10. Infectious diseases
A section of Biology, 9700
Listing 10 of 290 questions
When bacteria are grown in a Petri dish containing discs with antibiotics, there will be zones of inhibition of bacterial growth. antibiotic disc zone of inhibition area of bacterial growth The chart shows the size of the zones of inhibition when a species of bacteria was incubated on five different plates of agar, each containing a disc with a different antibiotic. zone of inhibition / mm antibiotic Which conclusions can be made about the most and least effective antibiotics on this species of bacteria?
9700_s23_qp_11
MCQ
2023
Paper 1, Variant 1
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Use Cell walls of bacteria contain peptidoglycans. Peptidoglycans are long chains of the sugars N-acetylmuranic acid (NAM) and N-acetylglucosamine (NAG) which alternate along the chain. A short peptide chain of three to five amino acids is attached to each NAM and these form cross-links with similar peptide chains from adjacent strands. shows a diagram representing part of a peptidoglycan structure. NAM peptide chains cross-link NAG NAM NAG NAM NAG NAM NAG NAM NAG NAM NAG Name the type of reaction that takes place to assemble the peptide chains that form the cross-links. Describe the mode of action of antibiotics, such as penicillin, on bacteria. Suggest the name of the type of enzyme that assembles the peptide chains that form the cross-links in peptidoglycans. Examiner’s Use State why antibiotics, such as penicillin, have no effect on viruses. Bacteria may be Gram-positive or Gram-negative. shows a diagram of part of the cell walls of both Gram-positive and Gram-negative bacteria. inner membrane peptidoglycan outer membrane inner membrane peptidoglycan periplasmic space Gram-positive Gram-negative Gram-positive bacteria cell walls have Gram-negative bacteria cell walls have a a peptidoglycan content of 50% peptidoglycan content of 10 – 20% Suggest why Gram-positive bacteria are more susceptible to the action of penicillin than Gram-negative bacteria. Examiner’s Use There is evidence that some bacteria have developed resistance to antibiotics. One form of pneumonia, a serious lung disease, is caused by the bacterium Streptococcus pneumoniae. The Canadian Health Service has carried out a survey to show how the resistance of S. pneumoniae to penicillin has changed over the last 20 years. shows the results of this survey. percentage of penicillin resistant S. pneumoniae year Describe the results shown in and explain how some strains of S. pneumoniae may have become resistant to penicillin.
9700_w09_qp_42
THEORY
2009
Paper 4, Variant 2
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The disease-causing bacterium, Pseudomonas aeruginosa, may occur in the form of a ‘biofilm’. A biofilm consists of a layer of bacteria, growing on a surface and attached to one another. Such biofilms are difficult to control by antibiotics. A mutant strain of P. aeruginosa has been found which produces biofilms that are indistinguishable from those of the wild-type bacteria. However, the mutant strain differs from the wild-type in its resistance to an antibiotic, A. Antibiotic A belongs to a group of antibiotics known as anti-pseudomonal penicillins. Describe the mode of action of penicillin on bacteria. Explain why penicillin does not affect viruses. Wild-type and mutant bacteria were grown on solid culture media both with antibiotic A and without antibiotic A. The subsequent change in numbers of living bacteria is shown in . relative number of living bacteria per cm2 time / hours × × without antibiotic A with antibiotic A key: mutant × × wild-type × × × × × × × × × × × × × × × × With reference to , describe the changes in numbers of the wild-type and mutant bacteria on culture media with antibiotic A and without antibiotic A. The wild-type and mutant strains of this bacterium have different DNA sequences in part of a gene coding for an enzyme which is needed to produce polymers of glucose, called glucans. Glucans are secreted by bacteria and can bind to various molecules, including those of antibiotic A. Explain how a mutation of a gene coding for an enzyme may result in an enzyme with reduced activity, the different effects of antibiotic A, shown in , on the wild-type and mutant strains of bacteria. Explain the role of natural selection in the evolution of antibiotic resistance in bacteria.
9700_w10_qp_41
THEORY
2010
Paper 4, Variant 1
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The disease-causing bacterium, Pseudomonas aeruginosa, may occur in the form of a ‘biofilm’. A biofilm consists of a layer of bacteria, growing on a surface and attached to one another. Such biofilms are difficult to control by antibiotics. A mutant strain of P. aeruginosa has been found which produces biofilms that are indistinguishable from those of the wild-type bacteria. However, the mutant strain differs from the wild-type in its resistance to an antibiotic, A. Antibiotic A belongs to a group of antibiotics known as anti-pseudomonal penicillins. Describe the mode of action of penicillin on bacteria. Explain why penicillin does not affect viruses. Wild-type and mutant bacteria were grown on solid culture media both with antibiotic A and without antibiotic A. The subsequent change in numbers of living bacteria is shown in . relative number of living bacteria per cm2 time / hours × × without antibiotic A with antibiotic A key: mutant × × wild-type × × × × × × × × × × × × × × × × With reference to , describe the changes in numbers of the wild-type and mutant bacteria on culture media with antibiotic A and without antibiotic A. The wild-type and mutant strains of this bacterium have different DNA sequences in part of a gene coding for an enzyme which is needed to produce polymers of glucose, called glucans. Glucans are secreted by bacteria and can bind to various molecules, including those of antibiotic A. Explain how a mutation of a gene coding for an enzyme may result in an enzyme with reduced activity, the different effects of antibiotic A, shown in , on the wild-type and mutant strains of bacteria. Explain the role of natural selection in the evolution of antibiotic resistance in bacteria.
