⚗️
Practical 2Spec ref: 1.4

Enzyme Activity

Linked to B2: Organisation

Aim

Investigate the effect of pH on the rate of amylase activity using iodine solution to detect starch.

Equipment

  • Amylase solution (1%)
  • Starch solution (1%)
  • Iodine solution
  • Buffer solutions (pH 4, 6, 7, 8, 10)
  • Spotting tile
  • Water bath at 35°C
  • Stopwatch
  • Pipettes

Variables

Independent variable
pH of buffer solution (4, 6, 7, 8, 10)
Dependent variable
Time for starch to be fully digested (iodine no longer turns blue-black)
Controlled variables
Temperature, concentration of amylase and starch, volume of solutions

Key Facts to Know

Amylase breaks down starch into maltose
Iodine turns blue-black with starch, orange-brown when starch is gone
Each enzyme has an optimum pH where it works fastest
Extreme pH causes denaturation — permanent change in active site shape
Denaturation is irreversible

⚠️ Common Mistakes

  • Saying enzyme is 'destroyed' by heat or pH — say 'denatured'
  • Not repeating experiment to calculate mean
  • Saying iodine disappears — say it stays orange-brown

💡 Exam Tips

  • Calculate rate = 1 ÷ time for Higher Tier
  • Shortest time = optimum pH
  • At low temperature: enzyme is slow, NOT denatured — important distinction