1. Unit 2:5 Micro-organisms and disease
Most micro-organisms are harmless. Many are even useful to us.
However, there are some micro-organisms that can make people ill.
They produce harmful substances called toxins, and they reproduce once inside your body. The toxins can damage your cells.
Diseases that are caused by micro-organisms are called infectious diseases, meaning the micro-organism can move from one body to another.
Some common examples of harmful micro-organisms:
Tuberculosis (TB) – a bacteria that grows in the lungs. Drugs called antibiotics can be used to kill bacteria that are causing disease.
Malaria – a disease caused by protozoan in the blood. The protozoa are passed from person to person by mosquitoes.
Influenza and colds – these are caused by viruses. A virus is even smaller than a bacterium. Viruses are so small you can only see them using an electron microscope. Viruses do not show the characteristics of living things until they get inside a living cell and force it to copy the virus.

2. Unit 2:5 Continued Louis Pasteur
Louis Pasteur was a born in France in 1822, a time when no-one knew about micro-organisms.
He was asked to investigate a disease that was killing silkworms. He conducted experiments that showed the disease passed from one silkworm to another through the air or when people handled them.
Pasteur had already discovered that microscopic organisms were involved in making wine from grapes. He thought perhaps other microscopic organisms were making silkworms ill.
His work gave other scientists ideas. By 1870, people had begun to use antiseptics (a substance used to kill micro-organisms outside the body) to prevent infections.
But it was many more years until doctors and biologists believed that micro-organisms caused infectious diseases.