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

WJEC GCSE Biology (Wales) — 2.6.1 Pathogens and disease · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

1. The skin forms a tough, dry outer layer that blocks pathogens from entering the body.
2. Mucus lining the airways traps inhaled pathogens.
3. Cilia in the respiratory tract beat rhythmically to move mucus (with trapped pathogens) out of the lungs toward the throat.
4. Stomach acid (hydrochloric acid) destroys pathogens that are swallowed.

Examiner tips

Use the exact terms: skin, mucus, cilia, stomach acid. Include the direction of movement (towards throat).
Show each defence as a separate point to match the 4 marks.

Common mistakes

Confusing mucus with saliva or mistaking cilia for mucus. Omitting the direction of ciliary movement. Using vague terms like "body’s defenses" instead of specific mechanisms.

Mark scheme (4 marks)

The skin acts as a physical barrier that prevents pathogens from entering the body
Mucus in the airways/respiratory tract traps pathogens
Cilia sweep mucus (containing trapped pathogens) away from the lungs / towards the throat
Stomach acid kills pathogens that are swallowed

Key terms in this question

pathogen · physical defence