A-LevelBiologyImmunity9700/22 · May/June 2021 · Q69 Marks

The diseases myasthenia gravis (MG) and HIV/AIDS both involve disorders of the immune system.

(a)The cause of MG involves a response by B-lymphocytes. Explain why MG is called a disorder of the immune system.[2]
(b)Studies have indicated that T-lymphocytes are involved in stimulating the B-lymphocyte response that causes MG. Research has been carried out on a vaccine that will provide a person with active immunity against these T-lymphocytes and B-lymphocytes. Suggest and explain how this vaccine will provide a person with active immunity against the T-lymphocytes and B-lymphocytes responsible for causing MG.[3]
(c)Many people who are living with HIV (infected with HIV) develop tuberculosis (TB). If a person does not have any symptoms of TB, one preventive measure is to prescribe antibiotics. This reduces the overall number of cases of TB and deaths from TB. State the disadvantage of prescribing antibiotics as a preventive measure against TB.[1]
(d)Fig. 6.1 is a summary of some of the statistics published by UNAIDS (Joint United Nations Programme on HIV and AIDS) about HIV and HIV/AIDS for the year 2017. The figures shown in Fig. 6.1 for 2017 are estimated. globally, 36.9 million people were living with HIV 35.1 million adults and 1.8 million children (under 15 years) 1.8 million people became infected with HIV 21.7 million were provided with ART (antiretroviral therapy) 940 000 people died from HIV/AIDS 47% of the people provided with ART, while still living with HIV, do not have detectable levels of the virus in their blood Fig. 6.1 One other statistic published by UNAIDS indicated that, in 2017, only 75% of the estimated 36.9 million people living with HIV knew that they had been infected with the virus. With reference to the information in Fig. 6.1, discuss the importance of this statistic.[3]

Mark scheme

Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.

[2] any two from 1 (MG is an) autoimmune, disease / disorder / condition ; A autoimmunity R autoimmune system 2 (disease in which) failure to distinguish / AW, between self and, non-self ; A between self and, non-self / foreign, antigens 3 (so, at neuromuscular junctions) ref. immune response occurs against / antibody produced against, self-antigens / receptors qualified (see list); A antibodies, bind to / block/attack/AW examples of receptors cell surface muscle cell ACh/neurotransmitter neuromuscular junction postsynaptic 4 idea that defective lymphocytes destroyed (during development);
[3] max 2 if wrong context e.g. vaccine contains, foreign antigens/antigens of pathogen/pathogen/antibody to bind to lymphocytes any three from 1 vaccine contains antigens ; in context of antigens of defective, T-lymphocytes and B-lymphocytes (accept antibody of defective B-lymphocyte as AW antigen) 2 stimulates an immune response ; 3 detail; e.g. macrophages and antigen presentation / AW ref. to specific lymphocytes involved clonal selection of lymphocytes recognition by / activation of, lymphocytes clonal expansion of lymphocytes production of plasma cells in context of B-lymphocytes production of memory cells T-helper cells produce cytokine 4 antibody produced against (defective), T-lymphocytes / B-lymphocytes / antibody (that binds ACh receptors) ; in context of primary or secondary response R if context is related to the vaccine containing antibody 5 memory cells, remain / give long-lasting effect / AW ; 6 memory cells allow secondary immune response to (defective) lymphocytes (newly produced) ;
[1] any one from antibiotic resistance, qualified ; A drug for antibiotic e.g. increases risk of antibiotic resistance developing may cause / could lead to problems of, antibiotic resistance an antibiotic resistant bacterial strain may develop R if, immune / immunity, included R antibiotic resistance / mutation, in, TB / disease / people / virus mutation(s) occur in bacteria which, make antibiotics ineffective / prevent antibiotic action ; A mutation occurs which may make bacteria resistant AVP; e.g. ref. to development of, DR-TB / MDR-TB / XDR-TB (if latent bacteria become active)
[3] max 2 if not in context of the statistic stated (using only Fig. 6.1) mps 2 -8 only points are in context of people who do not know any three from 1 9.2 million do not know that they are, living / infected with, HIV; ora 27.7 million people know risk to themselves 2 not accessing, ART / treatment; A only people who know will access ART A if tested, can access ART 3 high(er) viral, loads / levels (compared to many on ART); ora idea of no control over presence of virus in body 4 greater risk of, developing / dying from, HIV/AIDS / HIV-related diseases ; ora A AIDS for HIV/AIDS R HIV context could be, no ART/higher viral loads/no treatment of HIV-related diseases risk to others 5 greater risk of transmitting, virus / HIV; ora includes placental transmission R HIV/AIDS or AIDS context could be, higher viral load/not practising prevention 6 detail of prevention that may not be practised; ora e.g. are sharing contaminated needles are donating blood are breastfeeding are not, practising safe sex / using condoms / AW 7 (may develop opportunistic infection so) greater risk of spreading infectious diseases ; consequence for, health care / authorities 8 problems with increase in infection within a population ; ora e.g. increased cost of, care / medication increased pressure on medical staff reduction in size of labour force 9 ref. to testing for HIV ; R testing for HIV/AIDS e.g. indicates more, education / advertising, needed to encourage testing indicates more testing required / focusing on at risk groups 10 AVP; issues for authorities other than mp 8 and 9 e.g. if people do not know status, no contact tracing can occur focus efforts on countries where a high proportion do not know HIV status authorities provide free condoms to try and reduce overall transmission