A-LevelBiologyInfectious diseases9700/22 · Oct/Nov 2018 · Q415 Marks

Viruses share common structural features. Some viruses, such as human immunodeficiency virus (HIV), also have an outer envelope as part of their structure.

(a)Outline the key structural features of viruses.[3]
(b)(i)HIV can remain in a dormant state within infected immune system cells for many years. A person diagnosed as HIV-positive (HIV+) has the virus but does not have symptoms of HIV/AIDS. The chances of an HIV+ person developing HIV/AIDS can be greatly reduced with a drug treatment programme known as anti-retroviral therapy (ART). In 2010, the World Health Organization (WHO) published recommendations for the treatment of pregnant women living with HIV. This includes both HIV+ women and women who have developed HIV/AIDS. The publication recommended that all pregnant and breastfeeding women living with HIV should be provided with ART. [Figure 4.1] shows the number of pregnant women living with HIV, and the number of these receiving ART, between 2005 and 2013, in low and middle income countries. (i) From the data in Fig. 4.1, it can be calculated that 13% of pregnant women living with HIV received ART in 2005. Calculate the percentage of pregnant women living with HIV that received ART in 2013. answer ..................................................... %[1]
(b)(ii)Describe the trends shown in Fig. 4.1.[3]
(b)(iii)Suggest and explain the global importance of providing ART to all pregnant and breastfeeding women living with HIV.[3]
(c)(i)In a person who has been infected with HIV-1, the most common strain of HIV, a sample of blood can be tested for the presence of the virus. One test that can only be used in the early stages of infection involves a monoclonal antibody specific for p24, a structural protein present in the virus. [Figure 4.2] is a flow chart outlining the steps in the production of anti-HIV p24 monoclonal antibody. (i) State what is being injected into the mouse in step 1.[1]
(c)(ii)Explain why several weeks, rather than several days, separates step 1 and step 2.[1]
(c)(iii)State one feature of the myeloma mouse cells, used in step 3, that is essential for this production process.[1]
(c)(iv)Name the fused cells formed in step 4.[1]
(c)(v)Suggest why step 6 is necessary.[1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.

[1] protein coat / capsid ; I protein layer
[1] nucleic acid ; DNA or RNA ; R in nucleus I in cytoplasm I ref. to, double / single, strand
[1] acellular / not made of cells ; I absence of named cell structures
[1] AVP ; e.g. ref. to capsomeres size 15nm to 1000nm accept any in range (some) are enveloped / have phospholipid bilayer I with glycoproteins
[1] one value in the range 64% – 68% ; ((940 000 – 980 000) ÷ (1 440 000 – 1 480 000)) × 100
[1] (slight) decrease in (total) number of women living with HIV and (overall) increase in number of women living with HIV receiving ART ;
[1] slight decrease / plateau / AW, between 2009 to 2010, in number of women living with HIV receiving, ART / therapy ;
[1] proportion / percentage cover(age), of women receiving ART increases (in time period) ; A calculated values (approx. 13% to 66%) A number of women receiving ART increases more steeply than decrease in number of women living with HIV
[1] data to support mp1 or 2 ; mp1 two years and, two values / manipulated data, for either curve mp2 two values, 2009 compared to 2010 or manipulated data allow ± 20 000 for extracted values
[1] ref. to mother to child transmission; in context of HIV transmission A (because) HIV can be passed from mother to baby A decreases HIV transmission during, pregnancy / labour / birth / breastfeeding A reduces, number / proportion, of babies born with HIV (so fewer die) I stops transmission (as this is in context of global transmission this implies in all cases) I makes babies immune to HIV/AW or gives passive immunity allow idea that ART may be passed across, placenta/breastmilk, to baby and so provide(short-term) protection against any HIV transmitted from mother
[1] reduces number of, HIV positive women becoming ill (with HIV/AIDS) /women with HIV/AIDS dying from the disease ; A opportunistic infections / named examples e.g. TB
[1] example of reduces spread of HIV; in any correct context other than HIV mother to child e.g. child may grow up without HIV and will not pass on mother less likely to pass on to partner
[1] examples of, social / economic, effect ;; e.g. (healthy women) can contribute to work force
[1] examples of, social / economic, effect ;; e.g. can be main carer if partner has died (idea that children not orphaned) overall financial savings e.g. if infants are not born with HIV then no lifelong ART required ART may be less costly than treating HIV/AIDS makes breastfeeding safer when no other options exist to feed babies HIV negative children will become next workforce generation all women throughout world receive same treatment
[1] (HIV) antigen / p24; A capsid protein / capsomere(s) / protein coat R HIV
[1] (time needed) so, immune response / clonal expansion / production of B-lymphocytes / production of plasma cells, can occur ; A B-cells / splenocytes R plasma cells need to multiply I ref. to antibody production
[1] immortal / long-lived ;
[1] able to replicate / capable of cell division ;
[1] uncontrolled cell division, can grow / survive, in cell culture ;
[1] cannot grow on, HAT / hypoxanthine-aminopterin-thymidine / step 4, (culture) medium ; A do not have gene coding for ability to grow on HAT
[1] hybridoma ;
[1] (check cells for) production / AW, (by hybridoma cells) of, anti-HIVp24 antibody / antibody against p24 ; A the antibody / monoclonal antibody A check cells, contain / have / AW, desired antibody / AW
[1] idea that only want cells that produce desired antibody / do not want cells that produce different antibodies / need to remove cells that don't produce the antibody ;
[1] waste of, money / resources, to culture other cells / if no antibody produced ;