Carbon fixation during photosynthesis in plants involves the conversion of atmospheric CO2 into organic compounds, which are then used by the plant for growth and energy. This process is crucial for the absorption of atmospheric CO2 and plays a significant role in mitigating climate change. Two key enzymes involved in carbon fixation are ribulose bisphosphate carboxylase-oxygenase RuBisCO and phosphoenolpyruvate carboxylase PEPC .RuBisCO is the primary enzyme involved in the Calvin-Benson cycle, which is the most common pathway for carbon fixation in plants. In this cycle, RuBisCO catalyzes the reaction between CO2 and ribulose-1,5-bisphosphate RuBP , a 5-carbon sugar, to form two molecules of 3-phosphoglycerate 3-PGA , a 3-carbon compound. These molecules are then converted into glucose and other sugars, which are used by the plant for energy and growth. RuBisCO is a crucial enzyme in this process, as it is responsible for the initial fixation of CO2.PEPC, on the other hand, is involved in an alternative pathway for carbon fixation called C4 photosynthesis. This pathway is utilized by some plants, particularly those in hot and arid environments, to overcome the inefficiency of RuBisCO in these conditions. In C4 photosynthesis, PEPC catalyzes the reaction between CO2 and phosphoenolpyruvate PEP , a 3-carbon compound, to form oxaloacetate, a 4-carbon compound. This compound is then converted into malate or aspartate, which are transported to specialized cells called bundle sheath cells. Here, CO2 is released and refixed by RuBisCO in the Calvin-Benson cycle. This process effectively concentrates CO2 around RuBisCO, reducing its oxygenase activity and increasing its carboxylase activity, thus enhancing the efficiency of carbon fixation.The significance of these enzymes in the contribution of atmospheric CO2 absorption lies in their ability to catalyze the conversion of inorganic CO2 into organic compounds. By doing so, they enable plants to remove CO2 from the atmosphere and store it in the form of biomass. This process is essential for maintaining the balance of CO2 in the atmosphere and mitigating the effects of climate change. Additionally, understanding the mechanisms of these enzymes can help scientists develop strategies to improve the efficiency of photosynthesis and increase the capacity of plants to absorb atmospheric CO2.