| Date | May 2016 | Marks available | 1 | Reference code | 16M.2.HL.TZ0.1 |
| Level | Higher level | Paper | Paper 2 | Time zone | TZ0 |
| Command term | Describe | Question number | 1 | Adapted from | N/A |
Question
Type I diabetes is a leading cause of death in advanced countries and is associated with various severe or fatal complications, including blindness, kidney failure, heart disease, stroke, neuropathy, and amputations. Embryonic stem cells are considered to be a powerful tool in the treatment of diabetes.
In a study, embryonic stem cells were grown in culture and tested for insulin mRNA. A drug was injected into two groups of healthy mice in order to simulate type I diabetes 15 days prior to the transplant of embryonic stem cells. The mice in the transplant group received embryonic stem cells that produce insulin mRNA. The control group did not receive the transplant. The graph shows the blood glucose concentration in both groups.
A few years later, a third study used a treatment with umbilical cord stem cells on patients who had suffered from moderate or severe type I diabetes for an average of 8 years. They were divided into two groups: group 1 had moderate diabetes and group 2 had severe diabetes. The patients’ blood was circulated outside the body and exposed to umbilical cord stem cells before returning to the patients’ circulation. The control group had moderate diabetes and received the same treatment but without umbilical cord stem cells.
State the highest mean concentration of blood glucose in the mice with transplants.
..........................mg dL–1
Outline the cause of type I diabetes in humans.
Describe the reason for testing for insulin mRNA in the embryonic stem cell cultures.
Compare and contrast the concentration of blood glucose resulting from the embryonic stem cell transplant with the control.
Evaluate the effectiveness of the embryonic stem cell treatment in controlling blood glucose.
Compare and contrast the results of the treatment on group 1 with the results of the treatment on group 2.
Suggest an ethical advantage of using this type of therapy over embryonic stem cell therapy.
Using the data from all three studies, evaluate the use of embryonic stem cells as a treatment for type I diabetes.
Markscheme
470. Accept answers in the range of 460 to 480 «mg dL–1».
«Autoimmune» destruction of beta/β cells. (Accept B cells instead of β cells).
Reduced/insufficient/no production of insulin
Indicates «stem» cells can produce insulin
OR
is needed for insulin production
OR
shows insulin gene is working/being translated.
Insulin is needed to treat type I diabetes
OR
insulin is needed to bring blood glucose level down
Answers must relate to insulin mRNA.
Decrease in transplant group «after treatment» in contrast to control group which does not decrease/decreases only very slightly «initially»/increases/is higher than treatment group
Glucose «remains» lower in transplant group «than control group» for 2 max 2 weeks/3 weeks/for a time
«in the 4th week» transplant group rises back to level before transplant/to higher level than before transplant/to «near» level of control group
The answer must include some indication of time or non-permanency.
Glucose level still higher than normal/higher than 100 «mg»/higher than it was before the drug injection
Effective/lowers blood glucose for 3 weeks/temporarily/for a short time. This can either be positive (the treatment is effective for a while) or negative (it isn’t effective permanently).
OR
glucose level rises back in 4th week/by day 28
OR
rises back to level of control group
OR
rises again but not above control group
There must be a correct indication of the timing of the effects.
C-peptide increases after treatment in both groups. There must be an explicit comparison.
OR
treatment effective in both groups
OR
both groups rose higher than the control
Similar/same overall/total increase «in both groups»
OR
quoted figures to show this
Smaller percentage/% increase «pre to post treatment» in group 1 «than group 2» Reject answers relating to rates of increase.
OR
quoted figures to show this
Initial increase is greater in group 1
OR
increases slowing/finished/rate of increase reduced by end of study/by week 24 in group 1 but continuing in group 2
Group 1 rose above lower limit «by week 12» and group 2 remained below it «even at week 24»
Umbilical cord «stem» cells are discarded/die if not harvested
OR
harvesting umbilical cord cells does not harm the baby
OR
taking «stem» cells from an embryo may harm/kill it
Do not accept answers relating to consent.
Study 1/study with mice/embryonic stem cell study shows treatment can cause increased insulin production/ reduce blood glucose levels
«Insulin production/reduction in blood glucose in study 1 was» only temporary/did not reduce glucose to normal levels
Study 2 shows increases in C-peptide/insulin
OR
some type I diabetes patients required no insulin after treatment
Study 2 shows treatment effective for a long time/2 years
«Stem cell treatment in study 2» was more successful in some patients than others
OR
more successful for moderate «than more severe» diabetes
Study 3 shows that stem cells can cause C peptide/insulin levels to double/rise significantly/rise above lower limit «for normal C-peptide»/rise and stay raised
«Study 3» does not give evidence for embryonic stem cells
OR
used umbilical cord rather than embryonic stem cells
Examiners report
Most candidates successfully identified the highest mean blood glucose concentration.
Answers here were varied with many candidates correctly stating either that insulin is not produced or that beta cells are destroyed. A common incorrect answer was to state that diabetes is a purely genetic disease.
There were also varied answers here with some candidates not appreciating the significance of the presence of insulin mRNA or not stating it clearly enough.
Many candidates failed to pick out more than one significant trend here. The data before the transplant was not relevant so the three phases that could have been described were the initial drop in blood glucose in the transplant group, the period when both groups remain relatively constant but the transplant group stayed lower and finally the rise in the transplant group to the original level before the transplant. For the latter two points the timing was expected.
Very few candidates scored both marks here. The point commonly made was that the drop in the transplant group is temporary. Very few candidate also made the significant point that the transplant did not cause the blood glucose concentration to drop down to the level before diabetes had been induced, so even in the early stages the treatment was not fully effective.
This was another place where many candidates failed pick out enough significant similarities and differences. One similarity and four significant differences were included in the mark scheme but most candidates scored only one or two marks (out of three).
Most realised that there are ethical concerns if an embryo is damaged or killed and not if stem cells are taken from the placenta and umbilical cord before they are discarded, but the phrasing of answers was often too imprecise for a mark to be awarded. Terminology was frequently vague or incorrect. The terms embryo and fetus are not interchangeable, for example.
Many teachers correctly commented on G2 forms that there was an ambiguity in this question. It instructed candidates to use data from all three studies and also to evaluate the use of embryonic stem cells. Only study 1 had specifically been carried out using embryonic stem cells and study 3 was certainly done with umbilical cord rather than embryonic stem cells. It was therefore very important for candidates to quote which study they were using for a particular point and not all did this. Another weakness of some answers was to mention trends in the data without making them clearly a strength or weakness as is expected in an evaluation. The best answers coped well with the ambiguity in the question and scored full marks.
