A level biology _ module 8 (exam questions)

Haemophilia is a genetic condition in which blood fails to clot. Factor IX is a protein used to treat haemophilia. Sheep can be genetically engineered to produce Factor IX in the milk produced by their mammary glands. The diagram shows the stages involved in this process. Name the type of enzyme that is used to cut the gene for Factor IX from human DNA (Stage 1) . (1 mark)

restriction/endonuclease

The doctors mixed the stem cells with viruses. The viruses had been genetically modified to contain alleles of a gene producing full immunity. The doctors then injected this mixture into the child's bone marrow. The viruses that the doctors used had RNA as their genetic material. When these viruses infect cells, they pass their RNA and two viral enzymes into the host cells. (b) One of the viral enzymes makes a DNA copy of the virus RNA. Name this enzyme. (1 mark)

reverse transcriptase

Not all mutations result in a change to the amino acid sequence of the encoded polypeptide. Explain why. (1 mark)

- (genetic) code degenerate - mutation in intron

Silkworms secrete silk fibres, which are harvested and used to manufacture silk fabric. Scientists have produced genetically modified (GM) silkworms that contain a gene from a spider. The GM silkworms secrete fibres made of spider web protein (spider silk), which is stronger than normal silk fibre protein. Suggest why the plasmids were injected into the eggs of silkworms, rather than into the silkworms. (2 marks)

- (if injected into egg), gene gets into all/most of cells of silkworm - so gets into cells that make silk

The scientists analysed the DNA on the Y chromosome and the DNA in the mitochondria of the Swedish wolves. They concluded that the Swedish wolf population descended from one male wolf from Finland and one female wolf from Russia. (i) Explain why DNA on the Y chromosome helped them to reach this conclusion (1 mark)

Y chromosome inherited/comes from male parents/only found in males

Which person, H or G, was heterozygous, Aa? Explain your answer (2 marks)

(G because) - (heterozygous) only has half the amount of probe for A attaching/only half the amount of DNA/allele A (to bind to) - (so) only produced (about) half the light/glow/intensily (of H)(per cycle of PCR)

The jellyfish gene attached to the human Factor IX gene (Stage 2) codes for a protein that glows green under fluorescent light. Explain the purpose of attaching this gene. (2 marks)

- (act as a ) marker gene to show that the (human) gene has been taken up/expressed - (only) implant cells/embryos that show fluorescence/contain the jellyfish gene

Explain why the labelled DNA probe could be used to find out whether the haplotypes were the same. (2 marks)

- complimentary base sequence/complementary DNA, binds to both (haplotypes) - label would show up in both

More cancer cells could be destroyed if the drug was given more frequently. Suggest why the drug was not given more frequently. (2 marks)

- more/too many healthy cells killed - (so) will take time to place/increase in number - person may die/have side effects

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? (2 marks)

- restriction mapping - sanger method

It is important that scientists still report the results from failed attempts to produce transgenic animals. Explain why. (2 marks)

- saves time/money for others - same work is not repeated/methods can be compared/improved/amended/same errors are not made

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. Describe how you would plot a suitable graph of these data. Explain your choice of type of graph. (3 marks)

- scatter graph - fat on x axis and death rate on y axis - (because) looking at relationship between two discrete/independent variables

Phenylketonuria is a disease caused by mutations of the gene coding for the enzyme PAH. The table shows part of the DNA base sequence coding for PAH. It also shows a mutation of this sequence which leads to the production of non-functioning PAH. What is the maximum number of amino acids for which this base sequence could code? ( 1 mark)

4

Calculate the ratio of cytokinin : auxin that you would recommend to grow papaya plants by this method. (2 marks)

50:10

Suggest an explanation for your answer. (1 mark)

DNA/gene replication/synthesis occurs/longest stage

Name enzyme X. (1 mark)

RNA polymerase

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. (2 marks)

[(32.5-10.7)/10.7]x100=203.7%

The scientists expressed their results as percentages of the control values. Suggest why. (1 mark)

as a measure of the effect due to cadmium/to make a comparison

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

becoming more methylated

One mutation causing phenylketonuria was originally only found in one population in central Asia. It is now found in many different populations across Asia. Suggest how the spread of this mutation may have occurred. (1 mark)

founder effect/ colonies split off/migration/interbreeding

Two bands are usually seen for each person tested. Suggest why only one band was seen for Person L. (1 mark)

homozygous/(CAG) fragments are the same length/size/mass

Human cells also produce fatty acids. Isoniazid does not affect the production of these fatty acids. Use information in the diagram to suggest one reason why isoniazid does not affect the production of fatty acids in human cells. (1 mark)

human cells lack enzyme (B)/ have a different enzyme/produce different fatty acids/use different fatty acids/use different substances

