All lessons › Kitchen chemistry: fizz, foam and fountains › Lesson 1
Australian primary science · Years 5–6 · Lesson 1 of 8
Yeast balloon
Inquiry question: Can a living thing blow up a balloon?
Check practical materials
Fair testing
What students learn
Yeast is a living thing. With food and warmth it makes carbon dioxide gas, a new substance, and temperature changes how fast it works.
Success criteria
- I can explain that yeast is alive and makes a gas.
- I can keep everything the same except the water temperature.
- I can measure and compare balloon sizes over time.
Preparation and materials
Before this lesson: Students know that living things need food and suitable conditions.
- Dried yeast sachets — 13
- Sugar — 1 small bag
- Small plastic bottles (600 mL) — 26 (2 per pair)
- Balloons — 26 (plus spares)
- Funnels — 13
- Warm and cold tap water (teacher checks warm is below 40 °C) — 1 jug of each per table
- String and rulers — 13 of each
- Thermometers — 13
Teacher setup
- Stretch each balloon a few times so it inflates easily.
- Check the warm water is comfortably warm, about 35–40 °C.
Safety and adaptations
- Use warm tap water only, never boiling.
- Check for latex allergies; use latex-free balloons if needed.
- Don’t taste the mixture.
Review your school policies and curriculum requirements before teaching.
How to investigate
The lesson sequence should leave pupils with evidence to interpret, not only an activity to finish.
- Label your bottles Warm and Cold.
- Use a funnel to add 1/2 sachet of yeast and 1 spoon of sugar to each bottle.
- Your teacher adds 1 cup of warm water to one bottle and 1 cup of cold water to the other. Record each temperature.
- Stretch a balloon over each bottle straight away. Swirl gently.
- Measure around each balloon with string every 10 minutes for 30 minutes.
- Which balloon grew more? What made the gas?
Teacher modelling prompt
Stretch a balloon over an empty bottle. Wrap string around the widest part of the balloon and measure the string on a ruler. Say: “You’ll measure your balloons this way every 10 minutes. Same place, same way.”
Record and explain evidence
Recording question: Does water temperature change how much gas yeast makes?
| Time (minutes) | Warm balloon (cm around) | Cold balloon (cm around) | What I noticed |
|---|---|---|---|
| ________________ | ________________ | ________________ | ________________ |
Example recording headings; record actual observations, including inconclusive results.
Discussion prompt
How could we test Claim A? What control bottle would help?
Check understanding
What should pupils know? What gas does yeast make, and what does it need to make it?
Explain with evidence: Jai’s warm balloon grew to 30 cm and the cold one to 12 cm. What can he conclude?
Apply the idea: Why do bakers leave bread dough somewhere warm?
Teacher answer guidance and saved classroom work are available through the main lesson experience where supported.