What are non-specific defence mechanisms?

Defences that act quickly and respond in the same way for all pathogens.


There are two types of non-specific defence mechanism:

  1. Physical and chemical barriers that prevent the entry of pathogens
  2. Phagocytosis

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What are specific defence mechanisms?

Defences that act more slowly and produce specific responses for each pathogen.


There are two types of specific defence mechanism:

  1. The cellular response
  2. The humoral response

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How does the skin act as a physical barrier?

The skin acts as a physical barrier as it blocks pathogens from entering the body.

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How does the skin act as a chemical barrier?

The skin acts as a chemical barrier as it produces sebum, an antimicrobial substance that lowers pH.

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How does blood clotting defend against pathogens?

Blood clotting seals wounds and forms a scab to block entry of pathogens.

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What are antigens?

Antigens are unique molecules or proteins found on the surface of cells. 


They allow the immune system to distinguish between self and non-self cells.

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Why can transplanted organs be rejected?

Because the cells may have different antigens and are identified as foreign.

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Which cells or molecules can the immune system identify?

  1. Pathogens
  2. Abnormal body cells
  3. Toxins
  4. Cells from other organisms of the same species 

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