Biology

Pathogens are microorganisms - such as bacteria and viruses - that cause disease. Bacteria release toxins, and viruses damage our cells. White blood cells can ingest and destroy pathogens. They can produce antibodies to destroy pathogens, and antitoxins to neutralise toxins.

In vaccination pathogens are introduced into the body in a weakened form. The process causes the body to produce enough white blood cells to protect itself against the pathogens, while not getting diseased.

Antibiotics are effective against bacteria, but not against viruses. Some strains of bacteria are resistant to antibiotics.

Viruses can only reproduce inside host cells, and they damage the cell when they do this. A virus can get inside a cell and, once there, take over and make hundreds of thousands of copies of itself. Eventually the virus copies fill the whole host cell and burst it open. The viruses are then passed out in the bloodstream, the airways, or by other routes.

White blood cells can:

• ingest pathogens and destroy them
• produce antibodies to destroy pathogens
• produce antitoxins that neutralise the toxins released by pathogens
• In a written examination, it is easy to get carried away and waffle on about things such as invaders and battles, but stick to the point. Note that:
• the pathogens are not the disease – they cause the disease
• white blood cells do not eat the pathogens – they ingest them
• antibodies and antitoxins are not living things – they are specialised proteins

People can be immunised against a pathogen through vaccination.

Vaccination involves putting a small amount of an inactive form of a pathogen, or dead pathogen, into the body. Vaccines can contain:

• live pathogens treated to make them harmless
• harmless fragments of the pathogen
• toxins produced by pathogens
• dead pathogens