Gene Expression

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

  Methylation prevents transcription of gene

  Protein not produced that prevents cell division

  No control of mitosis
• Why would you use a scatter graph?

  To show the relationship between two independent variables.
• Apart from age, suggest two factors that the scientists should have considered when selecting volunteers for this trial.?

  Sex, Lifestyle, Bodymass, Health, Ethnicity, Genetic factors
•  Give two features of the design of this investigation that would ensure the reliability ofthe results obtained. (2)?

  Large Sample

  Long time period

  Different countries
•  In analysing the results of this investigation, the scientists took into account the age of the volunteers. Suggest why.?

  Age affects risk of 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.?

  Correlation does not mean causal relationship

  Tea/ coffee contains other substances

  No control group

  Only one tupe of cancer studied - further studies need to be established
•  Describe how the control group should have been treated.?

  Same but not caffeinated
• 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. (1)?

  Differences in Metabolism

  Absorb different amounts

  Broken down by enzymes

  Different blood volumes
• 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?

  Less oxygen/ glucose to cancer cells

  Less carcinogens

  Reduces spread of cancer cells
•  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.?

  Not ethical to fail to treat cancer
• 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.?

  Faulty protein can be recognised as an antigen

  T cells will bind to faulty protein

  (Sensitised) T cells will stimulate clonal section of Bcells

  resulting in release of antibodies against faulty protein
• 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.?

  Tumours may be different depths

  SHOULD measure tumour volume/ mass
•  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.?

  Allows tumours to grow

  So can investigate treatment rather than prevention of tumours
• 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.?

  Unethical to not treat patients/ may increase chance of getting more ill

  Use normal cancer drugs
•  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.?

  To allow comparison

  Because different numbers of cells in samples
• Imatinib is taken up by blood cells by active transport.

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

  At every conc - uptake is faster at 37°C

  Due to faster respiration/ ATP production
• 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?

  Uptake at 37°C only small increase

  Conc of imatinib is not limiting factor
• 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?

  Gives rise to new plants/ plantlets

  SO must be able to develop into different tissues/ other specialised cell types
• Papaya plants reproduce sexually by means of seeds. Papaya plants grown from seeds are very variable in their yield. Explain why.?

  Meoisis/ independent segregation

  Fusion of genetically different gametes / random fertilisation
• Explain the advantage of growing papaya plants from tissue culture rather than from seeds.?

  Will be clones / genetically identical
•  Describe what the graph shows about the effect of substrate concentration on the rate of this enzyme-controlled reaction.?

  Increases then plateaus up to about 28/27 units
• What limits the rate of this reaction between points A and B? Give the evidence from the graph for this.?

  Substrate concentration

  As substrate conc increases, rate increases
• Suggest a reason for the shape of the curve between points C and D.?

  All active sites are conncupied

  MAX # of E-Z complexes
•  Methotrexate is a drug used in the treatment of cancer. It is a competitive inhibitor and affects the enzyme folate reductase.

  (i)      Explain how the drug lowers the rate of reaction controlled by folate reductase.?

  Methotrexate is a similar shape to substrate so binds to active site

  Less EZ complexes formed
•  Methotrexate only affects the rate of the reaction controlled by folate reductase.

  Explain why this drug does not affect other enzymes.?

  Methotrexate is only similar shape to specific substrate

  SO only fits specific active site
•  Suggest how the scientists should have treated the control group.?

  given only saline

  otherwise treated exact same
•  Suggest and explain two factors which should be considered when deciding the number of mice to be used in this investigation.?

  Large Number - to improve reliability

  Number of mice related to cost

  Ethical considerations - does it lead to death or suffering of mice
• The scientists measured the volume of the tumours. Explain the advantage of using volume rather than length to measure the growth of tumours.?

  Vary in shape
•   In cells, taxol disrupts spindle activity. Use this information to explain the results in the group that has been treated with taxol.?

  In mitosis

  IF chromosomes cannot attach to spindle - or cannot separate on spindle

  Cell division slows down
• What information does standard deviation give about the volume of the tumours in this investigation??

  Variation from mean // degree of spread
•  Use Figure 2 and Figure 3 to evaluate the effectiveness of the two drugs when they are used separately and as a combined treatment?

  Both chemicals slow down growth so are both effective

  Taxol more effective than OGF

  combined treatment seems most effective

  SD overlap for OGF with taxol show - could be chance or both treatments = equally effective
•   The scientists put the same number of skin tumour cells in each dish at the start of this investigation. Explain why it was important to put the same number of cells in each dish.?

  To ensure they were the same colour at the start
• The scientists concluded that bromelain did not kill cancer cells but stopped them dividing. Does the graph support this conclusion? Explain your answer.?

  Yes as curve on graph with bromelain present remains constant - very slight rises

  Would decrease if killing of cells occured
•  An article in a newspaper claimed that these data show that bromelain can be used to treat cancer.

  Give three reasons why we should be careful about accepting this claim.?

  Use of mouse cells - not human cells

  Carroed out in vitro - not living organisms

  Only tested on one type of cancer

  Not possible to predict effect on humans
•  The rate of cell division is important in investigations into cancer. Suggest why.?

  The faster the rate of division the faster the cancer would grow

  By measuring rate of cell division - you could see how effective treatment was
• Scientists have investigated the effects of bromelain on cancer growth in humans. Suggest why they gave bromelain in addition to, rather than instead of, the usual treatment?

  Not ethical to replace conventional treatment

  As life of patient is at risk (if bromelain not effective)
• Why is it easier to give data in percentages?

  Easier to compare if sample size same

  Different numbers of people in each group
• Describe what is meant by a malignant tumour.?

  Mass of undifferentiated / unspecialised/ totipotent cells

  Uncontrolled cell division

  and they undergo metastasis - form new tumours and spread to other parts of body
•   Give one reason for the change in death rate from malignant skin tumours with increasing age.?

  Cancer takes time to develop

  immune system weaker in older people

  Longer exposure to UV and accumulation of mutagenic effects
• 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.?

  Light skinned people more affected as they lack melanin which serves as a protection so more risk of cancer in light skinned people

  + ALLOW CONVERSE