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206 SCIPAD - BIG IDEAS - BOOK 2
LIFE OF MICROBES
Viruses
Viruses are not cells, nor are they classified as living organisms. Of the eight features or processes
used to define living organisms (MRS C GREN), viruses are only capable of reproducing.
Viruses reproduce by invading a host cell and using its cellular processes to produce more viruses.
They are therefore classified as parasites.
Viruses are extremely small and are only visible under an electron microscope. Most viruses range
in size from 0.02 - 0.5 μm.
Viruses usually consist of a lipid (fatty) membrane which contains a number of proteins. Most
important of which are the spike proteins. Spike proteins allow the virus to attach to host cells.
Enclosed in the lipid membrane is the genetic material of the virus. Some viruses contain
deoxyribose nucleic acid (DNA) while others, like the coronavirus, contain ribonucleic acid (RNA).
Because viruses cannot move by themselves, they have to be transported in some way between
hosts. Many viruses that infect humans are transported by sharing body fluids such as blood, or in
droplets exhaled when sneezing.
1. Explain why scientists do not classify viruses as living organisms.
2. Outline what is meant by the sentence: "Viruses have only one function".
3. Complete the following sentences by filling in the missing words.
Viruses are composed of three types of molecule - an exterior coat made of
and . Inside this coat is the .
4. Outline the role of the spike proteins found on the outside of viruses.
5. Describe some of the ways viruses can move from one host to another.
Bacteriophage Virus
Spike protein
Lipid membrane
Genetic material (RNA)
Influenza Virus
Herpes Virus
Basic Structure of Coronavirus
Bacteriophage
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