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A-level Biology (7401/7402) Name:

Class: Section 8 Practical Skills

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Feversham College Q1.Scientists investigated the effect of drinking tea and coffee on reducing the risk of developing one type of brain cancer. The investigation involved 410 000 volunteers and was conducted in 10 European countries over a period of 8.5 years.

(a) (i) Apart from age, suggest two factors that the scientists should have considered when selecting volunteers for this trial.

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(ii) Give two features of the design of this investigation that would ensure the reliability ofthe results obtained.

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(b) The incidence for this type of brain cancer is 6 cases per 100 000 per year. Use this information to calculate the expected number of volunteers developing this cancer during the 8.5 year period of this investigation. Show your working.

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(c) In analysing the results of this investigation, the scientists took into account the age of the volunteers. Suggest why.

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(d) During the investigation, the volunteers were asked to estimate the volume of tea and/or coffee that they drank each day. The types of tea and coffee consumed in different countries varied. When the data from all the countries were collected there was a correlation between drinking more than 100 cm3of tea or coffee each day and a reduced risk of developing this type of brain cancer.

Tea and coffee contain caffeine. A newspaper reported the results of this investigation under the headline ‘Caffeine helps cut cancer risk’. Explain why scientists could not support this view solely on the basis of this investigation.

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(e) Another group of scientists investigated the effect of caffeine on blood flow to certain parts of the brain. Volunteers were given different concentrations of caffeine solution to drink. A control group was also set up.

(i) Describe how the control group should have been treated.

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(ii) Volunteers who drank the same concentration of caffeine solution often had different concentrations of caffeine in their blood. Suggest one reason for the difference in concentration of caffeine in the blood of volunteers.

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(iii) The investigation showed that caffeine reduces the blood flow to certain parts of the brain. Suggest one way in which this could lead to a reduced risk of brain cancers.

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Q2. A gene was broken into fragments using enzyme Z. The mixture of fragments produced was then separated by electrophoresis.

(a) What type of enzyme is enzyme Z?

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The table shows the number of base pairs present in the fragments.

Fragment Number of base pairs (× 103)

1 4.65

2 5.72

3 10.71

4 2.39

5 5.35

6 7.53

The diagram shows the electrophoresis gel used. The mixture of fragments was placed at the start point marked S and the process started. The boxes indicate the positions reached by the different fragments.

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(b) Explain why base pairs are a suitable way of measuring the length of a piece of DNA.

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(c) (i) Write 6 above the appropriate box on the diagram to show the position you would expect fragment 6 to have reached. (1)

(ii) Explain how you arrived at your answer.

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(d) Enzyme Z recognises a particular sequence of bases in the gene. How many times does this sequence appear in the DNA of this gene?

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Q3. The death rate from malignant skin tumours was investigated in the USA. The graph shows the results for fair-skinned men in different age groups.

(a) Describe what is meant by a malignant tumour.

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(b) Give one reason for the change in death rate from malignant skin tumours with increasing age.

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(c) The data for fair-skinned and dark-skinned people were collected separately. Explain why skin colour was a factor likely to affect the death rate.

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Q4. Scientists found a correlation between prostate cancer and exposure to cadmium ions.

The scientists investigated the effects of cadmium ions on cells from a human prostate gland. They grew a culture of these cells in liquid growth medium and removed samples at intervals.

For each sample they measured

• how much DNA was not methylated, • the activity of the enzyme methyltransferase.

Methyltransferase is an enzyme that adds methyl groups to some of the bases in DNA. The addition of a methyl group is called methylation.

(a) The scientists set up another culture as a control.

Describe how the scientists would have set up a control experiment for this investigation.

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(b) Figures 1 and 2 show the scientists’ results.

Figure 1 Figure 2

(i) The scientists expressed their results as percentages of the control values. Suggest why.

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(ii) Use information from Figure 1 to describe how exposure to cadmium ions affected the methylation of DNA.

