Advantages of C4 plants over C3 plants

1. C4 plants ably photosynthesize at very low CO₂ concentration (e.g. in dense tropical vegetation) because PEP carboxylase enzyme has a very high affinity for carbon dioxide.
2. Concentric arrangement of mesophyll cell produces a smaller area in relation to volume for better utilization of available water and reduces the intensity of solar radiations.
3. Photorespiration, which inhibits growth in C3 plants is avoided / reduced in C4 because

• the CO₂ fixing enzyme PEP carboxylase does not accept oxygen
• RuBISCO enzyme inside the bundle sheath cells is shielded from high oxygen concentration by the ring of palisade cells.

5. The CO₂ fixing enzymes in C4 plants are more active at hot temperature and high illumination, therefore photosynthesis occurs rapidly at low altitude, hot and brightly lit tropical conditions than in C3 plants.
6. The productivity of C4 almost four times greater than in C3 because:

• of the increased rate of CO₂ uptake caused by
• large internal leaf surface area
• short CO₂ diffusion distance
• CO₂ steep diffusion gradients

6. The bundle sheath cells in which dark reactions occur have

(i) a large photosynthetic surface area enabled by un-usually large chloroplasts

(ii) lack of grana on which O₂ would be produced, so no photorespiration.

7. The palisade cells in which light reactions occur have large grana to increase the photosynthetic surface area.