Warm them apart, mix, test every 30 seconds. Blue-black until the starch has gone.
Testing a starch and amylase mixture with iodine is one of the most common IGCSE Biology Paper 6 experiments. Here 5.0 cm³ of starch suspension and 1.0 cm³ of amylase solution are warmed in separate test-tubes in a water-bath, mixed, and sampled onto a spotting tile every 30 seconds until the iodine stays yellow-brown, at six temperatures. Watch the set-up built step by step, then build it yourself and check it against the points the examiners look for.
Past-paper referenceOriginal experiment, wording and figures, written in the style of Cambridge IGCSE Biology 0610 Paper 6 (Alternative to Practical). It is not copied from a past paper. The “what the examiners said” notes are our paraphrase of the Principal Examiner Reports for Teachers.
Practise next: 0610/62 October/November 2023, (amylase at two temperatures, samples every 30 s onto iodine on a spotting tile) · official past papers
Practise next: 0610/63 October/November 2024, (the effect of tea on amylase, drops of iodine on a white tile) · official past papers
Practise next: 0610/63 May/June 2024, (planning the effect of temperature on the breakdown of starch by amylase) · official past papers
Examiner reports used: 0610 November 2023 (Paper 62), June 2024 (Papers 61 and 63), November 2024 (Paper 63), June 2025 (Paper 63) and November 2025 (Paper 63).
This set-up builder needs JavaScript.
What a full-mark diagram shows
The apparatus
Starch suspension and amylase solution in separate test-tubes, standing in a thermostatically controlled water-bath with a thermometer; a spotting tile with one drop of iodine solution in each dimple.
Equilibrate, then mix
Both tubes stay in the bath for 5 minutes so their contents reach the bath temperature. Then the amylase is poured into the starch and the stopwatch is started at once.
The measurement
Every 30 s a drop of the mixture goes onto the iodine in the next dimple. The first drop that stays yellow-brown gives the time for all the starch to be digested.
A fair test and a control
The same volumes and concentrations and the same sampling interval every time; three runs and a mean at each temperature; boiled amylase as the control stays blue-black.
Habits the examiner reports keep asking for
Iodine stays yellow-brown when the starch has gone; blue-black means starch is still there. Do not call it orange or red: those are Benedict’s colours.
Put units only in the headings, for example time / s. Never write 60 s in a cell.
“Time” or “amylase” on its own is not a control variable: write the 30 s sampling interval, or the volume and concentration of amylase.
A thermometer only measures the temperature. To control it, use a thermostatically controlled water-bath or insulate the beaker.
The conclusion links temperature to amylase activity, not just to colours or times.