Microorganisms: life too small to see — Biology, 11–13 years
Bacteria, fungi and other tiny organisms live almost everywhere. Some help us, while others can cause disease.
What microorganisms are
Microorganisms are living things so small that most cannot be seen without a microscope. Bacteria, yeasts and many single-celled organisms belong here, but viruses are a different kind of infectious particle. Tiny does not mean unimportant: these life forms can make food, recycle matter or cause illness.
Why they matter
People once blamed bad smells or mysterious air for illness because they could not see germs. The microscope and careful experiments showed that particular microorganisms can enter a body, multiply and disturb it. The same idea also explains yoghurt, bread rising and decay: different microbes change materials in different ways.
A bread experiment
Put two equal slices of bread into separate, labelled bags. Leave one in a warm cupboard and one in a refrigerator, checking daily without opening them. After four days, the warm slice may show more mould: warmth allowed mould spores to grow faster, while the cold slowed their activity. This is evidence about growth, not proof that every microbe prefers warmth.
The common mix-up
A reasonable mistake is to call every tiny thing a bacterium, or to treat every microbe as harmful. We notice microbes most when they make us ill, so danger feels like their main purpose. In reality, many are harmless or useful, and viruses are not bacteria: antibiotics that target bacteria do not cure viral colds.
Where they show up
Microorganisms help turn milk into yoghurt and dough into risen bread. In soil and compost, they break down dead material and return nutrients to plants. Some are used to make medicines, while others spoil food, so washing hands, cooling food and keeping wounds clean can reduce unwanted growth.
Keep exploring
Other languages
Loading MyLeoNes™…