9700_w12_qp_43
A paper of Biology, 9700
Questions:
10
Year:
2012
Paper:
4
Variant:
3
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2
For Examiner’s Use The artificial plasmid, pBR322, was constructed to act as a vector. It has often been used to insert human genes, such as the human insulin gene, into the bacterium, Escherichia coli. The plasmid was constructed to include two genes, each giving resistance to a different antibiotic: an ampicillin resistance gene and a tetracycline resistance gene. The plasmid also has a target site for the restriction enzyme, BamHI, in the middle of the tetracycline resistance gene. A pBR322 plasmid was cut using BamHI and the cDNA gene for human insulin inserted into it. shows pBR322 and the recombinant plasmid. pBR322 recombinant plasmid human insulin gene tetracycline resistance gene G C G C A T T A C G C G ampicillin resistance gene target site for BamHI With reference to , describe how a cDNA human insulin gene can be inserted into pBR322 that has been cut by BamHI. For Examiner’s Use For Examiner’s Use Bacteria were then mixed with the recombinant plasmids. Those bacteria which had successfully taken up recombinant plasmids were identified using the following steps: step 1 – the bacteria were spread onto culture plates containing nutrient agar and ampicillin and incubated to allow colonies to form step 2 – some bacteria from each of the colonies growing on these plates were transferred to plates containing nutrient agar and tetracycline, as shown in . sterile sponge which transfers some of each colony, in the same relative positions, from plate A to plate T plate A plate T after incubation nutrient agar with tetracycline bacterial colony nutrient agar with ampicillin Explain why the bacteria were first spread onto plates containing ampicillin. For Examiner’s Use Explain why it is important, for identifying bacteria that have successfully taken up the recombinant plasmid, that on pBR322 the target site for BamHI is in the middle of the tetracycline resistance gene. Use a label line and the letter C to identify, on , a colony of bacteria that contain the recombinant plasmid. Put your answer onto on page 5. Plasmid vectors carrying antibiotic resistance genes are now rarely used in gene technology. Explain why antibiotic resistance genes are now rarely used. State one type of gene that has replaced antibiotic resistance genes in plasmid vectors and indicate how its presence can be detected. type of gene detection
19. Genetic technology  →  19.1. Principles of genetic technology
19. Genetic technology  →  19.2. Genetic technology applied to medicine
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For Examiner’s Use 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.
10. Infectious diseases  →  10.2. Antibiotics
17. Selection and evolution  →  17.2. Natural and artificial selection
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For Examiner’s Use shows a light micrograph of a section through a wheat grain. The structure of a wheat grain is very similar to that of a maize fruit. On , use label lines and letters to label each of the following parts. A endosperm B fused testa and pericarp (fruit coat) C embryo Wheat grains are ground to make flour, which can be used for making bread. Whole grain flour is made from the complete wheat grain. Refined flour is produced from wheat grains from which the embryo, aleurone layer and the fused testa and pericarp have been removed. Table 4.1 shows the carbohydrate, protein and dietary fibre content of bread made from whole grain flour and white flour. For Examiner’s Use Table 4.1 bread made from whole grain flour bread made from white flour protein / g per 100 g 9.4 7.9 dietary fibre / g per 100 g 7.0 2.5 carbohydrate / g per 100 g With reference to the structure of a wheat grain, explain the differences between the composition of the two types of bread shown in Table 4.1. The glycaemic index, GI, of a carbohydrate-containing food is a measure of the effect of its consumption on blood glucose concentration. If two foods containing the same mass of carbohydrate, but different GIs, are consumed, the food with the higher GI will increase blood glucose concentration more rapidly than the food with the lower GI. Suggest an explanation for each of the following. Foods containing starch have lower GIs than foods containing glucose. Foods containing starch made up mostly of amylose have lower GIs than foods containing starch made up mostly of amylopectin. For Examiner’s Use A diet containing large amounts of foods with a high GI can increase the risk of developing type II diabetes. A study was carried out into the effect of consuming whole cereal grains, refined cereal grains and fruit on the risk of developing type II diabetes. • In 1986, questionnaires about diet were completed by 41 836 women, all between the ages of 55–69 years old, in Iowa, USA. • The women were then divided into five groups according to their range of intake of each food type. • In 1992 the same women were asked whether or not they had developed type II diabetes. • Their answers were used to calculate the relative risk of developing type II diabetes for each of the five groups. For each food type, the group with the lowest intake of that food type was allocated a risk of 1.00. Table 4.2 shows the results of this study. Table 4.2 food type range of intake / servings per week relative risk of developing type II diabetes whole cereal grains 33.0 0.68 refined cereal grains 22.0 0.87 fruit 19.0 1.14 For Examiner’s Use Describe the effect of increased intake of whole cereal grains on the risk of developing type II diabetes. Explain why the results in Table 4.2 cannot be used to make a direct comparison of the effects of consuming whole cereal grains and refined cereal grains on the risk of developing type II diabetes. The results in Table 4.2 suggest that eating large quantities of fruit may slightly increase the risk of developing type II diabetes. Suggest a reason for this.
