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.