Question

describe the 3 stages of calvin cycle highlighting the role of rubisco

Answer 1

Calvin cycle or C3 cycle constitutes the dark phase of photosynthesis. It occurs in stroma of chloroplast of all photosynthetic plants utilising the products of light reactions (ATP and NADPH). It has three stages:
1) Carboxylation: CO₂ is utilized for carboxylation of RuBP (Ribulose 1, 5-bisphosphate and this reaction is catalyzed by RuBP carboxylase-Oxygenase (RUBISCO). The product formed by this reaction is two molecules of 3-PGA.
2) Reduction: This stage contains a series of reactions as a result of which glucose is formed. Photochemically made ATP and NADPH are used for this step. Two molecules each of ATP and NADPH are required for fixing 1 molecule of CO₂.
3) Regeneration: CO₂ acceptor ribulose-1,5-bisphosphate is formed again for continuation of cycle. One molecule ATP is required for this step.
For the formation of one molecule of glucose, six molecules of CO₂ need to be fixed; hence, six cycles are required.