Human Defence Systems
Recap Human Defence Systems for GCSE Biology with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Cover the non-specific defences — skin, nose, trachea and stomach acid — before you explain how white blood cells destroy pathogens.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
The human body has several non-specific defences that stop pathogens entering, and then a specific immune response if they do.
The skin acts as a barrier and produces antimicrobial secretions. The nose contains hairs and mucus that trap particles. The trachea and bronchi are lined with mucus and cilia, which waft mucus and trapped pathogens up to the throat to be swallowed. The stomach produces hydrochloric acid, which kills pathogens in swallowed mucus and food.
If a pathogen gets past these, white blood cells respond in three ways: phagocytosis, in which they engulf and digest pathogens; producing antibodies that target specific pathogens; and producing antitoxins that neutralise bacterial toxins.
Revision notes
Physical and chemical barriers
Skin: a physical barrier that also produces antimicrobial secretions. Nose: hairs and mucus trap particles.
Trachea and bronchi: mucus traps pathogens and cilia waft it to the throat to be swallowed. Stomach: hydrochloric acid kills pathogens.
White blood cell responses
Phagocytosis: the white blood cell engulfs the pathogen and digests it.
Antibody production: antibodies are specific to one pathogen and cause them to clump together for destruction. Antitoxin production: antitoxins neutralise the toxins produced by bacteria.
Specific versus non-specific
The barriers are non-specific — they act against all pathogens equally.
Antibodies are specific: each type recognises one particular pathogen only, which is why immunity to one disease gives no protection against another.
Key points
- Skin is a barrier and produces antimicrobial secretions.
- Nose hairs and mucus trap particles.
- Cilia waft mucus out of the trachea and bronchi.
- Stomach acid kills pathogens.
- White blood cells carry out phagocytosis.
- Antibodies are specific to one pathogen.
Worked examples
Example 1
Describe two ways the body prevents pathogens entering through the breathing system. [2 marks]
Model answer
Mucus in the trachea and bronchi traps pathogens (1 mark), and cilia waft the mucus up to the throat where it is swallowed (1 mark).
Example 2
Describe three ways white blood cells defend the body against pathogens. [3 marks]
Model answer
They engulf and digest pathogens by phagocytosis (1 mark). They produce antibodies that target specific pathogens (1 mark). They produce antitoxins that neutralise the toxins made by bacteria (1 mark).
Example 3
Explain why being immune to measles does not protect a person against mumps. [2 marks]
Model answer
Antibodies are specific to one particular pathogen (1 mark), so the antibodies made against the measles virus will not recognise or destroy the mumps virus (1 mark).
Common mistakes
Saying white blood cells eat pathogens.
The correct term is engulf and digest, or phagocytosis.
Confusing antibodies with antitoxins.
Antibodies target the pathogen itself; antitoxins neutralise the toxins it produces.
Forgetting the stomach acid.
It is one of the required non-specific defences.
Saying antibodies work against any pathogen.
Each antibody is specific to one pathogen only.
Exam tips
- Learn the barriers as a route through the body: skin, nose, trachea, stomach.
- Use the three white blood cell responses as a set of three marks.
- Say specific when describing antibodies.
- Use the word phagocytosis if you can spell it confidently.
Key terms
- Phagocytosis
- The engulfing and digesting of pathogens by white blood cells.
- Antibody
- A protein produced by white blood cells that targets a specific pathogen.
- Antitoxin
- A substance that neutralises bacterial toxins.
- Cilia
- Tiny hairs that waft mucus out of the airways.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.