Preventing and identifying disease

• Non-specific defence


  • Always present

  • Same for all organisms

  • Prevents pathogens from entering the body
• Examples of the body’s physical defence system

  • Skin - protective surface barrier

  • Blood clotting - platelets seal wounds preventing entry of pathogens into the blood

  • Respiratory tract - mucus traps pathogens, cilia waft mucus to the back of the throat where it is swallowed
• Examples of the body’s chemical defence system

  • Tears - contain lysozyme which digests bacterial cell walls, killing bacteria and protecting the eye

  • Hydrochloric acid in stomach - acidic pH kills pathogens that are swallowed
• The immune system 


  • The body’s defence against pathogens once they have entered the body

  • Aims to prevent or minimise disease caused by pathogens
• How do white blood cells detect pathogens in the body?

  Pathogens have unique antigens on their surface which are detected by specialised receptors on white blood cells
• How does the immune system destroy pathogens?

  • B-lymphocytes produce antibodies in response to a particular antigen and binds to it

  • Each antibody is specific to an antigen and binds to it

  • Antibodies ‘tag’ pathogens or clump them together, disabling them so that they can be killed by other white blood cells
• Memory lymphocytes


  • WBCs produced in response to a foreign antigen that remain in the body after a pathogen has been destroyed

  • Provide immunity - if the body is re-infected, antibodies are produced more rapidly and the pathogen is destroyed before it can produce disease symptoms
• Compare the primary and secondary immune responses

  The secondary immune response produces antibodies more rapidly and in higher concentrations than in the primary response. The pathogen is destroyed before it can cause symptoms.
• Vaccination 


  • Deliberate exposure of an individual to foreign antigens

  • Triggers an immune response (produces antibodies) and provides immunity (due to memory cells)

  • The individual does not contract the disease that they are being immunised against
• Describe the components of a vaccine

  Dead, weakened or inactive pathogens with their surface antigens still present
• Herd immunity


  Vaccination of a significant proportion of the population gives some protection to individuals who are not immune