Human Defence Systems — GCSE Biology Revision
Revise Human Defence Systems for GCSE Biology. Step-by-step explanation, worked examples, common mistakes and exam-style practice aligned to AQA, Edexcel, OCR, WJEC, Eduqas, CCEA, Cambridge International (CIE), SQA, IB, AP.
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Go to VaccinationWhat is Human Defence Systems?
The human body has several non-specific defence systems to prevent pathogens from entering. These include the skin as a physical barrier, mucus in the respiratory tract to trap pathogens, and hydrochloric acid in the stomach to kill bacteria. If pathogens do enter, the immune system mounts a specific attack using white blood cells.
Board notes: Covered by all major boards (AQA, Edexcel, OCR). The distinction between non-specific and specific defences is a key concept.
Step-by-step explanationWorked example
If you get a cut, bacteria can enter the body. Platelets clot the blood to seal the wound. Phagocytic white blood cells are attracted to the area and engulf any invading bacteria. Meanwhile, lymphocytes that recognise the bacteria will start to multiply and produce specific antibodies to help clear the infection.
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Common mistakes
- 1Forgetting the non-specific defences. The skin, tears, and stomach acid are the body's first line of defence and are crucial for preventing infection before the immune system even gets involved.
- 2Confusing the different types of white blood cells. Phagocytes engulf and digest pathogens (phagocytosis), while lymphocytes produce specific antibodies to neutralise pathogens and antitoxins to counteract toxins.
- 3Thinking the immune system is instantaneous. There is a time lag between infection and the production of enough specific antibodies to fight it off, which is why you feel ill.
Human Defence Systems exam questions
Exam-style questions for Human Defence Systems with mark-scheme style solutions and timing practice. Aligned to AQA, Edexcel, OCR, WJEC, Eduqas, CCEA, Cambridge International (CIE), SQA, IB, AP specifications.
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Step-by-step method
Step-by-step explanation
4 steps · Worked method for Human Defence Systems
Core concept
The human body has several non-specific defence systems to prevent pathogens from entering. These include the skin as a physical barrier, mucus in the respiratory tract to trap pathogens, and hydrochl…
Frequently asked questions
What is the body's first line of defence against infection?
The body's first line of defence is a series of non-specific barriers, including the skin, mucous membranes that trap microbes, and chemical barriers like stomach acid and enzymes in tears.
How do white blood cells fight infection?
White blood cells fight infection in two main ways: phagocytes engulf and destroy pathogens, and lymphocytes produce specific antibodies that lock onto pathogens and antitoxins that neutralise the toxins they produce.