The C4 plants differ from C3 plants with respect to the substance that accepts CO2 in carbon assimilation, type of end product, type of pigment involved in photosynthesis, and number of ATP that is consumed in preparing sugar.

The C4 plants differ from C3 plants with reference to the substrate that accepts CO2 in carbon assimilation. In the C3 plants, CO2 is assimilated by condensing with RuBP by the help of RuBisCO enzyme to yield the first stable product, three-carbon compound PGA. In C4 plants, CO2 is assimilated by condensing with PEP, by the help of PEPCase enzyme to yield the first stable product, four-carbon compound OAA.