Teaching overview

Learning points

Part 1

  • Bacteria are microscopic organisms that can live almost anywhere.
  • Our bodies contain friendly bacteria that help us to digest food.
  • Some bacteria cause diseases, which can be treated with a type of medicine called an antibiotic.
  • Antibiotic resistance is when bacteria stop being affected by antibiotics.

Curriculum keywords

  • Microorganisms
  • Bacteria
  • Health
  • Medicine
  • STEM

Learning points

Part 2

  • The chemicals produced by bacteria are a natural source of antibiotics.
  • Scientists are trying to find new antibiotics that superbugs haven’t yet developed a resistance to.

Spark a discussion

  • Have you ever had a cold or the flu? What did it feel like? How did you catch it?
  • How can we stop colds from spreading between people?
  • Why is regular hand washing important?
  • What are bacteria? Where can bacteria be found?
  • How are bacteria harmful to humans? Are all bacteria harmful?
  • How are bacteria helpful to humans? How can bacteria be good for our health?
  • What is a microorganism? What are the different types of microorganism?
  • Why do people need antibiotics? Have you ever taken antibiotics?
  • How do antibiotics affect bacteria? Do they have an effect on other types of microorganism?
  • What is antibiotic resistance?
  • What are scientists doing to discover new antibiotics?
  • Why is it important to find new antibiotics?

Multimedia toolbox

Multiplying bacteria video loop

Play the video loop as the children enter the classroom to spark discussion about what they are seeing, and how quickly they think bacteria reproduce.

Bacteria visual

Show the visual before the film and discuss what bacteria are, how small they are, where they live and how they affect humans.

Rotting food visual

Show the visual after the film and discuss what causes food to rot.

Antibiotic resistance visual
The ability of bacteria to become resistant to antibiotic drugs, meaning they are no longer affected by them.

Antibiotic resistance visual

Show the visual after the film to reinforce scientific terminology.


Rotting food

INVESTIGATE how moisture affects the rate at which microorganisms reproduce and cause food to rot.

Open detailed instructions

Other activity ideas

  • DEMONSTRATE the way that bacteria and other microorganisms can spread by putting UV lotion/powder on your hands and then shaking hands with children or passing objects around the classroom. Use a UV light to reveal how far the lotion has spread in a short space of time.
  • RESEARCH Alexander Fleming and the discovery of the antibiotic penicillin.
  • WRITE a recipe explaining how microorganisms are used to make yoghurt or cheese.
  • DESIGN a poster or information leaflet to show how bacteria can be both helpful and harmful to humans.
  • CREATE a superhero-style comic strip or animated short video about the lengths that scientists are going to in the fight against antibiotic resistant superbugs.
Print this sheet

Rotting food

Duration: 60 minutes


Key Learning:

This investigation supports the students’ understanding of how microorganisms such as mould cause food to rot, by allowing the class to observe the changes that occur in food over time.

Safety note: Throw the plastic bags away after the investigation – do not open them! Some mouldy food can be dangerous and make you sick.

Activity instructions:

  1. Discuss with the class what causes food to rot. You can use the following prompt questions:
    • Why do we keep food in fridges and freezers?
    • Why is food sold in sealed containers?
    • How does food change in appearance as it rots?
    • What types of food rot the fastest?
  2. Organise the class into groups and distribute the resources. Tell the class that they are going to investigate how different conditions affect the rate at which food rots. They will do this by placing three slices of bread into three separate plastic bags, and observing the changes that occur over the period of one week.
  3. Ask the students to suggest different conditions in which they could keep their bread samples. Remind the groups that in order to carry out a fair test they can only change one variable, and suggest that in this investigation they investigate the effects of different amounts of moisture. Ask the groups to plan the investigation using the Planning an investigation activity sheet.
  4. Ask the students to predict which slice of bread will become mouldy first, and encourage them to explain their choice. Take a class vote.
  5. Tell the groups to carry out the following instructions:
    • Use the sticky labels and marker pens to label the three plastic bags with the conditions they are investigating: dry, damp and wet. They can also add their group name and the date the investigation started.
    • Place a dry slice of bread in the “Dry” plastic bag and seal using masking tape.
    • Lightly sprinkle the second slice of bread with water, place in the “Damp” plastic bag, and seal the bag using masking tape.
    • Dip the third slice of bread in water, place in the “Wet” plastic bag, and seal the bag using masking tape.
    • Place the bags in a warm place.
  6. Ask the groups to check the three bread samples each day and make a note of any changes they observe. They could also make observational drawings or take photographs. Note: The samples can also be more closely observed using a hand lens.
  7. After one week, discuss the results with the class. You can ask the following prompt questions:
    • Which slice of bread started getting mouldy first?
    • When did the mould first appear?
    • Are all three slices of bread mouldy?
    • What colour is the mould?
    • What is the texture of the mould?
    • Where on the bread did the mould grow? Why do you think that is?
    • Which slice of bread has the most mould?
  8. Once their observations are complete, remember to dispose of the bags without opening them.
  9. Ask the students to use their findings to draw conclusions about how moisture affects mould growth.
  10. Explain to the class that mould is a kind of fungus. Moulds grow from tiny, microscopic spores that float around in the air. If these spores land on food, they start to grow, feeding on the food and causing it to break down and rot. Tell the students that in the 1920s, a scientist called Alexander Fleming discovered a type of mould that killed bacteria, and he used this to make an antibiotic called penicillin. Since then, many other antibiotic drugs have been made using moulds.

Background information

  • Microorganisms are living things that humans cannot see without the aid of a microscope. Microorganisms include bacteria, viruses and some fungi.
  • Some microorganisms are harmful and cause diseases such as measles, mumps and salmonella. Harmful microorganisms can be spread from person to person through direct contact, via an object or surface, or through the air.
  • Bacteria generally reproduce by dividing themselves in two. This can be as often as every 20 minutes. Viruses must invade body cells in order to reproduce. In doing so they destroy the host cell, causing it to erupt and spread the virus to surrounding cells. Fungi reproduce by producing spores.
  • Antibiotics are drugs that are used to fight harmful bacteria, either by killing them or stopping them from reproducing. Antibiotics can only be used to treat diseases caused by bacteria. They will not work for diseases that are caused by viruses, such as colds or flu.
  • Today we are able to treat many bacterial diseases with antibiotics. However, over time and with repeated exposure, bacteria can evolve to become resistant to an antibiotic, meaning that particular drug no longer has any effect. In response, scientists must search for new antibiotic substances, and use them to develop replacement medicines.


An organism that is too small to see without a microscope. Microorganisms include bacteria, viruses and some fungi.
Microscopic, single-celled living organisms. Some bacteria are beneficial, such as those that aid digestion, whilst others are harmful and cause diseases, such as tetanus and salmonella.
A substance that can slow down or prevent the reproduction of bacteria. Penicillin was one of the first antibiotics to be discovered and it is still widely used today.
Antibiotic resistance
The ability of bacteria to become resistant to antibiotic drugs, meaning they are no longer affected by them.

Explore our resources

Complete your lesson with teaching resources on microorganisms from Tigtag.

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