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(iii) Use information from Figure 2 to suggest what caused the change to the DNA shown in Figure 1.

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(c) Prostate gland cells contain a tumour suppressor gene called p16. During the investigation, the scientists also measured the amount of p16 protein produced.

Figure 3 shows their results.

Figure 3

The scientists found that the promoter DNA of the p16 gene had become methylated. The promoter is the sequence of bases where the enzyme RNA-polymerase binds to a DNA molecule.

Explain how methylation of the promoter sequence of the p16 gene could cause the changes shown in Figure 3.

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(d) Each week of the investigation, the scientists took samples of the cadmium-treated prostate cells from the laboratory cultures. They injected these cells into mice and monitored the mice for the growth of tumours.

It was only the samples taken in the tenth week that caused tumours to begin to grow in the mice.

Use information from Figures 1, 2 and 3 to suggest why.

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Q5.A husband and wife wanted to know whether they were carriers of the mutated form of a gene. This mutation is a deletion that causes a serious inherited genetic disorder in people who are homozygous.

A geneticist took samples of DNA from the husband and the wife. He used a DNA probe to look for the deletion mutation. The DNA probe was specific to a particular base sequence in an exon in the gene. Exons are the coding sequences in a gene.

The geneticist compared the couple’s DNA with that of a person known not to carry this mutation.

The chart shows the geneticist’s results.

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(a) The geneticist told the couple they were both carriers of the mutated gene. Explain how he reached this conclusion.

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(b) The DNA probe the geneticist used was for an exon in the DNA, not an intron. Explain why.

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(c) To make the DNA probe, the geneticist had to find the base sequence of the normal gene. Once he had copies of the gene, what methods would he use to find the base sequence of the gene?

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Q6. Figure 1 shows sections through relaxed and contracted myofibrils of a skeletal muscle. The transverse sections are diagrams. The longitudinal sections are electron micrographs.

Figure 1

(a) (i) The electron micrographs are magnified 40 000 times. Calculate the length of band X in micrometres. Show your working.

Length of band X =...... µm (2)

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(ii) Explain the difference in appearance between transverse sections A and C in Figure 1.

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(b) Explain what leads to the differences in appearance between the relaxed myofibril and the contracted myofibril.

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(c) Duchenne muscular dystrophy (DMD) is a condition caused by the recessive allele of a sex-linked gene. A couple have a son with DMD. They want to know the probability that they could produce another child with DMD. They consulted a genetic counsellor who produced a diagram showing the inheritance of DMD in this family. This is shown in Figure 2.

Figure 2

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The couple who sought genetic counselling are persons 6 and 7.

(i) Give the evidence to show that DMD is caused by a recessive allele.

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(ii) Give the numbers of two people in Figure 2 who are definitely carriers of muscular dystrophy.

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(iii) Complete the genetic diagram to find the probability that the next child of couple 6 and 7 will be a son with muscular dystrophy. Use the following symbols:

XD = normal X chromosome Xd = X chromosome carrying the allele for muscular dystrophy Y = normal Y chromosome

Parental phenotypes Unaffected Unaffected

Parental genotypes ......

Gametes ......

Offspring genotypes ......

Offspring phenotypes ......

Probability of having a son with DMD ...... (4)

(d) DMD is caused by a deletion mutation in the gene for a muscle protein called dystrophin. A deletion is where part of the DNA sequence of a gene is lost. People in different families may inherit mutations in different regions of this gene.

Scientists isolated the dystrophin gene from DNA samples taken from children 10, 11 and 12. They cut the gene into fragments using an enzyme. The scientists then used two DNA probes to identify the presence or absence of two of these fragments, called F and G.

Feversham College This allowed them to find the number of copies of each fragment in the DNA of a single cell from each child.

The table shows their results.

Number of copies of gene fragment per cell Child F G

10 (unaffected girl) 2 1

11 (unaffected girl) 2 2

12 (boy with DMD) 1 0

(i) The number of copies of gene fragments F and G shows that person 12 has DMD. Explain how.

