In which pathway of the light stage is oxygen produced?

• A. Pathway 1
• B. Pathway 3
• C. Pathway 4
• D. Pathway 2

Answer: (D)

Oxygen is produced during the light-dependent reactions when water is split by the oxygen-evolving complex of Photosystem II. Light energy drives this photolysis, releasing O2 gas along with protons and electrons. Those electrons then move through the electron transport chain to Photosystem I, helping generate ATP and NADPH for the Calvin cycle. The production of O2 is tied specifically to the water-splitting step in the pathway that involves non-cyclic electron flow; other pathways that skip water splitting or rely on cyclic flow do not release oxygen.