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Learn4BI1Paper 2B · Paper 2 (all content)Structure and functions in living organismsDisease and immunity
Structure and functions in living organisms · Subtopic 7 of 21

Disease and Immunity

Pathogens cause disease and spread by direct contact (blood, body fluids) or indirectly (air, water, food, vectors). The body's defences: skin, mucus and cilia, stomach acid, then white blood cells. Each pathogen carries antigens; lymphocytes make antibodies with complementary shapes that bind to them, marking pathogens for destruction. Memory cells remain, giving active immunity: a second infection is fought off faster and stronger. Vaccines contain harmless antigens to trigger this. Passive immunity (antibodies from breast milk or injection) is short-lived.

Cambridge 5090 Paper 1Cambridge 5090 Paper 2Cambridge 0610 Papers 2, 4Cambridge 0610 Papers 1, 3Edexcel 4BI1 Paper 1BEdexcel 4BI1 Paper 2B≈ 40 minRevision 1 · updated 2026-10-30
Section 1 of 14

Learning objectives

  • Describe how pathogens spread and the body's defences.
  • Explain the roles of antigens, antibodies and memory cells.
  • Compare active and passive immunity and explain vaccination.
Pause and think

Why do you usually catch chickenpox only once, but can catch a cold many times?

Section 2 of 14

Core idea

Start hereRemember the enemy

Your immune system has a memory. Meet a pathogen once and it can recognise it decades later, often destroying it before you even feel ill.

The big idea

Barriers keep most pathogens out. Those that get in carry antigens that trigger lymphocytes to make specific antibodies, and memory cells give long-term immunity.

1. The immune response

Fighting a pathogen

Specific antibodies and long-lasting memory.

Worked exampleActive vs passive

Compare a tetanus vaccine with an injection of anti-tetanus antibodies after a deep cut.

Goal
Type and duration of immunity.
Strategy
Who makes the antibodies?
  1. vaccine: active\text{vaccine: active}
    Your lymphocytes make antibodies and memory cells; long-lasting.
  2. antibody injection: passive\text{antibody injection: passive}
    Immediate protection but no memory cells; short-lived.
AnswerVaccine for long-term; antibodies for immediate emergency protection.
✓ CheckBoth are used after injuries ✓.
Exam tipHerd immunity When most of a population is vaccinated, the pathogen can't spread easily, protecting those who can't be vaccinated.
Pause and think

Why is a new flu vaccine needed every year?

Summary

  • Barriers first.
  • Antibodies are specific.
  • Memory cells, vaccines, active vs passive.
Key words
Antigen
Molecule on a pathogen that triggers an immune response.
Antibody
Protein made by lymphocytes that binds to a specific antigen.
Vaccine
Harmless antigens given to produce active immunity.
HistoryJenner and smallpox. In 1796 Edward Jenner inoculated a boy with cowpox and showed he became immune to smallpox. Global vaccination eradicated smallpox in 1980.
Fun factBillions of antibodies. Your immune system can make antibodies matching an estimated billions of different antigen shapes, including for pathogens it has never met.
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