How does the human body defend itself against pathogens?
The non-specific defences of the body (skin, nose, trachea, bronchi and stomach acid) and the role of the immune system, including phagocytosis, antibody production and antitoxins.
A focused answer to AQA GCSE Biology 4.3.1.2, covering the non-specific defences of the body and the role of white blood cells in phagocytosis, antibody production and antitoxin production.
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What this dot point is asking
AQA wants you to describe the body's non-specific defences against pathogens, and explain the three ways white blood cells of the immune system protect us: phagocytosis, producing antibodies, and producing antitoxins.
Non-specific defences
These first-line defences work against all pathogens, not just one type, and they try to stop pathogens entering the body in the first place:
- Skin: a physical barrier that pathogens cannot easily cross; it also makes antimicrobial secretions and scabs over wounds to seal them.
- Nose: hairs and mucus trap particles and pathogens in the air that is breathed in.
- Trachea and bronchi: lined with mucus that traps pathogens, and with cilia (tiny hair-like structures) that waft the mucus up and away from the lungs to be swallowed.
- Stomach: produces hydrochloric acid that kills most pathogens in swallowed food, drink and mucus.
The immune system
If a pathogen gets past the non-specific defences and enters the body, the immune system attacks it. The key cells are the white blood cells, which defend the body in three ways:
Because antibodies are specific to one pathogen's antigens, the body must make a different antibody for each pathogen. The first time a pathogen is met, this takes time, which is why you can feel ill before recovering. After the infection, memory cells remain, which is the basis of immunity and of how vaccines work.
It is worth being clear about the difference between the two stages of defence. The non-specific defences (skin, mucus, cilia, stomach acid) are always present and act against any pathogen, forming the body's first line. The immune response is specific: it is triggered only after a particular pathogen enters, and the antibody made fits the antigens of that one pathogen. AQA questions often combine the two, for example asking you to describe how a pathogen breathed in is first trapped by mucus and cilia (non-specific), and then, if it gets through, attacked by white blood cells through phagocytosis and antibody production (specific). Being able to keep these two stages separate while seeing how they work together is the understanding the higher-mark questions reward.
Try this
Q1. State two non-specific defences of the body and how each works. [2 marks]
- Cue. Skin (barrier) and stomach acid (kills pathogens); also nose, trachea and bronchi.
Q2. Describe the three ways white blood cells defend the body. [3 marks]
- Cue. Phagocytosis (engulfing pathogens), producing antibodies, and producing antitoxins.
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20194 marksDescribe how white blood cells defend the body against a pathogen that has entered the blood.Show worked answer →
A 4-mark describe question rewards the three roles of white blood cells.
Some white blood cells carry out phagocytosis: they engulf the pathogen and digest it. Other white blood cells (lymphocytes) produce antibodies. Each antibody has a shape complementary to the antigens on a specific pathogen, so it binds to that pathogen and marks it for destruction, and antibodies can also cause pathogens to clump together. White blood cells also produce antitoxins, which neutralise the toxins released by bacteria.
Markers reward phagocytosis (engulfing), antibody production with the idea of specificity to antigens, and antitoxin production.
AQA 20213 marksExplain how the non-specific defences of the body reduce the chance of a pathogen causing disease. Refer to at least three defences.Show worked answer →
A 3-mark explain question rewards three defences each with how it works.
The skin acts as a physical barrier that stops pathogens entering, and a scab seals a wound. The nose has hairs and mucus that trap pathogens in the air before they reach the lungs. The trachea and bronchi are lined with mucus that traps pathogens and cilia that waft the mucus up away from the lungs. The stomach produces hydrochloric acid, which kills pathogens in swallowed food and mucus.
Markers reward any three correct defences, each linked to how it stops or kills pathogens.
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Sources & how we know this
- AQA GCSE Biology (8461) specification — AQA (2016)