10. Infectious diseases
A section of Biology, 9700
Listing 10 of 290 questions
The main cause of tuberculosis (TB) in humans is the bacterium Mycobacterium tuberculosis. Most cases of the disease involve the lungs. The bacterium can enter cells and remain inactive in a latent state. However, the bacterium can become active to produce symptoms of the disease. In a person with active TB, the pathogen can be present in airborne droplets that are exhaled. Generally, a healthy person who inhales these droplets has effective defence mechanisms in the gas exchange system to prevent infection. One example of a defence mechanism against pathogens in the gas exchange system involves the action of macrophages. State the location in the body where macrophages have their origin. Describe the mode of action of a macrophage. It is sometimes possible for M. tuberculosis to survive within macrophages. Suggest one way in which M. tuberculosis may survive within a macrophage. A healthy person has other defence mechanisms in the gas exchange system to prevent bacteria entering cells. Describe these defence mechanisms and explain how bacteria in inhaled air are prevented from entering cells of the gas exchange system. In people with a weakened immune system, M. tuberculosis can infect other organs and tissues, such as the kidneys and joints. Suggest how the bacteria may spread from the lungs to other organs. TB in humans can be caused by another species of bacterium, M. bovis. State the mode of transmission of this pathogen to humans. The standard treatment for TB continues for six months and initially involves the use of four different antibiotics. If no antibiotic resistance is detected, the treatment is reduced to two of the four antibiotics. The two antibiotics used are rifampicin and isoniazid. Suggest the benefits of beginning the treatment with four different antibiotics. Multidrug-resistant TB (MDR-TB) occurs if resistance develops to rifampicin and isoniazid. The treatment for MDR-TB can last up to 30 months and involves different antibiotics to the standard treatment. Table 2.1 shows the number of reported cases of TB and MDR-TB in the South-East Asia region between 2005 and 2014, as published by the World Health Organization (WHO). Table 2.1 year total number of reported cases of TB total number of reported cases of MDR-TB 1 947 603 2 104 673 2 202 149 2 287 803 1 717 2 328 230 2 560 2 332 779 4 263 2 358 127 6 615 2 331 455 14 957 2 297 033 18 384 2 580 605 17 386 State the trends shown in Table 2.1. TB is a disease of global importance. Discuss the factors influencing the trends shown in Table 2.1.
9700_m18_qp_22
THEORY
2018
Paper 2, Variant 2
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In 2015, the World Health Organization (WHO) published the Global Technical Strategy for Malaria 2016–2030. The aim of this global strategy, which follows on from the 2008 Global Malaria Action Plan (GMAP), is to make progress in the control and elimination of malaria. Both the global strategy and GMAP aim to reduce: • the case incidence (number of new cases each year) of malaria • the mortality rate (number of deaths each year) from malaria. shows data for the four countries in the WHO Western Pacific Region that had the highest proportion of cases of malaria in 2015. For each of these four countries, the percentage change in the case incidence and the percentage change in the mortality rate over the five-year period from 2010 to 2015 are shown. –100 –80 –60 –40 –20 +20 +40 +60 +80 +100 percentage change Lao People’s Democratic Republic (Lao PDR) Cambodia case incidence mortality rate Solomon Islands Papua New Guinea Key With reference to , describe the progress made in the control of malaria in the four countries between 2010 and 2015. All the countries shown in supplied households at risk of malaria with insecticide-treated nets (ITNs). This is one of the recommendations in the GMAP and the global strategy. Describe and explain the role of ITNs. Another recommendation of the global strategy is to carry out rapid diagnostic testing (RDT) of individuals who may have malaria. This involves testing human blood samples for the presence of proteins specific to Plasmodium. Test sticks can be used. Table 3.1 contains information about two RDT test sticks. Table 3.1 test stick Plasmodium protein tested for species of Plasmodium that produce the protein pLDH (parasite lactate dehydrogenase) P. vivax P. falciparum P. ovale P. malariae HRP-2 (histidine-rich protein 2) P. falciparum only Some details of the design of these RDT test sticks are shown in . area with immobilised monoclonal antibodies area containing mobile monoclonal antibodies labelled with a coloured dye direction of movement of blood sample test window blood sample added to this area The immobilised monoclonal antibodies in the test window are not visible. If the blood sample contains a Plasmodium protein that can be detected by the RDT test stick: • the mobile monoclonal antibodies bind to one part of the protein • the immobilised monoclonal antibodies bind to another part of the protein • a coloured line in the test window indicates a positive result for the protein. With reference to Table 3.1 and , explain why test stick 1 and test stick 2 will contain different mobile monoclonal antibodies. Two blood samples were removed from a person. One sample was added to test stick 1 and the other sample was added to test stick 2. With reference to Table 3.1 and , explain what can be diagnosed for this person from a positive result for test stick 1 and a negative result for test stick 2.
