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Reference Page

Updated: Feb 24, 2021

We are going to be covering a range of diseases, therefore we thought it would be important we have a reference page so you know some of the basics!


  • Microscopic organism

  • Bacteria are single celled organisms with no membrane bound organelles, thus they are called prokaryotes

  • They do not contain a nucleus, instead, their DNA is found in a free floating form known as a nucleoid or a circular piece known as a plasmid


  • Microscopic organism (smaller than bacteria)

  • Variety

  • Viruses contain genetic material in the form of DNA or RNA, protected by a capsid or protein coat

  • Viruses cannot reproduce outside a host cell, they use host cell machinery to replicate


  • Eukaryotic single celled or multi celled organisms

  • They cause disease in plants and animals

  • They can cause disease when they overgrow and damage tissue


  • Parasites are organisms that live on or in another organism, it gains its nutrients at the expense of its host

  • There are three main classes that can cause disease in humans. These are protozoa (single celled organisms), helminths (multi celled organisms), and ectoparasites (multi celled organisms that live outside the body)

Definitions (note that these are in the context of infectious disease)

  • Pathogen: A disease causing organism. They can be categorised into four groups: bacteria, virus, fungi or parasite

  • Vector: An organism that transmits pathogens between humans, or from animal to humans

  • Host: The organism in which a bacteria/ virus/ parasite is living in/on

  • Transmission: The means by which an infectious agent spreads

  • Vector-borne disease (VBD): Disease transmitted by a vector

  • Mosquito - borne disease: Disease transmitted by a mosquito

  • Prokaryotes: Organisms made up of a single prokaryotic cell. The DNA in these cells is circular and found free in the cytoplasm. Bacteria are prokaryotes

  • Eukaryotes: Organisms containing eukaryotic cells. The DNA in these cells is contained in a membrane-bound nucleus. Plants, animals, fungi and protists are eukaryotes

  • Zoonosis: disease that can transmitted between animals and humans

  • Pandemic: the spread of a disease across a large area, i.e. several continents or globally

  • Endemic: when a disease is commonly found amongst people in a given area

  • Epidemic: the spread of a disease across a given population at a specific time

  • Genus: A biological classification that ranks above species. A genus consists of species with common characteristics (structurally or phylogenetically related species). E.g. Homo is the genus of Homo sapien

  • Species: A biological classification that ranks below genus. A species consists of organisms that are able to interbreed, and to create offspring that are fertile. E.g. Homo sapien is the species all humans belong to

  • Asymptomatic: A condition or individual that shows symptoms

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💪thanks for Glossary and it’s reminder Ed me if what I learnt years ago

? If I read correctly the DNA or RNA protected by protein coating means that a virus cannot replicate/ mutate without a host cell?scientifically should be looking at the specificDNA or RNA link required by a virus to variant itself??

Aimee Whalley
Aimee Whalley
Feb 25, 2021
Replying to

We're so glad you find it useful - we have put the glossary under the page 'Definitions' in the top right hand corner, and will add to it further! On our posts any key words will be highlighted and you can click on them to be referred to our definitions page 😀

Yes that's correct, viruses cannot replicate without a host cell. A virus will invade a host cell and inject its genetic material. The viral DNA or RNA will be incorporated into the host cell's own genetic material and hence causes it to replicate the virus' genome.

Hope that answer helps ☺️

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