Pathogens
Biology: Edexcel IGCSE, topic 1.2.6
Pathogens
Most microorganisms are harmless and cover our bodies inside and out. However, there are some microorganisms that cause disease; these are called pathogens. There are four main types of pathogen:
Viruses
- Viruses are tiny, non-living (do not contain cells) particles that can reproduce rapidly within any other living organism.
- An example of a plant virus is tobacco mosaic virus.
- Examples of human viruses are HIV and the flu virus.
Bacteria
- Bacteria are small living cells that either damage cells directly or by producing toxins (poisons).
- Pneumococcus bacteria cause pneumonia.
Fungi
- Fungi can be uni (single) or multicellular and are made up of hyphae (thread-like structures).
- The hyphae are able to grow and penetrate tissues, such as human skin or the surface of plants.
- Athlete's foot is caused by fungi.
Protoctists
- Protoctists are single-celled eukaryotic organisms (they have a nucleus).
- They are often transferred to the host organism by a vector, such as an insect or mosquito.
- Plasmodium is a protoctist, spread by mosquitoes, that causes malaria.