C4 plants lack the process of photorespiration , which is a wasteful process present in C3 plants where RuBisCO binds with O2 instead of CO2, leading to a loss of fixed carbon . Because C4 plants possess a mechanism to increase intracellular CO2 concentration , they ensure RuBisCO functions as a carboxylase. This makes C4 plants photosynthetically more efficient, showing greater productivity of biomass compared to C3 plants . This efficiency is generally cited as being approximately double that of C3 plants, giving a ratio of 2:1.