c3 pathway describtion for 2 marks and 5 marks all the answers need the same thing as we write for 5 marks?

Dear Student

Calvin Cycle (C₃ Cycle)

• The path of carbon in the dark reaction was traced by Melvin Calvin using radioactive carbon (¹⁴C).

• Calvin pathway occurs in all photosynthetic plants, irrespective of whether they have C₃ or C₄pathway.

• The primary acceptor of CO₂ was found to be a 5-carbon ketose sugar called Ribulose bisphosphate (RuBP). This was surprising as it was believed that for the formation of a 3-carbon product, CO₂ would have to be accepted by a 2-carbon compound.

• RuBP is used in a cyclic manner (regenerated) and a sugar is synthesised.

• 3 stages of Calvin cycle: Carboxylation, Reduction and Regeneration

• Carboxylation

  • Ribulose 1, 5-bisphosphate combines with CO₂, and fixes it to a stable organic intermediate (3-phosphoglycerate − 2 molecules).

  • Reaction catalysed by the enzyme RuBisCO (RuBP Carboxylase-Oxygenase)

  • 3 PGA is the first stable product of this cycle.

• Reduction

  • Here, 2 molecules each of ATP and NADPH are required for fixing 1 molecule of CO₂.

  • This stage contains a series of reactions.

  • Glucose is formed as a result of this series of reactions.

• Regeneration

  • RuBP regenerates to enable the cycle to continue uninterrupted.

  • 1 ATP molecule is required.

• For the formation of one molecule of glucose, six molecules of CO₂ need to be fixed; hence, six cycles are required.
  
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  ​​​​​** When asked for two marks you can give its site for occurrence and the three steps.
  ** When asked for five marks explain the whole thing with diagram.
  
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