Explanation

The first step in dark reaction of photosynthesis is Carboxylation, in which six molecules of carbon dioxide Carboxylation, in which six molecules of carbon dioxide combine with six molecules of ribulose 1, 5-biphosphate (RuBP) to form six molecules of unstable six carbon compound. Carboxylation of RuBP is catalysed by the enzyme RuBP carboxylase or RUBISCO.