In photosynthesis, the process that requires carbon dioxide (CO2) is known as the Calvin cycle, also referred to as the light-independent reactions or the dark reactions. This process occurs in the stroma of chloroplasts and plays a crucial role in converting CO2 into glucose.
During the Calvin cycle, CO2 is fixed into an organic molecule using the energy captured during the light-dependent reactions (ATP and NADPH). This cycle involves several steps, including the fixation of CO2 by an enzyme called RuBisCO, which combines CO2 with a five-carbon sugar called ribulose bisphosphate (RuBP). Through a series of enzymatic reactions, this process ultimately leads to the production of glucose, which plants use as an energy source for growth and development.
Without CO2, the Calvin cycle would not be able to function, and plants would be unable to synthesize the carbohydrates they need to survive. Thus, CO2 is an essential component in the photosynthesis process, particularly in the Calvin cycle.