2017 Bacteria Viruses STQ QP

2017 Bacteria and Viruses STQ 2017 / H2 / ACJC PRELIM / P2 Q8 (BE)1Speciation events have been observed to occur very frequently in bacteria. It was suggested that the high rate of speciation is due to the high level of variation in bacteria.(a)Transformation and conjugation are two processes which increase the level of variation in bacteria. Distinguish these two processes. [3] Bacterial evolution is one of the most dynamic and exciting areas in current biological research. Over the years, a barrier in this field of research is the difficulty in classifying bacterial species. However, in recent times, new analytical tools in molecular biology have offered new insights into the classification of bacterial species.(b) (i) Suggest why scientists had difficulties in the classification of bacterial species. [2](ii)Explain how analytical molecular tools have helped overcome this barrier in research.[2](c)

The outer layers of the two types of bacteria with peptidoglycan cell walls known as Gram-positive and Gram-negative bacteria are shown in Fig. 8.1 below. Penicillin is an antibiotic that is known to be effective against only one of the two types of bacteria above.With reference to the information given and your own knowledge, deduce which type of bacteria is susceptible to the action of penicillin and explain why.[3](d) Gram-negative bacteriaGram-positive bacteriaFig. 8.1

Explain how antibiotic-resistant bacteria can become increasingly common in a population of bacteria. [4][Total: 14 m]

2017 / H2 / AJC PRELIM / P2 Q52Fig. 5.1 represents a bacteria DNA and a eukaryotic chromosome in metaphase of mitosis, not drawn to scale. Fig. 5.1(a)State two ways in which the organization of genes found in these two structures differ and suggest one advantage of this to the bacterium. [3](b)In 1946, Joshua Lederberg and Edward Tatum proposed that bacterial cells undergo genetic recombination. To test their hypothesis, they conducted experiments using two bacteria strains of Escherichia coli (E.coli), A and B, with different nutritional requirements. Strain A, B and a mixture of both strains were grown on culture plates containing minimal medium that does not contain essential amino acids. The results are shown in Fig. 5.2.Mutant genes () do not code for enzymes that synthesize amino acids. Note that all five amino acids are required for bacterial growth.Bacterial strainsGenes for biosynthesis of amino acidsMutant genes for biosynthesis of amino acidsAthr+ leu+ thi+met bioBmet+ bio+thr leu thi

Fig. 5.2Another researcher, Bernard Davis also worked with the same hypothesis. In his experiment he constructed a U-tube in which the two arms were separated by a fine filter. The pores of the filter were too small to allow bacteria to pass through but large enough to allow easy passage of the fluid medium, any dissolved substances and free DNA. The results are shown in Fig. 5.3. Fig. 5.3

(i)Using the results of the two experiments shown in Fig. 5.2 and Fig. 5.3 and your understanding of genetic recombination in bacteria, state the genetic recombination that has taken place between Strain A and B. Explain your answer. [6](c)In 2016, a pathogenic strain of E.coli found on unwashed salad caused food poisoning in 151 people in Britain, leaving two of them dead. Describe how such pathogens are usually treated using a named example.[3][Total: 12 m]

2017 / H2 / CJC PRELIM / P2 Q8 (ETA)3Transpeptidase is a bacterial enzyme that cross-links cell wall peptides during the formation of bacterial cell walls. The antibiotic penicillin inhibits the activity of transpeptidase. Fig. 8.1 shows part of each of the molecular structures of a cell wall peptide and penicillin. Fig. 8.1(a)Comment on the structure of cell wall peptides and penicillin.…………………………………………………………………………………………………………….[1](b)Suggest why the penicillin molecule is an effective inhibitor of transpeptidase.………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….[2](c)Fig.8.2 shows an electron micrograph of an alveolar macrophage isolated from a tuberculosis patient.

Fig. 8.2(i)Describe the mode of transmission of Mycobacterium tuberculosis. ………………………………………………………………………………………………………...……………………………………………………………………………………………………. [1] (ii) Explain the appearance of the alveolar macrophage in Fig. 8.2.………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….[2](d)Tuberculosis patients are commonly treated with antibiotics, isoniazid and rifampicin. Recently, there is an increase in number of multi-drug resistant tuberculosis cases. State one reason why multi-drug resistant tuberculosis continues to emerge. ……..……………………………………………………………………………………………………. [1][Total 7]

2017 / H2 / DHS PRELIM / P2 Q4Question 4A student wanted to introduce ampicillin resistance gene (AmpR) to a strain of bacteria. Fig. 4.1 shows a drawing done by the student to summarize his experimental procedure and expected results. Fig. 4.1(a)(i)What is process X? [1](ii)What is the significance of the plate with no colonies? [2](iii)When the student carried out the experiment, he did not obtain any colonies on either plates. Explain why. [1]

In bacteria, genes coding for enzymes involved in the same metabolic pathway are arranged into operons. Fig. 4.2 shows the changes in the concentration of enzymes that synthesise tryptophan and utilise lactose in a bacteria cell after the addition of tryptophan and lactose. Fig. 4.2(b)(i)Describe the difference in the shape of the graph after the introduction of tryptophan and lactose. [2] (ii)Explain the change in concentration of tryptophan synthesizing enzyme after the introduction of tryptophan. [3]