What are the two major stages of photosynthesis in plants?

• A. Light reactions and electron transport chain
• B. Glycolysis and Krebs cycle
• C. Light reactions and Calvin cycle
• D. Nitrogen fixation and respiration

Answer: (C)

Photosynthesis has two main stages that work in sequence to turn light into stored chemical energy and then build sugars from carbon dioxide. First, the light-dependent reactions capture light in the thylakoid membranes to split water, release oxygen, and produce ATP and NADPH. These energized molecules then power the second stage, the Calvin cycle, which occurs in the stroma and uses ATP and NADPH to fix CO2 into sugars like glyceraldehyde-3-phosphate. This separation into a light-driven phase and a carbon-fixing phase is why those two terms are paired as the primary stages. The other options mix processes that aren’t separate stages of photosynthesis: one pairs light reactions with the electron transport chain (which is part of those reactions, not a distinct stage), another lists pathways from cellular respiration, and the last mentions nitrogen fixation, which isn’t part of photosynthesis.