IB Diploma · Biology A2.3
IB Biology A2.3: Viruses — Practice Questions & Answers
IB Biology A2.3 Viruses HL notes: viral structure, lytic and lysogenic cycles, diversity of viruses, rapid evolution, and origins of viruses.
Here are 10 practice questions with full answers and explanations.
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Practice questions with answers
1
Multiple choice
What was the first viral disease to be eradicated by the World Health Organization (WHO)?
- Smallpox
- Measles
- Polio
- Mumps
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WhySmallpox was the first viral disease declared eradicated by the WHO, in 1980, through global vaccination.
2
Multiple choice
What genetic material do all viruses contain?
- Either DNA or RNA
- Both DNA and RNA
- Proteins
- Lipids
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WhyEvery virus carries a genome of either DNA or RNA, but never both nucleic acids at once.
3
Multiple choice
What is the protein coat surrounding the viral genetic material called?
- Capsid
- Envelope
- Nucleoid
- Chromosome
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WhyThe capsid is the protein coat that encloses and protects the viral nucleic acid.
4
Multiple choice
Which type of viruses uses DNA intermediates (DNA molecule is created from an RNA template) to replicate?
- Retroviruses
- RNA viruses
- Bacteriophages
- Viroids
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WhyRetroviruses use reverse transcriptase to make a DNA copy from their RNA genome before integrating it into the host.
5
Multiple choice
What is the size range of most viruses?
- 20 nm to 500 nm
- 1 µm to 10 µm
- 10 µm to 100 µm
- 1 mm to 10 mm
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WhyMost viruses fall within roughly 20–500 nm, making them far smaller than typical cells.
6
Multiple choice
What type of microscope is required to view most viruses?
- Electron microscope
- Light microscope
- Compound microscope
- Stereo microscope
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WhyViruses are smaller than the wavelength of light, so an electron microscope is needed to resolve them.
7
Multiple choice
From where do enveloped viruses acquire their envelope?
- Host cell membrane
- Viral genome
- Capsid proteins
- Environment
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WhyEnveloped viruses acquire their lipid envelope from the host cell membrane as they bud out.
8
Multiple choice
What term describes viruses' dependence on host cells for replication?
- Obligate intracellular parasites
- Extracellular parasites
- Autotrophic organisms
- Mutualistic dependence
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WhyViruses are obligate intracellular parasites because they can only replicate using a host cell's machinery.
9
Multiple choice
What is the process by which some viruses enter host cells via membrane invagination?
- Endocytosis
- Receptor-mediated fusion
- Binary fission
- Budding
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WhyIn endocytosis the host membrane invaginates around the virus, drawing it into the cell inside a vesicle.
10
Multiple choice
What is the process by which some viruses bind to host cell receptors and fuse with the membrane?
- Receptor-mediated fusion
- Endocytosis
- Binary fission
- Exocytosis
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WhyIn receptor-mediated fusion the viral envelope binds host receptors and merges with the membrane, releasing the genome inside.
Key terms in Viruses
Virus: A non-cellular infectious particle consisting of a nucleic acid genome enclosed in a protein capsid, sometimes with a lipid envelope.
Capsid: The protein coat that surrounds and protects a virus’s genetic material.
Obligate intracellular parasite: An organism or particle that can only replicate inside a living host cell.
Host cell: The cell whose machinery a virus takes over in order to replicate.
Bacteriophage: A virus that infects bacteria, often with a double-stranded DNA genome and a head-and-tail structure.
Lytic cycle: A viral cycle in which the host cell is used immediately to make new viruses and is then burst (lysed).
Lysogenic cycle: A viral cycle in which the viral genome integrates into the host DNA and lies dormant before later activation.
Provirus: Viral genetic material that has integrated into and is replicated with the host genome.
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