Microbiology: virus classification · Class 11 Chapter 2 / MDCAT Unit 1 routes

MDCAT Biology · Unit 1: Acellular Life · Outcome 1.1

Virus classification means describing a virus using evidence about its genome, structure, host and disease association. The exam skill is to keep those properties separate, then combine them into a profile. An RNA genome does not tell you whether a virus infects plants, has an envelope or possesses a helical capsid.

Syllabus checked: 23 October 2026. PMDC's 2026 notice states that its final 2025 curriculum applies to MDCAT 2026. Outcome 1.1 covers classification by structure, strand number, diseases and hosts. This resource practises that outcome. It is an original topic question bank, not an official paper, a complete mock exam or a prediction of question frequency.

For the full biological explanation, read Viruses: Classification and Structure first. This companion focuses on interpreting classification clues and checking your reasoning. The 50 explained MCQs and the separate 50-question quiz use different question stems.

By the end, you should be able to: distinguish genome strands from segments; compare capsid symmetry and envelope status; combine host and disease evidence without guessing; and explain why an incorrect classification fails.

The four questions to ask about any virus

Start with a virion: a complete virus particle outside a host cell. It contains a nucleic-acid genome enclosed by a protein capsid. Some virions also have a lipid-containing envelope. The genome plus capsid is the nucleocapsid. None of these structures supplies the ribosomes and cellular organisation needed for independent reproduction.

If this distinction is unclear, revisit Cell Theory and the limits of cellular organisation. Acellular does not mean that a virus has no genetic information. It means that the particle is not organised as a cell.

Virus classification decision map separating genome type and strand number, capsid and envelope structure, host range, and disease association, with a tobacco mosaic virus example.
Original classification map: evaluate genome, structure, host and disease association independently, then combine the evidence. Strand number and genome segment number are different properties. Select the image to view full size.

1. Genome: chemistry, strandedness and segmentation

First identify whether the inherited viral genome is DNA or RNA. Then ask whether it is single-stranded (ss) or double-stranded (ds). Thus ssRNA and dsRNA are both RNA genomes, but their strand organisation differs.

Strands and segments are different measurements. A strand is a nucleic-acid chain. In a double-stranded genome, complementary chains pair. A segment is a separate genome piece. A segmented genome can therefore contain several double-stranded molecules. Rotavirus provides a useful example: its genome has eleven dsRNA segments. Calling it “eleven-stranded RNA” would confuse two independent properties.

Do not assume that RNA always means single-stranded. Also distinguish the packaged genome from a molecule made during infection. HIV packages ssRNA, although reverse transcription produces a DNA intermediate inside the host. Detailed HIV disease biology belongs to the next syllabus outcome, 1.2.

2. Structure: capsid symmetry and envelope status

In a helical nucleocapsid, repeating protein subunits are organised helically around the nucleic acid. Tobacco mosaic virus (TMV) is the familiar rod-shaped, non-enveloped example. In an icosahedral capsid, the geometry has twenty triangular faces and twelve vertices. Adenovirus and poliovirus are useful examples.

Complex architecture combines features that cannot be adequately described as one simple helical or icosahedral particle. T4 bacteriophage has an icosahedral head together with a tail and attachment structures. This is an example of a phage, not a drawing of every bacteriophage.

Record an envelope separately: enveloped or non-enveloped (naked). An envelope is an outer lipid-containing membrane, not a protein capsid, a bacterial wall or evidence of cellular life. Influenza illustrates why levels of description matter: its nucleocapsid organisation is helical, while its enveloped particles need not look like rigid rods.

3. Host: the cells that support infection

A bacteriophage infects bacteria. Plant viruses infect plant cells, while animal viruses infect animal cells. These are host categories; they do not determine the genome or shape of every member. T4 and TMV both have protein coats, yet their hosts and genomes differ.

Host range depends on biological compatibility. Surface attachment proteins must interact with suitable host features, and later intracellular steps must also be supported. Successful attachment alone does not prove productive infection. Equally, a geometric resemblance between particles does not establish that they infect the same host.

