Which reaction begins the Calvin cycle?

splitting of water

carbon fixation

formation of an "excited" electron

formation of NADPH

The reaction that begins the Calvin cycle is carbon fixation.

Explanation:

Calvin cycle is also called light independent reactions since it directly depend on light. Still it is indirectly dependent on light since the nergy carriers ATP and NADPH are produced by the light dependent reactions. the initial step of carbon cycle is converting inorganic carbon to organic form.

This process is called carbon fixation. It takes place inside the stroma where carbon dioxide molecule reacts with RuBP or Ribulose biPhosphate. The reaction is catalyzed by the enzyme RuBisCO.

The carbon dioxide then gets converted to phosphoglyceric acid.