WJEC (Wales) Biology GCSE

Topic 2.8: Disease, Defence and Treatment

Micro-organisms

• Microscopic organisms visible only under a microscope.
• Types:
  • Bacteria
  • Fungi
  • Viruses
  • Protists
• Beneficial effects include gut bacteria aiding digestion and skin flora reducing infections.

Structure of Micro-organisms

• Bacteria:
  • Single-celled with no nucleus or membrane-bound organelles.
  • Contains chromosomal DNA, plasmid DNA, cytoplasm, cell wall (murein), and cell membrane.
• Viruses:
  • Smaller than bacteria with a core of genetic material and protein coat.
  • Lacks cytoplasm and cell membrane.

Communicable Disease

• Pathogens: disease-causing organisms including bacteria, viruses, and fungi.
• Transmission methods:
  • Direct contact
  • Body fluids
  • Contaminated water/food
  • Animal vectors
  • Airborne pathogens
• Examples:
  • HIV/AIDS:
    • Pathogen: Human immunodeficiency virus
    • Transmission: Infected body fluids
    • Prevention: Safe sex, screening blood, needle exchange
  • Chlamydia:
    • Pathogen: Chlamydia trachomatis
    • Transmission: Sexual contact
    • Prevention: Safe sex, screening
  • Malaria:
    • Pathogen: Plasmodium protist
    • Transmission: Mosquito vectors
    • Prevention: Mosquito nets, repellants, antimalarial tablets

Defence Mechanisms

• Non-specific defence system: Prevents pathogen entry (e.g., skin barrier, blood clotting).
• Immune system: Targets specific pathogens using white blood cells (WBCs).
  • Phagocytes: Engulf and digest pathogens.
  • Lymphocytes: Produce antibodies and antitoxins.

Antigens and Antibodies

• Antigens: Molecules on cell surfaces recognized by the immune system.
• Antibodies: Proteins by lymphocytes, specific to antigens, neutralizing pathogens.
• Memory cells: Provide immunity by remembering pathogens.

Vaccinations

• Prevent diseases by exposure to pathogens to trigger immune response.
• Process:
  1. Administer dead/weakened pathogens.
  2. Antigens trigger antibody production.
  3. Memory cells provide long-term immunity.
• Considerations:
  • Weighing benefits vs. side effects, religious concerns, herd immunity.

Antibiotics

• Kill/inhibit bacteria, no effect on viruses.
• Example: Penicillin by Alexander Fleming.
• Challenges: Antibiotic resistance due to misuse.
• Prevention:
  • Screen new patients.
  • Hygiene in hospitals.
  • Careful prescription practices.

Testing Drugs

• Preclinical Trials:
  • Test on human cells and animals for safety and efficacy.
• Clinical Trials:
  • Test on healthy humans, then on patients for efficacy and dosage.
• Ethical Considerations: Animal testing vs. new technology.

Monoclonal Antibodies

• Identical antibodies produced from a single parent cell.
• Production Process:
  1. Inject antigen into animal.
  2. Extract lymphocytes.
  3. Fuse with myeloma cells (hybridoma).
  4. Culture hybridoma cells.
  5. Collect antibodies.

Medical Uses

• Diagnostic tests (HIV, Chlamydia)
• Tissue typing for transplants
• Monitoring malaria
• Cancer treatments with targeted drugs