Rubisco (RuBP carboxylase–oxygenase), glyceraldehyde-3-phosphate (G3P), and NADPH all function in which process of photosynthesis?

Introduction / Context:
Photosynthesis has two coordinated stages: the light reactions that capture light energy and the dark reactions (Calvin–Benson cycle) that fix CO2 into carbohydrates. This question asks you to identify where the enzyme Rubisco, the product G3P, and the reductant NADPH act together.

Given Data / Assumptions:

• Rubisco fixes CO2 by carboxylating ribulose-1,5-bisphosphate (RuBP).
• NADPH and ATP are produced by the light reactions.
• G3P is the 3-carbon triose phosphate formed downstream of CO2 fixation and reduction steps.

Concept / Approach:
Rubisco initiates the Calvin cycle in the chloroplast stroma. ATP provides energy and NADPH provides reducing power to convert 3-phosphoglycerate into glyceraldehyde-3-phosphate (G3P). A portion of G3P exits the cycle for carbohydrate synthesis; the rest regenerates RuBP to continue CO2 fixation.

Step-by-Step Solution:

Verification / Alternative check:
Calvin cycle flux measurements and labeling experiments show NADPH consumption and G3P production in the stroma; Rubisco abundance in chloroplasts aligns with its central role.

Why Other Options Are Wrong:

• Aerobic respiration/fermentation: mitochondrial or cytosolic processes, not chloroplast stroma reactions.
• Oxygen evolution: belongs to PSII light reactions, not Calvin cycle.

Common Pitfalls:
Equating “dark reactions” with nighttime; they are light-independent chemically but depend on light-generated ATP and NADPH.

Final Answer:
the dark reactions (Calvin–Benson cycle) of photosynthesis.