Question 1
What is a structural feature shared by all viruses?
A.
A double-stranded DNA chromosome
B.
A protein capsid enclosing genetic material
C.
Cytoplasm containing ribosomes
D.
A host-derived membrane envelope
Question 2
A newly discovered infectious particle is non-cellular, has a fixed diameter of about and contains RNA inside a protein coat. What additional observation would support its classification as a virus rather than as a cell?
A.
Presence of proteins on its surface
B.
Absence of cytoplasm and ribosomes
C.
Use of the genetic code for proteins
D.
Presence of nucleotides in its genome
Question 3
The table summarizes three viruses.
| Virus | Genome | Envelope | Typical host |
|---|---|---|---|
| Bacteriophage lambda | DNA | Absent | Escherichia coli |
| Coronavirus | RNA | Present | Animal cells |
| HIV | RNA | Present | Human immune cells |
What conclusion is supported by the table?
A.
All RNA viruses infect only human immune cells.
B.
All viruses that infect bacteria have an envelope.
C.
Viruses with DNA genomes cannot enter host cells.
D.
Viruses vary in genome type, envelope presence and host type.
Question 4
A diagram of an enveloped virus shows a membrane surrounding the capsid, with viral glycoproteins projecting from the membrane. What is the usual origin of this envelope?
A.
A bacterial cell wall synthesized by the virus
B.
Host cell membrane acquired during release or entry
C.
A protein shell assembled from capsid subunits
D.
A layer of cytoplasm retained inside the capsid
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Question 5
What is a prophage in the lysogenic cycle of bacteriophage lambda?
A.
Bacterial DNA released after host cell lysis
B.
A complete phage particle assembled inside the host
C.
An empty capsid remaining outside the bacterial cell
D.
Viral DNA integrated into the bacterial chromosome
Question 6
An electron micrograph shows many virus particles outside a bacterial cell. The particles are much smaller than the bacterium and each particle has a regular outline.
State one feature visible or implied by the micrograph that supports the idea that viruses are not cells.
[1]
Outline why a completed virus particle has a fixed size.
[2]
Question 7
What is the correct order of events in the lytic cycle of bacteriophage lambda after attachment to Escherichia coli?
A.
DNA entry, genome replication, protein synthesis, assembly, lysis
B.
Protein synthesis, DNA entry, lysis, assembly, genome replication
C.
Assembly, genome replication, DNA entry, protein synthesis, lysis
D.
DNA entry, lysis, protein synthesis, genome replication, assembly
Question 8
During the lytic cycle of bacteriophage lambda, the host bacterium is treated with an antibiotic that immediately stops ribosome function. What viral process would be directly prevented?
A.
Circularization of the phage DNA molecule
B.
Attachment of tail proteins to cell-surface receptors
C.
Translation of viral mRNA into capsid and tail proteins
D.
Injection of phage DNA through the tail
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Question 9
A population of Escherichia coli cells infected with bacteriophage lambda divides repeatedly without immediate cell lysis. Viral DNA is detected in all daughter cells. What has most likely occurred?
A.
The phage capsid has replicated independently in the bacterial cytoplasm.
B.
New phage particles have assembled and burst each host cell at every division.
C.
The bacterial ribosomes have been packaged into new viral particles.
D.
The phage DNA has integrated into the bacterial chromosome and is copied with it.
Question 10
What observation supports the view that viruses have evolutionary links with cellular organisms?
A.
Viruses increase in size before dividing into daughter cells.
B.
Viral genes are translated using essentially the same genetic code as cells.
C.
Every virus has a membrane envelope derived from a host cell.
D.
All viruses contain the same set of core metabolic genes.
Question 11
Two different influenza strains infect the same host cell. Progeny viruses are produced with a new combination of genome segments and surface antigens. What process has occurred?
A.
Integration of viral DNA as a prophage
B.
Translation of host mRNA into viral antigens
C.
Reassortment of a segmented RNA genome
D.
Reverse transcription of RNA into DNA
Question 12
Viruses are non-cellular infectious agents that can reproduce only inside host cells.
State two structural features that are shared by all viruses.
[2]
Explain how viruses can exist with so few genes.
[2]
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Question 13
The table compares three viruses: bacteriophage lambda, a coronavirus and HIV.
Virus | Host | Genetic material | Envelope | Structure |
|---|---|---|---|---|
Bacteriophage lambda | Bacteria | 1 dsDNA molecule | No | head and tail; tail fibres |
Coronavirus | Human cells | 1 ssRNA molecule | Yes | roughly spherical; spike proteins |
HIV | Human cells | 2 ssRNA molecules | Yes | roughly spherical; spike proteins |
Using the table, state one difference in structure between bacteriophage lambda and a coronavirus.
