Biology · 5 Enzymes · Paper 5/6 practical
Enzyme Activity. Find the optimum.
Investigate how temperature and pH change the rate of an enzyme reaction. Time how long amylase takes to digest starch (iodine end-point), or measure the oxygen catalase releases from hydrogen peroxide. Rate peaks at the optimum and falls to zero when the enzyme is denatured.
0610 Topic 5 — Enzymes
temperature · pH · denaturation
Paper 5/6 — Practical
00.0 s
end-point —
Variables
20
7
Keep the other variable constant — change only the one you're investigating.
Live readouts
Time to digest
—
Rate
—
Relative activity
—
Optimum
—
Above the optimum the enzyme's active site changes shape (denatures) and the rate falls to zero.
Results table
Record the rate at several values.
Rate vs temperature
📋 Method (Cambridge practical procedure)
- Amylase: mix amylase and starch solutions in a tube held in a water bath at the chosen temperature (or with a pH buffer).
- Every 30 s remove a drop and add it to iodine on a spotting tile.
- Record the time when the iodine stops turning blue-black — all the starch has been digested. Rate = 1 ÷ time.
- Catalase: add hydrogen peroxide to potato/liver and measure the oxygen given off (gas syringe or counting bubbles per minute).
- Repeat at a range of temperatures (or pH values) and plot rate against the variable.
⚠ Control variables & precautions
- Keep volumes and concentrations of enzyme and substrate the same each time.
- Allow the tubes to reach the water-bath temperature before mixing.
- Use a buffer to fix the pH when investigating temperature, and a fixed temperature when investigating pH.
- Repeat each value and take a mean; rate = 1/time so faster reactions give a higher rate.
🎯 Syllabus reference (0610)
- 5 Enzymes — investigate and describe the effect of temperature and pH on enzyme activity; explain in terms of kinetic energy, collisions, active site and denaturation.