4. Disease association: use a supported pairing

Keep the virus name and the disease name in separate columns. Poliovirus is associated with poliomyelitis; TMV causes mosaic disease in susceptible plants. HIV is the virus associated with the infection that can progress to AIDS. AIDS is not the name of a virus.

A disease name alone does not reveal every genome or structural property. When a case supplies only one observation, record that observation and leave the other columns unresolved. This is more accurate than completing a profile by guessing.

Comparison table: learn combinations rather than isolated labels

These are selected teaching examples. They are not a claim that PMDC prescribes each example by name, and the table is not a complete formal viral taxonomy.

ExampleGenomeArchitectureEnvelopeHost / association
TMVssRNAHelicalAbsentPlants; mosaic disease
T4 phagedsDNAComplex head-tailAbsentBacteria, including susceptible E. coli strains
AdenovirusdsDNAIcosahedralAbsentAnimal hosts; disease depends on virus type
PoliovirusssRNAIcosahedralAbsentHumans; poliomyelitis
RotavirusSegmented dsRNAIcosahedralAbsentAnimal hosts; gastroenteritis
Influenza virusSegmented ssRNAHelical nucleocapsidPresentAnimal hosts; influenza
HIVssRNA; retroviralConical mature capsidPresentHumans; HIV infection / AIDS

Worked classification cases

Case 1: use every clue

Evidence: a rod-shaped particle contains ssRNA, lacks an envelope and infects a plant. Reasoning: genome = ssRNA; architecture = helical in the familiar TMV comparison; envelope = absent; host = plant. TMV fits the complete profile. Choosing influenza merely because it has RNA and a helical nucleocapsid would ignore the envelope and host clues.

Case 2: recognise what you cannot conclude

Evidence: microscopy shows an icosahedral protein coat; no genome test has been performed. Conclusion: the capsid symmetry is established. DNA versus RNA is not. Adenovirus and poliovirus demonstrate why: both are icosahedral, but their genome chemistry differs.

Case 3: interpret a genome report

Evidence: eleven separate RNA molecules are isolated, each with paired complementary strands. Conclusion: segmented dsRNA. Eleven counts the segments, while ds describes each segment's strand pairing. This is consistent with the rotavirus example; it does not describe eleven strands wound into one molecule.

Case 4: correct one error without inventing another

Record: “Adenovirus: ssRNA, icosahedral, naked.” Correction: change ssRNA to dsDNA. The architecture and envelope entries are already consistent with adenovirus. A classification correction should repair the unsupported entry, not replace all the information.

Common MCQ traps and a quick revision method

  • RNA ≠ automatically ssRNA. Keep rotavirus as a counterexample.
  • Segmented ≠ double-stranded. Count pieces and paired chains separately.
  • Naked ≠ capsid-free. It means no outer lipid envelope.
  • Animal host ≠ DNA genome. Poliovirus is an RNA example.
  • All phages ≠ T4. A representative architecture is not universal.
  • Outer shape ≠ every internal feature. State whether a clue describes the whole particle or nucleocapsid.
  • Retroviral DNA intermediate ≠ packaged DNA genome. HIV packages RNA.

Cover one column of the comparison table and reconstruct it. Then explain why each rejected option in a case fails. Before accepting an answer, check genome, architecture, envelope and host independently. If evidence is missing, say so. This method prepares you for unfamiliar profiles rather than only memorised names.

50 original MCQs with hidden answers

Choose your answer before opening Show Answer. Each explanation tells you why the selected property is supported. These are original practice questions, not authenticated past-paper items.

1. Which structure is present in a conventional virion but does not make it a cell?

  1. Protein capsid
  2. Mitochondrion
  3. Cytoplasmic ribosomes
  4. Cellulose wall
Show Answer

Correct answer: A. Protein capsid

A capsid encloses the genome; a virion still lacks cellular organisation and ribosomes.

2. What does ssRNA identify?

  1. Double-stranded DNA genome
  2. A single protein subunit
  3. Single-stranded RNA genome
  4. One RNA segment only
Show Answer

Correct answer: C. Single-stranded RNA genome

The prefix ss describes strand number, not the number of separate genome molecules.

