Carbon fixation is a crucial part of the photosynthesis process, as it allows plants, algae, and certain bacteria to convert inorganic carbon dioxide CO2 into organic compounds, primarily glucose, which can be used as an energy source or as building blocks for growth. Photosynthesis can be divided into two stages: the light-dependent reactions and the light-independent reactions also known as the Calvin cycle . Carbon fixation occurs during the Calvin cycle.The Calvin cycle consists of three main steps: carbon fixation, reduction, and regeneration of the starting molecule ribulose-1,5-bisphosphate RuBP . In the first step, carbon fixation, CO2 is incorporated into an organic molecule through the action of the enzyme Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase . Rubisco catalyzes the reaction between CO2 and RuBP, resulting in an unstable 6-carbon intermediate, which quickly breaks down into two molecules of 3-phosphoglycerate 3-PGA .In the second step, reduction, the 3-PGA molecules are converted into glyceraldehyde-3-phosphate G3P through a series of reactions involving ATP and NADPH, which are produced during the light-dependent reactions of photosynthesis. G3P is a high-energy, 3-carbon sugar that can be used to synthesize glucose and other organic molecules.In the third step, regeneration, some of the G3P molecules are used to regenerate RuBP through a series of enzyme-catalyzed reactions, allowing the Calvin cycle to continue. For every three turns of the Calvin cycle, one G3P molecule exits the cycle and can be used to form glucose or other organic compounds, while the remaining G3P molecules are used to regenerate RuBP.Rubisco is a key enzyme in the carbon fixation process, as it catalyzes the first step of the Calvin cycle. However, Rubisco is not a very efficient enzyme, as it can also catalyze a competing reaction with oxygen O2 instead of CO2, leading to a process called photorespiration, which reduces the overall efficiency of photosynthesis. Despite its limitations, Rubisco is essential for carbon fixation and the conversion of inorganic carbon into organic compounds that can be used by plants and other photosynthetic organisms for growth and energy production.