9700_w10_qp_42
THEORY
2010
Paper 4, Variant 2
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Penicillin belongs to a group of antibiotics known as β lactams, which all act in the same way on bacteria. Describe how penicillin kills non-resistant bacteria. One of the ways in which a bacterium may be resistant to an antibiotic, such as a β lactam, is by having protein pumps in its cell surface membrane which expel the antibiotic from the bacterium. The gene coding for such an efflux pump is carried on a plasmid. Outline how the bacterium produces an efflux pump from a gene on a plasmid. A strain of the bacterium Pseudomonas aeruginosa, strain R, has a gene coding for an efflux pump and is resistant to a β lactam antibiotic. The minimum inhibitory concentration (MIC) of the β lactam for strain R was determined. The MIC is the lowest concentration of antibiotic that prevents a colony of the bacterium from growing. The MICs were also determined for two mutant strains derived from strain R, mutant strain 1 and mutant strain 2. Each of these strains differs from strain R in the expression of the gene coding for the efflux pump. The MICs for the three strains of P. aeruginosa are shown in Table 2.1. Table 2.1 strain of P. aeruginosa MIC of β lactam / μg cm–3 resistant strain R mutant strain 1 0.5 mutant strain 2 With reference to Table 2.1, suggest: why the MICs for mutant strains 1 and 2 differ from that for strain R mutant strain 1 mutant strain 2 how a population of strain R of P. aeruginosa could be replaced by mutant strain 2.
9700_w12_qp_41
THEORY
2012
Paper 4, Variant 1
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Penicillin belongs to a group of antibiotics known as β lactams, which all act in the same way on bacteria. Describe how penicillin kills non-resistant bacteria. One of the ways in which a bacterium may be resistant to an antibiotic, such as a β lactam, is by having protein pumps in its cell surface membrane which expel the antibiotic from the bacterium. The gene coding for such an efflux pump is carried on a plasmid. Outline how the bacterium produces an efflux pump from a gene on a plasmid. A strain of the bacterium Pseudomonas aeruginosa, strain R, has a gene coding for an efflux pump and is resistant to a β lactam antibiotic. The minimum inhibitory concentration (MIC) of the β lactam for strain R was determined. The MIC is the lowest concentration of antibiotic that prevents a colony of the bacterium from growing. The MICs were also determined for two mutant strains derived from strain R, mutant strain 1 and mutant strain 2. Each of these strains differs from strain R in the expression of the gene coding for the efflux pump. The MICs for the three strains of P. aeruginosa are shown in Table 2.1. Table 2.1 strain of P. aeruginosa MIC of β lactam / μg cm–3 resistant strain R mutant strain 1 0.5 mutant strain 2 With reference to Table 2.1, suggest: why the MICs for mutant strains 1 and 2 differ from that for strain R mutant strain 1 mutant strain 2 how a population of strain R of P. aeruginosa could be replaced by mutant strain 2.
9700_w12_qp_42
THEORY
2012
Paper 4, Variant 2
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Penicillin-binding proteins (PBPs) are proteins found in the cell surface membranes of bacteria. PBPs catalyse the final steps in the production of a peptidoglycan cell wall. From the information given above, describe the likely molecular structure of a PBP. Penicillin-resistant mutants of the bacterium, Staphylococcus aureus, produce a PBP, PBP2a, that does not bind well with penicillin. Suggest how the presence of PBP2a in the cell surface membrane provides S. aureus with resistance to the effects of penicillin. Explain why penicillin does not affect viruses.
9700_w12_qp_43
THEORY
2012
Paper 4, Variant 3
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Staphylococcus aureus is a bacterium that is the cause of many different infectious diseases. is a diagram of S. aureus. 1 +m Cell structures, such as mitochondria, endoplasmic reticula (ER), Golgi apparatus, lysosomes and chloroplasts are found only in eukaryotic cells. These are not present in . With reference to , describe other features that support the fact that S. aureus is a prokaryote. State the main difference in the composition of the plant cell wall compared to the bacterial cell wall. plant cell wall bacterial cell wall Bacterial cells behave in a similar way to plant cells when immersed in solutions of different water potential. Suggest and explain what would happen to bacteria placed in a solution with a water potential more negative than their cell contents. Some strains of S. aureus have become resistant to one or more of the antibiotics used to treat infections. The mechanisms of antibiotic resistance involve proteins, for example: • enzymes to breakdown antibiotics • membrane proteins that inactivate antibiotics • membrane proteins that pump out antibiotics. Explain why antibiotic resistance arises as a result of mutation.
9700_w13_qp_22
THEORY
2013
Paper 2, Variant 2
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Questions Discovered
290