Talk It Over
Enzymes are substances in cells that make a chemical reaction go faster. Yeast cells have an enzyme in them called catalase. It causes hydrogen peroxide to break down into oxygen gas and water. How can you observe this reaction? How can you measure whether an acid like lemon juice or a base like baking soda affects the reaction?
Get
- Glass or jar
- Measuring cup
- Measuring spoons
- Baking soda
- 1 gallon distilled water (available in the laundry products aisle of the supermarket)
- Spoons for stirring
- 5 straight-sided juice glasses
- Marker or labels
- Hydrogen peroxide
- Lemon juice
- Packet of dry yeast
- Ruler
Go
- Into a glass or jar, place ½ cup of distilled water and ½ teaspoon of baking soda. Stir to dissolve.
- Label the juice glasses 1–5. Add to them the substances shown in the table. Make sure you add the yeast last. Then stir briefly only to mix.
- Stand back and watch the glasses from the side. Make notes in your data table about what you see happening in each glass.
- When the reaction appears to have stopped, measure and record the height of the bubbles in each glass, like this:
The bubbles give you a measure of how much oxygen gas was released.
Stay Safe
Don't drink hydrogen peroxide. Don't get it on your skin unless you know you are not allergic. Dont get it on your clothes, because it takes the color out of some fabrics.
Go Easy
Use only glasses 1, 3, and 5.
Go Far
Set up more glasses and test other amounts of lemon juice and baking soda. Get some pH paper and measure the pH in each glass. How does pH relate to the height of the bubbles?
The reaction you saw is the result of enzyme action in yeast . . . or is it? See whether you can get similar results leaving out the yeast and using other small-grained additions such as fine sand or salt instead. Does added lemon juice or baking soda affect the height of bubbles in those setups? What can you conclude from comparing results?
Show Your Results
Put the heights of the bubbles in a data table like this for "Go Easy":
| Glass | Bubble Height | Observations |
|---|---|---|
| 1 | ||
| 3 | ||
| 5 |
For "Go," add glasses 2 and 4 to the table. For both, make a bar graph that shows how the heights of the bubbles compare. Write a few sentences on how an acid (the lemon juice) and a base (the baking soda) affect the amount of gas released.
For "Go Far," add other mixtures and pH measurements to your table. Make separate tables for the yeast substitutes such as salt and fine sand. Use bar graphs to answer the following question: Are the bubbles produced by an enzyme in the yeast or by the physical action of fine grains?
Tips and Tricks
- Make sure you understand the importance of glass 1 and why it is set up the way it is. It is the basis for comparison for what happens in all the other glasses.
- You'll get results that are more reliable if you conduct each test several times and average the results.
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