9700_m19_qp_22
THEORY
2019
Paper 2, Variant 2
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In March 2019, a tropical cyclone in the south-west Indian Ocean caused widespread flooding in a number of countries. The flooding and the damage caused by the cyclone meant that many people were at serious risk of cholera. After the natural disaster occurred, many different areas reported outbreaks of cholera. Within a short time the disease had spread widely and large numbers of people were affected. Cholera is caused by a bacterial pathogen. Name the bacterial pathogen that causes cholera. Suggest and explain why the people affected by the cyclone were at serious risk of cholera. In addition to the standard treatment for cholera, antibiotics are recommended for people who are moderately ill or seriously ill with the disease. Doxycycline is one of the main antibiotics used for the treatment of cholera. Doxycycline enters the pathogen and binds to one of the subunits of the bacterial ribosome. This prevents growth and reproduction of the bacterial cell. Suggest and explain how binding of doxycycline to ribosomes stops growth of the bacterial cell. Penicillin, which used to be prescribed for the treatment of cholera, has a different mechanism of action to doxycycline. State which part of the bacterial cell is affected by the action of penicillin. Mozambique was one of the countries badly affected by the cyclone. As part of the effort to prevent a greater number of cases of cholera from occurring, two different approaches were taken. • Approximately 900 000 doses of the oral cholera vaccine were sent to Mozambique and a large-scale vaccination programme was organised. • Medical centres were set up in Mozambique to treat people with cholera. Suggest and explain how the two different approaches helped to prevent a greater number of cases of cholera from occurring.
9700_m21_qp_22
THEORY
2021
Paper 2, Variant 2
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Tuberculosis (TB) is a major cause of ill health worldwide. State the name of a bacterium that causes TB in humans. is a scanning electron micrograph of bacteria that cause TB. X Y X Y magnification ×21 000 Calculate the actual length of the bacterial cell shown in , along the line X–Y. Write the formula you will use in the box. Give your answer in micrometres (μm) to two significant figures. formula actual length = μm Bacteria are unicellular prokaryotic cells with a diameter of 1–5 μm. State two other structural features that would identify a cell as prokaryotic. The World Health Organization (WHO) Global Tuberculosis Report for 2019 published data on the estimated number of deaths from TB and HIV / AIDS in 2018. All deaths of people from TB who were infected with HIV were also counted as deaths of people with HIV / AIDS. shows these data. The dark grey boxes show the estimated number of deaths of people from TB who were also counted as deaths of people with HIV / AIDS. 0.00 0.25 0.50 0.75 millions of deaths in 2018 1.00 1.25 1.50 deaths of people from TB deaths of people with HIV / AIDS not infected with HIV with HIV / AIDS from TB A student used the data in to predict that measures to control the spread of HIV will decrease the number of deaths from TB. Discuss whether the data in support this prediction. In healthy people, the number of T-helper cells ranges from 500 to 1200 cells per cm3 of blood. In untreated people infected with HIV, the number of T-helper cells can decrease to below 200 cells per cm3 of blood. Explain how a low number of T-helper cells makes it more likely that untreated people infected with HIV will die if they are also infected with TB.
9700_m22_qp_22
THEORY
2022
Paper 2, Variant 2
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Approximately 2 × 109 people in the world are currently infected with the bacterial disease tuberculosis (TB) caused by Mycobacterium tuberculosis. Early diagnosis is important so that treatment can begin. APOPO is a non-profit organisation that has trained African giant pouched rats, Cricetomys gambianus, to use their sense of smell to detect M. tuberculosis. They do this by sniffing a sample of thick mucus from the lungs of people who may have TB. The African giant pouched rats are able to detect the presence of M. tuberculosis with an accuracy of 87–93%. shows an African giant pouched rat. The type of receptor cell used by African giant pouched rats to detect M. tuberculosis is the same as that used in human taste buds. Name this type of receptor cell. Suggest why African giant pouched rats trained to detect M. tuberculosis may also be able to detect other species of Mycobacterium that cause TB. The African giant pouched rat belongs to the kingdom Animalia in the domain Eukarya. Complete Table 8.1 to show the full classification of the African giant pouched rat. Table 8.1 kingdom Animalia Chordata class Mammalia Rodentia family Nesomyidae species gambianus Differences between members of the domain Eukarya and members of the domain Bacteria include the presence or absence of particular membrane-bound cell structures. Outline other differences in the characteristic features of members of the domain Eukarya and members of the domain Bacteria. Describe, with reference to the structure of viruses, how viruses are classified.
9700_m24_qp_42
THEORY
2024
Paper 4, Variant 2
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Questions Discovered
290