Pearson Edexcel · GCSE · Biology
Course version: 1BI0 · Version from Sept 2016
Describe how the physical barriers and chemical defences of the human body…
Full specification wording
Topic 5 – Health, disease and the development of medicines: 5.12 Describe how the physical barriers and chemical defences of the human body provide protection from pathogens, including: a physical barriers, including mucus, cilia and skin b chemical defence, including lysozymes and hydrochloric acid
Pathogens must enter the body to cause harm, so the body blocks and kills them at surfaces.
Checked against the Pearson Edexcel 1BI0 specification (opens in a new tab) on .
- Point 12 of 21
Study notes
From the checked teaching notes for this specification point.
The idea
Pathogens must enter the body to cause harm, so the body blocks and kills them at surfaces. Physical barriers stop entry: intact skin is a tough, dry, keratinised covering that is hard to colonise and sheds outer cells; mucus traps microbes in the airways; cilia are tiny hair-like structures on airway cells that beat to sweep mucus, with trapped pathogens, up and away from the lungs. Chemical defences kill pathogens: lysozymes are enzymes that break down bacterial cell walls, found in tears and saliva; hydrochloric acid in the stomach is strongly acidic and kills many microbes swallowed in food and drink. Together these reduce the chance of infection before the specific immune system is needed.
What earns the marks
- Skin acts as a physical barrier: intact, tough and dry, hard for pathogens to penetrate or colonise.
- Mucus is a sticky physical barrier that traps pathogens in the airways.
- Cilia are hair-like structures that beat to move mucus and trapped pathogens away from the lungs.
- Lysozymes are enzymes that break down bacterial cell walls, present in tears and saliva.
- Hydrochloric acid in the stomach is a chemical defence that kills swallowed pathogens.
- Physical barriers prevent entry, whereas chemical defences kill or damage pathogens.
Common mistakes and how to put them right
Confusing cilia with mucus.
Put it right: Cilia are hair-like structures that beat, while mucus is the sticky substance that traps pathogens.
Thinking skin is a chemical defence.
Put it right: Skin is a physical barrier, though it also has some chemical properties.
Believing lysozymes are found only in the stomach.
Put it right: Lysozymes occur in tears and saliva, while hydrochloric acid is the stomach chemical defence.
Exam tips
- Link each named defence to its location: skin (body surface), mucus and cilia (airways), lysozymes (tears and saliva), hydrochloric acid (stomach).
- State whether a defence is physical (stops entry) or chemical (kills pathogens) to answer the question precisely.
- Use the correct term: cilia beat to move mucus; do not say cilia 'trap' pathogens.
Try the lesson
The start of the Topic 5 – Health, disease and the development of medicines: 5.12 Describe how the physical barriers and chemical defences of the human body provide protection from pathogens, including: a physical barriers, including mucus, cilia and skin b chemical defence, including lysozymes and hydrochloric acid lesson, made from checked teaching notes for this specification point.
Have a go first
Which statement correctly describes how cilia and mucus work together to protect the airways from pathogens?
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