A Levels Biology (9700)•9700/12/M/J/18
Explanation
Km is substrate concentration at half maximum velocity (Vmax/2)
Steps:
- Identify Vmax as the plateau rate on the graph.
- Compute half Vmax (Vmax/2).
- Locate substrate concentration [S] where reaction rate equals Vmax/2.
- This [S] value is Km, reading 1.5 mmol dm⁻³ from the graph.
Why C is correct:
- Km is defined as [S] at which velocity is Vmax/2 in Michaelis-Menten kinetics.
Why the others are wrong:
- A and B: Substrate concentrations below Vmax/2 point, underestimating Km.
- D: Substrate concentration above Vmax/2 point, overestimating Km.
Final answer: C
Topic: Mode of action of enzymes
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