Which process uses light energy to drive chemical reactions in leaves?

• A. Transpiration
• B. Fermentation
• C. Photosynthesis
• D. Respiration

Answer: (C)

Photosynthesis is the process by which leaves convert light energy into chemical energy stored in sugars. In chloroplasts, light energy drives reactions that split water and transfer energy to produce ATP and NADPH, which then power the Calvin cycle to fix carbon dioxide into glucose. Oxygen is released as a byproduct. This is what makes leaves the primary site for capturing light and building sugars that fuel plant growth.

Transpiration is about water vapor loss from the leaf through stomata, not about making sugars. Fermentation is an anaerobic pathway that can occur in some organisms and conditions but isn’t driven by light or the main energy source in leaves. Respiration uses sugars to release stored energy, but it is not powered by light itself; it happens all the time to meet the plant’s energy needs.