What is a pathogen?
Reveal answer
A microorganism or infectious agent (including viruses) that causes disease.
Key words: microorganism · disease
1(b) VARIETY OF LIVING ORGANISMS · RECALL
1.4 Pathogens, including viruses
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Which groups can include pathogens?
Reveal answer
Fungi, bacteria, protoctists and viruses.
Key words: fungi · bacteria · protoctists · viruses
Describe the structure of a virus.
Reveal answer
No cellular structure: a protein coat around one type of nucleic acid, either DNA or RNA.
Key words: protein coat · DNA or RNA
Name the three viruses in the specification and the disease or effect each causes.
Reveal answer
Tobacco mosaic virus: discoloured (mosaic) leaves in tobacco plants by preventing chloroplast formation. Influenza virus: flu. HIV: AIDS.
Key words: tobacco mosaic virus · influenza · HIV
Why are viruses not counted as living organisms?
Reveal answer
They have no cells and cannot carry out life processes on their own; they reproduce only inside living host cells.
Key words: host cell · not cells
What is meant by the term virus?
Reveal answer
An acellular infectious particle containing DNA or RNA inside a protein coat.
Key words: virus
What is meant by the term capsid?
Reveal answer
The protein coat surrounding viral genetic material.
Key words: capsid
What is meant by the term host?
Reveal answer
The organism or cell used by a parasite or pathogen.
Key words: host
What is meant by the term replication?
Reveal answer
The production of new copies; viral replication requires a living host cell.
Key words: replication
What is meant by the term vector?
Reveal answer
An organism that carries a pathogen between hosts, such as a mosquito carrying Plasmodium.
Key words: vector
Four sources of infectious disease: for Fungus, give the cellular status and the representative example.
Reveal answer
Cellular status: Eukaryotic cell or hyphae with chitin walls. Representative example: Trichophyton causing athlete’s foot.
Key words: Fungus
Four sources of infectious disease: for Bacterium, give the cellular status and the representative example.
Reveal answer
Cellular status: Living prokaryotic cell. Representative example: Pneumococcus causing pneumonia.
Key words: Bacterium
Four sources of infectious disease: for Protoctist, give the cellular status and the representative example.
Reveal answer
Cellular status: Living eukaryotic cell. Representative example: Plasmodium causing malaria.
Key words: Protoctist
Four sources of infectious disease: for Virus, give the cellular status and the representative example.
Reveal answer
Cellular status: Acellular particle containing DNA or RNA in a protein coat. Representative example: Influenza virus, HIV or TMV.
Key words: Virus
True or false, and why? “All microorganisms are pathogens.”
Reveal answer
False. A microorganism is microscopic; a pathogen specifically causes disease.
True or false, and why? “Viruses are tiny bacteria.”
Reveal answer
False. Bacteria are prokaryotic cells. Viruses are acellular particles without cytoplasm or ribosomes.
True or false, and why? “A virus divides into two.”
Reveal answer
False. Viral components are made by host machinery and assembled into new particles.
True or false, and why? “HIV and AIDS are the same thing.”
Reveal answer
False. HIV is the virus; AIDS is a late-stage syndrome that untreated HIV infection can cause.