3. What does dsDNA identify?

  1. Two separate DNA segments
  2. A double lipid envelope
  3. DNA and RNA as equal genomes
  4. Double-stranded DNA genome
Show Answer

Correct answer: D. Double-stranded DNA genome

The paired strands belong to DNA; ds does not describe an envelope.

4. Which classification pair describes two independent properties?

  1. Capsid and protein coat
  2. RNA genome and animal host
  3. Non-enveloped and naked
  4. RNA genome and RNA genome
Show Answer

Correct answer: B. RNA genome and animal host

Genome chemistry and host are different classification axes.

5. A capsid is composed mainly of what?

  1. Protein
  2. Peptidoglycan
  3. Starch
  4. Cellulose
Show Answer

Correct answer: A. Protein

Capsid proteins assemble into the protective coat around viral nucleic acid.

6. What is the nucleocapsid?

  1. Bacterial wall plus membrane
  2. Host nucleus containing DNA
  3. Genome together with its capsid
  4. Envelope alone
Show Answer

Correct answer: C. Genome together with its capsid

The nucleocapsid includes nucleic acid and the protein coat.

7. What distinguishes an enveloped virus from a naked virus?

  1. Presence of a genome
  2. Independent ATP production
  3. An additional outer lipid membrane
  4. Presence of capsid proteins
Show Answer

Correct answer: C. An additional outer lipid membrane

An envelope surrounds the nucleocapsid in enveloped virions.

8. Which description best fits helical organisation?

  1. Twenty triangular faces
  2. Capsid subunits arranged around nucleic acid in a helix
  3. A bacterial flagellum
  4. A double nuclear envelope
Show Answer

Correct answer: B. Capsid subunits arranged around nucleic acid in a helix

Helical symmetry concerns repeating capsid subunits, not a cellular organelle.

9. An ideal icosahedron has how many triangular faces?

  1. 12
  2. 6
  3. 20
  4. 8
Show Answer

Correct answer: C. 20

An icosahedron has twenty faces and twelve vertices.

10. Which standard example has complex head-tail architecture?

  1. Adenovirus
  2. T4 bacteriophage
  3. Poliovirus
  4. Tobacco mosaic virus
Show Answer

Correct answer: B. T4 bacteriophage

T4 combines an icosahedral head with a tail and attachment structures.

11. The word bacteriophage specifies which property?

  1. Bacterial host
  2. RNA genome in every case
  3. A lipid envelope in every case
  4. Human disease
Show Answer

Correct answer: A. Bacterial host

A bacteriophage infects bacteria; its genome and structure require separate evidence.

12. Which host category applies to tobacco mosaic virus?

  1. Bacterial
  2. Fungal only
  3. Human only
  4. Plant
Show Answer

Correct answer: D. Plant

TMV is a plant virus associated with mosaic symptoms.

13. Which genome description fits tobacco mosaic virus?

  1. dsRNA
  2. ssDNA
  3. dsDNA
  4. ssRNA
Show Answer

Correct answer: D. ssRNA

TMV carries a single-stranded RNA genome.

14. Which structural profile fits tobacco mosaic virus?

  1. Icosahedral and enveloped
  2. Helical and non-enveloped
  3. A cellular rod with ribosomes
  4. Complex head-tail and enveloped
Show Answer

Correct answer: B. Helical and non-enveloped

TMV is a classic non-enveloped helical virus.

15. Which genome description fits T4 phage?

  1. dsRNA
  2. ssDNA
  3. ssRNA
  4. dsDNA
Show Answer

Correct answer: D. dsDNA

The genetic material inside the T4 head is double-stranded DNA.

16. Which profile fits adenovirus?

  1. Enveloped helical ssRNA virus
  2. Non-enveloped helical ssRNA virus
  3. Complex bacterial cell
  4. Non-enveloped icosahedral dsDNA virus
Show Answer

Correct answer: D. Non-enveloped icosahedral dsDNA virus

Adenoviruses combine a DNA genome with a non-enveloped icosahedral capsid.

17. Which profile fits poliovirus?

  1. Non-enveloped helical dsDNA virus
  2. Non-enveloped icosahedral ssRNA virus
  3. Complex dsRNA phage
  4. Enveloped dsDNA virus
Show Answer

Correct answer: B. Non-enveloped icosahedral ssRNA virus

Poliovirus is a non-enveloped RNA virus with icosahedral capsid symmetry.