[1]
Compare the genetic material of the three viruses.
[2]
Suggest why enveloped viruses commonly have viral proteins embedded in the envelope.
[1]
Question 14
HIV is an enveloped retrovirus that infects human immune cells.
State the role of reverse transcriptase in HIV replication.
[1]
Distinguish between an enveloped virus and a non-enveloped virus.
[2]
Question 15
Bacteriophage lambda can enter a lysogenic cycle in Escherichia coli.
Define prophage.
[1]
Explain how lysogeny allows viral genetic material to persist without immediate production of new virus particles.
[2]
Question 16
A table compares structural features of purified particles of three viruses with two cellular organisms.
Organism | Nucleic acid genome | Protein capsid | Ribosomes | Cytoplasm | Diameter / nm |
|---|---|---|---|---|---|
bacteriophage lambda | yes | yes | no | no | 60 |
influenza virus | yes | yes | no | no | 100 |
HIV | yes | yes | no | no | 120 |
E. coli | no | no | yes | yes | 2000 |
yeast cell | no | no | yes | yes | 5000 |
Using the table, identify two features present in all three viruses but absent from both cellular organisms.
[2]
Calculate how many times larger the diameter of E. coli is than the diameter of bacteriophage lambda.
[1]
Explain why the viruses in the table must use a host cell for protein synthesis.
[1]
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Question 17
Three viruses were compared for genome type, external structure, host cell and mode of entry.
Virus | Genome type | External structure | Host cell | Mode of entry |
|---|---|---|---|---|
Coronavirus | single-stranded RNA | enveloped, roughly spherical with spike proteins | human respiratory epithelial cells | binds receptor and enters by membrane fusion/endocytosis |
HIV | single-stranded RNA; reverse-transcribed to DNA | enveloped, roughly spherical with glycoprotein spikes | human T helper lymphocytes | binds receptor and fuses with host membrane |
Bacteriophage lambda | double-stranded DNA | protein capsid head and tail; no envelope | Escherichia coli | injects DNA through tail into host cell |
Identify the virus in the table that is non-enveloped and state the evidence for your answer.
[2]
Compare the genetic material of coronavirus and HIV using the table.
[1]
Explain how the table illustrates diversity of structure in viruses.
[2]
Question 18
The diversity of viral genomes and structures has led to the hypothesis that viruses have several origins. What statement best explains why shared viral features may still occur under this hypothesis?
A.
All present-day viruses inherited the same capsid gene from one viral ancestor.
B.
Host cells independently evolved viral capsids to prevent infection.
C.
Similar selection pressures favoured small infectious particles with protected genomes.
D.
Viruses became cellular organisms and then lost their host range.
Question 19
HIV treatment often uses a combination of antiretroviral drugs rather than a single drug. What is the main evolutionary reason for this strategy?
A.
Several drugs increase the generation time of HIV until evolution stops.
B.
A virus with mutations conferring resistance to several drugs is less likely to arise and survive.
C.
Combination therapy prevents reverse transcriptase from making any copying errors.
D.
Using several drugs makes host immune cells genetically identical.
Question 20
The diagram represents stages in the lytic cycle of bacteriophage lambda in Escherichia coli.
Outline two events that occur after the viral DNA has entered the bacterial cell and before lysis.
[2]
Explain how lysis contributes to the spread of bacteriophage lambda.
[2]
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Question 21
Bacteriophage lambda was added to two flasks containing nutrient medium. One flask contained living Escherichia coli cells and the other contained no cells. The number of virus particles was monitored over time.
Describe the pattern shown by the graph.
[1]
Explain why bacteriophage lambda cannot multiply in nutrient medium without host cells.
[2]
Question 22
The life cycle followed by bacteriophage lambda depends on conditions inside the bacterial host cell.
Compare the outcome for the host cell in the lytic and lysogenic cycles.
[2]
Suggest why lysogeny may be advantageous to bacteriophage lambda when host cells are scarce.
[2]
Question 23
Viruses are extremely diverse, but they share an obligate parasitic mode of existence.
State one piece of evidence linking viruses with cellular life.
[1]
Explain why viral diversity supports the idea that viruses have had several origins from other organisms.
[3]
Question 24
Influenza viruses have RNA genomes divided into separate segments. Two different influenza strains may infect the same host cell.
