10. Infectious diseases
A section of Biology, 9700
Listing 10 of 290 questions
Cholera is an infectious disease caused by the bacterium Vibrio cholerae. The pathogen causes disease by disrupting the activity of the epithelial cells in the human intestine. Complete Table 3.1 to compare the structure of V. cholerae and an epithelial cell from the human intestine. Use a tick (3) to indicate the presence of the structure. Use a cross (7) to indicate the absence of the structure. The first row has been completed for you. Table 3.1 cell structure V. cholerae epithelial cell from the human intestine cell wall cell surface membrane ribosomes large permanent vacuole organelles surrounded by a double membrane Describe the methods that can be used to prevent the spread of cholera. The World Health Organization has suggested that people with HIV/AIDS take a longer time to recover from cholera and are at an increased risk of death from cholera. The human immunodeficiency virus (Honly infects certain types of cell. These cells have CD4 receptor proteins in their cell surface membrane. Helper T-lymphocytes have CD4 receptor proteins. is a diagram of HIV showing the glycoprotein gp120. This glycoprotein is embedded in a membrane envelope which surrounds the viral protein coat. gp120 envelope protein coat genetic material The glycoprotein gp120 is important in allowing HIV to only infect certain types of cell. Suggest the role of gp120. People with HIV/AIDS have a low helper T-lymphocyte count. Explain how a low helper T-lymphocyte count could reduce the body’s ability to produce antibodies against V. cholerae.
9700_s19_qp_23
THEORY
2019
Paper 2, Variant 3
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The Bacillus Calmette-Guérin (BCG) vaccine is the only vaccine used to provide protection against the infectious bacterial disease tuberculosis (TB). Most countries of the world have a BCG vaccination programme. TB is most commonly transmitted from person to person by aerosol infection. The causative organism is present in airborne droplets. Name the species of causative organism of TB commonly passed from person to person by aerosol infection. In general, the countries that do not have a BCG vaccination programme are high-income countries that have a low number of cases of TB. In most of these countries, the vaccine is given only to babies and children at high risk of developing TB. Suggest one reason why a child in a country with a low number of cases of the disease could be at a high risk of developing TB. Countries are classified by the World Bank into one of four income groups. Table 3.1 shows the estimated incidence of TB for 2012 to 2016 for these income groups. The incidence represents the number of new cases of TB occurring per 100 000 people in one year. The new cases include the number of cases that have occurred again after a period of recovery (relapse TB). Table 3.1 incidence per 100 000 people year income group low lower middle upper middle high Describe the patterns and trends shown in Table 3.1. There is evidence that the BCG vaccine has also provided protection against the disease leprosy. Leprosy is caused by a bacterium that is closely related to the bacteria that cause TB. Suggest why the BCG vaccine can also provide protection against leprosy. A baby can gain artificial active immunity to TB after having the BCG vaccine. A baby can also gain natural passive immunity to TB. State the differences between artificial active immunity and natural passive immunity.
9700_s20_qp_22
THEORY
2020
Paper 2, Variant 2
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In 2016, the highest number of cases of malaria and deaths caused by the disease were in sub‑Saharan Africa. In many areas of sub‑Saharan Africa, malaria is endemic (continually present) and people are at high risk of becoming infected with the Plasmodium pathogen. In high risk areas it is recommended that: • homes are provided with insecticide‑treated nets (ITN) • the surfaces inside homes where Anopheles mosquitoes may rest are sprayed with insecticide. This is known as indoor residual spraying (IRS). Explain how the use of ITN and IRS can help break the transmission cycle of malaria. shows the proportion of the population in sub‑Saharan Africa at risk of malaria that is protected by using IRS or ITN, or both, in the years 2010 to 2016. percentage of population protected year IRS only ITN & IRS ITN only Key The main trend in shows that there is an increase in the percentage of the population protected over time. State one other trend shown in . Explain why the main trend shown in could be a concern for the World Health Organization. With reference to , suggest a reason for the difference in trends shown for ITN only compared with IRS only. In a primary immune response, antibodies against Plasmodium are produced within one to two weeks following infection. In some people, the pathogen is eliminated and the concentration of antibodies in the circulation decreases over time. Infection again by Plasmodium with the same antigens causes a secondary response that also involves antibody production. State and explain how the antibody response following a second infection will differ from the primary immune response. In malaria, the production of antibodies is beneficial to recovery, whereas in the disease myasthenia gravis the production of antibodies is harmful. Explain why the production of antibodies in a person with myasthenia gravis is harmful.
