Question

Why are C₄ plants more efficient than C₃ plants?

Answer 1

The efficiency of C₄ plants:

1. Due to their reduced rate of photorespiration and high rate of photosynthesis, C₄ plants are more efficient than C₃ plants.
2. The main enzyme of carbon fixation in the Calvin cycle is RuBisCO.
3. It shows an affinity for both CO₂ and O₂.
4. RuBisCO takes up oxygen to perform photorespiration when carbon dioxide concentration is low.
5. In C₄ plants, since carbon dioxide concentration is high at the RuBisCO site thus, photorespiration is highly reduced.
6. C₄ plants possess special leaf anatomy called ‘Kranz anatomy’ and undergo the C₄ pathway of photosynthesis.
7. In this case, CO₂ is first accepted by phosphoenolpyruvate (PEP) in the mesophyll cells that produce oxaloacetic acid (OAA) which is a 4-carbon organic acid.
8. Conversion of OAA to malic acid takes place then which is transported to bundle sheath cells.
9. In the bundle sheath cells, CO₂ is released and enters the Calvin cycle, and is acted on by RuBisCO.
10. Due to the higher concentration of carbon dioxide in the bundle sheath cells, photorespiration is minimized.