: CO2 compensation point is the certain CO2 concentration at which rate of photosynthesis is just equal to rate of respiration or photosynthesis just compensates respiration or apparent photosynthesis is nil. CO2 compensation point is very low in C−4 plants, i.e., 0 to 5 ppm whereas high CO2 compensation point is found in C−3 plants, i.e. 25 to 100 ppm.