Explain how enzyme activity is affected by factors such as temperature, pH, presence of inhibitors and substrate concentration.

Explain why increasing substrate concentration beyond a certain point does not increase the rate of an enzyme-catalysed reaction.

A student investigated the effect of substrate concentration on the initial rate of reaction for the enzyme catalase. At a substrate concentration of 0.8 mM, the initial rate was 12 μmol/min. At 1.6 mM, the rate increased to 20 μmol/min. At 3.2 mM and 6.4 mM, the rate remained constant at 24 μmol/min. Which statement best explains these results?

A researcher investigates the effect of adding a competitive inhibitor to an enzyme-catalysed reaction. Initial reaction rate is measured at a substrate concentration of 0.8 mmol/L without inhibitor, then again at the same substrate concentration after adding 2.0 mmol/L of the competitive inhibitor. The initial rate decreases from 45 μmol/min to 18 μmol/min. Explain how the competitive inhibitor caused this observed decrease in reaction rate.