GCSE Biology · AQA 8461 · Topic 4.3.1
Communicable diseases
Key points
- Spread of disease is reduced by hygiene, isolating infected people, destroying vectors and vaccination.
- Viruses: measles (spread in droplets, rash and fever), HIV (attacks white blood cells, controlled by antiretroviral drugs), TMV (mosaic pattern on leaves, less photosynthesis).
- Bacteria: salmonella (food poisoning from undercooked food), gonorrhoea (sexually transmitted, treated with antibiotics; condoms prevent spread). Protist: malaria carried by mosquitoes.
- Defences: skin, mucus and cilia, stomach acid. White blood cells engulf pathogens (phagocytosis), make antibodies and make antitoxins.
- Vaccines contain dead or inactive pathogens; memory cells mean antibodies are made fast on reinfection. Herd immunity protects others.
- Antibiotics kill bacteria only; painkillers treat symptoms. Resistant strains are an increasing problem.
- New drugs are tested for toxicity, efficacy and dose: preclinical tests on cells and animals, then clinical trials, often double-blind with a placebo.
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Communicable diseases are caused by pathogens that can pass from one organism to another. This sub-topic gives the named diseases you must know, the body's defences, and how medicines are found, tested and used.
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