Topic 5 of 8 · Form 4
Diseases and immunity
Pathogens (bacteria, viruses, fungi, protoctists) cause transmissible diseases spread by direct contact, contaminated food and water, air and vectors (e.g. Anopheles mosquitoes and malaria).
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Pathogens and transmissible diseases
Pathogens (bacteria, viruses, fungi, protoctists) cause transmissible diseases spread by direct contact, contaminated food and water, air and vectors (e.g. Anopheles mosquitoes and malaria).
Body defences
Skin, mucus and cilia, stomach acid, blood clotting; white blood cells – phagocytes engulf pathogens; lymphocytes produce antibodies specific to antigens.
Immunity
- Active immunity: the body makes its own antibodies and memory cells after infection or vaccination – long-lasting.
- Passive immunity: antibodies received from another source (breast milk, across the placenta) – short-term.
- Vaccination programmes control diseases such as measles and polio.
Controlling disease
Clean water supply, sanitation, hygiene, food safety, vector control (mosquito nets, removing breeding sites), antibiotics for bacterial infections (not viruses) and the problem of antibiotic resistance.
Cholera and HIV
Cholera bacteria release a toxin causing loss of water and ions from the gut (treatment: oral rehydration). HIV attacks lymphocytes, weakening the immune system; spread by sexual contact, blood and from mother to child; managed with antiretroviral drugs.
Check yourself
- What is an antigen?
- Distinguish between active and passive immunity.
- Give two ways of reducing the spread of malaria.
Show answers
- A molecule on a pathogen's surface that triggers an immune response.
- Active: body makes its own antibodies (long-lasting); passive: antibodies are received (short-lived).
- Any two: mosquito nets, insecticide spraying, draining stagnant water, antimalarial drugs.
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