Answer :
The compound required for the carboxylation step of the Calvin cycle is RuBP (d).
In the Calvin cycle, RuBP (ribulose-1,5-bisphosphate) is the compound needed for the carboxylation step.
Carboxylation is the first phase of the Calvin cycle, during which [tex]CO_2[/tex] is fixed to the 5-carbon sugar RuBP by the enzyme RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase).
This reaction produces an unstable 6-carbon compound, which then rapidly splits into two molecules of 3-PGA (3-phosphoglycerate).
ATP and NADPH, which are generated in the light-dependent reactions of photosynthesis, are utilized later in the cycle to synthesize glucose and regenerate RuBP.
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