NEET2026BiologyChapterActual
Carboxylation is considered the most crucial step of the Calvin cycle. Which of the following events specifically characterizes this stage?
Options
- AUtilization of ATP and NADPH to reduce intermediates into triose phosphate
- BCondensation of CO₂ with ribulose-1,5-bisphosphate to yield two molecules of 3-PGA
- CPhosphorylation of a sugar intermediate to regenerate the primary CO₂ acceptor
- DFixation of CO₂ by phosphoenolpyruvate to form oxaloacetic acid
Correct answer
B. Condensation of CO₂ with ribulose-1,5-bisphosphate to yield two molecules of 3-PGA
Step-by-step solution
The Calvin cycle consists of three main stages: carboxylation, reduction, and regeneration. Carboxylation is the most crucial step of the Calvin cycle where CO₂ is utilized for the carboxylation of RuBP. This reaction is catalyzed by the enzyme RuBisCO, which results in the condensation of CO₂ with a 5-carbon compound, ribulose-1,5-bisphosphate (RuBP), to yield two molecules of the 3-carbon compound, 3-phosphoglyceric acid (3-PGA). Utilization of ATP and NADPH occurs during the reduction stage to form triose phosph