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Microbes are tiny living things. They are so small that you cannot see them with your eyes alone.

There are three big groups of microbes: bacteria, viruses and fungi. They come in lots of shapes and sizes.

Microbes are found almost everywhere on Earth. Some even help to keep us healthy.

Many microbes are useful. A fungus called yeast makes bread dough rise. Microbes also help to make yoghurt and cheese.

Experiment: The yeast balloon

1. The teacher puts one teaspoon of yeast and one teaspoon of sugar into each bottle.
2. Pour warm tap water into one bottle and cold water into the other, about a quarter full. Swirl gently.
3. Stretch a balloon over the top of each bottle.
4. Look every ten minutes. What happens to the balloons?
5. Draw the two balloons. Which one grew more?

	Warm water balloon	Cold water balloon
At the start	Which balloon will grow bigger: warm or cold?
After 10 minutes	Which balloon will grow bigger: warm or cold?
After 30 minutes	Which balloon will grow bigger: warm or cold?

Questions

1. Draw a microbe. Is it a bacterium, a virus or a fungus?

   🍎

2. Name one food that microbes help to make.

3. In the experiment, the bigger balloon was the…

   warm one / cold one

4. Why should we wash our hands with soap?

Sources for every fact on this sheet: echoesof.science/school/microbes/sources/

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