light independent reaction

• ATP and NADPH from the light dependent reaction are used in the Calvin cycle. 

   
• Three stages:

  • Carbon fixation 
  • Reduction 
  • Regeneration 
• Phase 1:

  CO2 enters the leaf via the stomata and diffuses into the stroma where its combined with ribulose bisphosphate (5-carbon compound) using an enzyme called rubisco. This gives an unstable 6-carbon compound which breaks down into two molecules of a 3-carbon compound called glycerate 3-phosphate. 

   
• Phase 2:

  ATP from the LDR is hydrolysed and provides energy to reduce the 3-carbon GP into a different 3-carbon compound called triose phosphate. This reaction also requires H+ ions which come from NADPH. NADPH is oxidised to make NADP+ and returns to the LDR. Triose phosphate is then converted into many useful organic compounds like glucose. 

   
• Phase 3:

  Some of the triose phosphate is used to regenerate RuBP so the Calvin cycle can continue. 5 out of 6 TP molecules are used for regeneration. Regenerating RuBP requires the rest of ATP which was produced by the LDR.