| Date | November 2009 | Marks available | 1 | Reference code | 09N.2.HL.TZ0.1 |
| Level | Higher level | Paper | Paper 2 | Time zone | TZ0 |
| Command term | Distinguish | Question number | 1 | Adapted from | N/A |
Question
Type II diabetes is having an impact on the health of many individuals worldwide. The condition is characterized by elevated levels of both insulin and glucose in the bloodstream. Some animals produce an insulin-degrading enzyme (IDE) which breaks down the insulin molecule. In an attempt to develop a model of type II diabetes, genetically modified mice have been developed. In these mice, both copies of the IDE gene have been removed (IDE − /−) and the enzyme is not produced. The bar chart below shows the mean concentration of insulin in the bloodstream of IDE − /− mice and that of control mice (IDE + /+).
In another experiment, groups of IDE − /− and IDE + /+ mice were injected with a fixed amount of glucose. The levels of blood glucose were measured at various time intervals following glucose injection. The data are shown in the graph below.
In animals that do not have type II diabetes, insulin stimulates glucose uptake into skeletal muscle. Glucose uptake into skeletal muscle is also stimulated when skeletal muscle is exercised. Genetically modified mice have been developed in which the insulin receptor is not produced in skeletal muscle and these are known as MIRKO mice. In another experiment, the effect of insulin and exercise on glucose uptake in skeletal muscle from control and MIRKO mice was examined. The results are shown in the bar chart below.
Calculate the percentage increase between mean blood insulin levels in IDE + /+ mice and those in IDE − /− mice.
Explain the difference in blood insulin concentrations between the two groups of mice.
Distinguish between the response of the two groups of mice to the injection of glucose.
Deduce, with a reason, whether transgenic IDE −/− mice are an appropriate model of type II diabetes.
Explain the reason for the differences in insulin-stimulated glucose uptake between control mice and MIRKO mice.
Distinguish between the effects of insulin alone and exercise alone on glucose uptake in skeletal muscle of MIRKO mice.
Evaluate, using the data, whether exercise would be an appropriate therapy for human patients with type II diabetes.
State which cells secrete insulin and the organ in which they are located.
Cells:
Organ:
State the name of one hormone other than insulin involved in the regulation of blood glucose.
Markscheme
200 %
IDE -/- mice do not have the enzyme to break down insulin; (accept converse)
therefore insulin levels higher in IDE -/- mice / lower in IDE +/+ mice;
in IDE +/+ mice, glucose (levels in the blood) peaks / starts to reduce after 30 minutes / in IDE -/- mice, glucose levels remain high for longer / continues to rise for 60 minutes;
blood glucose level is always higher in IDE -/- mice than in IDE +/+ mice / blood glucose level in IDE +/+ mice decreases rapidly to original level but remains high in IDE -/- mice ;
both blood glucose and insulin levels are higher in IDE -/- mice / high blood glucose levels and insulin levels are seen in type II diabetes;
due to this, IDE -/- mice are a good model for type II diabetes; (to award this mark answer needs justification)
(in both cases) when insulin is present control mice are better at taking up glucose than MIRKO mice;
no insulin receptors in skeletal muscle of MIRKO mice; (accept converse)
exercise increases glucose uptake more than insulin
Award [0] for simply just restating figures.
exercise stimulates glucose uptake into muscle / exercise lowers blood glucose;
exercise is more effective in reducing blood glucose in MIRKO mice (than in control mice);
exercise and insulin combined are more effective in both (MIRKO and control) mice;
exercise combined with insulin would be an appropriate therapy;
cells: β cells (in islets of Langerhans);
organ: pancreas;
glucagon / adrenaline / cortisol
Examiners report
Over half of the candidates failed to calculate the percentage increase of 200%.
The majority of candidates made the correct conclusion about insulin levels. However the second mark was often missed through lack of reference to the enzyme.
The action verb 'distinguish' was poorly understood, with too many candidates simply restating the figures. Surprisingly the mark for stating that the concentration was always higher for the IDE -/- mice was rarely seen.
Many candidates missed the fact that both blood glucose concentration and insulin concentration are elevated in type II diabetes (stated in the introduction to the question), as happens in the IDE -/- mice, so they are a good model.
Weaker candidates did not read the question correctly, also writing about exercise which was not required.
As in part e, weaker candidates did not distinguish between the correct bars, answering for the control mice.
Most gained a mark for saying that exercise does stimulate uptake. However only the better candidates took this further to say that the combined effect of insulin and exercise were far better than the insulin alone.
A surprising number of candidates were not able to state beta cells and the pancreas.
Most gave glucagon (although not always spelled correctly) some also correctly gave adrenalin/epinephrine or cortisol.
