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

Where in the plant does photosynthesis occur?

1. In the roots

2. In the stem

3. In the leaves

4. Within the chloroplasts

The correct answer is: Within the chloroplasts

Photosynthesis occurs primarily within the chloroplasts, which are specialized organelles found in plant cells. Chloroplasts contain chlorophyll, the green pigment that captures sunlight, and are essential for converting light energy into chemical energy through the process of photosynthesis. Although leaves are the main sites of photosynthesis because they contain a high concentration of chloroplasts and are often optimized for light capture and gas exchange, chloroplasts themselves are the specific structures where the biochemical reactions of photosynthesis take place. Therefore, identifying chloroplasts as the location emphasizes the cellular level at which photosynthesis occurs, highlighting their crucial role in the overall process. While roots and stems play essential roles in a plant's growth and nutrient uptake, they do not contain the chlorophyll-rich structures required for photosynthesis. Thus, focusing on chloroplasts directly addresses the mechanism by which plants convert light energy into glucose and oxygen, the fundamental outputs of photosynthesis.