Answer: Each turn fixes one CO 2 and regenerates RuBP; 3 CO 2 are needed to produce 1 net G3P (a 3-carbon molecule).
- A Mainly a single CO<sub>2</sub> molecule is ever fixed across the entire three-turn cycle process as frequently observed in practice
- B Each turn fixes one CO<sub>2</sub> and regenerates RuBP; 3 CO<sub>2</sub> are needed to produce 1 net G3P (a 3-carbon molecule)
- C The cycle consumes exactly three ATP molecules during each individual turn taken in many documented cases
- D Ribulose bisphosphate itself is built from a three-carbon precursor skeleton structure according to conventional understanding
Correct answer: B. Each turn fixes one CO<sub>2</sub> and regenerates RuBP; 3 CO<sub>2</sub> are needed to produce 1 net G3P (a 3-carbon molecule)
Explanation: Calvin cycle: 3 CO<sub>2</sub> + 3 RuBP → 6 PGA → 6 G3P. 5 G3P are used to regenerate 3 RuBP, leaving 1 net G3P. Full cycle uses 9 ATP and 6 NADPH for 3 CO<sub>2</sub>.
Simplified photosynthesis diagram: light energy, CO2, and H2O enter the leaf and are converted in the chloroplast into glucose and O2.
Concept context
Light reactions, the Calvin cycle, C 3 /C 4 /CAM pathways, photorespiration, and factors affecting the rate of photosynthesis. One of the highest-yield NEET chapters.