Explanation

The Calvin cycle occurs in the stroma of chloroplast of $C_{3}$ plants and consists of three main parts, i.e., carboxylation, reduct5ion and regeneration. Carboxylation involves addition of carbon dioxide to ribulose 1,5-bisphosphate in presence of RUBISCO enzyme to form 3-PGA (3-phosphoglyceric acid), i.e., single carboxylation occurs in Calvin cycle.