10.1. Infectious diseases
A subsection of Biology, 9700, through 10. Infectious diseases
Listing 10 of 208 questions
Tuberculosis (TB) is an infectious disease caused by a bacterium. In the majority of people, only the lungs are affected. In most cases, the transmission of TB from an infected person to an uninfected person involves Mycobacterium tuberculosis. A different species of bacterium is involved in the transmission of TB from cattle, such as dairy cows, to humans. Name the species of bacterium causing the transmission of TB from dairy cows to humans. In some areas, cattle cannot be regularly tested or treated for TB. In these areas, milk and dairy products from infected dairy cattle may enter the human food chain. Outline a control measure that can be taken to protect people that consume milk and dairy products from these infected cattle. Cattle are not usually affected by M. tuberculosis, but the pathogen can cause disease in other animals. A few cases of transmission of TB from people to animals have been reported. Explain the most likely mode of transmission of TB from an infected person to an animal. In most people, the response of the immune system to the infection of lung tissue by M. tuberculosis can prevent the spread of the bacterium to other organs of the body. The bacterium is contained in the lungs in a dormant state. This is known as latent TB. Outline the treatment that is used to kill M. tuberculosis in latent TB infections. M. tuberculosis can spread in the blood and lymph to other organs in the body. In very rare cases, a disease known as mycotic aneurysm can be caused by infection of the arterial wall, particularly in elastic arteries. The damage caused by the pathogen can lead to a rupture of the artery. With reference to the structure of the wall of elastic arteries, suggest how damage caused by M. tuberculosis infection can lead to the rupture of the artery. You may draw a diagram if you wish. Space for diagram
9700_w23_qp_22
THEORY
2023
Paper 2, Variant 2
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The infectious disease cholera is caused by a bacterium. shows a transmission electron micrograph of this bacterium. ×30 000 Name the bacterium that causes cholera. The bacterium in is an example of a prokaryotic cell. Each of the descriptions A to C describes a cell structure found in prokaryotic cells and in plant cells. For each of the descriptions A to C: • name the cell structure described • state one difference in this structure between a prokaryotic cell and a plant cell. A the site of polypeptide synthesis cell structure difference B the genetic material of the cell cell structure difference C the structure that provides a rigid shape to the cell and prevents osmotic lysis cell structure difference Cholera is an example of an infectious disease. Explain what is meant by an infectious disease. The symptoms of cholera are caused by choleragen, a toxin released by the bacterium. Choleragen is a protein made up of six polypeptides: • a single copy of a polypeptide known as the A subunit that includes an extended alpha helix • five polypeptides that together make the B subunit. The B subunit of choleragen binds to a cell surface membrane component, known as GM1, of an intestinal epithelial cell. The complete choleragen protein then enters the cell by endocytosis. Once inside the cell, the A subunit of the protein acts as an enzyme, disrupting the normal functioning of the cell. List the levels of protein structure present in choleragen. Outline the mechanism by which choleragen enters the cell. You may use the space for annotated diagrams. Using genetic engineering, it is possible to produce a form of choleragen consisting of only subunit B. This can be combined with inactivated bacterial cells to produce a vaccine against cholera. Suggest why subunit B, rather than subunit A, is used in the vaccine. Outline how this vaccine can give protection against cholera.
9700_m17_qp_22
THEORY
2017
Paper 2, Variant 2
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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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Questions Discovered
208