AQA GCSE Biology: Infection and Response

Pathogens and Diseases

• Pathogens: Microorganisms like viruses and bacteria causing diseases in animals and plants.
  • Depend on host for growth and reproduction
  • Produce toxins causing tissue damage and illness
• Disease Avoidance:
  • Reduce contact with pathogens
  • Use natural barriers (skin, mucous membranes)
• Immune System:
  • Destroys pathogens, preventing disease
• Vaccination: Enhances natural defense against specific diseases
• Antibiotics: Used since the 1940s to treat bacterial diseases, but resistance is a growing problem

Communicable Diseases

4.3.1.1 Infectious Diseases

• Pathogen Spread:
  • Via direct contact, water, or air
  • Bacteria and viruses reproduce rapidly inside the body
  • Bacteria produce toxins; viruses cause cell damage

4.3.1.2 Viral Diseases

• Measles:
  • Symptoms: fever, red rash
  • Spread by droplets; vaccination important
• HIV/AIDS:
  • Initial flu-like symptoms, attacks immune cells
  • Spread by sexual contact, blood exchange
  • Managed with antiretroviral drugs
• Tobacco Mosaic Virus (TMV):
  • Affects plants, causing leaf discoloration

4.3.1.3 Bacterial Diseases

• Salmonella:
  • Spread by contaminated food
  • Symptoms: fever, cramps, vomiting, diarrhea
• Gonorrhoea:
  • STD, symptoms include discharge, pain
  • Treat with antibiotics; resistant strains exist

4.3.1.4 Fungal Diseases

• Rose Black Spot:
  • Causes leaf spots, reduced photosynthesis
  • Spread by water/wind; treat with fungicides

4.3.1.5 Protist Diseases

• Malaria:
  • Spread by mosquitos
  • Symptoms include recurrent fever
  • Control by reducing mosquitos and using nets

Human Defence Systems

• Non-Specific Defences:
  • Skin, nose, trachea, bronchi, stomach
• White Blood Cell Roles:
  • Phagocytosis, antibody, and antitoxin production

Vaccination

• Prevents illness by stimulating antibody production
• Herd Immunity: Reduces pathogen spread by immunizing large populations

Antibiotics and Painkillers

• Antibiotics: Cure bacterial diseases by killing bacteria
• Resistance: A major concern in bacteria
• Painkillers: Address symptoms but don’t kill pathogens

Discovery and Development of Drugs

• Drug Discovery:
  • Extracted from plants/microorganisms (e.g., digitalis, aspirin, penicillin)
  • New drugs are synthetically produced
• Testing Stages:
  • Preclinical (cells, tissues, animals)
  • Clinical (human volunteers)
  • Double-blind trials used for efficacy

Monoclonal Antibodies (Biology Only)

4.3.2.1 Production

• Produced by hybridoma technology combining mouse lymphocytes with tumor cells

4.3.2.2 Uses

• Diagnostics (e.g., pregnancy tests), research, treatment (e.g., cancer)
• Ethical considerations and side effects exist

Plant Disease (Biology Only)

4.3.3.1 Detection and Identification

• Symptoms: Stunted growth, spots, rot, growths, discoloration
• Identification Tools: Manuals, lab testing, monoclonal antibody kits

4.3.3.2 Defence Responses

• Physical Defenses: Cell walls, waxy cuticle, bark
• Chemical Defenses: Antibacterial chemicals, poisons
• Mechanical Defenses: Thorns, drooping leaves, mimicry

Understanding these topics is crucial for evaluating disease prevention and treatment strategies in both human and plant health.