Gene mutations occur spontaneously. (i) During which part of the cell cycle are gene mutations most likely to occur? (1 mark)

interphase/S/synthesis (phase)

What name is used for the non-coding sections of a gene? (1 mark)

introns

Suggest why DNA in the mitochondria helped them to reach this conclusion. (1 mark)

mitochondria in egg/female gamete/no mitochondria come from sperm/male gametes

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. (1 mark)

not ethical to fail to treat cancer

Oestrogen only affects target cells. Explain why oestrogen does not affect other cells in the body. (1 mark)

other cells do not have the/oestreogen/ER receptor

(ii) electrophoresis? (1 mark)

to separate the (pieces of) DNA

Explain the advantage of growing papaya plants from tissue culture rather than from seeds. (1 mark)

will be clones/produced by mitosis/will be genetically identical/less variation/all plants will have desired characteristics

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. (5 marks)

(yes for group T) - least tumours per animal - lowest (mean) tumour area/size - lowest top of range (but) - means (tumour area) are similar - ranges overlap/share values so difference may not be real/treatments may be just effective in reducing tumour - range affected by outliers/SD's would be better - done one mice/not done on women/humans - only 10 mice used per group/small sample size so may not be representative/reliable - might be side effects - only did for 15 weeks so maximum effect of drugs may not have been seen

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. (2 marks)

- (anastrozole) prevents/reduces oestrogen production - (fluverstrant) stops remaining oestrogen bindin/less oeastrogen binds to receptors

Chemotherapy is the use of a drug to treat cancer. The drug kills dividing cells. The figure below shows the number of healthy cells and cancer cells in the blood of a patient receiving chemotherapy. The arrows labelled F to I show when the drug was given to the patient. Calculate the rate at which healthy cells were killed between days 42 and 46. (1 mark)

- 1280-560=720 - 720/4=180

The promoter DNA from sheep (Stage 3) causes transcription of genes coding for proteins found in sheep milk. Suggest the advantage of using this promoter DNA (2 marks)

- Factor IX present in/extracted from milk - gene only expressed in mammary glands/udder/gene not expressed elsewhere - do not need to kill sheep (to obtain Factor IX)

how mutation 2 could lead to the formation of a non-functional enzyme. (3 marks)

- Leu replaces Val/change in amino acid (sequence)/primary structure - change in hydrogen/ionic bonds which alters tertiary structure/active site - substrate cannot bind/no longer complementary/ no enzyme-substrate complex form

Some of the children in the trial developed cancer. How might the insertion of the DNA have caused cancer? (2 marks)

- affects tumour suppressor gene - inactivates (tumour suppressor) gene - rate of cell division increased/ tumour cells continue to divide

Scientists wanted to measure how much mRNA was transcribed from allele A of a gene in a sample of cells. This gene exists in two forms, A and a. The scientists isolated mRNA from the cells. They added an enzyme to mRNA to produce cDNA. (a) Name the type of enzyme used to produce the cDNA. (1 mark)

reverse transcriptase

The diagram only shows part of the gel. Suggest how the scientists found the number of CAG repeats in the bands shown on the gel. (1 mark)

run fragments of known length/CAG repeats (at the same time)

The ecologist calculated the total prey index by combining the prey indices and the total number of animals of each species present in 1000 km2 . He plotted this information on the graph. What does the graph suggest about the factors that determine wolf numbers in North America? Explain your answer. (2 marks)

- limited by food/prey, as prey increases so do wolf numbers/positive correlation - large range so other factors involved

Papaya plants reproduce sexually by means of seeds. Papaya plants grown from seeds are very variable in their yield. Explain why. (2 marks)

- meiosis/independent assortment/crossing over - (fusion of) genetically different gametes/random fertilisation

Imatinib is taken up by blood cells by active transport. (i) Explain how the data for the two different temperatures support this statement. (2 marks)

- (at every concentration) uptake is faster at 37 C/at higher temperature - due to faster respiration/ATP production

