Physical and chemical barriers

• Non specific immune responses attacks all pathogens:

  • physical barriers
  • chemical defences
  • phagocytes
• A physical barrier is one that traps pathogens and prevents them entering the body.
• A chemical defence is one that kills pathogens.
• Specific immune response attacks specific pathogens:

  • antibodies produced by B lymphocytes (white blood cells)
• Defence mechanisms


  • hydrochloric acid
  • mucus
  • cilia
  • hair
  • lysozyme
  • skin
• Hydrochloric acid


  This is an example of a chemical defence.

  It is found in the stomach.

  It protects the body by killing pathogens from destroying the cell wall of the pathogen.
• Mucus


  This is an example of a physical barrier.

  It is found in the trachea.

  It protects the body as mucus is sticky therefore it traps pathogens.
• Cilia


  This is an example of a physical barrier.

  It is found in the trachea.

  It protects the body as there are tiny hairs that move mucus with trapped pathogens to the back of the throat.

  This will cause a cough(phlem).
• Hair


  This is an example of a physical barrier.

  It is found in the nose.

  It protects the body as it traps pathogens.
• Lysozyme


  This is an example of a chemical defence.

  It is found in tears.

  It protects the body through killing pathogens by destroying the cell wall of the pathogen.
• Skin


  This is an example of a physical barrier.

  It is found all over the body.

  It protects the body as it is impenetrable only when there is an open wound so pathogens can enter. However scabs prevent pathogens entering.
• What is a phagocyte?


  white blood cell
• Phagocytosis 


  • pathogen enters the body.
  • phagocyte engulfs the pathogen.
  • enzymes inside white blood cell destroys pathogen.