure. This layer is characterized by loosely arranged cells with many air spaces between them, which enhances the movement of gases. When stomata, the small openings on the leaf surface, open, carbon dioxide from the atmosphere can enter and diffuse through the air spaces in the spongy layer, where it is then accessible to the palisade layer for photosynthesis. Conversely, oxygen, a byproduct of photosynthesis, can diffuse out through the spongy layer and exit the leaf via the stomata. This efficient diffusion process ensures that the leaf has the necessary gases for photosynthesis and respiration, facilitating overall plant health and function. In contrast, while the production of glucose is an essential function of photosynthesis, it is not a direct mechanism by which the spongy layer facilitates gas exchange. The large surface area is beneficial for various processes in the leaf, but it is not the primary function of the spongy layer concerning gas exchange. Secreting moisture could aid in creating a humid environment around the leaf, which may affect gas diffusion, but it is not the