Carbon fixation primarily occurs in the stroma of the chloroplast in plants and algae during the Calvin cycle, which is part of the light- independent reactions of photosynthesis
. The stroma is the fluid-filled space surrounding the thylakoid membranes inside the chloroplast. In C3 plants, carbon fixation involves the enzyme RuBisCO attaching inorganic CO2 to an organic molecule in the stroma
. In C4 plants, the initial carbon fixation occurs in the chloroplasts of mesophyll cells , where CO2 is fixed by the enzyme PEP carboxylase before being transported to bundle sheath cells
. In summary:
- C3 plants and algae: Carbon fixation occurs in the chloroplast stroma.
- C4 plants: Initial fixation occurs in mesophyll cell chloroplasts, then carbon is shuttled to bundle sheath cells for further processing.
This process is essential for converting atmospheric CO2 into organic molecules that can be used for energy and growth
