The C, plants are twice as efficient as C3 plants in terms of fixing CO2 but lose only ...... as much water C3 plants for the same amount of CO2 fixed.

Half, The evolution of the C, or plants photosynthetic system is probably one of the Strategies for maximising the ability of CO3 while minimising water loss. C4 Plants are twice as efficient as C, plants in terms of fixing carbon in the form of glucose, but lose only half aS much water as aC, plant for the Same amount of C2 fixed.