18. Which disease pairing is correct?

  1. TMV — AIDS
  2. Poliovirus — poliomyelitis
  3. Adenovirus — plant mosaic disease
  4. T4 — influenza
Show Answer

Correct answer: B. Poliovirus — poliomyelitis

Poliomyelitis is the named disease caused by poliovirus.

19. Which example demonstrates that some RNA viruses are double-stranded?

  1. Influenza virus
  2. TMV
  3. Rotavirus
  4. Poliovirus
Show Answer

Correct answer: C. Rotavirus

Rotavirus has a double-stranded RNA genome, so RNA does not automatically mean ssRNA.

20. Rotavirus has eleven genome segments. What does this count describe?

  1. The number of paired strands in each piece
  2. The number of host species
  3. Separate genome pieces
  4. The number of capsid faces
Show Answer

Correct answer: C. Separate genome pieces

Segment number counts separate nucleic-acid molecules; each rotavirus segment is dsRNA.

21. Influenza virus is correctly described as having what?

  1. No envelope and dsDNA genome
  2. Eleven dsRNA segments
  3. A bacterial cell wall and ssRNA
  4. An envelope and segmented ssRNA genome
Show Answer

Correct answer: D. An envelope and segmented ssRNA genome

Influenza viruses have segmented single-stranded RNA and a lipid envelope.

22. In influenza classification, helical refers primarily to what?

  1. A bacterial tail
  2. Nucleocapsid organisation
  3. A rigid rod shape of every whole virion
  4. A nuclear chromosome
Show Answer

Correct answer: B. Nucleocapsid organisation

The internal ribonucleoprotein organisation is helical even when outer virion shape varies.

23. What is the packaged genome type of HIV?

  1. ssRNA
  2. dsRNA
  3. No nucleic acid
  4. dsDNA
Show Answer

Correct answer: A. ssRNA

HIV packages RNA; the DNA intermediate made during infection does not change that classification.

24. Which virus is associated with AIDS?

  1. TMV
  2. HIV
  3. T4
  4. Poliovirus
Show Answer

Correct answer: B. HIV

HIV causes the infection that can progress to AIDS; disease and virus names are different.

25. Does HIV forming DNA inside a host make its packaged genome DNA?

  1. Yes; an intermediate always replaces the original genome
  2. No; classify the virion genome as RNA
  3. Yes; all retroviruses package dsDNA
  4. No; HIV has no genome
Show Answer

Correct answer: B. No; classify the virion genome as RNA

Classification distinguishes the packaged genome from intermediates generated during replication.

26. What does host range describe?

  1. Number of genome strands
  2. Number of capsid subunits
  3. Virion diameter alone
  4. Hosts or cells a virus can infect
Show Answer

Correct answer: D. Hosts or cells a virus can infect

Host range concerns biological compatibility, not particle dimensions.

27. Why is a compatible receptor not always sufficient for productive infection?

  1. Every attached virion becomes a bacterium
  2. Capsids manufacture host ribosomes
  3. Receptors determine the number of DNA strands
  4. Later intracellular processes must also be supported
Show Answer

Correct answer: D. Later intracellular processes must also be supported

Entry compatibility and intracellular permissiveness are separate requirements.

28. Two viruses share an icosahedral capsid. What can be concluded?

  1. They must share a genome type
  2. They share a symmetry category
  3. They cause the same disease
  4. They infect the same host
Show Answer

Correct answer: B. They share a symmetry category

Similar capsid geometry alone does not establish host, genome or disease identity.

29. Two viruses both infect animals. Which feature still needs evidence?

  1. Genome type
  2. Meaning of the word host
  3. Whether their hosts are animals
  4. Whether animal cells are cellular
Show Answer

Correct answer: A. Genome type

A shared host category does not determine genome chemistry.

30. Which claim is too broad?

  1. TMV infects plants
  2. Adenovirus contains DNA
  3. T4 is a bacteriophage
  4. All bacteriophages have T4-like head-tail structures
Show Answer

Correct answer: D. All bacteriophages have T4-like head-tail structures

Bacteriophages are diverse; T4 is a representative example, not a universal template.

