1. Stopping Microorganisms

2. Microorganisms can be harmful or undesirable
Microorganisms can be harmful or undesirable. Some microorganisms cause disease and we call these pathogens. Other microorganisms cause effects such as rotting or spoiling of food. It is important to know how to stop, slow or kill microorganisms.

3. Barriers
The first and simplest way to stop the spread and growth of a microorganism is to prevent it moving to where it is not wanted. e.g. Sealed food packets Cans Condoms Surgical masks

4. Barriers need to be able to prevent the microorganism travelling through them. Any holes in the barrier need to be smaller than the microorganism for the barrier to be effective. This is very difficult with viruses as they are the of the microorganisms.

5. Chemicals
Some chemicals kill microorganisms. Disinfectants These are chemicals that are poisonous to microorganisms and quite often us as well. e.g.

6. Antiseptics These are milder forms of disinfectants that can be used on living things, especially of cuts or sores where it is important to stop microorganisms. e.g.

7. Antibiotics Some chemicals, originally made by types of fungi, kill bacteria very effectively. e.g.

8. Resistance
If you kill off some of a microorganism with a chemical then only the ones that are better at resisting it survive. The survivors breed and pass on the genes for resistance to their offspring. Eventually you get a new type of microorganism that can resist, or is immune to, that type of chemical.

9. Creating resistant strains of microorganism is very dangerous
Creating resistant strains of microorganism is very dangerous. Some types of microorganisms have become so resistant to all known chemicals that they are called “superbugs”. Whole areas in some hospitals have had to be sealed because they are contaminated by these microorganisms.

10. The Immune System
Some microorganisms can invade us and cause disease. We call microorganisms that cause disease pathogens. If we do become infected by a pathogen our bodies can try to fight it.

11. Every time we are affected by a pathogen our white blood cells change so that they can fight it better next time. The white blood cells become able to recognise chemicals on or made by the microorganism called antigens.

12. When white blood cells recognise an antigen they produce antibodies
When white blood cells recognise an antigen they produce antibodies. Antibodies either destroy the pathogen or more commonly allow white blood cells to destroy it.

13. Our immune system learns to produce different antibodies when it is exposed to different antigens. This means that after we are exposed to a pathogen we are better at fighting it next time as our body already knows how to make the right antibody. This is how vaccination works.

14. Hot and Cold
Enough heat can kill most microorganisms. We use this by sterilising things in a fire, cooking, and by boiling water. Cold does not usually kill very many microorganisms but it slows down their growth and reproduction. We use this fact to preserve food.

15. Radiation
Radiation can kill microorganisms. Many types of radiation are used this way from UV light (mild) to gamma radiation(really nasty).

16. Drying
Most microorganisms need water to survive. If we keep an object dry we can stop or slow microorganisms from growing. Some ways of drying can be Dehydrating e.g. Dried Fruit Salting e.g. Corned Beef Adding sugar e.g. Jam