1 Viruses are often described as:
(a) non-cellular
(b) obligate intracellular parasites
Use your knowledge of biology to suggest why each of these terms is appropriate.
2 Construct a table of your own design to summarise the five types of virus covered in the presentation. For each, show the presence or absence of an outer envelope, the nature of the nucleic acid core and the nature of the cells infected.
3 We have used the term ‘type’ to describe viruses.
(a) Explain why it is not possible to refer to a species of virus.
(b) Suggest a system that could be used to classify the different types of virus.
4 The influenza virus has a fragmented genome. Explain what this means.
5 Explain why viruses are specific in the host cells they infect.
6 Cold sores around the mouth are caused by the herpes simplex virus (HSV). The sores typically heal within 2 –3 weeks. Suggest why some people are prone to repeated outbreaks of cold sores in the same area of the mouth.
7 Read the following passage.
Guinea is one of the countries in West Africa in which there has been an Ebola epidemic.
To date, there have been 3786 cases and 2520 deaths reported in Guinea.
In July 2015, a peer-reviewed paper reported that a new vaccine against Ebola had been successfully trialled in Guinea. The trial had involved over 4000 people and was described as remarkable because it had been completed in just 12 months, whereas clinical trials normally take more than 10 years.
The usual method of testing a vaccine involves recruiting volunteers from a population at risk and, using a double-blind design, vaccinating half of them with the trial vaccine and giving the other half a placebo. In the Guinea trial, a ‘ring’ design was used. In this design, when researchers discovered an outbreak of Ebola, they visited the affected village and vaccinated all the willing family, friends and neighbours of the sick. Children and pregnant women were excluded from the vaccination.
The results showed that, 10 days after they had been vaccinated, none of the villagers developed symptoms of Ebola infection.
5
10
14
Philip Allan Publishers
© 2015 www.hoddereducation.co.uk/biologicalsciencesreview

Use information from the passage and your own knowledge to answer the following questions.
(a) Explain the importance of a scientific paper being ‘peer-reviewed’ (line 3).
(b) The trial had involved over 4000 people (line 4). Explain the importance of using this number of people in the trial.
(c) In Guinea, the trial was completed in a much faster time than is usual for clinical trials (lines 5 –6).
(i) Give two reasons why clinical trials normally take more than 10 years.
(ii) Suggest why it was decided to complete the trials in Guinea so quickly.
(d) What is a ‘double-blind’ design (line 8)?
(e) Suggest two features of a placebo that would be appropriate in this double-blind investigation
(line 9).
(f) Suggest why children and pregnant women were excluded from the trial (lines 11 –12).
(g) The researchers tested people for signs of Ebola infection 10 days after vaccination (lines 13 and 14). Suggest why they chose a period of 10 days.
Philip Allan Publishers
© 2015 www.hoddereducation.co.uk/biologicalsciencesreview

1 (a) Cells, whether prokaryotic or eukaryotic, possess a cell-surface membrane and cytoplasm containing ribosomes. Viruses lack these structures.
(b) A parasite is an organism that lives in, or on, another organism causing it harm but itself deriving benefit. Although not organisms, viruses ‘live’ in a host and cause harm to it. Since viruses are replicated inside cells of the host, they are intracellular parasites. The term ‘obligate’ tells us that being an intracellular parasite is the only way in which viruses can be replicated (there is no alternative).
2 A possible table is shown below.
Virus
Ebola virus
Envelope
Absent
Human immunodeficiency virus
Present
Influenza virus Present
λ phage
Tobacco mosaic virus
Absent absent
Nucleic acid core Cells infected ssRNA ssRNA ssRNA
Many different human cells, including liver cells, macrophages, fibroblasts and dendritic cells
T helper cells and macrophages
Epithelial cells of nose, throat and lungs of humans dsDNA ssRNA
Escherichia coli
Plants, especially tobacco plants
(a) A classical definition of a species is a group of organisms that have the potential to interbreed and produce fertile offspring. Viruses are not living organisms and are not capable of reproducing.
(b) A sensible suggestion would be to use the shape of the virion and any of the features in the table above.
4 The genome is the total gene complement. The genome of the influenza virus is divided into eight short strands of RNA, hence fragmented.
5 Glycoproteins on the surface of the virion are complementary only to those on one type of cell. Only if there is a collision between complementary glycoproteins at an appropriate angle and the appropriate speed can a virus attach to the surface of any cell.
6 Following infection, the HSV remains dormant (in the facial nerves) in the same area of the mouth in which the cold sore appeared. Reactivation of the virus (often caused by physiological stress) results in cold sores in the same area.
7 Suitable answers will include the following points.
(a) ‘Peer-reviewed’ means that the report of the research has been evaluated by other scientists in the same field of research. Readers can, therefore, be confident that the methodology was valid, the data are reliable and the conclusions are based on appropriate statistical analysis of the data.
(b) Using a large number of people ensures that any anomalous data have a small impact on the outcome of the research.
Philip Allan Publishers
© 2015 www.hoddereducation.co.uk/biologicalsciencesreview

(c) Suggestions might include the following:
(i) Trials are first carried out in the laboratory using, for example, cell culture. They are then carried out on animals, which involves application for a licence. If successful, they are then carried out on a small group of volunteers, often under hospital conditions. Finally, trials are extended to a large scale following approval from government health departments.
(ii) There had been a large number of deaths from Ebola infection (over 2500 in Guinea and many more in other West African countries). The authorities (including the WHO and the Guinean government) decided the risk of the vaccine was less than the risk of further deaths from the Ebola virus.
(d) Neither the person administering the treatment nor the person receiving it knows whether it involves the active drug/vaccine or the placebo.
(e) It would have the same colour/consistency/viscosity/diluent/flavour (it was actually injected but students cannot deduce this from the passage) as the vaccine.
(f) The effect of the vaccine was unknown. Neither a fetus nor a child is able to make an adult decision/is legally responsible, so it would be unethical to expose them to the vaccine.
(g) Ten days is long enough for symptoms of Ebola infection to appear and is long enough for the primary immune response to occur.
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© 2015 www.hoddereducation.co.uk/biologicalsciencesreview