Final answer:
The Calvin cycle is called the C3 pathway because the CO₂ is first incorporated into a 3-carbon compound. It uses ATP and NADPH to create G3P molecules, storing energy from photosynthesis, and regenerates RuBP, making the process cyclic.
Step-by-step explanation:
The Calvin cycle, also known as the C3 pathway, involves the fixation of CO₂ into organic molecules within the stroma of chloroplasts in plants and cyanobacteria. The cycle is called C3 because the CO₂ is initially incorporated into a 3-carbon compound, 3-phosphoglycerate (3-PGA). The cycle utilizes RuBisCO, the most abundant enzyme on Earth, to catalyze the reaction with CO₂ and ribulose biphosphate (RuBP), producing two molecules of 3-PGA. It takes three turns of the Calvin cycle to synthesize one molecule of glyceraldehyde-3-phosphate (G3P), which can then be used to generate glucose and other carbohydrates.
The Calvin cycle is essential in photosynthesis as it harnesses energy in the form of ATP and NADPH, produced in the light-dependent reactions. These forms of chemical energy are used to produce G3P molecules, which store energy from photosynthesis. Moreover, the cycle regenerates RuBP, allowing the process to be cyclic and enabling the continuous fixation of CO₂.
Overall, the Calvin cycle acts as a biochemical pathway that translates inorganic carbon into organic molecules, essential for life on Earth. It is fundamental to the productivity of both aquatic and terrestrial ecosystems and is central to the global carbon cycle.