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Junior School: Microorganisums

“Books are a uniquely portable magic.”



Micro-organisms (also known as microbes) cannot be seen by the naked eye (micro means tiny and organism means a living creature); many hundreds of them would fit on the full stop at the end of this sentence.

They are found everywhere, in soil, air, water, on your skin and in your guts. Most of the time, when they are in the right place the majority of micro-organisms are not harmful to people and often do a lot of good such as breaking down waste and making bread. We couldn’t live without them!

There is a huge variety of micro-organisms. They can work alone or in colonies. They can help you or hurt you. Most importantly, they make up the largest number of living organisms on the planet. There aren’t millions, billions, or trillions. There are trillions of trillions of trillions of microbes around the Earth. Maybe more!

The five types of living micro-organisms are bacteria, viruses, fungi, algae and protozoa.

  1. Bacteria can be rod-shaped, spiral-shaped or spherical. Some bacteria can be useful, such as certain types found in the stomach, but other nasty kinds can give you a bad tummy ache or a sore throat.
  2. Viruses are parasites, which means they can only survive inside the cells of other living things. They can cause infectious diseases, such as chicken pox or measles.
  3. Fungi can be different sizes ranging from a single cell, like yeast (used to make bread rise), or other fungi such as moulds or toadstools.
  4. Algae can also be many different sizes – some single-celled algae are actually used in toothpaste!
  5. Protozoa are single-celled organisms and can cause many diseases, although they are occasionally helpful too.



Protozoa are single-celled organisms that act a lot like animals in that they move around and feed on prey


  • Micro-organisms first appeared on earth about 3.5 billion years ago. They were very important in sustaining life on our planet.
  • Microbes generate at least half the oxygen we breathe.
  • Microbes thrive in extremes of heat, cold, radiation, pressure, acidity and darkness, and often where no other life forms could exist and where nutrients come only from inorganic matter.
  • Typically there are between 10,000 and 10 million bacteria on each hand!The number of germs on your ?ngertips doubles after you use the toilet.
  • When you cough germs can travel about 3 metres if you do not cover your nose and mouth.
  • Almost one million bacteria can be created by one person in a school day.
  • There are more bacterial cells in our bodies than there are human cells.
  • While bacteria on the outside of your body can cause serious infections, the bacteria inside your body can protect against it. Studies have shown that animals without gut bacteria are more likely to catch serious infections.
  • Humans have used bacteria to help us in other ways for thousands of years. Bacteria are used to make yogurt and cheese. The flavour of these foods comes from bacterial by products!


Bacteria are tiny little organisms that are everywhere around us. We can't see them without a microscope because they are so small, but they are in the air, on our skin, in our bodies, in the ground, and all throughout nature. Bacteria are single-celled microorganisms.



Viruses are microscopic parasites, generally much smaller than bacteria. They lack the capacity to thrive and reproduce outside of a host body. 


Fungi are a group of living organisms which are classified in their own kingdom. This means they are not animals, plants, or bacteria. Fungi are found throughout the Earth including on land, in the water, in the air, and even in plants and animals.


Algae are organisms, or living things, that are found all over the world. Algae are very important because they make much of Earth's oxygen, which humans and other animals need to breathe. Some algae, such as seaweed, look like plants. However, algae are actually neither plants nor animals


The four major types of germs are bacteria, viruses, fungi, and protozoa. They can invade plants, animals, and people, and sometimes they can make us sick. Bacteria (say: BAK-teer-ee-uh) are tiny, one-celled creatures that get nutrients from their environments in order to live.