In which stage of photosynthesis does carbon dioxide provide carbon for carbohydrate formation?

• A. Light dependent stage
• B. Dark stage
• C. Light independent stage
• D. Both stages

Answer: (C)

The carbon in carbohydrates is fixed during the light-independent stage, also known as the Calvin cycle. In this stage, carbon dioxide is captured and transformed into sugars, with the actual sugar-building steps relying on ATP and NADPH that were produced by the light-dependent stage. So carbon comes from CO2 here, while the energy to drive the process comes from the products of the earlier light reactions. That’s why this stage is called light independent. The light-dependent stage does not fix carbon; it supplies the energy carriers, not the carbon source.