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How does the body defend against pathogens, and how does immunisation work?

Describe the physical and chemical defences of the human body, the role of the specific immune system including antigens, antibodies and memory cells, and explain how immunisation works.

A focused answer to Edexcel GCSE Biology 5.12 to 5.15B, covering the body's physical and chemical barriers, the specific immune response with antigens, antibodies and memory cells, immunisation, and herd immunity.

Generated by Claude Opus 4.810 min answer

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  1. What this dot point is asking
  2. Physical and chemical defences
  3. The specific immune system
  4. Immunisation
  5. Try this

What this dot point is asking

Edexcel statements 5.12 to 5.15B want you to describe the body's physical and chemical defences, explain the specific immune system (antigens, antibodies and memory cells), explain how immunisation works, and discuss the advantages and disadvantages of immunisation including herd immunity (5.15B Biology only).

Physical and chemical defences

These defences are non-specific, meaning they act against any pathogen rather than one in particular.

The specific immune system

When a pathogen gets past the barriers, the immune response follows these steps:

  1. The body is exposed to the pathogen, which carries antigens recognised as foreign.
  2. The antigens trigger lymphocytes to produce antibodies, proteins with a shape that exactly matches the antigen and binds to it, marking the pathogen for destruction.
  3. Once the pathogen is destroyed, some lymphocytes remain as memory cells.

The memory cells are the key to long-term immunity: if the same pathogen returns, they make the correct antibodies faster and in larger amounts, so the person destroys it before becoming ill. This is the secondary response.

Immunisation

Immunisation (vaccination) uses the memory-cell idea to protect people before they ever meet the live pathogen:

  1. A vaccine containing a dead or inactive form of the pathogen (carrying its antigens) is injected. It cannot cause the disease.
  2. The antigens trigger the immune system to make antibodies and memory cells, just as a real infection would.
  3. If the live pathogen later enters the body, the memory cells produce antibodies quickly, destroying it before illness develops.

Try this

Q1. State one physical and one chemical defence of the human body. [2 marks]

  • Cue. Physical: skin, mucus or cilia. Chemical: stomach acid or lysozyme in tears.

Q2. Explain the role of memory cells in immunity. [2 marks]

  • Cue. Memory cells remain after an infection and, on re-exposure, make the correct antibodies faster and in larger amounts, destroying the pathogen before illness.

Exam-style practice questions

Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

Edexcel 20194 marksExplain how the specific immune system responds when a pathogen enters the body for the first time.
Show worked answer →

A 4-mark explain question rewards the steps of the specific immune response.

  1. The pathogen carries antigens (molecules on its surface) that the body recognises as foreign.
  2. The antigens trigger an immune response in which white blood cells called lymphocytes are activated.
  3. The lymphocytes produce specific antibodies that bind to the antigens, helping to destroy the pathogen.
  4. Some lymphocytes become memory cells, which stay in the body so a faster, stronger response can be made if the same pathogen returns.

Markers reward antigens recognised as foreign, antibody production by lymphocytes, and the formation of memory cells. Confusing antibodies with antigens, or leaving out memory cells, loses marks.

Edexcel 20214 marksExplain how immunisation with an inactive form of a pathogen makes a person immune to a disease.
Show worked answer →

A 4-mark explain question rewards the link from vaccine to memory cells.

  1. The vaccine contains a dead or inactive form of the pathogen, carrying its antigens, which cannot cause the disease.
  2. The antigens trigger the immune system to produce the specific antibodies, just as a real infection would.
  3. Memory cells are produced and remain in the body.
  4. If the live pathogen later enters, the memory cells make the correct antibodies quickly and in large amounts, destroying the pathogen before the person becomes ill.

Markers reward the inactive pathogen carrying antigens, antibody and memory-cell production, and the fast secondary response on re-exposure. Saying the vaccine gives you antibodies directly is wrong; the body makes its own.

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