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(ii) The number of copies of gene fragments F and G shows that person 12 is male. Explain how.

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(iii) The genetic counsellor examined the scientists' results. He concluded that person 10 is a carrier of DMD but her sister, 11, is not.

Describe and explain the evidence for this in the table.

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(e) Person 12 took part in a trial of a new technique to help people with DMD.

Doctors took muscle cells from person 12’s father and grew them in tissue culture.

They suspended samples of the cultured cells in salt solution and injected them into a muscle in person 12’s left leg. They injected an equal volume of salt solution into the corresponding muscle in his right leg. Person 12 was given drugs to suppress his immune system throughout the trial.

Four weeks later, the doctors removed a muscle sample from near the injection site in each leg. They treated these samples with fluorescent antibodies. These antibodies were specific for the polypeptide coded for by gene fragment G of the dystrophin gene.

The results are shown in the table.

Percentage of muscle Location and fibres labelled with treatment antibody

Left leg - injected with cultured cells suspended in salt solution 6.8

Right leg - injected with salt solution

(i) Why was it necessary to treat person 12 with drugs to suppress his immune system?

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(ii) Explain why salt solution was injected into one leg and cultured cells suspended in salt solution into the other.

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(iii) This technique is at an early stage in its development. The doctors suggested that further investigations need to be carried out to assess its usefulness for treating people with DMD.

Explain why they made this suggestion.

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Q7. Cocaine is a highly addictive and illegal drug.

The release of the neurotransmitter dopamine in specific synapses in the brain leads to feelings of pleasure. Dopamine is removed from synapses by dopamine transporter proteins in the plasma membrane of neurones. Cocaine binds to the dopamine transporter protein.

Figure 1 shows a dopamine transporter protein and molecules of cocaine and dopamine.

Figure 1

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(a) Using all of the information, suggest how cocaine leads to feelings of pleasure.

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(b) (i) Scientists isolated a mutated gene for the dopamine transporter protein.

Name one method that the scientists could have used to produce many copies of the mutated gene in the laboratory.

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(ii) Copies of the gene were then inserted into early embryos of mice. When these mice were born, samples of their DNA were tested using DNA probes to make sure that the mutated gene was present in the mice.

What is a DNA probe?

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(c) Figure 2 shows dopamine transporter proteins produced from the normal gene and from the mutated gene.

Figure 2

Explain how the mutation leads to the production of a protein that transports dopamine but is not affected by cocaine.

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Q8.Some species of crop plant produce a substance called glycinebetaine (GB).

Scientists transferred the gene for GB into a species of crop plant that does not normally produce GB. These genetically modified plants then produced GB.

The scientists grew large numbers of the same crop plant with and without the gene at different temperatures. After 3 days, they found the increase in dry mass of the plants.

Figure 1 shows their results. Page 18 Feversham College Figure 1

(a) Describe the effect on growth of transferring the gene for GB into this plant.

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(b) The scientists measured the rate of photosynthesis in plants that produce GB and plants that do not produce GB at 25°C, 35°C and 45°C.

Figure 2

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(i) The scientists concluded that the production of GB protects photosynthesis from damage by high temperatures.

Use these data to support this conclusion.

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(ii) Use the data from Figure 2 for plants that do not produce GB to explain the effect of temperature on changes in dry mass of the plants shown in Figure 1.

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Rubisco activase is an enzyme found in chloroplasts. It activates the light-independent reaction of photosynthesis.

The scientists discovered that, as temperature increased from 25°C to 45°C, rubisco activase began attaching to thylakoid membranes in chloroplasts and this stopped it working.

(c) Rubisco activase stops working when it attaches to a thylakoid.

Use your knowledge of protein structure to explain why.

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(d) The scientists investigated the effect of GB on attachment of rubisco activase to thylakoid membranes at different temperatures.

