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

What component of the leaf is responsible for photosynthesis?

1. Spongy layer

2. Palisade cells

3. Stomata

4. Waxy cuticle

The correct answer is: Palisade cells

The palisade cells are the primary site of photosynthesis in the leaf due to their structure and arrangement. These cells are located just beneath the upper epidermis of the leaf and are packed with chloroplasts, which contain chlorophyll—the pigment essential for capturing light energy. The arrangement of palisade cells maximizes their exposure to sunlight, allowing for efficient absorption of light. This process, combined with carbon dioxide entering the leaf through the stomata and water absorbed by the roots, facilitates the overall reaction of photosynthesis, producing glucose and oxygen. In contrast, while the spongy layer contributes to gas exchange, it is the palisade cells that directly carry out the conversion of light energy into chemical energy through photosynthesis. The stomata are responsible for the exchange of gases, and the waxy cuticle helps to prevent water loss, but neither is directly involved in the photosynthetic process itself.