Mechanisms of Defence (WJEC GCSE Biology: Combined Science)

• The human body defends itself against disease in many ways
• One example is the skin
  • The skin is a structures that make it difficult for pathogens to get into the body
    • It covers almost all parts of your body to prevent infection
    • If the skin is cut or grazed, blood clots form to seal wounds by forming a scab
    • This prevents the entry of pathogens
  • On the surface of the skin is a community of micro-organisms called the skin flora
    • These bacteria compete with any invading pathogenic bacteria preventing them from becoming established
• If pathogens enter the body, different defence mechanisms are activated
• For example, through activation of white blood cells
• Different types of white blood cells work to prevent pathogens from reaching areas of the body they can replicate in
  • Phagocytes engulf and digest pathogenic cells
  • Lymphocytes
    • produce antibodies which clump pathogenic cells together so they can’t move as easily, and release chemicals that signal to other cells that they must be destroyed
    • produce antitoxins which counteract the toxins produced by bacteria

Phagocyte ingesting a pathogen diagram

Phagocytes engulf pathogens and digest them to prevent them causing harm