Free Worksheets, Lessons, Quizzes

Microorganisms and Disease

What is the tiniest microorganisms?


E.g. – It would take 6 million of one of the smallest viruses to make a row just 1 mm long.

Basic structure of a virus

Basic structure of a virus


Examples of illnesses caused by microorganisms

See the following table to know about the illnesses caused by bacteria, illnesses caused by viruses, illnesses caused by fungi.

Examples of illnesses

caused by bacteria

  • Food poisoning 
  • Whooping cough 
  • Boils
  • Some kinds of pneumonia
  • Leprosy
  • Diphtheria
  • Tooth decay

Examples of illnesses

caused by viruses

  • Colds 
  • Influenza (‘flu) 
  • Measles 
  • Mumps 
  • Chickenpox

 Examples of illnesses

caused by fungi

  • Athlete’s foot
  • Ringworm


Spreading germs


What are the ways that cause germs to spread and multiply?


1) Sneezing and coughing

Coughs and sneezes spread diseases

Coughs and sneezes spread diseases


2) Dirty skin and hands

3) Unbrushed teeth

4) Being careless when storing, preserving or handling food.

5) Dirty dustbins can attract flies, rats and mice.

Dirty dustbins can attract flies, rats and mice

Dirty dustbins can attract flies, rats and mice


6) By touching a person who already has some kinds of illness.

7) Animals like flies carry germs on their legs and mouthparts, can leave germs when they have been feeding.

8) Uncooked food (especially meat) can contain bacteria. The bacteria are killed when the food is cooked properly. But if you eat food that has not been cooked properly, the bacteria may survive and make you feel very ill.

E.g – Mould is a type of micro-organism that grows on decaying food. It can make you ill if you eat it.


Food spoilage - Mouldy bread

Food spoilage – Mouldy bread




How are colds caused?


By viruses


How can you get cold from a person who has got cold?


1) When the person who has got cold coughs or sneezes, some of the viruses will be shot out into the air.

2) If you breathe in some of these viruses, they will settle in your nose and throat where it is warm and moist.

3) There the viruses will multiply rapidly (quickly) and soon you too will have a cold.


Fighting disease


What are the two types of blood cells?


1) Red blood cells

2) White blood cell


What gives blood its colour?

Red blood cells

What gives red blood cells their colour?


Haemoglobin in red blood cells gives them their colour.


Why are red blood cells important?


1) They give blood its colour.

2) Haemoglobin in red blood cells carries oxygen all over the body.


Why are white blood cells important?


White blood cells help to protect us from disease.


How do white blood cells fight when bacteria get into a cut, sore or wound?


1) The white blood cells move in great numbers towards the cut.

2) Then they surround the bacteria and kill them.

3) In doing this, many of the white blood cells die.

4) Their dead bodies form part of the ‘pus’ which comes out of the infected cut, sore or wound.


How do white blood cells fight against the poisons produced by bacteria?


1) Some of the white blood cells produce chemicals.

2) These chemicals can neutralize, or make harmless, the poisons produced by bacteria.


Why are people more often ill during the winter than they are during the rest of the year?


1) Throughout the year our homes maintain a good flow of air with the outside and we keep the temperature cool.

2) In winter the bacteria and viruses can remain alive or active inside because it is too cold outside.

3) We keep our houses closed up from outside and keep it warm.

4) So the bacteria and viruses survive in these warmer environments and reproduce more and more.

5) Therefore most of the people get sick this time of year.


What kind of illnesses do people often get during the winter?


1) Flu and cold

2) Fever

3) Sore throat

4) Stomachache

5) Chickenpox


How are these illnesses spread?


In winter season people travel to visit with family and also there are lots of crowds in public places (like shopping malls) to buy items. This helps spread the illnesses around to other people and places.

How to avoid spreading germs?


To avoid spreading harmful microorganisms, you must;

  • wash your hands before eating, after preparing food and after using the toilet.
Washing Hands

Washing Hands

  • cover your mouth when you cough or sneeze.

cover your mouth when you cough or sneeze

  • keep away from other people if you have a disease that is easily spread.
  • not eat food which is not fresh or has not been cooked properly.
  • keep  uncooked meat separate from other food in the fridge.


Read the lesson Microorganisms to know what they are.