Leave a loaf of bread out too long and greenish spots appear, and cabbage left in salt turns into tangy kimchi a few days later.
Both are the work of living things too small to see, called microorganisms. You can only make them out by magnifying them a lot under a microscope.
Microorganisms come in groups such as bacteria, fungi like mould, and protists, and they live everywhere: in soil, water, air, and on and inside our bodies.
Switch between the three groups with the buttons to compare them under the microscope, then sort out which microorganisms help us and which harm us.
What is a microorganism?
🔬 Living things too small to see
①Microorganisms are living things too small to see with the naked eye
②Bacteria are especially tiny, so they must be magnified about ten times more than protists to look about the same size
③Even a spoonful of soil holds countless microorganisms
④Bacteria, fungi such as mould, and protists are typical microorganisms
Groups of microorganisms
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Bacteria, mould, and protists seen through a microscope
Bacteria · Mould · Protists
Groups of microorganisms
Helpful and harmful microorganisms
🥛 Microorganisms that help us
①Lactic acid bacteria ferment cabbage and milk into kimchi and yoghurt
②Yeast gives off gas inside bread dough and makes the bread rise
③Koji mould and bacteria ferment soybean blocks into soybean paste and soy sauce
④The first medicine to fight bacteria came from a blue-green mould
⑤Microorganisms in the soil break down fallen leaves and dead living things and return them to the soil
⚠️ Microorganisms to watch out for
①Food-poisoning bacteria multiply in spoiled food and cause stomach upsets
②Do not eat mouldy food, even if you cut off the mouldy part
③Bacteria that cause illness can pass from person to person
④Washing your hands well and keeping food cold stops harmful microorganisms from multiplying
Helpful microorganisms change the taste and smell of the ingredients
🎯 Key points
①Microorganisms are living things too small to see with the naked eye
②They can be grouped into bacteria, mould and other fungi, and protists
③Helpful microorganisms make fermented foods like kimchi and yoghurt and break down dead living things
④Harmful microorganisms spoil food and cause illness
⑤Washing hands and storing food properly keeps harmful microorganisms away
Examples and Unit Test
Example 1
Why can't we see microorganisms with the naked eye, and how do we observe them?
1
Microorganisms are such tiny living things that we cannot see them with the naked eye.
2
So we have to magnify them dozens to about a thousand times under a microscope to see them.
▸ They are too small to see, so we observe them with a microscope
Choose bacteria in the picture and you will see they are shown at a higher magnification than protists.
Example 2
Which microorganism helps make kimchi and yoghurt, and what is that process called?
1
Lactic acid bacteria are bacteria that are helpful to us.
2
They change substances in cabbage and milk and give them a tangy taste; this is called fermentation.
▸ Lactic acid bacteria / fermentation
Spoiling and fermenting are both done by microorganisms, but when the result is good for us we call it fermentation.
Unit-test style
Which statement about microorganisms is correct?
①All microorganisms are harmful to people
②Lactic acid bacteria make helpful foods by fermentation
③Microorganisms are easy to see with the naked eye
④Mould is not a microorganism
⑤Microorganisms live only in soil
▸ ② Lactic acid bacteria make helpful foods by fermentation
1
Lactic acid bacteria ferment food ingredients and make helpful foods such as kimchi and yoghurt.
2
Some microorganisms are helpful (①), they are too small to see without a microscope (③), mould is a microorganism too (④), and they live everywhere, in soil, water, air, and our bodies (⑤).