Fig. 1 shows results from an oral glucose tolerance investigation. Four volunteers drank the same glucose solution after fasting. The lines show the percent...
Question 1 Report
Fig. 1 shows results from an oral glucose tolerance investigation. Four volunteers drank the same glucose solution after fasting. The lines show the percentage change in blood glucose concentration from each volunteer’s fasting value. Volunteer D had previously been diagnosed with type 2 diabetes. The other volunteers had no diagnosis. The investigator used percentage change so that people with different starting concentrations could be compared on one graph.
(a) Describe the result for volunteer A after drinking the glucose solution. [3]
(b) Which volunteer, A, B or D, has the greatest percentage increase in blood glucose concentration? [1]
(c) Give one conclusion supported by the result for volunteer D. [2]
(d) Explain why blood glucose concentration normally falls after reaching a peak in a healthy volunteer. [4]
(e) Describe one control used in this investigation and explain why it was needed. [2]
(f) Give two improvements that would make the conclusion about type 2 diabetes more reliable. [2]
Answer Details
(a) Volunteer A's blood glucose concentration increases after the drink [1], reaches a peak [1], then falls back close to the fasting value [1].
(b) The trace with the greatest percentage increase is that of volunteer D. [1]
(c) Volunteer D has a larger rise and/or remains higher for longer than the other volunteers [1]. This is consistent with a reduced response to insulin, as occurs in type 2 diabetes [1]. It supports the diagnosis but does not by itself prove cause and effect.
(d) In a healthy person, the raised blood glucose concentration is detected by the pancreas [1]. Beta cells release insulin [1], causing body cells and liver cells to take up glucose [1]. Liver cells convert glucose to glycogen, so blood glucose concentration falls towards normal [1].
(e) One valid control is using the same glucose solution and volume, so each volunteer receives the same glucose dose [2]. Other valid control-reason pairs are fasting beforehand so recent food does not affect starting concentration, or taking samples at the same times so changes can be compared.
(f) Accept any two improvements: test more volunteers; repeat each volunteer's test; use volunteers of similar age or body mass, or record these variables; take more readings; or confirm diagnosis using an independent blood test. [2]
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