Final answer:
Oxygen is produced during the light-dependent reactions of photosynthesis, where sunlight energy splits water molecules releasing oxygen.
Step-by-step explanation:
The step of photosynthesis that produces oxygen is the light-dependent reaction. During light-dependent reactions, energy from sunlight is absorbed by pigments in the photosynthetic membrane and used to split water molecules, releasing oxygen as a byproduct. This process occurs in the thylakoid membranes of chloroplasts where chlorophyll and other pigments capture the energy of light.
These reactions convert light energy into chemical energy, forming ATP and NADPH. Both ATP and NADPH are important energy carriers that power the light-independent reactions, also known as the Calvin cycle, which synthesize sugar molecules from carbon dioxide. Nevertheless, the direct production of oxygen is achieved exclusively during the light-dependent reactions.