Photosynthesis and photorespiration in algae

The CO₂ exchange of several species of fresh water and marine algae was measured in the laboratory to determine whether photorespiration occurs in these organisms. The algae were positioned as thin layers on filter paper and the CO₂ exchange determined in an open gas exchange system. In either 21 or 1% O₂ there was little difference between ¹⁴CO₂ and ¹²CO₂ uptake. Apparent photosynthesis was the same in 2, 21, or 50% O₂. The compensation points of all algae were less than 10 μl 1⁻¹. CO₂ or ¹⁴CO₂ evolution into CO₂-free air in the light was always less than the corresponding evolution in darkness. These observations are inconsistent with the proposal that photorespiration exists in these algae.