Instructions (regular)

Instructions (explosive)

1. Ask your parents before conducting this experiment. IT WILL GET MESSY

2. Pour 1/2 cup of hydrogen peroxide (H2O2) into the plastic bottle. Avoid contact with your eyes or open cuts. Hydrogen peroxide is an antiseptic and will burn.

3. Add a few squirts of dish soap to the bottle and swirl to mix. You DO NOT want to shake and make bubbles.

4. In a separate container (a bowl or cup works) stir together 1 tablespoon of yeast and 3 tablespoons of warm water. The water should feel warm to the touch, but not be too hot to touch.

5. Place your plastic bottle on a tray and move outside to an easily washed area, if possible.

6. When ready, quickly pour the yeast mixture into the plastic bottle and stand back!

7. If you are having trouble or want more detailed instructions, check out the original Scientific American article here.

The science

Yeast may not look like it is alive, but it is actually a small fungal organism. All living organisms perform a process known as cellular respiration. Cellular respiration takes sugar and oxygen and produces an energy molecule called ATP and carbon dioxide. ATP is a form of energy the cell can use to perform different functions, similar to how electricity is a form of energy you can use in your home to watch TV, turn on the lights, or use appliances.

In the non-explosive half of this experiment, look at the changes you may observe in the balloon over top of the bottle. When you started it was flat and had no air. After letting the experiment run for awhile, the balloon inflates! That is because the yeast cells are breaking down the sugar to form ATP and carbon dioxide. While we can't measure the ATP that is being produced directly, we can directly measure how much carbon dioxide is being produced. Scientists use this same idea to indirectly measure how well yeast are transforming sugars to cellular energy. This can tell them about what types of sugars are easiest to break down and how healthy the cell is. You can try adding different amounts of sugar to your bottle and observing changes in how much the balloon inflates.

Learn more about cellular respiration with the video below.

Cellular respiration can be risky! Breaking down sugars requires reactive chemistry, which can be helpful when it is used properly by the cell, but can cause damage if it gets out of control. For example, hydrogen peroxide (H2O2) can be produced during cellular respiration. Sometimes, H2O2 is useful and can be used to signal other parts of the cell. But too much can destroy the cell completely! To prevent this, cells produce an enzyme called catalase and yeast cells produce a lot of this. Enzymes take a substrate, which is the thing you want to break down, and a change in shape of the enzyme breaks the substrate to form a product. The enzyme breaks apart the hydrogen peroxide substrate (H2O2) atoms and forms the products water (H2O) and oxygen (O2), which are both safer to keep in the cell.

In the explosive half of this experiment, you saw so many bubbles form that they explode out of the plastic bottle. This is because the yeast cells are using catalase to break down the hydrogen peroxide substrate you added to the bottle. The oxygen that is produced by this reaction creates bubbles in the dish soap. Actually, it creates A TON of bubbles and makes a yeast-oxygen volcano! Just think: that small amount of yeast you added to the bottle produced all those bubbles. That's a lot of enzymatic activity!