Final answer:
The purpose of the nine ATP molecules used in the Calvin cycle is to provide energy for the conversion of 3-PGA into G3P and to regenerate RuBP.
Step-by-step explanation:
The purpose of the nine ATP molecules used in the Calvin cycle is to provide energy for the conversion of 6 molecules of 3-PGA into 6 molecules of glyceraldehyde 3-phosphate (G3P). This conversion requires the input of ATP and NADPH, which are produced in the light-dependent reactions of photosynthesis.
The G3P molecules store the energy captured from photosynthesis, while the remaining ATP molecules are used to regenerate the starting molecule of the Calvin cycle, ribulose-1,5-bisphosphate (RuBP).