Microorganisms KS2

What is a microorganism?

There are millions of organisms all around us that we cannot see. They are called micro-organisms, or microbes for short. A microorganism is living thing that is too small to be seen with the naked eye. In order to see microorganisms we have to use powerful microscopes. Microorganisms include bacteria, fungi and viruses.

Even though microorganisms are invisible to the naked eye, we can often see evidence of them:

• When food goes mouldy, the mould is from microbes breaking down the food. Even though it's not very nice for us, having fungi break down food is very important.
• The holes in bread are air bubbles. These bubbles are produced by yeast. Yeast is a microorganism that is used in bread-making to make the bread rise. The yeast feeds on the bread and then produces CO² gas which forms the air bubbles. The more the yeast feeds on the dough, the more gas will be produced and the more the bread will rise.

You need a powerful microscope to see microorganisms.

What different types of microorganisms are there?

Microorganisms can be classified into three groups:

Protists: Protists are micro-organisms that are usually made up of just one cell. Protists usually live in water and stay in one place. They can include algae and amoeba.  

Fungi: Fungi need to absorb nutrients from their surroundings to survive. Examples of fungi includes mushrooms, mould and yeast.

Bacteria: Bacteria form the largest group of any kingdom by far. Bacteria can be used in food production, such as to turn milk into yoghurt. They can also cause diseases.

This is what the bacteria Salmonella looks like under the miscroscope. Salmonella causes food poisoning.

What do microorganisms need to survive?

Just like plants and animals, microorganisms need certain things to survive. They need water and food but some create their own food, like plants do, while others feed off the objects around them. Some also need oxygen. Different types of micro-organisms can survive in different places. Some live in freezing conditions, others in boiling hot temperatures.

What can microorganisms be used for?

Microorganisms are crucial to the survival of all organisms on Earth. They help break down dead plants and animals, and are responsible for much of the process of photosynthesis that plants rely on to create nutients and therefore produce oxygen for the planet. Microbes keep our bodies healthy and balanced, as well as keeping soil healthy.

But they can also be used by humans for many other purposes, such as food production. Mould from microbes is used to break down foods but it can also be cultivated to make food, such as the veins in blue cheese. These moulds are safe to eat. Microorganisms are also used a lot in other types of food production. Cheese and yogurt, for example, use lactic acid to turn them into these products from milk. Wine and beer need yeast to be brewed. Bread needs yeast to make it rise.

The mould on blue cheese is caused by microbes and is safe to eat.