Figure 3

Use information from Figure 2 and Figure 3 to suggest how GB protects the crop plant from high temperatures. Page 21 Feversham College ......

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(e) The scientists’ hypothesis at the start of the investigation was that crop plants genetically engineered to produce GB would become more resistant to high environmental temperatures. The scientists developed this hypothesis on the basis of previous research on crops that are grown in hot climates.

Suggest how the scientists arrived at their hypothesis.

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Q9.Imatinib is a drug used to treat a type of cancer that affects white blood cells. Scientists investigated the rate of uptake of imatinib by white blood cells. They measured the rate of uptake at 4°C and at 37°C. Their results are shown in the table.

Mean rate of uptake of imatinib into

cells / μg per million cells per hour

Concentration of imatinib 4°C 37°C

outside cells / μmol dm–3

0.5 4.0 10.5

1.0 10.7 32.5

5.0 40.4 420.5

10.0 51.9 794.6

50.0 249.9 3156.1

100.0 606.9 3173.0

(a) The scientists measured the rate of uptake of imatinib in μg per million cells per hour. Explain the advantage of using this unit of rate in this investigation.

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(b) Calculate the percentage increase in the mean rate of uptake of imatinib when the temperature is increased from 4°C to 37°C at a concentration of imatinib outside the cells of 1.0 μmol dm−3 .

Give your answer to one decimal place.

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(c) Imatinib is taken up by blood cells by active transport.

(i) Explain how the data for the two different temperatures support this statement.

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(ii) Explain how the data for concentrations of imatinib outside the blood cells at 50 and 100 μmol dm−3 at 37°C support the statement that imatinib is taken up by active transport.

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Q10.Metastatic melanoma (MM) is a type of skin cancer. It is caused by a faulty receptor protein in cell-surface membranes. There have been no very effective treatments for this cancer.

Dacarbazine is a drug that has been used to treat MM because it appears to increase survival time for some people with MM.

Doctors investigated the use of a new drug, called ipilimumab, to treat MM. They compared the median survival time (ST) for two groups of patients treated for MM:

• a control group of patients who had been treated with dacarbazine • a group of patients who had been treated with dacarbazine and ipilimumab.

The ST is how long a patient lives after diagnosis.

The doctors also recorded the percentage of patients showing a significant reduction in tumours with each treatment.

The total number of patients in the investigation was 502.

The table below shows the doctors’ results.

Treatment Median survival time (ST) / Percentage of patients showing significant months reduction in tumours

Dacarbazine 9.1 10.3

Dacarbazine and 11.2 15.2 ipilimumab

(a) The doctors compared median survival times for patients in each group.

How would you find the median survival time for a group of patients?

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(b) In many trials of new drugs, a control group of patients is given a placebo that does not contain any drug.

The control group in this investigation had been treated with dacarbazine. Suggest why they had not been given a placebo.

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Feversham College (c) A journalist who read this investigation concluded that ipilimumab improved the treatment of MM.

Do the data in the table support this conclusion? Give reasons for your answer.

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(d) MM is caused by a faulty receptor protein in cell-surface membranes. Cells in MM tumours can be destroyed by the immune system.

Suggest why they can be destroyed by the immune system.

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Q11.(a) Explain how the methylation of tumour suppressor genes can lead to cancer.

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Scientists investigated a possible relationship between the percentage of fat in the diet and the death rate from breast cancer in women from 10 countries.

Their data is shown in the table below.

Percentage of fat in Death rate of women diet of population from breast cancer per 100 000 women

9.5 1.5

15.0 7.0

20.0 12.0

25.0 9.0

32.0 15.0

35.0 8.0

35.0 20.0

40.5 18.0

43.0 24.0

45.0 26.0

(b) Describe how you would plot a suitable graph of these data. Explain your choice of type of graph.

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(c) What can you conclude from these data?

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Q12.Oestrogen is a substance produced by the enzyme aromatase. In females, the main source of oestrogen is the ovaries but aromatase is produced by many other organs in the body, including the lungs. Oestrogen can stimulate the development of some lung tumours. In these tumours, binding of oestrogen to cell-surface receptors stimulates cell division.

