Q51 - C3 vs C4 Photosynthesis
The figure shows CO₂ assimilation rate (A) as a function of intercellular CO₂ concentration (Ci) for two plants. Plant 1 has a lower CO₂ compensation point and reaches saturation at lower Ci. Plant 2 has a higher compensation point and continues to increase its assimilation rate at higher Ci values.
True or false?
Q51.1. At ambient atmospheric CO2, plant number 1 has a higher net CO2 assimilation rate than plant number 2.
Q51.2. At 400 ppm Ci, net CO2 assimilation of plant number 1 is limited by carboxylation.
Q51.3. At high CO2 concentrations, photosynthesis is limited by the capacity of the Calvin cycle to regenerate the acceptor molecule ribulose-1,5-bisphosphate.
Q51.4. At ambient atmospheric CO2, plant number 1 has greater photosynthetic water use efficiency than plant number 2.
Q51.5. Reducing oxygen concentration from 20% to 2% would shift the Ci response curve of plant number 2 toward that of plant number 1.
Q51.6. C3 photosynthesis is favored in high temperature environments, while C4 is favored in high CO2 environments.
Question reproduced from IBO 2023, Theoretical Paper 2, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF