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Overview of Pathogens and Human Defense

Apr 24, 2025

Notes on AQA Biology GCSE: Infection and Response

Introduction to Pathogens

  • Definition: Microorganisms (viruses, bacteria) that cause diseases in animals/plants.
  • Dependency: Depend on host for growth, reproduction, and nutrients.
  • Effect: Produce toxins damaging tissues, causing illness.

Avoidance and Defense Against Pathogens

  • Disease Prevention: Reduce contact with pathogens.
  • Body Barriers: Skin, mucus, stomach acid, immune system responses.
  • Immune System: Destroys pathogens, can be enhanced through vaccination.

Antibiotics

  • Development: Since 1940s; successful against bacterial diseases.
  • Resistance: Many bacteria have become resistant, necessitating new antibiotic development.

Communicable Diseases

4.3.1.1 Communicable (Infectious) Diseases

  • Spread of Diseases:
    • Via direct contact, water, air.
    • Caused by viruses, bacteria, protists, fungi.
  • Pathogens:
    • Bacteria: Rapid reproduction, produce toxins.
    • Viruses: Live and reproduce inside cells.

4.3.1.2 Viral Diseases

  • Measles:
    • Symptoms: Fever, rash; can be fatal.
    • Prevention: Vaccination, spread via droplets.
  • HIV:
    • Initial symptoms: Flu-like; progresses to AIDS if untreated.
    • Spread: Sexual contact, blood.
  • Tobacco Mosaic Virus (TMV):
    • Affects plants, causes leaf discoloration, impedes photosynthesis.

4.3.1.3 Bacterial Diseases

  • Salmonella:
    • Spread: Contaminated food.
    • Symptoms: Fever, cramps, vomiting, diarrhea.
  • Gonorrhoea:
    • Spread: Sexual contact.
    • Symptoms: Discharge, pain; resistant to penicillin.

4.3.1.4 Fungal Diseases

  • Rose Black Spot:
    • Symptoms: Black spots on leaves, reduced photosynthesis.
    • Spread: Water, wind; treated with fungicides.

4.3.1.5 Protist Diseases

  • Malaria:
    • Vector: Mosquitoes.
    • Symptoms: Fever, potentially fatal.
    • Control: Prevent mosquito breeding, use nets.

Human Defence Systems

  • Non-Specific Defences:
    • Skin, nose, trachea, bronchi, stomach.
  • Immune System:
    • White blood cells (phagocytosis, antibody production, antitoxin production).

Vaccination

  • Mechanism: Introduces inactive pathogen to stimulate antibody production.
  • Effectiveness: Quick response on re-exposure, prevents infection.

Antibiotics and Painkillers

  • Antibiotics:
    • Cure bacterial diseases by killing bacteria.
    • Resistance is a concern.
  • Painkillers: Alleviate symptoms, do not kill pathogens.

Drug Discovery and Development

  • Historical Drugs: Extracted from plants/microorganisms.
    • Examples: Digitalis (foxgloves), Aspirin (willow), Penicillin (mould).
  • New Drug Testing:
    • Preclinical: Labs, animals.
    • Clinical: Human trials, double-blind tests.

Monoclonal Antibodies (Biology Only)

4.3.2.1 Production

  • Process: From a clone of cells, specific to one protein.
  • Use: Produced using mouse lymphocytes and tumour cells (hybridoma).

4.3.2.2 Uses

  • Applications:
    • Diagnosis (e.g., pregnancy tests).
    • Lab research (detect pathogens, measure hormones).
    • Treatment (target cancer cells).

Plant Disease Detection and Identification

  • Symptoms: Stunted growth, spots, decay, growths, discoloration.
  • Pathogen Identification: Manuals, lab testing, monoclonal antibodies.
  • Deficiency Conditions:
    • Nitrate deficiency: Stunted growth.
    • Magnesium deficiency: Chlorosis.

Plant Defence Responses

  • Physical: Cell walls, waxy cuticles, dead cell layers.
  • Chemical: Antibacterial chemicals, poisons.
  • Mechanical: Thorns, mimicry.

Key Skills Development

  • Understanding and applying scientific knowledge to real-world contexts.
  • Evaluation of scientific methods and ethical considerations.