Required practical · AQA, EDEXCEL, OCR
Required practical: Investigate the effect of pH or temperature on enzyme activity
Aim
To measure how an enzyme-catalysed reaction rate changes with pH or temperature, using a repeatable measurement (gas volume, time to disappear colour, etc.).
Method (step-by-step)
- Choose a system: e.g. catalase + H₂O₂ (gas) or amylase + starch + iodine (time to starch gone).
- Keep substrate concentration and enzyme concentration fixed; vary pH buffers or temperature water-baths.
- Run multiple repeats at each condition; standardise timing and mixing.
- Record rate (cm³ s⁻¹, or 1/time) and plot vs pH or temperature.
- Identify optimum and explain denaturation at extremes.
Equipment
- Buffers or water-baths
- measuring cylinders
- gas syringe optional
- stopclock
Variables
- Independent: pH or temperature (one at a time).
- Dependent: Initial rate of reaction.
- Control: Substrate volume; enzyme volume; total volume; timing start point
Results & analysis
Expect a peak (optimum) and drop-off; link high temperature / extreme pH to active site shape change.
Graphs & interpretation
Sketch / interpret bell-shaped or asymmetric curves; quote optimum range in °C or pH.
Common mistakes (high yield)
- Varying both temperature and pH together.
- Using ‘amount’ instead of concentration.
- Ignoring that initial rate ≠ total gas after 10 minutes unless justified.
Exam-style question prompts
- Explain what happens to the enzyme at high temperature.
- How could you control pH fairly?
Exam tips
- Use ‘active site’ and ‘denature’ correctly
- Initial rate from tangent or first 30 s
Related topic revision
FAQs
Exam boards differ in wording; always follow your specification and your teacher’s practical notes. Back to GCSE Biology required practicals hub.