The C₄ -plants differ from the C₃ -plants with reference to the

The C₄ -plants differ from the C₃ -plants concerning the Compound that accept CO₂ in carbon assimilation, the Type of the first stable product produced, and also the Number of ATP's required from starch.
C₃ photosynthesis produces a three-carbon compound via the Calvin cycle while C₄ photosynthesis makes an intermediate four-carbon compound that splits into a three-carbon compound for the Calvin cycle.
The first stable compound produced in the Calvin cycle is a 3-carbon compound, which is 3 phosphoglyceric acid (PGA). In the C₄ plant, the first stable product is a 4-carbon compound, which is Oxaloacetic Acid (OAA).
In the C₄ cycle of photosynthesis, a total of 30 ATPs are needed whereas, For the C₃ cycle to repair 6CO₂, 18 ATPs are needed.