Photosynthesis: formation of glucose molecule from simple inorganic substances like CO2 and H2O by use of ATP is called photosynthesis and it occurs in all green plants only.
Photosynthesis consist of two important steps viz.
1) Light Reaction and 2) Dark Reactions
Dark reaction occurs during day, since there is no role of light in dark phase it is independent of light. Dark phase of photosynthesis fixes carbon dioxide where as light phase photolysis water.
Calvin cycle is a part of dark reaction in which fixation of carbon molecules occurs.
We know, a glucose molecule consist of 6 carbon atoms (i.e. C6H12O6). One turn of Calvin cycle fixes only one CO2 molecule hence for the formation of a glucose molecule SIX TURNS OF CALVIN CYCLE IS REQUIRED.
NOTE: CALVIN CYCLE IS INVENTED BY SIR MELVIN CALVIN.