The process which makes major difference between C3 and C4 plants is: Photorespiration, Respiration, Glycolysis, Calvin cycle

C3 plants exhibit photorespiration owing to the affinity of RuBisCo for oxygen which in turn causes loss of carbon by the formation of 2-phosphoglycolate in the chloroplast by oxygenation of ribulose-1,5 bisphosphate. Spatial separation of carbon dioxide fixation and RuBisCo activity in mesophyll and bundle sheath cells of C4 plants respectively avoids photorespiration by concentrating CO2 in bundle sheath cells to scale down the oxygenase activity of RuBisCo and increase its efficiency. Therefore, the correct answer is option A.