Measuring the Rate of an Enzyme – Amylase and Starch

 

GCSE Biology

Measuring the Rate of an Enzyme – Amylase and Starch

Enzymes are biological catalysts — they speed up reactions inside living organisms without being used up. One of the simplest and most reliable experiments at GCSE Biology measures the rate at which amylase breaks down starch into maltose.

This practical introduces students to reaction rates, variables, and the principles of enzyme action, such as temperature, pH, and substrate concentration.

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The Science Behind the Practical

Amylase is an enzyme produced in the salivary glands and pancreas.
Its job is to catalyse the breakdown of starch, a long-chain carbohydrate, into maltose, which can be further digested into glucose.

The key ideas students learn:

• Enzymes have an active site where substrates bind

• They have an optimum temperature and pH

• High temperatures denature enzymes

• Reaction rate can be measured by tracking the disappearance of starch

The amylase–starch experiment is a perfect way to bring these concepts to life.

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The Practical

Equipment:

• Amylase solution

• Starch solution

• Iodine in potassium iodide

• Spotting tile

• Water bath

• Pipettes

• Stopwatch

• Beakers/test tubes

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Method

1. Warm amylase and starch solutions in a water bath to the chosen temperature.

2. Mix a set volume of amylase with a set volume of starch and start the stopwatch.

3. Every 10 or 20 seconds, place a drop of the reaction mixture onto a drop of iodine in a spotting tile.

4. Iodine turns blue–black in the presence of starch.

5. Continue sampling until the iodine no longer changes colour.

6. Record the time taken for starch to disappear.

7. Repeat at different temperatures or pH levels for comparison.

The shorter the time taken, the faster the reaction rate.

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Typical Results

Effect of Temperature on Amylase Activity

Temperature (°C)	Time for Starch to Disappear (s)	Relative Rate
0	180	Slow
20	70	Moderate
37	30	Fast (optimum)
60	200	Very slow (enzyme partially denatured)
80	No reaction	Denatured

Students clearly see that amylase works fastest at human body temperature (~37°C) and slows dramatically when heated or cooled.

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Variables Students Control

• Independent variable: temperature / pH/enzyme concentration

• Dependent variable: time for starch to disappear

• Controlled variables: volume of solutions, concentration, water bath conditions, sampling interval

This helps build solid, practical, and exam skills.

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Skills Highlight

• Using iodine to test for starch

• Measuring reaction rate via the disappearance of the substrate

• Controlling variables for fair testing

• Drawing graphs of rate vs temperature or pH

• Linking data to enzyme structure and denaturation

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Why It Works in Teaching

The amylase practical is simple, visual, and meaningful. Students watch a colour change disappear, linking biological theory with chemical testing. The experiment also prepares them for practical questions in GCSE exams and strengthens their understanding of enzymes at work inside the digestive system. Many students are amazed at how fast enzymes work.