Human defence systems — AQA GCSE Biology
Test yourself on Human defence systems with AQA GCSE practice questions.
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Human defence systems explained
Non-specific defences stop pathogens entering the body or trap and destroy them before they cause infection.
Read the full explanation
They are not tailored to one pathogen. The skin is a physical barrier: its outer layer of dead cells is tough, and glands secrete antimicrobial substances. The nose has hairs and sticky mucus that trap particles and microorganisms in inhaled air. In the trachea and bronchi, ciliated epithelial cells beat mucus, with trapped pathogens, upwards towards the throat to be swallowed. The stomach contains hydrochloric acid, which is very acidic and kills many pathogens that are swallowed in food, drink or mucus. Together these defences reduce the chance of pathogens reaching tissues where they could multiply.
Your focus
- Describe how the skin, nose, trachea and bronchi, and stomach defend the body.
- Explain how each defence prevents pathogens from causing infection.
- Distinguish non-specific defences from specific immune responses.
Human defence systems exam tips
Marking Points
- Non-specific defences act against many pathogens and are not targeted at one specific pathogen.
- The skin acts as a physical barrier and produces antimicrobial secretions.
- The nose traps pathogens using hairs and sticky mucus.
- The trachea and bronchi are lined with cilia that move mucus containing pathogens away from the lungs.
- The stomach produces hydrochloric acid, which kills many swallowed pathogens.
- Mucus and cilia work together to remove pathogens from the airways.
Examiner Tips
- 💡Name each defence and state exactly how it stops pathogens, using the correct structure.
- 💡Use the words mucus and cilia accurately and link them to the airways.
- 💡For the stomach, name hydrochloric acid rather than just saying acid.
Common Mistakes
- Calling these defences specific to one pathogen; the correction is that they are non-specific and act against many pathogens.
- Saying cilia trap pathogens; the correction is that mucus traps pathogens and cilia move the mucus.
- Saying the stomach produces enzymes that kill pathogens; the correction is that hydrochloric acid kills them.