Fig. 3. Model comparisons of 1st-order (A) versus Michaelis-Menten (B) reaction kinetics on time courses of central O₂ concentrations during step-change experiments (i.e. external concentration changed from 280 to 0 nmol cm^–3 and then vice versa). Under first-order reaction kinetics, larger gives larger initial drawdown (see Fig. 2), and the step-down and step-up-traces are always symmetrical. Analogously, under Michaelis–Menten kinetics, larger V_max gives greater initial drawdown. However, here the step-down and step-up-traces are asymmetrical, with the asymmetry exaggerated by larger initial drawdown.