The diagram shows the results of an investigation in which a student measured the rate of an enzyme-controlled reaction at different substrate concentration...
Question 1 Report
The diagram shows the results of an investigation in which a student measured the rate of an enzyme-controlled reaction at different substrate concentrations. The amount of enzyme, pH and temperature were kept constant. Curve A was obtained using 1 cm3 enzyme solution. Curve B was obtained using 2 cm3 enzyme solution.
(a) Describe the change in rate shown by curve A as substrate concentration increases. [2]
(b) Use the diagram to explain why curve A becomes nearly horizontal at high substrate concentration. [3]
(c) Explain why curve B has a higher maximum rate than curve A. [3]
Answer Details
(a) For curve A, the rate initially increases as substrate concentration increases. [1 mark] It then levels off, reaching a maximum rate. [1 mark]
(b) At high substrate concentration, all enzyme active sites are occupied by substrate molecules. [1 mark] Enzyme concentration has become the limiting factor. [1 mark] Adding more substrate cannot increase the number of enzyme-substrate complexes formed each second, so the curve becomes nearly horizontal. [1 mark]
(c) Curve B used more enzyme molecules. [1 mark] It therefore has more active sites available. [1 mark] More substrate molecules can be converted to product each second, giving a higher maximum rate. [1 mark]
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