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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

  • 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

  • Bacteria are small living cells that either damage cells directly or by producing toxins (poisons).
  • Pneumococcus bacteria cause pneumonia.
Fungi

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

  • 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.
Jump to other topics
1

The Nature & Variety of Living Organisms

2

Structure & Functions in Living Organisms

3

Organism Functions

3.1

Respiration

3.2

Gas Exchange

3.3

Transport

3.4

Excretion

3.5

Coordination & Response

4

Reproduction & Inheritance

5

Ecology

6

Biological Resources

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