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Text Box: MO’s – Microorganisms WHB – White blood cells BIOLOGY 2 – KEEPING HEALTHY

What’s up, doc?

Passing it on

Infections are caused by some MO’s that invade the body. MO’s are viruses, bacteria & fungi.

When diseased MO’s get inside your body, they reproduce very quickly. This causes symptoms.

What are MO’s like?

MO’s are very small. To see bacteria you need a microscope. Viruses are even smaller. They are measured in nanometres (NM) and one NM is only one millionth of a millimetre.

Reproduction in bacteria is simple. Each bacterium splits into two new ones. These grow for a short time before splitting again. If conditions are right –warmth, nutrients, moisture – they can split every 20 minutes.

Fighting back

The body’s main defenders are the white blood cells. One type of WBC engulfs (surrounds) the bacteria and digests them.

The worn-out WBC, dead bacteria and broken cells collect as pus. Redness and pus show that your body is fighting infections. As bacteria are killed, the inflammation and pus gets less until the tissues heals completely.

Your body’s army – fighting infection

The parts of your body that fight infections are called your immune system. WBC are an Important part of your immune system. Antibiotics are antimicrobial chemicals that kill bacteria and fungi but not viruses. Different antibiotics affect different bacteria or fungi.

If antibodies are so good why do I get ill?

Viruses can’t be treated with antibiotics. The antigens on every MO are different. So your body has to make different antibody for each new kind of MO. This takes a few days, so you get ill before your body has destroyed the invaders.

Why do you get some diseases just once?

Once your body has made an antibody it can react faster next time. Some of the white blood cells, called memory cells, that make the antibody stay in your blood. If the same MO invades again, these white blood cells recognise it, reproduce very quickly, and start making the right antibody. This means that the body reacts much faster the second time you meet a particular MO. Your body destroys the invaders before they make you feel ill. So you are immune to that disease.

Viruses have a very high mutation rate. This means that their DNA changes regularly. So do the antigen markers on the surface. The antibody that worked last time will no longer match the marker. Your body has to make a different antibody to fight the virus. This is why we suffer they symptoms of a cold all over again.


Vaccinations make use of the body’s own defence system. They kick-start your WBC into making antibodies. So you become immune to a disease without having to catch it first.

Are vaccines safe?

Any medical treatment you haves should do two things:

·         Improve your health

·         Be safe to use

Vaccines can improve your health by protecting you from disease. They are tested to make sure they are safe to use…


Anisa Akhtar



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