Oestrogen is a hormone that affects transcription. It forms a complex with a receptor in the cytoplasm of target cells. Explain how an activated oestrogen receptor affects the target cell. (2 marks)

- (receptor/transcription factor) binds to promotor which stimulates RNA polymerase/enzyme X - transcribes gene/increase transcription

What can you conclude from these data? (2 marks)

- (trend) shows positive correlation/shows the more fat in diet, the higher death rate from breast cancer - but number of points off line/anomalies

A mutation of a tumour suppressor gene can result in the formation of a tumour. Explain how. (2 marks)

- (tumour suppressor) gene inactivated/not able to control/slow sown cell division - rate of cell division too fast/out of control

A mutation in the gene coding for enzyme B could lead to the production of a non-functional enzyme. Explain how. (3 marks)

- change in base sequence (of DNA/gene) leading to change in amino acid sequence/primary structure (of enzyme) - change in hydrogen/ionic/disulphide bonds leading to change in the tertiary structure/active site (of enzyme) - substrate not complementary/cannot bind (to enzyme/active site)/no enzyme-substrate complexes form

Scientists can use protein structure to investigate the evolutionary relationships between different species. Explain why. (2 mark)

- closer the (amino acid) sequence the closer the relationship - (protein structure) related to (DNA) base/triplet sequence

Human immunodeficiency virus (HIV) particles have a specific protein on their surface.This protein binds to a receptor on the plasma membrane of a human cell and allows HIV to enter. This HIV protein is found on the surface of human cells after they have become infected with HIV. Scientists made siRNA to inhibit expression of a specific HIV gene inside a human cell. They attached this siRNA to a carrier molecule. The flow chart shows what happens when this carrier molecule reaches a human cell infected with HIV. When siRNA binds to mRNA, name the complementary base pairs holding the siRNA and mRNA together. One of the bases is named for you. (1 mark)

- cytosine with guanine - adenine with uracil

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. (3 marks)

- faulty protein recognised as an antigen/as a 'foreign' protein - T cells will bind to faulty protein/to (this) 'foreign' protein - (sensititised) T cells will stimulate clonal selection of B cells - (resulting in) release of antibodies against faulty protein

Suggest two reasons why it was important that the spider gene was expressed only in the silk glands of the silkworms. (2 marks)

- so that protein can be harvested - fibres in other cells might cause harm

Describe similarities and differences in the response of healthy cells and cancer cells to the drug between times F and G. (3 marks)

(similarities) - same/similar pattern/both decrease, stay the same then increase - number of cells stays the same for same length of time (differences) - greater/faster decrease in number of healthy cells/more healthy cells killed/healthy cells killed faster - greater/faster increase in number of healthy cells/more healthy cells replaced/divide/healthy cells replaced/divide faster

Five out of the 20 children in the trial developed cancer. Although the cancer was treated successfully, the doctors decided to stop the trial in its early stages. They then reviewed the situation and decided to continue. Do you agree with their decision to continue? Explain your answer. (2 marks)

yes - SCID patients unlikely to survive/quality of life poor unless treated - cancer that develops is treatable/only affects 25%/five children no - risk of developing cancer is high/25% - cancer may recur/may not be treated successfully in future/ only short time scale so more may develop cancer

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. (2 marks)

- tumours may be different depths/area does not take depth into account/tumours are 3-D/are not 2-D - (measure) tumour volume/mass/weight

PAH catalyses a reaction at the start of two enzyme-controlled pathways. The diagram shows these pathways. Use the information in the diagram to give two symptoms you might expect to be visible in a person who produces non-functioning PAH. (2 marks)

- lack of skin pigment/pale/light skin/albino - lack of coordination/muscles action affected

Explain how the methylation of tumour suppressor genes can lead to cancer. (3 marks)

- methylation prevents transcription of gene - protein not produced that prevents cell division/causes cell death/apoptosis - no control of mitosis

Scientists investigated three genes, C, D and E, involved in controlling cell division. They studied the effect of mutations in these genes on the risk of developing lung cancer. The scientists analysed genes C, D and E from healthy people and people with lung cancer. • If a person had a normal allele for a gene, they used the symbol N. • If a person had two mutant alleles for a gene, they used the symbol M. They used their data to calculate the risk of developing lung cancer for people with different combinations of N and M alleles of the genes. A risk value of 1.00 indicates no increased risk. The following table shows the scientists' results What do these data suggest about the relative importance of the mutant alleles of genes C, D and E on increasing the risk of developing lung cancer? Explain your answer (3 marks)

