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#Unit 6. System Physiology – Plant
That time, there was no selective pressure for rubisco to discriminate between CO2 and O2.
The Km for CO2 is about 9 microM, and that for O2 is about 350 microM. The modern atmosphere contains about 20% O2 and only 0.04% CO2, so an aqueous solution in equilibrium with air at room temperature contains about 250 microM O2 and 11 microM CO2—concentrations that allow significant O2 “fixation” by rubisco and thus a significant waste of energy.
