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The Calvin cycle consists of 15 chemical reactions that synthesize carbohydrates from CO₂. These reactions can be grouped into three main steps: (1) carboxylation, in which CO₂ is added to a 5-carbon molecule; (2) reduction, in which energy and electrons are transferred to the compounds formed in step 1; and (3) regeneration of the 5-carbon molecule needed for carboxylation (Fig. 8.5).