Photosynthesis needs sunlight, water and carbon dioxide, and it gives off oxygen.
Tips
memory
光 'light' + 合 'to combine' + 作用 'process': light putting things together. The reverse process in cells, which burns sugar for energy, is 呼吸作用 'respiration'.
usage
光化作用 once also meant photosynthesis but now covers any reaction driven by light. For plants, say 光合作用.