31. A lipid envelope is lost from a particle during preparation. Which inference is safest?

  1. The particle became a prokaryote
  2. The virus was necessarily non-enveloped
  3. The original envelope status needs independent confirmation
  4. The genome changed from RNA to DNA
Show Answer

Correct answer: C. The original envelope status needs independent confirmation

Sample preparation can affect observed structures, so absence in one preparation may mislead.

32. Which missing observation would distinguish ssRNA from dsRNA?

  1. Whether symptoms include fever
  2. Whether the capsid is round
  3. Whether complementary strands are paired
  4. Whether the host has a nucleus
Show Answer

Correct answer: C. Whether complementary strands are paired

Strandedness is a genome property that cannot be read from these other features.

33. Which is a valid four-part classification record?

  1. Ribosome, mitochondrion, tissue, organ
  2. Age, nucleus, chloroplast, seed
  3. Colour, price, habitat, body mass
  4. Genome, structure, host, disease association
Show Answer

Correct answer: D. Genome, structure, host, disease association

These axes match the classification skills in the syllabus outcome.

34. What is wrong with calling a capsid a bacterial cell wall?

  1. They differ in composition and biological organisation
  2. Bacteria have no walls
  3. All capsids contain peptidoglycan
  4. A capsid is always a lipid bilayer
Show Answer

Correct answer: A. They differ in composition and biological organisation

A viral protein coat is distinct from a bacterial wall, commonly containing peptidoglycan.

35. Which structure do viruses lack for autonomous protein synthesis?

  1. Attachment proteins
  2. Ribosomes
  3. Capsid proteins
  4. A genome
Show Answer

Correct answer: B. Ribosomes

Viruses depend on host translation machinery rather than their own ribosomes.

36. An RNA virus infects plants, but its symmetry was not observed. Which entry is justified?

  1. Definitely a bacteriophage
  2. Definitely helical
  3. Plant RNA virus; symmetry undetermined
  4. Definitely enveloped
Show Answer

Correct answer: C. Plant RNA virus; symmetry undetermined

Record the supported evidence and leave unmeasured properties open.

37. Which observation directly supports an envelope classification?

  1. A lipid membrane outside the capsid
  2. Infection of a plant
  3. Twenty capsid faces
  4. DNA inside a protein coat
Show Answer

Correct answer: A. A lipid membrane outside the capsid

The outer membrane is the defining structural evidence for an envelope.

38. Which pair is correctly matched by host?

  1. T4 — bacteria; TMV — plants
  2. T4 — humans; TMV — fungi
  3. T4 — animals only; TMV — bacteria
  4. T4 — plants; TMV — bacteria
Show Answer

Correct answer: A. T4 — bacteria; TMV — plants

Host labels distinguish these examples independently of their genomes.

39. Which pair shares ssRNA but differs in envelope status?

  1. Adenovirus and T4
  2. T4 and rotavirus
  3. Adenovirus and rotavirus
  4. TMV and influenza virus
Show Answer

Correct answer: D. TMV and influenza virus

TMV is non-enveloped, whereas influenza is enveloped; both have ssRNA genomes.

40. Which pair shares dsDNA but differs in architecture?

  1. HIV and TMV
  2. Rotavirus and influenza
  3. TMV and poliovirus
  4. T4 and adenovirus
Show Answer

Correct answer: D. T4 and adenovirus

T4 has complex head-tail architecture; adenovirus is icosahedral without a tail.

41. An icosahedral non-enveloped RNA virus could match which example?

  1. Adenovirus
  2. TMV
  3. T4
  4. Poliovirus
Show Answer

Correct answer: D. Poliovirus

Poliovirus matches all three properties; the other options fail at least one.

42. A non-enveloped helical plant virus could match which example?

  1. T4
  2. Adenovirus
  3. TMV
  4. HIV
Show Answer

Correct answer: C. TMV

The combined host and structural clues identify the TMV example.

43. Which observation rules out the statement that every virus is enveloped?

  1. An RNA genome in HIV
  2. A bacterial host for T4
  3. A verified non-enveloped poliovirus particle
  4. An enveloped influenza particle
Show Answer

Correct answer: C. A verified non-enveloped poliovirus particle

One genuine counterexample disproves a universal assertion.

