Without photorespiration, fixing CO2 into carbohydrate end products costs 2 NADPH and 3 ATP in C3 plants.
If 25% of the injected CO2 leaks out of the bundle sheath, 2 NADPH and 4.7 to 5.7 ATP are required in C4 plants.
C4 photosynthesis has a greater ATP cost due to the energy required to pump CO2 into the bundle sheath.
The energy costs of photosynthesis in C3 plants climb as the rate of photorespiration increases, until they are similar to those of C4 plants at 25° to 30°C, and more at around 30°C.
C4 plants:
A C4 plant is one that converts CO2 into four-carbon sugar molecules in order to enter the Calvin cycle.
These plants produce a lot of energy and are particularly efficient in hot, dry areas.
Corn, pineapple, and sugar cane are examples of C4 plants that we eat.