Pathogens and how they spread
Four kinds of pathogen
A pathogen is a microorganism that causes an infectious disease.
Diseases caused by pathogens are communicable: they pass from one person (or plant) to another. Heart disease or scurvy are non-communicable: nothing is caught.
- Bacteria reproduce quickly and may release toxins that damage tissues.
- Viruses are far smaller. They live and reproduce inside cells, damaging them.
- Fungi and protists cause disease in plants and animals too.
Pathogens spread by air (droplets from coughs and sneezes), by water, by direct contact, and through vectors such as mosquitoes.
The diseases you need
| Disease | Pathogen | Spread | Control |
|---|---|---|---|
| measles | virus | droplets | vaccinate children |
| HIV | virus | sex, shared needles | condoms, clean needles; antiretroviral drugs |
| tobacco mosaic virus | virus | plant contact, tools | destroy infected plants |
| salmonella | bacterium | undercooked food | vaccinate poultry, cook well |
| gonorrhoea | bacterium | unprotected sex | condoms, antibiotics |
| rose black spot | fungus | spores in wind and water | remove leaves, fungicide |
| malaria | protist | mosquito bites | nets, stop mosquitoes breeding |
Edexcel and OCR also use cholera (water), tuberculosis (droplets), chlamydia and ash dieback.
Viruses are not killed by antibiotics. Salmonella and gonorrhoea are bacteria; measles and HIV are viruses.
How fast bacteria multiply
Each division turns one bacterium into two, so the number doubles every division.
number of bacteria = starting number × 2ⁿ (n = number of divisions)
n = time ÷ mean division time
- 20 bacteria, dividing every 30 minutes, for 4 hours
- 4 × 60 = 240 minutes; 240 ÷ 30 = 8 divisions
- 20 × 2⁸ = 20 × 256 = 5120 = 5.12 × 10³
Multiply by 2 once for every division: 2⁸, not 2 × 8.
Loading the question
This question is in Brainlag Plus