5.1.5 Light Independent Reaction

The energy and hydrogen are used during the light-independent reactions (known collectively as the Calvin cycle) to produce complex organic molecules, including (but not limited to) carbohydrates, such as:
  * Starch (for storage)
  * Sucrose (for translocation around the plant)
  * Cellulose (for making cell walls)
This stage of photosynthesis %%does not, in itself, require energy from light%% (hence light-independent) and can therefore %%take place in light or darkness.%% However, as it %%requires inputs of ATP and reduced NADP from the light-dependent stage, the Calvin cycle cannot continue indefinitely in darkness, as these inputs will run out%%
4 main stages to Calvin Cycle:
  * %%Rubisco joins RuBP and CO2 to create 6C intermediate%%
  * 6C intermediate %%splits into 2 molecules of glycerate 3 phosphate (GP)%%
  * GP is %%reduced to triose phosphate (TP)%% in a process involving %%reduced NADP and ATP%%
  * %%RuBP is regenerated from TP%% in reactions that use ATP

%%CO2 combines with%% 5C compound called %%ribulose bisphosphate%%
Enzyme %%rubisco%% catalyses this reaction
The result is an %%unstable 6C intermediate compound%%
This %%splits to result in 2 molecules of glycerate 3 phosphate%%
The carbon dioxide has been ‘fixed’ (it has been removed from the external environment and has become part of the plant cell)

ATP and reduced NADP produced from light dependant reaction are needed for this
%%Reduced NADP provides a H%% (is oxidised) %%to reduce the glycerate 3 phosphate%%, making it a reducing agent
%%ATP is used to provide energy%% by being hydrolysed
One-sixth of the triose phosphate (TP) molecules are used to produce useful organic molecules needed by the plant
Therefore, %%1 C atom is used to create organic products, the other 5 can be recycled to begin the cycle again%%

%%Five-sixths of the triose phosphate (TP) molecules are used to regenerate ribulose bisphosphate (RuBP)%%
This process %%requires ATP%%