Viral, Bacterial, Fungal and Protist Diseases — AQA GCSE Biology
Pathogens are microorganisms that cause communicable disease. There are four types, each with named examples to learn.
How pathogens cause disease
- Bacteria reproduce rapidly and may produce toxins that damage tissues.
- Viruses reproduce inside cells, damaging or destroying them.
Named diseases
Viral:
- Measles — spread by droplets; fever and rash; can be serious. Prevented by the MMR vaccine.
- HIV — spread by bodily fluids or sharing needles; attacks immune cells; controlled with antiretroviral drugs; late stage is AIDS.
- Tobacco mosaic virus (TMV) — a plant disease causing a mosaic leaf pattern that reduces photosynthesis.
Bacterial:
- Salmonella — from contaminated food; causes food poisoning (fever, cramps, vomiting, diarrhoea). Poultry are vaccinated.
- Gonorrhoea — sexually transmitted; treated with antibiotics (resistant strains exist); reduced by barrier contraception.
Fungal:
- Rose black spot — purple/black spots on leaves; reduces photosynthesis; spread in water/wind; treated with fungicides.
Protist:
- Malaria — spread by mosquito vectors; causes recurrent fevers; controlled by preventing mosquito breeding and using nets.
Reducing spread
Spread can be reduced by hygiene, isolating infected individuals, destroying vectors and vaccination.
Exam tips
- Learn each disease with its type, symptoms, how it spreads and how it's prevented/treated.
- Bacteria make toxins; viruses damage cells.
- Note the two plant diseases (TMV and rose black spot).
- Malaria is caused by a protist spread by a mosquito vector.