Twelve more ATP molecules are required for glucose formation in C4 palnts because 2 additional ATP molecules are utilized per turn in
Regeneration of PEP
The regeneration of PEP from pyruvic acid after it is transported back into mesophyll cells requires 2 ATP molecules per molecule of CO2 fixed. Hence 12 additional ATP molecules are required for the production of one molecule of glucose in C4 plants. Rest all the steps consume the same amount of energy as in C3 plants.