Microorganisms – JSS3 Intermediate Science Lesson Note (First Term)

Microorganisms (microbes) are tiny living things that can only be seen clearly with a microscope.

• Where they live: in air, soil, water, food and inside the human body.
• Everyday signs of microbes: milk going sour and a small cut becoming swollen and painful.

Behavioural objectives

By the end of the lesson, students should be able to:

1. Define microorganisms and name the four main groups.
2. Describe the features and give examples of bacteria, fungi, protozoa and viruses.
3. State the useful and harmful roles of microorganisms.
4. Name diseases caused by each group of microorganisms.
5. List ways of protecting ourselves from harmful microorganisms.

What are the types of microorganisms?

There are four main types of microorganisms: bacteria, fungi, protozoa and viruses.

1. Bacteria

Bacteria are single-celled microorganisms with no true nucleus.

• Cocci: bacteria shaped like tiny balls.
• Bacilli: bacteria shaped like rods.
• Spirals: bacteria shaped like coils or corkscrews.
• Examples: the bacteria that cause tetanus, cholera and tuberculosis (TB).

2. Fungi

Fungi are organisms that feed on dead or living matter. Some are large, but many are microscopic.

• Yeasts: single-celled fungi used to make bread rise.
• Moulds: fungi that grow as furry threads on old bread or spoiled oranges.
• Mushrooms: large fungi that can be seen without a microscope.

3. Protozoa

Protozoa are single-celled, animal-like microorganisms that are more complex than bacteria.

• Habitat: they usually live in wet places such as ponds, streams and muddy ground.
• Amoeba: a protozoan that moves and feeds by changing its shape.
• Plasmodium: the protozoan that causes malaria.

4. Viruses

Viruses are the smallest microorganisms and can multiply only inside the living cells of a host.

• Not fully alive: outside a host cell they cannot grow or multiply.
• Size: they are much smaller than bacteria.
• Hosts: people, animals and plants.
• Examples: the viruses that cause the common cold, flu and COVID-19.

How do the four groups compare?

What is the difference between a virus and a bacterium?

A bacterium is a single-celled organism that can live and multiply on its own.

A virus is a much smaller particle that can multiply only inside a living host cell.

What are the useful roles of microorganisms?

Many microorganisms are helpful to people and to the environment.

• In the kitchen: yeast makes bread soft and fluffy, and certain bacteria turn milk into yoghurt and cheese.
• In the soil: microbes break down dead plants and animals into nutrients for crops. This is called decomposition.
• Nitrogen-fixing bacteria: some bacteria in the soil and in the roots of beans make the soil more fertile.
• In medicine: some antibiotics, such as penicillin, are made from fungi.
• In the body: “good bacteria” in the gut help us digest food.

What are the harmful roles of microorganisms?

Harmful microorganisms that cause disease are called pathogens, or germs.

Causing diseases

• Bacteria: tetanus, cholera and tuberculosis (TB).
• Viruses: polio, measles and the common cold.
• Protozoa: malaria and amoebic dysentery.
• Fungi: skin problems such as ringworm and athlete’s foot.

Other harmful effects

• Food spoilage: microbes make food rot, smell bad or taste sour. Eating spoiled food can cause food poisoning.
• Damage to materials: microbes can rot wood, leather shoes and clothes that stay damp for a long time.

How can we protect ourselves from harmful microorganisms?

We protect ourselves by stopping microbes from entering the body and by controlling where they breed.

1. Wash your hands: soap and clean water lift microbes off the skin and wash them away.
2. Cook food properly: high heat kills most harmful bacteria and worms.
3. Keep surroundings clean: do not leave stagnant water where mosquitoes, which carry the malaria protozoan, can breed.
4. Get vaccinated: a vaccine trains the body to fight dangerous viruses before they cause illness.
5. Cover and store food: this slows down spoilage and keeps flies away.

• Note: antibiotics treat bacterial infections but do not work against viruses.

Evaluation

1. Define microorganisms and name the four main groups.
2. Name the three shapes of bacteria.
3. Give one way bacteria help us and one way they harm us.
4. State two differences between a virus and a bacterium.
5. List three ways of preventing the spread of disease-causing microbes.

Assignment

Draw a table with four columns: group of microorganism, one example, one disease it causes and one way to prevent that disease.