A-LevelBiologyImmunity9700/22 · Feb/Mar 2020 · Q511 Marks

Myasthenia gravis and HIV/AIDS both involve disorders of the immune system.

(a)Outline why myasthenia gravis is described as a disorder of the immune system.[2]
(b)A person with HIV/AIDS has a weakened immune system. This is because HIV infects cells of the immune system, in particular T-helper lymphocytes (T₁ cells). The pathogen can remain inactive within host cells. In some people, the pathogen becomes active and causes the number of T₁ cells to decrease. Antiretroviral therapy (ART) is used to treat people who are infected with HIV (living with HIV). ART aims to keep the number of Tĥ cells at a healthy level. State the full name of the pathogen known as HIV.[1]
(c)Explain why it is important that ART maintains a healthy number of T₁ cells in a person living with HIV.[3]
(d)(i)Fig. 5.1 shows global estimates of: • the percentage of people living with HIV who received treatment with ART in each year from 2000 to 2015 • the number of people who died from HIV/AIDS in each year from 2000 to 2015. [Figure 5.1] Describe the trends shown in Fig. 5.1.[3]
(d)(ii)It is recommended that ART is given to all people living with HIV. Some countries that support this recommendation find it difficult to provide ART to everyone living with HIV. Other than the high cost of treatment, suggest two reasons why it is difficult to provide ART to everyone living with HIV.[2]

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 (Feb/Mar 2020). The mark or mark type is shown in brackets.

[2] 5(a) A ref. to receptors (at neuromuscular junctions) for self-antigens
any two from:
1 autoimmune disease ;
2 failure to distinguish self and non-self (antigens) ;
A foreign for non-self
3 immune response / antibodies produced, against self-antigens ;
4 binding of (specific) antibody to self-antigen (on the external cell surface membranes of muscle cells) ;
5 faulty / AW, lymphocytes not destroyed;
[1] 5(b) human immunodeficiency virus ;
[3] 5(c) any three from:
if Th cell number is low:
1 low Th cells means increased risk of developing an infectious disease ;
2 low levels / less, cytokine, secreted / AW;
role of cytokine:
3 stimulates activity of macrophages / produces angry macrophages ;
4 stimulates, B-lymphocytes / plasma cells / humoral, response ;
A activate B-lymphocytes
5 (so lower concentrations / less / no), antibody, produced / secreted ;
6 stimulates, T-cytotoxic / T-killer, cells ;
7 (so) fewer infected cells killed ;
8 more time for pathogens to, reproduce / spread ;
9 fewer memory cells (to fight future infection);
[3] 5(d)(i) any three from:
receiving treatment (max 2):
1 percentage of people living with HIV receiving treatment increases ;
2 low rate of increase between 2000 and, 2003/2004 ;
3 data to support ;
e.g. 3%/4%, in 2000–2003, 45% in 2015
deaths:
4 increase in HIV / AIDS-related deaths to, 2004 / 2005, then decrease ;
A peak in 2004 / 2005
5 data to support ;
e.g. two of: start at 1.5 million, peak at 2 million, end at 1.2 million (2 of these)
[2] 5(d)(ii) any two from:
1 lack of trained personnel to deliver treatment ;
2 some people unwilling to take treatment;
3 isolated areas / difficulty getting treatment to people;
4 inability to, supply / produce, enough drugs ;
5 not all people living with HIV, know their status / have been diagnosed ;
6 AVP;