State one reason why RNA viruses such as influenza can evolve rapidly.
[1]
Explain how co-infection by two influenza strains can produce a new strain.
[2]
Suggest why influenza vaccines may need to be updated.
[1]
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Question 25
Purified virus particles and intact host cells were incubated in a nutrient solution containing glucose, amino acids and nucleotides. Changes in ATP concentration and protein production were measured.
Sample type | ATP at 0 min / a.u. | ATP at 30 min / a.u. | ATP at 60 min / a.u. | Labelled amino acid incorporation at 60 min / % of uninfected-cell control |
|---|---|---|---|---|
Purified virus particles | 0.0 | 0.0 | 0.0 | 1 |
Uninfected host cells | 0.0 | 4.0 | 8.0 | 100 |
Virus-infected host cells | 0.0 | 3.8 | 7.6 | 75 |
Describe the difference in ATP production between purified virus particles and uninfected host cells.
[1]
Compare incorporation of labelled amino acids into protein in purified virus particles and virus-infected host cells.
[2]
Suggest why purified virus particles did not produce new viral proteins in the nutrient solution.
[2]
Question 26
A culture of E. coli was infected with bacteriophage lambda under conditions favouring the lytic cycle. Bacterial turbidity and free phage particles were measured for one hour.
Time / min | Bacterial turbidity / a.u. | Free phage concentration / particles |
|---|---|---|
0 | 0.71 | |
10 | 0.71 | |
20 | 0.70 | |
24 | 0.70 | |
25 | 0.68 | |
26 | 0.64 | |
30 | 0.58 | |
35 | 0.46 | |
40 | 0.34 | |
45 | 0.25 | |
50 | 0.20 | |
60 | 0.20 |
State the time at which free phage particles first show a rapid increase.
[1]
Describe the relationship between bacterial turbidity and free phage concentration after this time.
[2]
Explain the changes in the graph using events in the lytic cycle of bacteriophage lambda.
[2]
Question 27
Bacteriophage lambda infections of E. coli were carried out at different host-cell densities. The percentage of infected cells entering lysogeny rather than the lytic cycle was recorded.
Describe the trend shown in the graph.
[1]
State the percentage of infected cells entering lysogeny at the lowest host-cell density shown.
[1]
Suggest why lysogeny may be favoured when host cells are scarce.
[2]
Question 28
Influenza virus samples were collected over six consecutive seasons. Antigenic distance from the vaccine strain and vaccine effectiveness were estimated for each season.
Describe the relationship between antigenic distance and vaccine effectiveness.
[1]
Using the graph, estimate the change in vaccine effectiveness between the season with the lowest antigenic distance and the season with the highest antigenic distance.
[2]
Explain why influenza vaccines may need to be updated frequently.
[2]
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Question 29
The shared structural features of viruses may have evolved independently in different viral lineages.
Outline what is meant by convergent evolution.
[1]
Discuss how convergent evolution could explain common viral features.
[3]
Question 30
The frequency of an HIV variant resistant to drug X was measured during two treatments: drug X alone and a combination of three antiretroviral drugs.
Describe the effect of drug X alone on the frequency of the resistant HIV variant.
[1]
Explain why resistant HIV variants can become common during treatment with a single drug.
[2]
Evaluate the use of a combination of antiretroviral drugs based on the data.
[1]
Question 31
Samples of four viruses were treated with a mild detergent that disrupts membranes and with a protease that digests exposed proteins. Infectivity was then measured as a percentage of untreated controls.
Identify the two viruses most likely to be enveloped.
[1]
Explain the effect of detergent on infectivity of an enveloped virus.
[2]
Suggest why protease reduced infectivity of bacteriophage lambda even though it is not enveloped.
[1]
Question 32
Researchers tested how inhibitors of host-cell processes affect the yield of bacteriophage lambda during the lytic cycle in E. coli. Each inhibitor was added immediately after phage DNA entry.
Identify the treatment that most strongly reduced production of complete phage particles inside the cells.
[1]
Explain why inhibition of host ribosomes reduces phage yield.
[2]
Suggest why inhibition of cell wall breakdown resulted in many intracellular phage particles but few extracellular phage particles.
[2]
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Question 33
A lysogenic strain of E. coli carrying bacteriophage lambda DNA was grown for several generations. Some cultures were then exposed to ultraviolet light. PCR was used to detect a bacterial attachment site, a prophage junction and free circular lambda DNA.
Identify the lane that provides evidence for a prophage in the bacterial chromosome.
