The product of the Calvin cycle is a triose-phosphate sugar that is either exported from the chloroplast or used to regenerate RUBP. How many times must each of the reactions in the Calvin cycle take place in order to complete the synthesis of one 3-carbon triose phosphate sugar molecule?

3 times

Explanation:

The Calvin cycle is the second phase of photosynthesis (the first being light dependent phase) involving three major stages viz: carbon fixation, reduction and regeneration of RUBP.

In the carbon fixation stage, CO2 is accepted by RUBP molecule to form six-carbon compound, which soon disintegrates into two molecules of 3-carbon compound called PGA.

In the reduction stage, PGA is reduced to G3P (glyceraldehyde-3-phosphate). The G3P (triose phosphate molecule) is either transported out of the chloroplast to make glucose or used to regenerate RUBP in the last stage. Either ways, It takes the reactions involved in Calvin cycle to occur "THRICE" in order to synthesize one 3-carbon triose phosphate sugar molecule (G3P).

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