10.1. Infectious diseases
A subsection of Biology, 9700, through 10. Infectious diseases
Listing 10 of 208 questions
Countries that have a high number of cases of malaria also have problems with diseases caused by bacteria. This means that many people in these countries are prescribed antibiotics, such as penicillin, for the treatment of bacterial infections. Outline how penicillin acts on bacterial cells. The female Anopheles mosquito is the vector of the Plasmodium pathogen that causes malaria. The insect takes in Plasmodium when feeding on blood from an infected person. At a later stage the insect can transmit the pathogen when taking a blood meal from an uninfected person. Name one of the four species of Plasmodium that can cause malaria. The male Anopheles mosquito does not feed on blood and so does not act as a vector. Suggest why there is a difference in this feeding behaviour between male and female Anopheles. Research has shown that Plasmodium is not always transmitted to uninfected people. Two main reasons for this have been suggested. • The immune system of mosquitoes kills Plasmodium while it is still in the gut. • Bacteria living in the gut of mosquitoes compete with Plasmodium so it does not survive to continue its life cycle. A study was carried out to see if taking antibiotics affects the risk of transmission of malaria. Some observations and results of the study are summarised in . individuals with malaria are taking antibiotics Anopheles mosquitoes take blood meals higher survival rate of Plasmodium in gut of Anopheles individuals with malaria are not taking antibiotics Anopheles mosquitoes take blood meals lower survival rate of Plasmodium in gut of Anopheles Suggest explanations for the results shown in and comment on the importance of these results for doctors working in countries that have malaria and a high number of bacterial infections. After many years of intense research and development, WHO reported in 2016 that a pilot vaccination programme would be trialled between 2017 and 2020. The programme uses a vaccine acting against the most widespread species of Plasmodium. Explain the difficulties faced by researchers in developing a malaria vaccine.
9700_w19_qp_22
THEORY
2019
Paper 2, Variant 2
View
Cholera is an infectious disease caused by the bacterial pathogen Vibrio cholerae. Describe how V. cholerae is transmitted from an infected person to an uninfected person. V. cholerae releases a toxin called choleragen. Choleragen is a protein molecule made up of six polypeptides . is a ribbon diagram of a molecule of choleragen. T Describe what is shown by the part of the molecule labelled T. Vaccination can be used to prevent the spread of cholera. The vaccine used contains part of the choleragen molecule and also contains dead cells of V. cholerae. Phagocytes play an important role in the immune response to a vaccine. Phagocytes contain many lysosomes. Describe the function of lysosomes in phagocytes. Suggest the advantage of having a vaccine that includes dead cells of V. cholerae and part of the choleragen molecule. The World Health Organization states that most cases of cholera can be treated with oral rehydration therapy. To reduce the risk of antibiotic resistance developing, antibiotics are only recommended for the most serious cases. Discuss the consequences of the development of antibiotic resistance in V. cholerae.
9700_w21_qp_21
THEORY
2021
Paper 2, Variant 1
View
Plasmodium falciparum is one species of Plasmodium that causes the life-threatening disease malaria. With early diagnosis and the correct drug treatment, the pathogen can be eliminated from the body, particularly if the disease is not severe. Name the type of pathogen that causes malaria. To help prevent the development and spread of drug resistance in Plasmodium, the World Health Organization (WHO) recommends using a treatment known as artemisinin-based combination therapy (ACT). ACT involves two different types of drug: • a fast-acting drug derived from a compound known as artemisinin, which causes a rapid decrease in the number of P. falciparum • one or more longer-acting, non-artemisinin, drugs that eliminate any remaining pathogens. Suggest why using ACT with the two different types of drug is more effective in preventing the development of drug resistance in Plasmodium than a treatment using only one type of drug. In some areas, partial artemisinin resistance has developed. This means ACT takes a longer time for the pathogen to be eliminated from the body. Explain why there is an increased risk of transmission of the pathogen to other people if a person is receiving ACT and the pathogen has partial artemisinin resistance. ACT can act on the stage of the life cycle of P. falciparum that occurs within red blood cells. The cells of P. falciparum in this stage are known as trophozoites. is a photomicrograph of a blood smear (thin layer of cells). Some of the red blood cells contain trophozoites. trophozoite PfK13 is a protein that has an important role in the development of the trophozoite stage of P. falciparum. The gene kelch13 codes for PfK13. Two different mutations of kelch13, known as F446I and C580Y, were investigated to see if they were associated with partial artemisinin resistance. Details of these mutations are summarised in Table 3.1. Table 3.1 name of mutation change in DNA change in protein PfK13 nucleotide present in kelch13 nucleotide present after mutation amino acid before mutation amino acid after mutation F446I thymine (T) adenine (A) phenylalanine isoleucine C580Y guanine (G) adenine (A) cysteine tyrosine Using gene kelch13 and mutation F446I as examples, explain the difference between a gene and a gene mutation. In the investigation, the survival rate of trophozoites within red blood cells was determined for two different concentrations of an artemisinin-based drug known as DHA. Two different strains, A and B, of P. falciparum were tested. Three different cultures of each strain were involved: • no mutation in kelch13 • kelch13 F446I mutation • kelch13 C580Y mutation. Table 3.2 shows the six different cultures tested and the trophozoite survival rate for each culture. Table 3.2 culture number culture details mean percentage survival rate of trophozoite DHA concentration 20 nmol dm–3 DHA concentration 700 nmol dm–3 strain A no mutation 3.15 0.00 strain A, F446I mutation 26.00 0.73 strain A, C580Y mutation 33.08 0.91 strain B no mutation 2.86 0.00 strain B, F446I mutation 13.50 0.53 strain B, C580Y mutation 17.50 0.63 State the main conclusions that can be drawn from the results shown in Table 3.2.