[1]
Explain why daughter cells of the lysogenic strain also contain lambda DNA before ultraviolet exposure.
[2]
Suggest what the appearance of free circular lambda DNA after ultraviolet exposure indicates about the viral life cycle.
[2]
Question 34
The diagram summarizes two hypotheses for viral origins and gives examples of viral features that could arise under similar selection pressures.
Identify the hypothesis represented by a mobile genetic element gaining genes for transmission between cells.
[1]
Explain how the shared genetic code links viruses with living organisms.
[1]
Discuss how the diagram supports the idea that evolution is not always characterized by increasing complexity.
[2]
Question 35
A newly discovered infectious agent was isolated from a lake water sample. It contains a nucleic acid genome inside a protein coat and only replicates after entering cells of a freshwater alga.
Identify two features in the diagram that support classifying the infectious agent as a virus.
[2]
The agent contains only a few genes. Explain how it can reproduce with so little genetic information.
[2]
I.
State why the agent cannot carry out ordinary cellular metabolism outside the host cell.
[1]
II.
Explain why the shared genetic code of host cells and viruses is important for viral replication.
[1]
Question 36
A laboratory compared the survival of an enveloped animal virus and a non-enveloped virus after drying and after exposure to a detergent.
I.
Define viral envelope.
[1]
II.
State the outer protective layer of a non-enveloped virus.
[1]
Explain why detergent may reduce infectivity of an enveloped virus more than a non-enveloped virus.
[2]
Discuss why envelope presence is only one aspect of viral diversity and not a feature common to all viruses.
[2]
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Question 37
Protein sequences from several viral groups were compared with sequences from cellular organisms. The presence of selected genes and the closest sequence match were recorded.
Selected gene | Group 1 | Group 2 | Group 3 | Group 4 | Closest cellular match |
|---|---|---|---|---|---|
DNA polymerase | present | present | absent | present | eukaryotic |
Helicase | present | absent | present | absent | bacterial |
Integrase | absent | present | present | absent | archaeal |
Reverse transcriptase | absent | absent | present | present | eukaryotic |
State one observation from the table that argues against all viruses descending from a single recent viral ancestor.
[1]
Outline evidence from the table that viruses may have several origins from other organisms.
[2]
Evaluate the conclusion that shared viral features are the result of convergent evolution.
[2]
Question 38
In a clinical study of HIV, the frequency of drug-resistant viral genomes was measured during treatment with one antiretroviral drug or with a combination of three antiretroviral drugs. Viral load was also recorded.
Time after treatment / weeks | Genomes resistant to 1 drug / % | Genomes resistant to 3 drugs / % | Viral load / RNA copies mL (1 drug) | Viral load / RNA copies mL (3 drugs) |
|---|---|---|---|---|
0 | 1.0 | 0.1 | 60000 | 200 |
4 | 5.0 | 0.2 | 55000 | 150 |
8 | 20.0 | 0.3 | 65000 | 100 |
12 | 45.0 | 0.5 | 80000 | 80 |
16 | 70.0 | 0.8 | 95000 | 50 |
Compare the change in frequency of resistant HIV genomes during monotherapy and triple-drug therapy.
[2]
Explain why HIV can evolve drug resistance rapidly within one person.
[2]
Evaluate why the data support the use of combination antiretroviral therapy.
[1]
Question 39
Three viruses are shown: bacteriophage lambda, a coronavirus and HIV.
I.
Identify which of the three viruses is a bacteriophage.
[1]
II.
State one structural feature visible in the diagram that is shared by all three viruses.
[1]
Compare and contrast the structure of bacteriophage lambda with the structure of HIV.
[4]
Discuss how the examples shown illustrate diversity among viruses despite the few features shared by all viruses.
[2]
Question 40
A culture of Escherichia coli was infected with bacteriophage lambda under conditions favouring the lytic cycle. Samples were taken over time to measure the number of intact bacterial cells and the number of free phage particles.
I.
State the stage of the lytic cycle represented by the initial delay before free phage particles increase.
[1]
II.
Identify the event causing the sharp decrease in intact bacterial cells.
[1]
Explain how bacteriophage lambda uses the host cell during the lytic cycle.
[3]
Evaluate one advantage and one disadvantage of the lytic cycle for the virus population.
[2]
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Question 41
Some cells in a culture of E. coli infected by bacteriophage lambda continue dividing for many generations without producing new phage particles. After exposure to ultraviolet radiation, the same culture releases many phages.
I.
Define prophage.
[1]
II.
