how does gaseous exchange affect the rate of photosynthesis in a plant?

Dear Student, Carbon dioxide is the main gas which affects the rate of photosynthesis. CO 2 Concentration Major limiting factor. Usually low in atmosphere (0.03 − 0.04%). Up to 0.05% − increases rate of CO 2 fixation. > 0.05% − damaging effect. Though both C 3 and C 4 show increase in rate of photosynthesis at high light intensity accompanied by high CO 2 concentration, the saturation point for C 3 is obtained at higher concentrations as compared to C 4 . Therefore, CO 2 concentration is more of a limiting factor for C 3 plants. Increased CO 2 concentration is beneficial for greenhouse crops such as tomatoes and bell paper. Regards