During photosynthesis, where do light-dependent reactions occur and what gas is released?

• A. In the stroma of mitochondria; carbon dioxide (CO2) is released.
• B. In the cytoplasm; nitrogen gas (N2) is released.
• C. In the thylakoid membranes of chloroplasts; oxygen (O2) is released.
• D. On the outer membrane of the nucleus; methane (CH4) is released.

Answer: (C)

Light-dependent reactions occur in the thylakoid membranes of chloroplasts, where sunlight-driven processes power the photosynthetic electron transport chain. Water is split here, releasing oxygen gas as a byproduct, which exits the plant. This location is distinct from where the Calvin cycle happens in the stroma, and it’s the reason oxygen is produced rather than carbon dioxide, nitrogen, or methane.