You Will Need:

• ½ sachet baker’s yeast (about 3–3.5 g)

• ½ cup warm water (about 125 mL)

• 2 teaspoons sugar

• 1 empty plastic bottle

• 1 balloon

Method:

1. Add the yeast and sugar to the bottle.

2. Pour in the warm water and gently swirl to mix.

3. Stretch the balloon over the top of the bottle.

4. Leave for 10–20 minutes and observe what happens.

What’s happening?

Yeast is a living organism. Like all living things, it needs water and nutrients to grow and respire.

In this experiment, the yeast feeds on the sugar and produces carbon dioxide gas. The gas builds up inside the bottle and inflates the balloon.

This is the same process that makes bread light and fluffy — the carbon dioxide gas produced by yeast creates bubbles in dough as it rises.