Answer:
Regeneration of RUBP
Explanation:
Calvin cycle also known as light independent stage is the second stage of the photosynthetic process. It occurs in the Stroma of the CHLOROPLAST. The Calvin cycle can be broken down to three major steps: carbon fixation, reduction and regeneration.
Carbon fixation as described in the question is when 3 molecules of RuBP (CO2 acceptor) combine with 3 molecules of CO2 to produce 3 six-carbon molecules, which are then split to produce 6 molecules of 3-phosphoglycerate (PGA). This fixation is catalyzed by RUBISCO enzyme.
The 6 molecules of PGA are then converted to 6 molecules of Glyceraldehyde-3-phosphate (G3P) by ATP and NADPH (from light stage) in a process called reduction.
After these initial two stages, one of the G3P molecules leave the cycle to contribute to the formation of organic food (glucose) while the remaining 5 G3P molecules are used to regenerate RUBP molecule in order for the cycle to commence all over again starting from fixation.
