The floating-disk assay yields the following ET50 (time for 5/10 disks to float) values across bicarbonate concentrations.
Which interpretation is best supported by the data?
- Acheck_circle
Increasing bicarbonate increases photosynthesis up to a saturation point
- B
Photosynthesis is fastest at 0% bicarbonate
- C
Bicarbonate concentration has no effect on the disks
- D
Photosynthesis occurs only in the absence of CO2
Explanation
Higher bicarbonate (more CO2 substrate) shortens ET50, indicating faster photosynthesis. The plateau between 0.2% and 0.5% suggests CO2 is no longer limiting; another factor (e.g., light) becomes limiting.