VirusesEdexcel A-Level Biology B: Mind map

Exam questions on Viruses

1. Human immunodeficiency virus (HIV) is an enveloped virus that infects helper T cells. Each virus particle contains two molecules of RNA and the enzyme reverse transcriptase. Zidovudine, an antiviral drug, inhibits reverse transcriptase. Penicillin, an antibiotic, has no effect on HIV.
   Explain how zidovudine reduces the replication of HIV.2 marks
2. Lambda phage is a virus that infects the bacterium Escherichia coli. After infecting a bacterium, the phage can either destroy the cell within about an hour, releasing around 100 new phages, or have its DNA inserted into the bacterial chromosome and copied each time the bacterium divides. After many generations, exposure of the infected bacteria to ultraviolet light causes many of them to burst and release new phages.
   Suggest two advantages to the virus of latency.2 marks
3. The 2014 outbreak of Ebola virus disease in West Africa spread rapidly through Guinea, Sierra Leone and Liberia. Ebola is an RNA virus spread by contact with the body fluids of infected people, including people who have died of the disease. At that time no licensed vaccine or antiviral drug existed. The response included isolating patients, tracing their contacts, training health workers to wear protective clothing and organising safe burials with community leaders.
   Explain why control of the outbreak focused on preventing the spread of the virus rather than treating infected people.3 marks