Final answer:
The exclusive occurrence in the Calvin cycle is the fixation of atmospheric CO2 into organic molecules through the enzyme RuBisCO, leading to the production of 3-PGA and G3P.
Step-by-step explanation:
One thing that occurs exclusively in the Calvin cycle is the fixation of atmospheric carbon dioxide (CO2) into organic molecules. During this process, an enzyme called ribulose biphosphate carboxylase (RuBisCO) facilitates the reaction between CO2 and a compound called ribulose bisphosphate (RuBP).
This leads to the production of a three-carbon compound known as 3-phosphoglycerate (3-PGA), which is subsequently used to generate glyceraldehyde-3-phosphate (G3P). The energy for these reactions is derived from ATP and NADPH, which are produced during the light-dependent reactions of photosynthesis.
Overall, the Calvin cycle harnesses the energy stored in ATP and NADPH to fix carbon dioxide into a stable form, glucose, that can be used by the plant for energy and growth. Moreover, the Calvin cycle is an essential component of the light-independent reactions of photosynthesis, where it repeats multiple times to produce one glucose molecule from the fixed carbon.