1. In C3 plants, bundle sheath cells do not contain chloroplasts. So, carbon fixation and Calvin Cycle reactions occur in mesophyll cells (and in the presence of oxygen). In C4 plants, the bundle sheath cells contain chloroplasts. So, carbon is fixed in mesophyll cells, then transported to bundle sheath cells where Calvin Cycle reactions occur in the absence of oxygen.
2. C4 plants have a concentric arrangement of bundle sheath and mesophyll layer. The bundle sheath is also thicker which is not the case in C3 plants.
3. In C4 plants, there are only 4 mesophyll cells between one bundle sheath to another. In C3 plants, there are 12 mesophyll cells between two bundle sheaths.
4. C4 plants are more adapted to environments with more oxygen, and C3 plants are more adapted to environments with more carbon dioxide.
5. C4 plants such as maize, sorghum, and sugarcane, approximately have 50% higher photosynthesis efficiency than those of C3 plants such as rice, wheat, and potato.
6. C4 plants have CO2 concentrating mechanism, enabling prolonged stomatal closure, which is absent in C3 plants.