- (mutation) in E produces highest risk/1.78 - (mutation) in D produces next highest risk/1.45 - (mutation) in C produces least risk/1.30

Prostate gland cells contain a tumour suppressor gene called p16. During the investigation, the scientists also measured the amount of p16 protein produced. 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. (2 marks)

- RNA-polymerase could not bind (to DNA/to promoter) - mRNA of p16 could not be made/no transcription of p16 gene

Huntington's disease is always fatal. Despite this, the allele is passed on in human populations. Use information in the graph to suggest why. (2 marks)

- age of onset can be high/symptoms appear later in life - (so) individuals have already had children/allele has been passed on OR - individuals have passed on the allele/already had children - before symptoms occur

Wolves eat different mammals. An ecologist investigated factors that affect wolf numbers in North America. He collected data from different field studies carried out in different places. The wolf numbers are given per unit area. Explain why. (2 marks)

- allow comparison - different (sized) areas covered

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. (2 marks)

- allows tumours to grow/develop/form - (so) can investigate treatment rather than prevention (of tumours)/when tumour/cancer is more advanced

The other viral enzyme is called integrase. Integrase inserts the DNA copy anywhere in the DNA of the host cell. It may even insert the DNA copy in one of the host cell's genes. (c) (i) The insertion of the DNA copy in one of the host cell's genes may cause the cell to make a non-functional protein. Explain how (2 marks)

- alters base/nucleotides sequence/causes frame shift - different sequence of amino acids in polypeptide/protein/primary structure alters the tertiary structure

Some cancer cells have a receptor protein in their cell-surface membrane that binds to a hormone called growth factor. This stimulates the cancer cells to divide. Scientists have produced a monoclonal antibody that stops this stimulation. Use your knowledge of monoclonal antibodies to suggest how this antibody stops the growth of a tumour (3 marks)

- antibody has specific tertiary structure/binding site/variable region - complementary (shape/fit) to receptor protein/GF/dinds to receptor protein/to GF - prevents GF binding (to receptor)

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. (4 marks)

- cadmium causes expression of methyltransferase gene/increased activity transferase (from 2 to 3 weeks in) - methyl groups on to promoter/p16 gene/suppressor (gene) - (p16) normally suppresses tumour growth - p16 protein/p16 expression falls after 4 weeks/after methylation - tumour formation occurs (after 10 weeks) after p16falls/after supressor gene activity falls

The carrier molecule on its own may be able to prevent the infection of cells by HIV. Explain how. (2 marks)

- carrier binds to (protein on) HIV - prevents HIV/it binding to (receptor on human) cell

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 geneticist told the couple they were both carriers of the mutated gene. Explain how he reached this conclusion. (3 marks)

- carriers are heterozygous/ have one normal copy and one mutant copy of the gene/have one recessive allele/don't have the condition - both have DNA that binds (about) half/50% amount of probe (that non-carrier does) - probe binds to dominant/healthy allele so only one copy of exon in their DNA/have one copy of gene without exon/base sequence for probe to bind to

Mycolic acids are substances that form part of the cell wall of the bacterium that causes tuberculosis. Mycolic acids are made from fatty acids. Isoniazid is an antibiotic that is used to treat tuberculosis. The diagram shows how this antibiotic inhibits the production of mycolic acids in this bacterium. Treatment with isoniazid leads to the osmotic lysis of this bacterium. Use information in the diagram to suggest how. (2 marks)

- cell wall not formed/production inhibited -lower water potential in bacterium - water enters and causes lysis/expansion/pressure

Explain how this mutation leads to the formation of non-functioning PAH. (3 marks)

- change in amino acid/ (sequence of) amino acids/primary structure - change in hydrogen/ionic/disulphide bonds leading to change in the tertiary structure/active site (of enzyme) - substrate not complementary/cannot bind (to enzyme/active site)/no enzyme-substrate complexes form

Plant physiologists attempted to produce papaya plants using tissue culture. They investigated the effects of different concentrations of two plant growth factors on small pieces of the stem tip from a papaya plant. Their results are shown in the table. Callus is a mass of undifferentiated plant cells. Plantlets are small plants. (a) Explain the evidence from the table that cells from the stem tip are totipotent. (2 marks)

