The Calvin cycle, also known as the C3 photosynthetic pathway or light-independent reactions, is a series of biochemical reactions that occur in the chloroplasts of photosynthetic organisms. It utilizes enzymes to fix carbon dioxide CO2 and synthesize carbohydrates, specifically glucose, during photosynthesis. The Calvin cycle consists of three main stages: carbon fixation, reduction, and regeneration.1. Carbon fixation: The enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase RuBisCO catalyzes the reaction between CO2 and ribulose-1,5-bisphosphate RuBP , a 5-carbon sugar. This reaction produces an unstable 6-carbon intermediate, which rapidly breaks down into two molecules of 3-phosphoglycerate 3-PGA , a 3-carbon compound.2. Reduction: In this stage, the 3-PGA molecules are converted into glyceraldehyde-3-phosphate G3P , a high-energy 3-carbon sugar, through a series of enzyme-catalyzed reactions. First, 3-PGA is phosphorylated by ATP, forming 1,3-bisphosphoglycerate 1,3-BPG . Then, NADPH donates electrons to 1,3-BPG, reducing it to G3P. During this process, NADPH is oxidized to NADP+ and ATP is hydrolyzed to ADP.3. Regeneration: The majority of G3P molecules produced in the reduction stage are used to regenerate RuBP, allowing the Calvin cycle to continue. This process involves a complex series of enzyme-catalyzed reactions that rearrange the carbon skeletons of G3P molecules to produce RuBP. Additional ATP is used to phosphorylate intermediates in this stage.For every three turns of the Calvin cycle, one G3P molecule exits the cycle and can be used to synthesize glucose or other carbohydrates. The remaining G3P molecules are used to regenerate RuBP, ensuring the continuous fixation of CO2 and synthesis of carbohydrates during photosynthesis.