9700_s20_qp_23
THEORY
2020
Paper 2, Variant 3
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The diseases myasthenia gravis (MG) and HIV/AIDS both involve disorders of the immune system. The cause of MG involves a response by B‑lymphocytes. Explain why MG is called a disorder of the immune system. 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. Many people who are living with HIV (infected with Hdevelop 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. 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 for 2017 are estimated. globally, 36.9 million people were living with HIV 1.8 million people became infected with HIV 940 000 people died from HIV/AIDS 21.7 million were provided with ART (antiretroviral therapy) 35.1 million adults and 1.8 million children (under 15 years) 47% of the people provided with ART, while still living with HIV, do not have detectable levels of the virus in their blood 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 , discuss the importance of this statistic.
9700_s21_qp_22
THEORY
2021
Paper 2, Variant 2
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Smallpox, measles and HIV/AIDS are infectious diseases caused by different viruses. These different viruses share some structural features. State one structural feature that would confirm that a pathogen is a virus. The virus that causes smallpox belongs to a different genus to the virus that causes measles. Name the viruses that cause these diseases. smallpox measles Explain why antibiotics, such as penicillin, cannot be used to treat measles. Antibiotics may be prescribed for a person with HIV/AIDS. Suggest why antibiotics may be prescribed for a person with HIV/AIDs. Smallpox is the only infectious disease of humans that has been globally eradicated. This eradication was due mainly to a successful global vaccination programme. Most people who were given the vaccine gained immunity to the disease. A student correctly listed four reasons for the success of the global vaccination programme for smallpox. These reasons are listed in . • The virus did not mutate. • A live virus, closely related to the smallpox virus, was used in the vaccine. • The vaccine was freeze-dried and so was thermostable (heat stable). • The vaccine was easy to administer , so little training was required. Discuss how the reasons listed in contributed to the success of the eradication of smallpox. Table 2.1 lists four types of immunity. Complete each row of Table 2.1 with a tick (3) or a cross (✗) to summarise the types of immunity gained by a person who received the smallpox vaccine. Table 2.1 type of immunity gained (3) not gained (✗) active immunity artificial immunity natural immunity passive immunity
9700_s21_qp_23
THEORY
2021
Paper 2, Variant 3
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Cholera is a life-threatening and infectious disease caused by the bacterium Vibrio cholerae. One of the symptoms of the disease is severe diarrhoea. V. cholerae O1 and V. cholerae O139 are the two forms of the pathogen that are associated with cholera epidemics (large outbreaks). These two forms have different antigens that can be detected. If an outbreak of cholera is suspected but not confirmed, a standard home treatment for diarrhoeal diseases can be used immediately to help prevent severe illness as a result of dehydration. If cholera is the cause of the disease, this standard treatment also helps to prevent a larger outbreak of the disease. Outline the standard treatment that can be used for suspected cholera cases. Suggest and explain why this treatment can help to prevent a larger outbreak of cholera. Rapid diagnostic testing (RDT) can be used to diagnose cholera by detecting the presence of V. cholerae. One type of RDT involves using a dipstick that contains mobile and immobilised monoclonal antibodies. Monoclonal antibodies (mAbs) are specific in their action. shows a simplified diagram of an RDT dipstick that can be used to distinguish between V. cholerae O1 and V. cholerae O139. A faecal sample from a person with suspected cholera is collected and added to a reagent solution to form the test mixture. direction of flow of test mixture area where dipstick can be held 4 control area 3 test area containing immobilised monoclonal antibody that binds antigen-antibody complex O1 2 test area containing immobilised monoclonal antibody that binds antigen-antibody complex O139 1 area containing two different mobile monoclonal antibodies: • anti-O1 antibody • anti-O139 antibody area where dipstick is inserted into the test mixture The test mixture moves up the dipstick through area 1. The mobile monoclonal antibodies are attached to tiny gold particles. If these antibodies collect in test area 2 or 3, a coloured band becomes visible. A coloured band that becomes visible in area 4 confirms that the test strip is working and that the results are valid. Explain how the structure of the monoclonal antibodies in the dipstick allows them to be specific in their action. shows the results for samples taken from two different people, A and B, who are suspected of having cholera. person A person B With reference to , state and explain the conclusions that can be drawn from the results of the RDT dipsticks for each person. Table 2.1 shows the results of an investigation to evaluate the effectiveness of an RDT dipstick in diagnosing cholera. Samples taken from 156 people were tested using a dipstick and compared to the results obtained by culturing the pathogen in a laboratory for accurate identification. Table 2.1 number of test results using culture techniques (to obtain accurate identification) using dipstick correct diagnosis incorrect diagnosis positive results for cholera negative results for cholera With reference to Table 2.1, calculate the percentage chance of an RDT dipstick correctly confirming that a person with cholera has the disease. Using an RDT dipstick to diagnose cholera is much cheaper than culturing the pathogen and requires less technical skill. Suggest one additional advantage of using an RDT dipstick, rather than culture techniques, to diagnose cholera.
9700_s22_qp_22
THEORY
2022
Paper 2, Variant 2
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Questions Discovered
290