Question

Where is the most energy used in the Calvin cycle?

- in the regeneration of RuBP
- in the rearrangement of the six-carbon molecule made from RuBP and CO2 into the three-carbon molecules of PGA
- in the fixation of CO2 to RuBP
- in the linkage of two G3P molecules together to form glucose
- in the conversion of PGA to G3P

Answer 1

The regeneration of ribulose bisphosphate (RuBP) consumes the most energy in the Calvin cycle, using three ATP molecules per turn, which is a significant amount given the multiple turns required to maintain the cycle.

Step-by-step explanation:

The most energy in the Calvin cycle is used in the regeneration of RuBP. The process utilizes energy in the form of ATP to prepare for more CO₂ fixation. Specifically, during the regeneration stage, energy from a total of three ATP molecules is used per turn of the cycle. Considering that each turn generates two Glyceraldehyde-3-phosphate (GA3P) molecules, and it takes three turns to fix enough carbon to export one GA3P, we can conclude that the regeneration of RuBP requires a significant amount of energy as it repeats this process multiple times to sustain continuous operation of the Calvin cycle.

In the Calvin cycle, the most energy is used in the fixation of CO2 to RuBP. This process requires energy in the form of 6 ATP and 6 NADPH, which are used to produce Glyceraldehyde-3-phosphate (G3P) molecules. These molecules store the energy captured from photosynthesis. The Calvin cycle also utilizes additional energy in the regeneration of RuBP, which requires 3 more molecules of ATP.