Defence against infectious disease

Nature of science:

Risks associated with scientific research—Florey and Chain’s tests on the safety of penicillin would not be compliant with current protocol on testing. (4.8)

• 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 diseases.
• 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.

Applications and skills:

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

• The spread and containment of diseases such as bird flu require international coordination and communication.

Utilization:

• An understanding of immunity has led to the development of vaccinations.
  • Syllabus and cross-curricular links:
  • Biology
  • Topic 5.2 Natural selection
  • Chemistry
  • Topic D2 Aspirin and penicillin

Aims:

• Aim 8: The social as well as the economic benefits of the control of bacterial diseases around the world should be stressed.
• Aim 9: Science has limited means in the fight against pathogens, as shown by the spread of new diseases and antibiotic-resistant bacteria.

• Diagrams of skin are not required.
• Subgroups of phagocyte and lymphocyte are not required but students should be aware that some lymphocytes act as memory cells and can quickly reproduce to form a clone of plasma cells if a pathogen carrying a specific antigen is re-encountered.
• The effects of HIV on the immune system should be limited to a reduction in the number of active lymphocytes and a loss of the ability to produce antibodies, leading to the development of AIDS.