The light-independent reaction

  • Namely ATP and reduced NADP are used to reduce glycerate 3-phosphate in the second stage of photosynthesis
  • Unlike the first stage, this stage does not require light directly and in theory occurs whether there or not light is available 
  • It is therefore called the light-independent reaction
  • In practise, it requires the products of the light-dependent stage and so rapidly ceases when light is absent
  • The light-independent reaction takes place in the stroma of the chloroplasts

The calvin cycle:

  • 1 - carbon dioxide from the atmosphere diffuses into the leaf through stomata and dissolves in water around the walls of the mesophyll cells. It the diffuses through the cell-surface membrane into the stroma of the chloroplast
  • 2 - in the stroma, the carbon dioxide reacts with the 5-carbon compound ribulose diphosphate (RuBP) a reaction catalysed by an enzyme called ribulose diphosphate carboxylase, otherwise known as rubisco 
  • 3 - the reaction between carbon dioxide and RuBP produces two molecules of the 3-carbon glycerate 3-phosphate (GP)
  • 4 - reduced NADP from the light-dependent reaction is used to reduce glycerate 3-phosphate to triose phosphate (TP) using energy supplied by ATP
  • 5 - the


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