Pathogens, disease and primary defences
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Question
What is a pathogen?
Answer
An **organism or particle that causes disease** — a bacterium, virus, fungus or protist.
Question
Name the four main types of pathogen.
Answer
**Bacteria, viruses, fungi and protists.**
Question
What are the two main ways a pathogen harms the body?
Answer
By **damaging the cells** it infects, and by releasing **toxins** that disrupt how cells work.
Question
What is a primary (first-line) defence?
Answer
A barrier that **stops pathogens entering** the body in the first place — the skin, mucous membranes and stomach acid.
Question
Name the three primary defences.
Answer
The **skin**, the **mucous membranes** (mucus + cilia) and **stomach acid**.
Question
How does the skin defend the body?
Answer
It is a tough, dry **physical barrier** of dead cells that pathogens cannot easily cross while it is unbroken.
Question
How do mucous membranes defend the body?
Answer
They make sticky **mucus** that **traps** pathogens; in the airways, **cilia** then sweep the mucus away.
Question
How does stomach acid defend the body?
Answer
Its strong acid (very **low pH**) **kills most pathogens** that are swallowed in food or mucus — a **chemical** barrier.
Question
Which primary defence is chemical, not physical?
Answer
**Stomach acid** — it chemically kills pathogens. Skin and mucus are physical barriers.
Question
Why are primary defences described as non-specific?
Answer
They work against **any pathogen**, not just one particular kind.
Question
Why is a cut or wound dangerous?
Answer
It **breaks the skin barrier**, giving pathogens a direct way into the body.
Question
Why might less stomach acid increase the risk of gut infection?
Answer
Less acid **kills fewer swallowed pathogens**, so more survive, reach the gut and cause infection.
Question
How can severe watery diarrhoea cause death?
Answer
Through **dehydration** — a large loss of water (and salts) from the body, which can be fatal.
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Topic 3.7 hub
Defence against infectious disease
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