Final answer:
The Calvin cycle occurs when ATP and NADPH are synthesized and used to convert carbon dioxide into glucose.
Step-by-step explanation:
The Calvin cycle occurs when ATP and NADPH are synthesized and used to convert carbon dioxide into glucose. The cycle takes place in the stroma of the chloroplasts and is the second stage of photosynthesis. Light energy captured during the light reactions of photosynthesis is converted to chemical energy in the form of ATP and NADPH, and these energy carriers are used in the Calvin cycle to power the reduction of carbon dioxide into glucose.