- gives rise to new plants/plantlets - so must be able to develop into different tissues/other specialised cell types/differentiate

Some gene mutations affect the amino acid sequence. Some mutations do not. Use the information from Figure 1 and Figure 2 to explain (i) whether mutation 1 affects the amino acid sequence (2 marks)

- has no effect/same amino acid (sequence)/same primary structure - glycine named as same amino acid

The DNA probe the geneticist used was for an exon in the DNA, not an intron. Explain why (3 marks)

- introns not translated/not in mRNA/(exons) code for amino acids/introns do not code for amino acids - mutations of these (exons) affect amino acid sequences (that produce) faulty protein/change tertiary structure of protein - so important to know if parents' exons affected, rather than any other part of DNA/introns

The scientists used this method with cells from two people, H and G. One person was homozygous, AA, and the other was heterozygous, Aa. The scientists used the PCR and the DNA probe specific for allele A on the cDNA from both people. Explain the curve for person H (3 marks)

- more probe binding/more cDNA/mRNA/more allele/gene A means more light - DNA (with A) doubles each (PCR) cycle - so light (approximately) doubles/curve steepens more and more (each cycle)/curve goes up exponentially/increases even faster

Many attempts to produce transgenic animals have failed. Very few live births result from the many embryos that are implanted. (i) Suggest one reason why very few live births result from the many embryos that are implanted. (2 marks)

- mutation/nucleus/chromosomes/DNA may be damages/disrupts genes - may interfere with proteins (produced)/gene expression/translation OR - embryo/antigens foreign - embryo is rejected/attacked by immune system

Huntington's disease is a genetic condition that leads to a loss in brain function. The gene involved contains a section of DNA with many repeats of the base sequence CAG. The number of these repeats determines whether or not an allele of this gene will cause Huntington's disease. • An allele with 40 or more CAG repeats will cause Huntington's disease. • An allele with 36 - 39 CAG repeats may cause Huntington's disease. • An allele with fewer than 36 CAG repeats will not cause Huntington's disease. The graph shows the age at which a sample of patients with Huntington's disease first developed symptoms and the number of CAG repeats in the allele causing Huntington's disease in each patient. People can be tested to see whether they have an allele for this gene with more than 36 CAG repeats. Some doctors suggest that the results can be used to predict the age at which someone will develop Huntington's disease. Use information in the graph to evaluate this suggestion. (3 marks)

- negative correlation - wide range - overlap - (graph suggests that) other factors may be involved (in age of onset)

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. The scientists set up another culture as a control. Describe how the scientists would have set up a control experiment for this investigation. (2 marks)

- no cadmium - other conditions same as cadmium-treated group

Suggest why the scientists used a marker gene and why they used the EGFP gene. (2 marks)

- not all eggs will successfully take up the plasmid - silkworms that have taken up gene will glow

This siRNA would only affect gene expression in cells infected with HIV. Suggest two reasons why. (4 marks)

- only infected cells have HIV protein on surface - so carrier only attaches to/specific to these cells/siRNA can only enter these cells OR - siRNA (base sequence) complementary/specific to one mRNA - only infected cells contain mRNA of HIV/this gene/stops translation of this gene/only binds to this mRNA/destroys this mRNA

Scientists took DNA samples from three people, J, K and L. They used the polymerase chain reaction (PCR) to produce many copies of the piece of DNA containing the CAG repeats obtained from each person. They separated the DNA fragments by gel electrophoresis. A radioactively labelled probe was then used to detect the fragments. The diagram shows the appearance of part of the gel after an X-ray was taken. The bands show the DNA fragments that contain the CAG repeats. Only one of these people tested positive for Huntington's disease. Which person was this? Explain your answer. (2 marks)

- person K - (as has) high(est) band/band that travelled a short(est) distance/ (er) so has large(st) fragment/ number of CAG repeats

The scientists used the polymerase chain reaction (PCR) to produce copies of the cDNA. They added a DNA probe for allele A to the cDNA copies. This DNA probe had a dye attached to it. This dye glows with a green light only when the DNA probe is attached to its target cDNA. (b) Explain why this DNA probe will only detect allele A. (2 marks)

- probe (base sequence) complementary (to DNA of allele A/where A is (and) binds by forming base pairs/hydrogen bonds - so (only) this DNA labeled/has green dye/gives out (green) light

