What is the overall outcome of photosynthesis?

• A. Photosynthesis results in the reduction of CO2 and the oxidation of H2O, producing O2.
• B. It oxidizes CO2 and reduces H2O to form methane.
• C. It consumes O2 to form CO2.
• D. It converts light energy directly into mechanical work.

Answer: (A)

Photosynthesis uses light energy to build organic molecules from inorganic CO2 and H2O. In this process, carbon dioxide is reduced (its electrons increase) to form carbohydrate, while water is oxidized (its electrons are removed) to produce oxygen. The overall result is the release of O2 and the formation of glucose (or other sugars) from CO2 and H2O, captured energy from light drives this redox chemistry. Net reaction can be summarized as CO2 and H2O plus light yielding carbohydrate and O2. This is why the outcome is described as reduction of CO2 and oxidation of H2O, with O2 produced. Methane formation isn’t a product of photosynthesis, it doesn’t consume O2, and while light energy powers the process, it isn’t converted directly into mechanical work.