School โบ Microbes โบ Ages 10โ11
Bacteria, viruses and fungi
How bacteria, viruses and fungi differ, how small they are, why antibiotics do not work on viruses, and a fair test with yeast.
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Microbes are living things too small to see without a microscope. They are the oldest life on Earth: fossils of microbe communities in Australia are about 3.5 billion years old.[3][1]
Bacteria are single cells with no nucleus. They can be shaped like balls, rods or spirals, and most are less than five thousandths of a millimetre wide.[5]
Viruses are much smaller: most are up to 100 times smaller than a bacterium. A virus is not a cell. It can only make copies of itself inside the cells of another living thing.[3][6]
Fungi include single-celled yeasts and moulds made of long threads. Yeast feeds on sugar and gives off carbon dioxide gas, which makes bread rise.[5]
Microbes help make cheese, bread, yoghurt, chocolate and vinegar. Microbes that cause disease are called pathogens, but they are less than 1% of all kinds of microbes.[2][3]
Antibiotics are medicines that work against bacteria. They do not work against viruses. Using antibiotics when they are not needed helps bacteria become resistant.[4][9]
Try it: Does yeast like it warm?
You need
- Three identical small plastic bottles and three balloons
- Dried baker's yeast and sugar
- Measuring spoons and a measuring jug
- Cold tap water, room-temperature water and warm tap water (about hand-warm)
- A thermometer
- A piece of string and a ruler
Safety
Use tap water no hotter than hand-warm; no kettles. Do not taste the mixture. Wash hands afterwards. Use latex-free balloons for anyone with a latex allergy. Do not try to grow other microbes from hands or surfaces.
What to do
- Plan a fair test: what will you change (water temperature), what will you measure (size of the balloon) and what will you keep the same?
- Put exactly 1 teaspoon of yeast and 2 teaspoons of sugar in each bottle.
- Add 100 mL of cold, room-temperature or warm water to each bottle. Measure and record each temperature.
- Quickly stretch a balloon over each bottle. Start the timer.
- Every 10 minutes, measure round the widest part of each balloon with string and a ruler. Record the results and draw a bar chart.
Play: Which microbe am I?
Read each clue. Is it about bacteria, viruses or fungi? Pick the right box.
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Quiz
Other ages: Ages 6โ7 ยท Ages 15โ16