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 doctors compared median survival times for patients in each group. How would you find the median survival time for a group of patients? (2 marks)

- rank all STs in ascending order - find value with same number (of people) above and below

Comparing the base sequence of genes provides more evolutionary information than comparing the structure of proteins. Explain why. (4 marks)

- reference to base triplets/triplet code/more bases than amino acids/longer base sequence than amino acid sequence - introns/non-coding DNA/degeneracy of code/more than one code for each amino acid

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. (2 marks)

- removes (main/largest) source of oestrogen/ (different) mice produce different amounts of oestrogen - (allows) oestrogen to be controlled/ oestrogen to be made by aromatase only/only oestrogen made in lungs to be involved

Some breast tumours are stimulated to grow by oestrogen. Tamoxifen is used to treat these breast tumours. In the liver, tamoxifen is converted into an active substance called endoxifen. Figure 2 shows a molecule of oestrogen and a molecule of endoxifen. Use Figure 2 to suggest how endoxifen reduces the growth rate of these breast tumours. (2 marks)

- similar shape to oestrogen - binds receptor/prevents oestrogen binding - receptor not activated/will not attach to promoter/no transcription

Explain how the structure of DNA is related to its functions (6 marks)

- sugar-phosphate (backbone)/double stranded/helix so provides strength/stability/protects bases/protects hydrogen bonds - long/large molecule so can store lots of information - helix/coiled so compact - base sequence allows information to be stored/ base sequence codes for amino acids/protein - double stranded so replication can occur semi-conservatively/strands can act as templates/complementary base pairing/A-T and G-C so accurate replication/identical copies can be made - (weak) hydrogen bonds for replication/ unzipping/ strand separation/ many hydrogen bonds so stable/strong

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. 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. (2 marks)

- to allow comparison - because different number of cells in samples/different times for incubation/numbers become easier to manipulate

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. (2 marks)

- uptake at 37 C only small increase/leveling off/almost constant as carrier proteins full - concentration of imatinib is not the limiting factor

SCID is a severe inherited disease. People who are affected have no immunity. Doctors carried out a trial using gene therapy to treat children with SCID. The doctors who carried out the trial obtained stem cells from each child's umbilical cord. (a) Give two characteristic features of stem cells. (2 marks)

- will replaced themselves/keep dividing/replicate - undifferentiated/can differentiate/develop into other cells/totipotent/multipotent/pluripotent

The ecologist calculated the total prey index for each of the places that had been studied. In order to do this, he gave each prey species a value based on how much food was available to wolves from the prey animal concerned. He called this value the prey index. The ecologist considered that the prey index gave a better idea of the food available than the prey biomass in kg. Suggest why the prey index gives a better idea of food available. (2 marks)

- wolves do not eat all of prey animal/do not eat (large) bones/skin - inedible parts make up different proportions/wolf eats different proportions

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

production of more methyltransferase enzyme/increased activity of transferase

The scientists ensured the spider gene was expressed only in cells within the silk glands. (c) What would the scientists have inserted into the plasmid along with the spider gene to ensure that the spider gene was only expressed in the silk glands of the silkworms? (1 mark)

promoter (region/gene)

There are wolves in many European countries. Scientists investigated the genetic diversity of these wolves. They collected samples of DNA from the mitochondria of wolves from different countries. For each sample they identified which haplotypes were present in the DNA. A haplotype is a particular sequence of bases on DNA. Mutations can produce new haplotypes. The scientists wanted to find out whether one of the haplotypes in the Portuguese wolves was the same as one of those in the Spanish wolves. They used a restriction endonuclease, electrophoresis and a labelled DNA probe. For what purpose did they use (i) the restriction endonuclease (1 mark)

to cut the DNA

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 (2 marks)

unethical (not to treat patients)/may increase probability of patients dying/getting more ill - use normal cancer drugs/ treatment (i.e chemotherapy)

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. (4 marks)

yes since with ipilimumab - median ST increased by 2.1 months -percentage of patients showing reduction in tumours increased from 10.3% to 15.2% no because: -no standard errors shown/no (student) t-test/no statistical test carried out - (so) not able to tell if differences are (statistically) significant/due to chance (alone) - improvement might only be evident in some patients/no improvement in some patients - quality of (extra) time alive not reported