What happens to the O2 levels during the light and dark?

Hello, This might help. Unidirectional O2 fluxes were measured with 18O2 in a whole plant of wheat cultivated in a controlled environment. At 2 or 21% O2, O2 uptake was maximum at 60 microliters per liter CO2. At lower CO2 concentrations, it was strongly inhibited, as was photosynthetic O2 evolution. At 2% O2, there remained a substantial O2 uptake, even at high CO2 level; the O2 evolution was inhibited at CO2 concentrations under 330 microliters per liter. The O2 uptake increased linearly with light intensity, starting from the level of dark respiration. No saturation was observed at high light intensities. No significant change in the gas-exchange patterns occurred during a long period of the plant life. An adaptation to low light intensities was observed after 3 hours illumination. These results are interpreted in relation to the functioning of the photosynthetic apparatus and point to a regulation by the electron acceptors and a specific action of CO2. The behavior of the O2 uptake and the study of the CO2 compensation point seem to indicate the persistence of mitochondrial respiration during photosynthesis.

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