Which statement about the relationship between light-dependent reactions and the Calvin cycle in photosynthesis is correct?

Which statement about the relationship between light-dependent reactions and the Calvin cycle in photosynthesis is correct?

• A. Light-dependent reactions produce O2 but do not affect the Calvin cycle.
• B. Calvin cycle uses CO2 and light to generate energy.
• C. Light-dependent reactions produce ATP and NADPH and split water; Calvin cycle uses ATP and NADPH to fix CO2 into sugar.
• D. Both processes occur in the mitochondria.

Answer: (C)

The key idea is that photosynthesis has two connected parts: the light-dependent reactions capture energy and reducing power to drive the Calvin cycle. During the light-dependent reactions, light energy is used to split water, releasing oxygen, and to produce ATP and NADPH. Those ATP and NADPH molecules then power the Calvin cycle, where CO2 is fixed into sugars, with ATP providing energy and NADPH supplying the reducing power to convert carbon dioxide into the sugar precursor. The Calvin cycle happens in the chloroplast stroma and does not require light itself, but it relies on the products of the light reactions. The other statements miss this linkage or location: energy and electrons aren’t produced by the Calvin cycle, the cycle doesn’t use light directly, and these processes aren’t in mitochondria.

The key idea is that photosynthesis has two connected parts: the light-dependent reactions capture energy and reducing power to drive the Calvin cycle. During the light-dependent reactions, light energy is used to split water, releasing oxygen, and to produce ATP and NADPH. Those ATP and NADPH molecules then power the Calvin cycle, where CO2 is fixed into sugars, with ATP providing energy and NADPH supplying the reducing power to convert carbon dioxide into the sugar precursor. The Calvin cycle happens in the chloroplast stroma and does not require light itself, but it relies on the products of the light reactions. The other statements miss this linkage or location: energy and electrons aren’t produced by the Calvin cycle, the cycle doesn’t use light directly, and these processes aren’t in mitochondria.