What is the overall purpose of the Calvin cycle?

• A. To generate ATP directly.
• B. To produce NADPH.
• C. To fix CO2 into sugars using ATP and NADPH.
• D. To oxidize glucose to CO2.

Answer: (C)

The Calvin cycle fixes CO2 into sugars using the energy from ATP and the reducing power of NADPH produced by the light reactions. In the chloroplast stroma, CO2 is first captured by Rubisco and turned into a three-carbon compound, which is then reduced with ATP and NADPH to form glyceraldehyde-3-phosphate. This fixed carbon can be assembled into glucose and other carbohydrates, and RuBP is regenerated to keep the cycle going. This process does not produce ATP directly; it consumes ATP. It does not generate NADPH; it relies on NADPH from the light-dependent reactions. It also isn’t about oxidizing glucose—that’s the role of cellular respiration.