Class 11 NEET Biology Photosynthesis in Higher Plants

(c) In C4 plants every CO2 molecule has to be fixed twice, so these plants are needed more energy for the synthesis of hexose sugar molecules than C3 plants in which CO2 has to be fixed only once. 18 ATP molecules are required by C3 plants for the synthesis of one molecule of hexose sugar while 30 ATP molecules are needed by the C4 plants for the same. Thus C4 plants have a need of 12 ATP molecules extra than C3 plants for the synthesis of one molecule of hexose sugar.