6.3  Defence Against Infectious Disease

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Essential Idea:

The human body has structures and processes that

resist the continuous threat of invasion by pathogens


  • The skin and mucous membranes form a primary defence against pathogens that cause infectious disease
  • Cuts in the skin are sealed by blood clotting
  • Clotting factors are released from platelets
  • The cascade results in the rapid conversion of fibrinogen to fibrin by thrombin
  • Ingestion of pathogens by phagocytic white blood cells gives non-specific immunity to disease
  • Production of antibodies by lymphocytes in response to particular pathogens gives specific immunity
  • Antibiotics block processes that occur in prokaryotic cells but not in eukaryotic cells
  • Viruses lack a metabolism and cannot therefore be treated with antibiotics
  • Some strains of bacteria have evolved with genes that confer resistance to antibiotics and some strains of bacteria have multiple resistance


  • Causes and consequences of blood clot formation in coronary arteries
  • Florey and Chain’s experiments to test penicillin on bacterial infections in mice
  • Effects of HIV on the immune system and methods of transmission