UK Revision Notes

B3 – Infection and Reponse

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💥 Communicable Diseases

Communicable diseases are infectious – they spread between people or animals and are caused by pathogens.

🔬 Types of Pathogens

  1. Bacteria
    • Tiny cells that reproduce rapidly
    • Release toxins that damage tissues
    • Example: Salmonella, Gonorrhoea
  2. Viruses
    • Much smaller than bacteria
    • Invade and reproduce inside cells, causing them to burst
    • Example: HIV, Measles
  3. Fungi
    • Some are single-celled; others have hyphae (thread-like structures)
    • Can grow and penetrate skin/plants
    • Example: Athlete’s foot, Rose black spot
  4. Protists
    • Single-celled organisms, often carried by vectors (e.g. mosquitoes)
    • Example: Malaria caused by a protist spread by Anopheles mosquitoes

🔄 How Pathogens Spread

  • Air – Droplets from coughing/sneezing (e.g. flu, measles)
  • Water – Contaminated water or food (e.g. cholera)
  • Direct contact – Touching contaminated surfaces or people (e.g. athlete’s foot)

🧬 Examples of Diseases

Virus

  • Measles – Fever, rash, can be serious; prevented by MMR vaccine
  • HIV – Initially flu-like, attacks immune system; treated with antiretroviral drugs
  • TMV (Tobacco Mosaic Virus) – Affects plants, causes discolouration, reduces photosynthesis

Bacteria

  • Salmonella – Food poisoning, vomiting and diarrhoea; prevented by poultry vaccination
  • Gonorrhoea – STD, pain when urinating, discharge; treated with antibiotics

Fungus

  • Rose black spot – Purple/black spots on leaves; affects growth; treated with fungicides and removing affected leaves

Other

  • Malaria – Mosquito-borne, causes fever, can be fatal; prevented by mosquito nets and killing mosquitoes

🧫 The Body’s Defence System

Your body has several ways to stop pathogens:

1️⃣ Physical Barriers

  • Skin – Tough and waterproof
  • Hairs and mucus in nose – Trap particles
  • Stomach acid – Kills pathogens in food/drink

2️⃣ Immune System (White Blood Cells)

  • Phagocytosis – Engulf and digest pathogens
  • Antibody production – Target specific antigens
  • Antitoxin production – Neutralise toxins from bacteria

💉 Vaccinations

Vaccines contain small amounts of dead or inactive pathogens. This:

  • Triggers an immune response (white blood cells produce antibodies)
  • Prepares the body for future infections
  • Leads to immunity

Herd immunity protects the whole population if enough people are vaccinated.

💊 Treating Disease

1️⃣ Painkillers

  • E.g. paracetamol
  • Relieve symptoms but don’t kill pathogens

2️⃣ Antibiotics

  • Kill bacteria, not viruses
  • E.g. Penicillin
  • Antibiotic resistance is a growing problem (e.g. MRSA)

🧪 Developing New Drugs

Stages of Drug Development:

  1. Preclinical Testing – Tested on cells and animals
  2. Clinical Trials –
    • Small group of healthy volunteers (check safety)
    • Then tested on patients (check effectiveness + dosage)

Double-Blind Trials

  • Neither doctor nor patient knows who gets real drug/placebo
  • Reduces bias

🌿 Plant Defences

Plants can get diseases too. They have:

  • Physical defences: waxy cuticle, bark, cell walls
  • Chemical defences: antibacterial chemicals, poisons
  • Mechanical defences: thorns, hairy stems, leaves that curl when touched

Identifying plant disease: spots, stunted growth, decay, discolouration

  • Tools: gardening books, lab testing, monoclonal antibodies

Usefull Sources

📘 Revision Notes & Guides

  • BBC Bitesize – Infection and Response
    Interactive explanations, diagrams, and quizzes tailored to the AQA specification.
    👉 (bbc.co.uk)
  • Physics & Maths Tutor – Topic 3: Infection and Response
    Comprehensive notes, flashcards, mind maps, and exam-style questions.
    👉 (physicsandmathstutor.com)
  • Save My Exams – Infection and Response
    Concise revision notes with diagrams and exam tips.
    👉 (savemyexams.com)

🖨️ Printable Resources

🎮 Interactive & Gamified Tools

  • Quizlet – B3 Infection and Response Flashcards
    Pre-made flashcards covering key terms and concepts.
    👉 (quizlet.com)
  • Knowunity – B3 Infection and Response Notes
    Student-made summaries with examples of diseases and prevention methods.
    👉 (knowunity.co.uk)

🎥 Video Tutorials

  • AQA GCSE Biology in 10 Minutes! | Topic 3 – Infection and Response
    A concise video covering the entire topic, ideal for quick revision.
    👉 (youtube.com)
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