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

Where does photosynthesis primarily take place in plant cells?

1. In the nucleus

2. In the mitochondria

3. In the chloroplasts

4. In the cytoplasm

The correct answer is: In the chloroplasts

Photosynthesis primarily takes place in the chloroplasts of plant cells because these organelles contain chlorophyll, the pigment responsible for capturing light energy from the sun. This captured energy is then used to convert carbon dioxide and water into glucose and oxygen through a series of biochemical reactions. The chloroplasts are specifically structured to facilitate this process, incorporating two membranes and internal thylakoid membranes where the light-dependent reactions occur. In contrast, the other organelles listed do not carry out photosynthesis: the nucleus houses genetic material, the mitochondria are involved in cellular respiration to produce energy for the cell, and the cytoplasm serves as the site for various metabolic processes but does not conduct photosynthesis.