Why are c4 plants more efficient than c3 plants at fixing carbon?

C4 plants like maize, sugarcane etc. possess a special type of cell called "Bundle Sheath Cells" around vascular bundle.

While C3 plants like wheat, bajra etc. don't possess these cells.

The speciality about these cells is that they are able to fix up CO2 in the absence of atmospheric CO2 while C3 plants can't fix this.

This pathway is called as C4 pathway as the first stable compound formed in this pathway is of 4 C atoms.

When it fix 3 moles of CO2 it passes CO2 to vascular bundle performing normal C3 cycle.

So efficiency of C4 plants is greater than C3 plants.