State why daughter bacterial cells inherit lambda DNA during lysogeny.
[1]
Explain the main differences between the lysogenic cycle and the lytic cycle of bacteriophage lambda.
[3]
Suggest why lysogeny may be advantageous when susceptible host cells are scarce.
[2]
Question 42
Influenza viruses have RNA genomes divided into separate segments. Two influenza strains can infect the same host cell.
I.
Define a segmented genome.
[1]
II.
State one influenza surface protein that acts as an antigen.
[1]
Explain how mutation and reassortment can produce new influenza strains.
[3]
Discuss why influenza vaccines may need to be updated regularly.
[2]
Question 43
HIV populations sampled from one untreated patient over several years showed increasing genetic diversity in the gene coding for an envelope protein. Antiretroviral treatment was then started using either one drug or a combination of three drugs.
I.
Identify the enzyme responsible for making DNA from the RNA genome of HIV.
[1]
II.
State why this enzyme contributes to high genetic variation in HIV.
[1]
Explain how antiretroviral drugs can act as a selection pressure on an HIV population.
[3]
Evaluate why combination therapy is usually more effective than treatment with one antiretroviral drug.
[3]
Question 44
Four unknown viruses were analysed. Their genomes were classified as single-stranded RNA, double-stranded RNA, single-stranded DNA or double-stranded DNA. All four viruses were able to replicate only inside host cells.
Virus | Genome type | Envelope present |
|---|---|---|
Virus A | single-stranded RNA | Yes |
Virus B | double-stranded RNA | No |
Virus C | single-stranded DNA | Yes |
Virus D | double-stranded DNA | No |
I.
State the two possible nucleic acid types used as viral genetic material.
[1]
II.
State what is meant by a double-stranded viral genome.
[1]
Explain why genome type alone is insufficient to determine whether an unknown particle is a virus.
[2]
Discuss how variation in genome type and envelope presence contributes to viral diversity.
[3]
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Question 45
Viruses have few features in common but show great diversity in genome type, shape, host and replication strategy. Biologists have proposed that different virus groups may have originated independently from cellular material.
I.
State one feature shared by viruses and living organisms.
[1]
II.
State one feature common to viruses that could be regarded as a result of convergent evolution.
[1]
Explain how the shared genetic code provides evidence linking viruses with cellular life.
[2]
Discuss the evidence that viruses may have had several origins rather than a single common viral ancestor.
[4]
Question 46
Bacteriophage lambda can enter either the lytic or lysogenic cycle after infecting E. coli. A student claims: "The lysogenic cycle is always better for the virus because it does not kill the host cell."
I.
State the first step common to both cycles.
[1]
II.
State the main outcome of the lytic cycle.
[1]
Explain how lysogeny allows lambda DNA to persist in a bacterial population.
[3]
Evaluate the student's claim by considering conditions in which each cycle could be advantageous.
[3]
Question 47
Two viral diseases are being considered for vaccine development. Disease X is caused by an influenza virus. Disease Y is caused by HIV.
Feature | Influenza virus | HIV |
|---|---|---|
Genome type | Segmented RNA genome | RNA genome in a retrovirus |
Main source of new variation | Errors during RNA genome replication | Errors made by reverse transcriptase |
Additional way variation can arise | Reassortment if two strains infect the same cell | Rapid selection of variants within a host under immune or drug pressure |
Prevention/treatment consequence | Surface antigens can change, so vaccine strains may need updating; prior immunity may be less effective | Surface protein variation makes a universal vaccine difficult; drug-resistant variants can be selected, so combination therapy is used |
I.
State one reason why influenza viruses can evolve rapidly.
[1]
II.
State one reason why HIV can evolve rapidly.
[1]
Compare the mechanisms producing genetic variation in influenza viruses and HIV.
[3]
Discuss consequences of rapid evolution for prevention or treatment of these two viral diseases.
[3]
Question 48
Two hypotheses for the origin of viruses are shown. Hypothesis 1 proposes that viruses evolved from mobile genetic elements that gained genes for transmission between cells. Hypothesis 2 proposes that viruses evolved from parasitic cellular organisms that lost genes and structures over time.
I.
Identify the hypothesis in which viruses evolved by gaining transmission structures from mobile genetic elements.
[1]
II.
Identify the hypothesis in which viruses evolved by loss of genes and cellular structures.
[1]
Explain how obligate parasitism in viruses could favour simplification during evolution.
[3]
Evaluate the claim that evolution is always characterized by increasing complexity, using viruses as evidence.
[3]
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