Describe how the body's physical defences help to prevent pathogens from entering the body.

OCR GCSE Biology A: Gateway Science (J247) — B6.3 Monitoring and maintaining health · Describe · 4 marks · View as Markdown

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

A student learns that the human body has several layers of defence against communicable diseases. The first line of defence involves physical and chemical barriers that stop pathogens before they can cause infection.

Model answer (4 marks)

The skin forms a tough, dry outer layer that physically blocks pathogens from entering the body.

Mucus lining the airways traps inhaled pathogens.

Cilia in the respiratory tract beat rhythmically to move the mucus (and trapped pathogens) upward toward the throat where they can be swallowed or expelled.

Stomach acid (hydrochloric acid) in the stomach destroys pathogens that are swallowed, preventing them from reaching the intestines.

Examiner tips

  • Use the exact terms: skin, mucus, cilia, stomach acid. Explain the action of each defence. Keep each point brief but clear.
  • common_mistakes
  • :
  • Confusing mucus with saliva. Omitting the role of cilia. Forgetting that stomach acid is hydrochloric acid.

Mark scheme (4 marks)

  1. The skin acts as a physical barrier to pathogens
  2. Mucus in the airways traps pathogens / airborne pathogens
  3. Cilia beat / waft to move mucus (and trapped pathogens) away from the lungs / up towards the throat
  4. Stomach acid / hydrochloric acid kills pathogens that are swallowed

Key terms in this question

pathogen

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