To tell whether a temperature treatment temporarily slowed amylase or caused a lasting loss of activity, retest every sample at the same temperature. Use fresh starch and the same observation time for each sample.
The 2027 SEC G3 Biology K325 syllabus includes explaining the effect of temperature on enzyme-catalysed reactions. This example uses an iodine test to show why a common retest temperature helps interpret the results.
- Treat the amylase samples separately from the starch.
- Bring all samples to the same test temperature.
- Add equal amounts of fresh starch.
- Use the same timing and compare with a control.
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Keep the treatment and the test separate
Imagine three equal samples of the same amylase solution. One is chilled, one is heated strongly, and the third is kept at the chosen test temperature. After the treatments, bring all three to the same test temperature before adding the starch. Keep the pH and volumes the same.
Iodine turns blue-black when starch is present. During the test, take equal drops from the mixtures at the same intervals and add them to iodine on a spotting tile. Compare how long it takes for the drops to stop turning blue-black.
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Worked example | One sample recovers and one remains slow
Suppose the chilled sample and untreated control stop turning iodine blue-black after about two minutes. The strongly heated sample still gives a blue-black result after five minutes. The chilled sample shows activity similar to the control after warming. The heated sample shows much lower starch breakdown during the time observed.
The results support the explanation that strong heating denatured the amylase, changing its active site so starch binds less effectively. The final observation alone does not tell you whether a small amount of enzyme activity remains.
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Check that the result is interpretable
A mixture of starch and water without amylase should still turn iodine blue-black under the same conditions. This confirms what a starch-positive result looks like in the setup. The untreated amylase sample shows that the test conditions allow the enzyme to act.
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Frequently asked questions
Why add fresh starch after the treatment?
This way, every sample starts its measured reaction with the same amount of starch at the same temperature. Earlier starch breakdown cannot affect the comparison.
What does a blue-black drop establish?
Starch is still detectable in that drop. The colour does not tell you exactly how much starch is left.