27 exam-style questions on Viruses — topic A2.3 of Unity and diversity in the IB Biology syllabus — with answers and explanations. Samples below; the full set is free with an account.
State the feature that best justifies classifying viruses as non-living.
Answer: They cannot metabolise or reproduce alone
Viruses have no metabolism and must hijack a host cell's machinery to replicate, so they are considered non-living despite carrying genetic material and protein.
Determine which structural components are common to ALL viruses.
Answer: A protein capsid and a nucleic acid
Every virus has a protein capsid enclosing a nucleic acid genome; envelopes are only present in some viruses, and no virus contains both DNA and RNA as its genome.
Explain why retroviruses such as HIV require the enzyme reverse transcriptase.
Answer: To synthesise a DNA copy from their RNA genome
Retroviruses have an RNA genome; reverse transcriptase produces complementary DNA that can then be integrated into the host genome.
Distinguish the lysogenic cycle from the lytic cycle by identifying the key event unique to the lysogenic pathway.
Answer: Integration of the viral genome as a prophage
In the lysogenic cycle the viral genome integrates as a prophage and is replicated with the host DNA without immediately destroying the cell.
Suggest why an RNA virus such as influenza tends to mutate faster than a typical DNA virus.
Answer: RNA replication lacks proofreading, unlike DNA
RNA-dependent polymerases lack proofreading activity, so RNA viruses accumulate mutations rapidly, driving antigenic change.
Bacteriophages and poliovirus differ in the type of nucleic acid in their genomes. Identify the correct statement.
Answer: Many phages are DNA viruses; poliovirus is RNA
Poliovirus is a single-stranded RNA virus, whereas many well-known bacteriophages (such as lambda and T-even phages) carry double-stranded DNA genomes.
That was 6 of 27 Viruses questions.
Practise all 27 freeStateAO1 · 1–2 marks
One word or one short sentence. No explanation, no working: the mark is for the fact itself.
ExplainAO3 · 3–8 marks
Give reasons or causes: say what happens AND why, linking each step with 'because' or 'so that'.
DistinguishAO2 · 1–4 marks
Make the difference clear for BOTH terms — a definition of one of them is only half an answer.
27 Viruses questions — free with an account. Spaced repetition, streaks and full exam simulations included.
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