Grade 12 · 🧬 Biology · Enzymes
Find the enzyme in a potato
Add hydrogen peroxide to raw and boiled potato and watch the enzyme catalase at work — then see what heat does to it.
Why this matters
Enzymes make bread rise, turn milk into ergo and cheese, and are used in washing powders and medicine. Your own liver is packed with catalase to break down harmful hydrogen peroxide. Understanding why enzymes stop working at high temperature explains why a high fever is dangerous.
Watch the demo
Video coming soon
We're recording a demo for this experiment. Until then, follow the step-by-step guide below.
The science
Enzymes are biological catalysts
Enzymes are proteins that speed up reactions without being used up. Catalase speeds up the breakdown of hydrogen peroxide: 2H₂O₂ → 2H₂O + O₂.
Denaturation
Each enzyme has an active site with a precise shape. High temperatures change that shape — the enzyme is denatured and stops working, permanently.
You'll need
- A raw potato
- A boiled potato (cooled)
- 3% hydrogen peroxide↳ Sold in pharmacies as a wound cleaner
- 3 small clear cups or glasses
- A knife and a small spoon
Safety first
- Hydrogen peroxide can irritate eyes and skin. Wear gloves or wash immediately if it touches your skin. Never drink it.
- Ask an adult to help with cutting and boiling.
Step by step
0/4 doneWhat you should see
The raw potato fizzes with lots of small bubbles. The boiled potato produces almost none. The control cup with no potato shows no bubbles.
Why it happens
Raw potato cells contain catalase, which rapidly breaks hydrogen peroxide into water and oxygen gas — the bubbles. Boiling denatured the catalase, changing its active site so it can no longer bind hydrogen peroxide. The control shows the peroxide doesn't break down quickly on its own.
Didn't work? Try this
Very few bubbles even with raw potato.
Your hydrogen peroxide may be old (it slowly breaks down). Use a fresh bottle, and grate the potato for more surface area.
The boiled potato still bubbled a lot.
It wasn't boiled long enough to denature all the enzyme. Boil for at least 5 minutes.
Still stuck? Ask the lab assistant
Check your understanding
1. What gas is in the bubbles?
2. Why does the boiled potato produce almost no bubbles?
Your lab notebook
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