Influenza is a communicable disease caused by a virus. Explain how the human body's defence mechanisms attempt to prevent the influenza virus from entering the body and, if it does enter, how the immune system responds to destroy it.

Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 5.2 Pathogens and infection · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Influenza ('flu') spreads between people via droplets released when an infected person coughs or sneezes. Each year, thousands of people in the UK are hospitalised as a result of influenza infections.

Model answer (5 marks)

1. The mucus lining of the nose, trachea and airways traps the influenza virus before it can enter the body.
2. Cilia move the mucus and trapped virus up and out of the lungs towards the throat, where it is swallowed or expelled.
3. If the virus breaches these barriers, white blood cells such as macrophages engulf and destroy it by phagocytosis.
4. B‑lymphocytes recognise the viral antigen and produce specific antibodies.
5. The antibodies bind to the viral antigens, neutralising the virus or marking it for destruction by other immune cells.

Examiner tips

  • Use the exact terms: mucus, cilia, phagocytosis, B‑lymphocytes, antibodies. Show the sequence: barrier → removal → phagocytosis → antibody response. Keep each point short and to the point to hit the 5 marks.

Common mistakes

  • Mixing up T‑cells for the antibody response. Forgetting to mention the mucus and cilia as the first line of defence. Using vague phrases like "immune system" without specifying the mechanisms.

Mark scheme (5 marks)

  1. The mucus lining of the nose/trachea/airways traps pathogens (including viruses) before they can enter the body
  2. Cilia waft/move the mucus (and trapped pathogens) away from the lungs towards the throat so pathogens are removed
  3. If the virus enters the body, white blood cells / phagocytes can engulf and destroy the pathogen by phagocytosis
  4. B-lymphocytes recognise the specific antigen on the influenza virus and produce complementary antibodies
  5. Antibodies bind to the antigens on the influenza virus, neutralising/marking the virus for destruction / triggering an immune response that destroys the pathogen

Key terms in this question

communicable disease

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