Human & Social Biology - Immunity

Basic information on immunity.

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The body's major defence mechanisms against invadi

The body has four major defence mechanisms against invading microbes:

  • Skin: acts as a barrier
  • Platelets: seal our wounds by clotting if the skin is cut
  • Organs that assist with breathing: produce mucus to cover the lining of these organs and trap the microbes.
  • Blood: contains white blood cells
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The job of white blood cells and antbodies

White Blood Cells

In the event that microbes enter the body, they need to be neutralised or killed. This is done by white blood cells. These cells:

  • engulf and digest microbes 
  • produce antibodies to neutralise microbes
  • produce antitoxins to neutralise the toxins produced by microbes


Antibodies are produced in the following manner:

1. White blood cell "sees" antigen (microbe)

2. Cell produces antibodies to "fit" antigen

3. Antibodies fit onto antigens and cause them to "clump"

4. Antigens are "eaten" (broker down) by white blood cells

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Types of immunity

The four main types of immunity are:

  • Active Natural: Antibodies are produced by a person when needed because they become infected with disease. 
  • Passive Natural: Antibodies passed on by mother during pregnancy or during breastfeeding.
  • Active Artificial: Vaccine with dead or weakened microbes is injected into body and the body is "tricked" into producing antibodies ready for the real thing.
  • Passive Artificial: Antibodies are injected directly into body.
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