44. What is the best first step in a classification case?

  1. Treat all shapes as the same virus
  2. Separate observations into independent axes
  3. Guess the disease from particle colour
  4. Assume every RNA genome is single-stranded
Show Answer

Correct answer: B. Separate observations into independent axes

Organising evidence prevents one clue from being used to invent unrelated properties.

45. If only disease name is provided, which conclusion is unsafe without further evidence?

  1. That a disease association was reported
  2. That more information may be needed
  3. The exact number of genome segments
  4. That virus and disease names can differ
Show Answer

Correct answer: C. The exact number of genome segments

Disease association alone does not supply every structural or genomic detail.

46. Which phrase correctly distinguishes strand and segment?

  1. Single-stranded means unsegmented
  2. Two segments always mean dsDNA
  3. A segment may itself be double-stranded
  4. Each segment is necessarily one strand
Show Answer

Correct answer: C. A segment may itself be double-stranded

Strandedness and segmentation measure different aspects of a genome.

47. Which label describes an outer covering rather than genome chemistry?

  1. Enveloped
  2. dsDNA
  3. ssRNA
  4. dsRNA
Show Answer

Correct answer: A. Enveloped

Enveloped describes a lipid-containing outer layer, not nucleic-acid chemistry.

48. Why can a spherical-looking particle still have icosahedral capsid symmetry?

  1. Every sphere contains dsRNA
  2. An icosahedron has no faces
  3. Overall appearance and capsid organisation are different descriptions
  4. Only bacteria have geometric symmetry
Show Answer

Correct answer: C. Overall appearance and capsid organisation are different descriptions

A rounded appearance, particularly with an envelope, need not reveal internal symmetry directly.

49. A proposed table lists adenovirus as ssRNA. What is the necessary correction?

  1. Change its genome to dsDNA
  2. Add a T4-like tail
  3. Change its host to bacteria
  4. Change all DNA viruses to RNA
Show Answer

Correct answer: A. Change its genome to dsDNA

Adenoviruses have double-stranded DNA genomes; other properties should not be changed without reason.

50. Which revision habit best prepares for unfamiliar classification questions?

  1. Ignore exceptions to universal claims
  2. Infer host solely from capsid shape
  3. Memorise that every virus resembles TMV
  4. Justify each chosen property from a clue or verified example
Show Answer

Correct answer: D. Justify each chosen property from a clue or verified example

Reasoning across independent properties transfers to unfamiliar cases.

Separate 50-question interactive quiz

Attempt all 50, then select Check quiz. There is no timer or negative marking in this practice component. Unanswered items are counted separately. You can change answers and check again, or reset for a fresh attempt.

