Conversion of CO2 to simple (reduced) organic compounds is called CO2 assimilation or CO2 fixation or carbon fixation. This fixation pathway was elucidated in the early 1950s by Melvin Calvin and co-workers and is often called as Calvin cycle. Since one molecule of carbon is fixed in one tum of the Calvin cycle. So, six turns of the cycle are required to fix the glucose molecule containing 6 carbon atoms.