Human Defence Systems (AQA GCSE Combined Science: Trilogy: Biology): Revision Note

Non-specific defences

• The human body has a number of mechanisms that are the first line of defence against an infection

• The non-specific defence systems of the human body against pathogens include:

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The immune system

• The immune system of the body is highly complex, with white blood cells being the main component

• Once a pathogen has entered the body, the role of the immune system is to prevent the infectious organism from reproducing and to destroy it

• White blood cells help to defend against pathogens by:

  • Phagocytosis

  • Production of antibodies

  • Production of antitoxins (these are special types of antibodies)

Phagocytosis

• Phagocytes destroy pathogens in a non-specific way through phagocytosis

• The phagocyte:

  • engulfs the pathogen

  • releases enzymes to digest and destroy the pathogen

Production of antibodies

• Antibodies are proteins that are produced by white blood cells known as lymphocytes

• The antibodies produced need to be specific (complementary in shape) to the antigens on the surface of the pathogen

  • This is a specific immune response

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Production of antitoxins

• Some pathogens (usually bacteria) can produce substances that act as toxins and cause illness

• Lymphocytes can produce antibodies against these substances – in this case, they are called antitoxins

• The antitoxins neutralise the effects of the toxin 

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