In the Calvin cycle (carbohydrate-synthesizing reactions of photosynthesis), carbon fixation and reduction directly require which inputs?

• A. NADH and FADH2
• B. ATP and NADPH from the light reactions
• C. Chlorophyll molecules and photons of light
• D. Oxygen and glucose

Answer: (B)

Verified step by step guidance

1. Understand that the Calvin cycle is the set of reactions in photosynthesis where carbon dioxide is fixed and converted into carbohydrates.
2. Recall that the Calvin cycle has three main phases: carbon fixation, reduction, and regeneration of the starting molecule (RuBP).
3. Identify the molecules that provide energy and reducing power for the carbon fixation and reduction phases. These are products of the light reactions of photosynthesis.
4. Recognize that ATP provides the energy needed for the reactions, while NADPH provides the reducing power (electrons) to convert 3-phosphoglycerate into glyceraldehyde-3-phosphate.
5. Conclude that the direct inputs required for carbon fixation and reduction in the Calvin cycle are ATP and NADPH, which come from the light reactions.