1. A student records an agent as RNA, naked, helical and plant-infecting. Which example fits the whole record?
2. An unknown particle has a DNA-filled head and tail fibres and infects E. coli. Which familiar example is most consistent?
3. A worksheet calls a virus double-stranded because it has two RNA segments. What should be checked instead?
4. Which observation belongs in the host column of a viral classification table?
5. Which observation belongs in the genome column?
6. A capsid has twenty triangular faces. Which category should be entered?
7. A student labels the outer lipid layer of influenza as the capsid. Which correction is appropriate?
8. Which comparison tests envelope status while holding genome category constant?
9. Which comparison tests architecture while holding dsDNA genome type constant?
10. An examiner describes RNA enclosed within a protein coat but gives no outer-layer data. Which property remains unresolved?
11. Which result would contradict a claim that an agent is a virus rather than a cell?
12. A student says all animal viruses contain DNA. Which example directly challenges the claim?
13. A student says all RNA viruses have one strand. Which example challenges that claim?
14. A sample has eleven separate double-stranded RNA pieces. Which entry is correct?
15. Which clue most directly distinguishes T4 from TMV?
16. The genome of an unknown virus is DNA. Which additional conclusion follows automatically?
17. Which classification is consistent with a verified adenovirus sample?
18. Which classification is inconsistent with a verified poliovirus sample?
19. An influenza particle looks roughly spherical. Why should it not be relabelled as an icosahedral capsid solely from this?
20. A student lists AIDS as a virus name. What should replace it in the virus column?
21. Which observation concerns a replication intermediate rather than the packaged genome of HIV?
22. A virus attaches successfully but fails to produce progeny in a cell. What is the best explanation?
23. A profile states plant host but gives no genome evidence. Which classification would be premature?
24. What would be the clearest label for nucleic acid plus its surrounding protein coat?
25. Which investigation most directly addresses whether a virus is enveloped?
26. A table has columns DNA/RNA, ss/ds, shape and host. Where should segmented/unsegmented be added?
27. Two virus isolates share capsid symmetry and envelope status. What remains possible?
28. Which evidence supports the pairing poliovirus–poliomyelitis?
29. Which statement avoids overgeneralising from a T4 diagram?
30. A student changes a virus from animal to bacterial because its capsid is icosahedral. What is the error?
31. Which pair both lacks a lipid envelope in the standard examples?
32. Which feature is shared by TMV and T4?
33. Which feature is shared by adenovirus and poliovirus?
34. Which set contains an RNA virus and a DNA virus, respectively?
35. A report only says the virus causes disease in humans. What cannot be deduced from that alone?
36. What does the prefix ds fail to tell you?
37. Which proposed profile contains an internal contradiction?
38. A particle lacks a nucleus. Why does this alone not establish that it is a bacterium?
39. Why should viral RNA not be labelled cytoplasm in a diagram?
40. Which information would complete the profile ssRNA + helical + plant host?
41. Which change repairs the statement TMV is a naked dsDNA plant virus?
42. Which change repairs the statement T4 is an RNA virus with a complex tail?
43. A virus has an envelope. Which claim remains false?
44. Which observation distinguishes rotavirus from the listed ssRNA examples?
45. A teacher gives TMV, adenovirus and T4 as examples. Which approach builds a useful comparison?
46. Which statement about formal viral taxonomy is appropriate for this revision task?
47. An unknown RNA virus is non-enveloped. Why can it not automatically be called TMV?
48. Which description separates a measured result from an assumption?
49. Which question most directly tests disease association rather than morphology?
50. A complete case identifies RNA, a helical nucleocapsid, an envelope and an animal host. Which familiar example is consistent?

Frequently asked questions

How do I classify a virus in an MDCAT question?

Separate the clues into genome chemistry and strandedness, capsid architecture and envelope status, host, and disease association. Choose a profile only when its properties agree with the evidence.

Are all RNA viruses single-stranded?

No. Rotavirus has a double-stranded RNA genome. The term RNA identifies chemistry; ss or ds identifies strand organisation.

What is the difference between capsid and envelope?

A capsid is the protein coat enclosing the genome. An envelope is an additional outer lipid-containing membrane in some viruses. A naked virus still has a capsid.

What is the difference between a strand and a segment?

Strandedness describes whether complementary nucleic-acid chains are paired. Segmentation describes separate genome pieces. Each separate piece can itself be double-stranded.

Is HIV a DNA or RNA virus?

HIV packages an ssRNA genome. It makes a DNA intermediate during infection through reverse transcription; that intermediate does not make the packaged genome DNA.

Are all bacteriophages shaped like T4?

No. Bacteriophage identifies a bacterial host. T4 is one familiar example of complex head-tail architecture, not a universal diagram of every phage.

Do these 100 questions come from official MDCAT past papers?

No. They are original educational practice questions. The first 50 have expandable explanations; the separate quiz contains 50 different question stems.

Which syllabus outcome comes next?

Unit 1 outcome 1.2 covers AIDS and HIV infection, including cause, transmission and symptoms. That resource is queued separately; this page focuses on outcome 1.1.

Continue learning

Return to the MDCAT resource collection, review the full virus structure and classification lesson, or strengthen the cell comparison prerequisite with Prokaryotic vs Eukaryotic Cells. Coming next in this track: AIDS and HIV infection (outcome 1.2).

Sources and further reading

Scope and example properties were checked against official curriculum and biological reference sources. Explanations, cases and questions are original.

Last scientific and syllabus review: 23 October 2026. Educational biology revision; disease names are used for classification, not personal diagnosis.