Odd One Out

Small but powerful

Activity overview

15 mins
Ages 9 – 11

Science topics:

Living things and their habitats , Topical science

Put your class' observation skills to the test with these three microorganisms. This activity is great for promoting observation and discussion skills.

Run the activity

1. Show the three images above and ask everyone to come up with as many similarities and differences as they can. If they get stuck, prompt them to think about:

  • appearance
  • what they do
  • where they might be found

2. Then, everyone needs to decide which one is the odd one out and why. Encourage a reason for every answer and there is no wrong answer!

Background science

It can be easy for children to think that all microorganisms are harmful agents of disease but in fact, we use them to make some foodstuffs and depend upon them to breakdown decaying matter. Millions of microbes have made our bodies their habitat and most of them will never do us any harm. This Odd One Out activity introduces a virus, bacterium and fungus (yeast).

A virus is a tiny infective agent that can replicate only within the living cells of an organism. There are many types of viruses and they can infect all types of life forms, from plants and animals to bacteria.

When humans are infected by a microorganism, such as the influenza virus pictured (left), our immune system recognises it as ‘foreign’ and responds to prevent it from spreading. This leads to the symptoms we see when we have ‘flu'. A raised temperature indicates that our body is working hard to rid us of the virus. We might get a sore throat because the virus has infected cells in the lining of the throat and we cough to release mucus from our lungs that contain dead cells and virus particles. We’ll continue to spread virus particles in coughs and sneezes until our bodies can overcome the infection by producing antibodies to target the virus so that other specialised cells are activated to kill the infection.

Bacteria are all around us and most of the time they do us no harm. They grow and replicate (by dividing in two) and so unlike a virus they do not need a host. The bacteria pictured (middle), called Escherichia coli (or E.coli for short) are commonly found in our large intestine. They are mostly harmless and part of our natural gut flora which keep us healthy. 

Yeast is classified as a fungus. Saccharomyces cerevisiae is also known as baker’s yeast. Yeasts are all around us, like the whiteish bloom you find on the skin of grapes. They replicate mostly by budding when a new cell forms by budding off from the parent cell. We make use of the carbon dioxide released from the fermentation of sugars to help bread to rise.

Take it further

For further activities to understand how we spread diseases, look at the free resources produced by e-bug. There are activities suitable for all primary aged pupils. 

To explore more how we interact with microorganisms, why not look at our activity What if no one cleaned the house?

We have written this article on Microorganisms to help equip you with enough knowledge about them and how they affect us and our bodies, to be able to respond with confidence to any tricky questions that you may encounter.

Wellcome has also created an information hub about COVID-19 vaccines.