9700_w22_qp_22
THEORY
2022
Paper 2, Variant 2
View
Some people who are infected with HIV develop HIV/AIDS. shows the number of people that have been newly infected with HIV (new infections) in 2018 across the world and the percentage changes in the number of new infections since 2010. A (North America and West and Central Europe) 68 000 new infections 12% decrease 150 000 new infections 29% increase 310 000 new infections 9% decrease B (Eastern Europe and Central Asia) C (Asia Pacific) 20 000 new infections 10% increase 800 000 new infections 28% decrease 280 000 new infections 13% decrease 100 000 new infections 7% decrease D (Middle East and North Africa) E (East and Southern Africa) F (Western and Central Africa) G (Latin America) 16 000 new infections 16% decrease H (Caribbean) State the full name of the pathogen HIV. Using only the data in , state what can be concluded about the change in number of new HIV infections across the world between 2010 and 2018. You may use the letters in to identify the regions of the world. People who develop HIV/AIDS have fewer T-helper cells as the pathogen destroys these cells. This makes them more susceptible to tuberculosis (TB). Explain why people with HIV/AIDS are more likely to develop TB. A person infected with HIV may develop a heart condition called cardiac tamponade. The pericardium is a thin sac surrounding the heart, as shown in the healthy heart in . When a person develops cardiac tamponade, the pericardium starts to fill with blood. This prevents the ventricles functioning efficiently. pericardium sac pericardium sac filled with blood pressure in the pericardium healthy heart heart with tamponade People with cardiac tamponade experience a variety of symptoms including low blood pressure and an increased breathing rate. Suggest why a person with cardiac tamponade would experience symptoms of low blood pressure and an increased breathing rate.
9700_w23_qp_21
THEORY
2023
Paper 2, Variant 1
View
Outline the biological basis of the effect of the contraceptive pill. In Uganda, many children are infected with HIV from their mothers. This is called vertical HIV transmission. Uganda has used two ways of trying to reduce vertical HIV transmission. These methods are • to increase the use of antiretroviral drugs (ARVs) by HIV-infected pregnant women • to reduce, through contraception, the numbers of unwanted pregnancies. Table 5.1 shows the percentage reductions in the number of children born with HIV infections and the number of pregnancies in HIV-infected women, that were brought about as a result of the use of ARVs and contraception in 2007. Table 5.1 also shows the predicted reductions in 2012 if usage of ARVs and contraception increase as expected. Table 5.1 percentage reduction caused by use of ARVs by contraception in 2007 predicted in in 2007 predicted in pregnancies in HIV-infected women 21.7 34.0 births of HIV- infected children 8.1 18.1 21.6 32.9 It is estimated that if no ARVs had been used in 2007, 27 000 children would have been born with HIV infection. Calculate the actual number of children born with HIV infection in 2007. Show your working. answer With reference to Table 5.1, explain the difference between the effects of ARVs and contraception on the numbers of pregnancies in HIV-infected women. There is only a limited amount of money to spend on HIV prevention in Uganda. With reference to Table 5.1, suggest arguments for spending at least as much money on increasing access to contraception as on providing ARVs to HIV-infected pregnant women.
9700_s12_qp_42
THEORY
2012
Paper 4, Variant 2
View
Questions Discovered
208