Enzymes: Temperature and pH

IGCSE Edexcel Biology
2.10-2.13 Enzymes and Conditions
Key Concept: Enzymes are biological catalysts with specific active sites that can be denatured by extremes of temperature or pH.

Section A: Enzymes

1. Define the term enzyme and state its role in cells. [2]
2. Explain what is meant by an enzyme's active site. [2]

Section B: Temperature and pH

3. Describe how temperature affects enzyme activity, including denaturation. [4]
4. Describe how pH affects enzyme activity. [3]

Section C: Practical

5. Outline a practical to investigate the effect of temperature on an enzyme reaction. [4]
Total marks: 15

Mark Scheme

1. Enzyme = biological catalyst; speeds up reactions without being used up [2]
2. The active site is the specifically shaped region where the substrate binds [2]
3. Rate increases with temperature to an optimum as collisions increase; high temperature changes active site and denatures enzyme so rate falls [4]
4. Each enzyme has an optimum pH; extremes of pH change the active site and reduce activity/denature enzyme [3]
5. Use an enzyme and substrate, vary temperature with water baths, keep pH and concentrations constant, measure time/rate, repeat for reliability [4]