Enzymes and Metabolism · Paper 1 — Free Biology SL Practice Questions

In an experiment using catalase, the rate of oxygen production is measured at increasing hydrogen peroxide concentrations. At low concentrations, the rate increases proportionally, but above a certain concentration the rate remains constant regardless of further increases in substrate. Which of the following best explains this plateau?

An enzyme has a Michaelis constant ($K_m$) of $2.0 \ \text{mmol dm}^{-3}$. At a substrate concentration of $4.0 \ \text{mmol dm}^{-3}$, the reaction velocity $V_0$ is approximately 67 percent of $V_{max}$. A student predicts that doubling the substrate concentration to $8.0 \ \text{mmol dm}^{-3}$ will raise $V_0$ to 90 percent of $V_{max}$. Which statement correctly evaluates this prediction using the Michaelis–Menten equation $V_0 = \dfrac{V_{max}[S]}{K_m + [S]}$?