2. Biological molecules  →  2.2. Carbohydrates and lipids
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For Examiner’s Use Many couples who are not able to have children naturally are treated using in-vitro fertilisation (IVF). Describe how and where fertilisation occurs during IVF. The embryos resulting from IVF are transferred into the mother’s uterus. This is sometimes done after 3 days, and sometimes after 5 days. Suggest one advantage and one disadvantage of transferring the embryos after 5 days rather than 3 days. advantage disadvantage Many IVF clinics usually transfer two or more embryos to the mother’s uterus, to increase the chances of a successful pregnancy occurring. However, this increases the risk of more than one embryo developing in the uterus, which in turn increases the risk of problems with the pregnancy or birth. A study was carried out to compare the success rates of transferring: • a single embryo that had been carefully chosen as being of ‘top quality’ • a non-selected single embryo • two or more embryos. shows the results of this study. For Examiner’s Use 1559 IVF treatment cycles 1464 embryo transfers 105 pregnancies 19 pregnancies 366 pregnancies 299 transfers of a single top-quality embryo 86 transfers of a single, non- selected embryo 1059 transfers of two of more embryos With reference to , explain why transferring a single top-quality embryo is now considered to be the best method to maximise the chance of a successful pregnancy. State one ethical implication of transferring single top-quality embryos in IVF.
18. Classification, biodiversity and conservation  →  18.3. Conservation
16. Inheritance  →  16.1. Passage of information from parents to offspring
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For Examiner’s Use In mice, fur colour is controlled by a gene with multiple alleles. These alleles are listed below in no particular order. black and tan = Cbt yellow = Cy agouti = Ca black = Cb Suggest explanations for the results of the following crosses between mice. Mice with agouti fur crossed with mice with black fur may produce all agouti offspring or some agouti and some black offspring. Crosses between heterozygous parents with the genotype Cy Cb always produce a ratio of two yellow mice to one black mouse. For Examiner’s Use Mice with yellow fur crossed with mice with black fur will produce one of the following outcomes: • some yellow offspring and some agouti offspring • some yellow offspring and some black and tan offspring • some yellow offspring and some black offspring. A test cross is used to determine the genotype of an organism. Describe how you would carry out a test cross to determine the genotype of a black and tan mouse.
16. Inheritance  →  16.2. The roles of genes in determining the phenotype
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For Examiner’s Use Explain the advantages to a plant species of cross-pollination compared to self-pollination. Some of the most important food plants for humans depend on insect pollinators, such as the honeybee, Apis mellifera. shows a honeybee. For Examiner’s Use A study was carried out in 2006 to show how four food crops are pollinated. shows the results of this study. almond apple orange plant peach pollinated by honeybee pollinated by other insects pollinated by birds / wind / rainwater Key number of plants pollinated The populations of honeybees in some parts of the world have declined in recent years. With reference to , explain which crop will be most affected and which crop will be least affected by the decline in honeybees. most affected least affected For Examiner’s Use Suggest reasons why honeybee populations have declined.
19. Genetic technology  →  19.3. Genetically modified organisms in agriculture
18. Classification, biodiversity and conservation  →  18.3. Conservation
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For Examiner’s Use outlines some steps in glucose metabolism in mammalian cells. glucose reduced NAD NAD lactate oxygen not available glucose glycogen oxygen available oxygen available NAD ADP ATP pyruvate With reference to : name the part of the cell where glucose is converted to pyruvate explain why, in the absence of oxygen, pyruvate needs to be converted to lactate name the enzyme responsible for the conversion of pyruvate to lactate name the type of reaction and the type of bonds formed when glucose molecules are used to make glycogen. reaction bonds For Examiner’s Use Describe how anaerobic respiration in yeast cells differs from anaerobic respiration in mammalian cells. The respiratory quotient (RQ) is used to determine the type of respiratory substrate, such as carbohydrate or lipid, which an organism uses at any one time. State how the RQ is calculated. State the typical RQ values obtained from the respiration of carbohydrates and lipids. carbohydrate lipid Suggest what would happen to the RQ value when respiration becomes anaerobic.
12. Energy and respiration  →  12.2. Respiration
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