Plants and people need lots of chemistry to live! Our bodies are chemical plants using food and oxygen in chemical reactions to do all the wonderful things we do every day. Our bodies use special molecules, called enzymes to make these reactions go smoothly and quickly.
Catalase is a common enzyme. It helps change peroxides (which are created in other reactions and aren’t good for living things) into water and oxygen. It does this very quickly. Most living tissue contains catalase. We can use potatoes to help see catalase work because bubbles of oxygen form when we put potatoes into hydrogen peroxide. We can also see how to stop enzymes from working.
When potatoes are cooked, the structure of the enzyme changes and it doesn’t work. Cooked potatoes won’t make bubbles of oxygen. Even though catalase is present in living things, the amount may vary. Apples contain very little catalase . Putting apples in peroxide causes only a few bubbles to form.
Hydrogen Peroxide (available in the first aid section of most pharmacies or supermarkets)
A small pot (for cooking some of the potato)
1) Label the cups: a. Hydrogen peroxide plus raw potato b. Water plus raw potato c. Hydrogen peroxide plus cooked potato d. Hydrogen peroxide plus apple
2) Cut small pieces of potato. Leave some raw. Boil some pieces for 5-10 minutes (until they are soft)
3) Cut small pieces of apple.
4) Put a small amount of hydrogen peroxide or water (as labeled) into each cup.
5) Add raw potato to the cup with hydrogen peroxide and the cup with water. What happens in each cup?
6) Add cooked potato to the cup with hydrogen peroxide. Does it behave like the raw potato?
7) Add the apple to the hydrogen peroxide. Do you see any bubbles? Look carefully, especially around the apple pieces.
8) Try this! Put other fruits or vegetables into the peroxide (try carrots, mushrooms, grapes or zucchini). Which ones make lots of bubbles?