(a)     Outline two differences between bacteria and viruses.

(b)     Antiviral drugs are used for the treatment of HIV and other viral infections. Describe two ways in which antiviral drugs work.

(c)     Discuss why viral infections are generally harder to treat than bacterial infections.

(a)     bacteria are self-reproducing units while viruses are not / viruses need living hosts/cells to multiply / OWTTE;

bacteria are able to grow/metabolise/feed and excrete / viruses lack metabolic functions;

bacteria contain various cell subunits/organelles/cell wall (performing specific functions) / viruses consist only of genetic material and protective coating;

bacteria are (many times) larger than viruses / viruses are smaller than bacteria;

bacteria have more complex DNA / viruses have simpler DNA;

viruses mutate/multiply (much) faster than bacteria / bacteria mutate/multiply slower than viruses;

If comparative term used e.g. smaller what it’s compared to is not required.

(b)     alter cells genetic material so that virus cannot use it to multiply;

prevent viruses from multiplying by blocking enzyme activity within host cell / inhibit the synthesis of viral components by blocking enzymes inside the cell;

prevent viruses from entering (human) cell / bind to cellular receptors targeted by viruses / bind to virus-associated proteins/VAPs which target cellular receptors;

prevent/hinder the release of viruses from the cell;

(c)     viruses mutate quickly so adapt to drugs/evade immune system response / OWTTE;

bacteria are more complex and thus can be targeted in more ways / viruses lack subunits/functions targeted by antibacterials / OWTTE;

bacteria can be killed/impaired by simple chemical agents / viruses cannot be killed and must be targeted on genetic level / OWTTE;

different types of bacteria employ similar metabolic processes and thus can be targeted by common antibacterials / each kind of virus usually requires special drugs/approaches / OWTTE;

This was probably the question in this option that candidates found most difficult and whilst many could give correct differences between viruses and bacteria they seemed to have little knowledge about the action of antiviral drugs or the reasons why viral infections are more difficult to treat.