Scientists investigated whether two drugs could prevent lung tumours in female mice. First, they removed the ovaries from these mice. They then injected the mice with a tumour-causing chemical found in tobacco twice a day for 4 weeks. The mice were then randomly allocated to one of four groups. Each group contained 10 mice.

• Group Q was given a placebo. This placebo did not contain either drug. • Group R was given the drug anastrozole. This inhibits the enzyme aromatase. • Group S was given the drug fulvestrant. This binds to oestrogen receptors. • Group T was given both anastrozole and fulvestrant.

The mice were given these drugs each week during weeks 5−15 of the investigation.

(a) The scientists removed the ovaries from the mice for the investigation. They also gave the mice injections of the substrate of aromatase each day.

Explain why these steps were necessary.

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(b) The scientists predicted that fulvestrant would be more effective when given with anastrozole than when given alone.

Use the information provided to suggest why they predicted this.

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At week 15, the lungs of the mice were removed and examined. The scientists then determined the number of tumours present and the mean tumour area for each group.

Figure 1 and Figure 2 show the scientists’ results.

Figure 1

Figure 2

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(c) The scientists concluded that both drugs should be used together to reduce the risk of lung cancer in women exposed to tobacco products.

Do you agree? Explain your answer.

(d) The scientists used tumour area as an indicator of tumour size.

Explain why tumour area may not be the best indicator of tumour size and suggest a more reliable measurement.

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(e) The scientists repeated the investigation but this time they did not give the drugs until week 9.

Suggest why they gave the drugs at week 9, rather than at week 5.

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(f) Another group of scientists is currently using these drugs in human trials. However, the control group is not being given a placebo.

Suggest why a placebo is not being given and what is being given to this group instead.

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Q13.Some populations of flies are becoming resistant to insecticides intended to kill them.

Scientists developed a method for finding out whether a fly was carrying a recessive allele, r, that gives resistance to an insecticide. The dominant allele, R, of this gene does not give resistance.

The scientists: • crossed flies with genotype RR with flies with genotype rr • obtained DNA samples from the parents and offspring • used the same restriction endonuclease enzymes on each sample, to obtain DNA fragments.

(a) Explain why the scientists used the same restriction endonuclease enzymes on each DNA sample.

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The scientists added two different primers to each sample of DNA fragments for the polymerase chain reaction (PCR).

• Primer A3 only binds to a 195 base-pair fragment from allele r. • Primer A4 only binds to a 135 base-pair fragment from allele R.

The scientists separated the DNA fragments produced by the PCR on a gel where shorter fragments move further in a given time.

Their results are shown in Figure 1.

Figure 1

(b) Explain why primer A3 and primer A4 only bind to specific DNA fragments.

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(c) Use all the information given to explain the results in Figure 1.

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(d) The scientists wanted to know on which chromosome the gene with alleles R and r was located. From the flies with genotype RR, they obtained cells that were in mitosis and added a labelled DNA probe specific for allele R. They then looked at the cells under an optical microscope.

Explain why they used cells that were in mitosis.

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(e) Another group of scientists thought that pesticide resistance in some flies was related to increased activity of an enzyme called P450 monooxygenase (PM). This enzyme breaks down insecticides.

The scientists obtained large numbers of resistant and non-resistant flies. They then set up the following experiments.

• Non-resistant flies exposed to insecticide. • Resistant flies exposed to insecticide. • Resistant flies treated with an inhibitor of PM and then exposed to insecticide.

They then determined the percentage of flies that were dead at different times after being exposed to insecticide.

Figure 2

Feversham College (i) Explain why the scientists carried out the control experiment with the non-resistant flies.

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(ii) The scientists concluded that the resistance of the flies to the insecticide is partly due to increased activity of PM but other factors are also involved.

Explain how these data support this conclusion.

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