1. 1
   Two adults, X and Y, take an oral glucose tolerance test. After an overnight fast, each drinks a solution containing 75 g of glucose and their blood glucose concentration is measured. Person X: 4.8 mmol L⁻¹ before the drink, rising to a peak of 7.9 mmol L⁻¹ at 30 minutes and back to 5.0 mmol L⁻¹ at 2 hours. Person Y: 7.4 mmol L⁻¹ before the drink, rising to a peak of 14.2 mmol L⁻¹ at 60 minutes and still 12.1 mmol L⁻¹ at 2 hours.

   (a)

   Which cells secrete insulin in response to the rise in blood glucose?

   [1 mark]

   • Aα (alpha) cells of the pancreatic islets
   • Bβ (beta) cells of the pancreatic islets
   • CHepatocytes in the liver
   • DExocrine cells of the pancreas that secrete digestive enzymes

   (b)

   Which effect of insulin on its target cells helps return person X's blood glucose to the set point?

   [1 mark]

   • AStimulating muscle and liver cells to take up glucose and convert it to glycogen
   • BStimulating liver cells to break down glycogen to glucose
   • CStimulating the kidneys to excrete glucose in urine
   • DStimulating α cells to secrete glucagon

   (c)

   Explain why the data suggest that person Y has diabetes.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An open-water swimmer enters a lake at 14 °C wearing only a swimsuit. Within a few minutes her skin becomes pale, the hairs on her arms stand up and she begins to shiver. Her core body temperature stays close to 37 °C for the first 30 minutes of the swim.

   (a)

   Which structure receives impulses from the peripheral thermoreceptors and coordinates the swimmer's responses?

   [1 mark]

   • APituitary gland
   • BThyroid gland
   • CCerebellum
   • DHypothalamus

   (b)

   Why does the swimmer's skin become pale?

   [1 mark]

   • AVasodilation of skin arterioles increases heat loss
   • BSweat glands secrete more sweat
   • CVasoconstriction of skin arterioles reduces blood flow to the skin, reducing heat loss
   • DBrown adipose tissue in the skin removes blood

   (c)

   Outline how brown adipose tissue helps to maintain the swimmer's core temperature.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A three-year trial recruited 2000 adults with a body mass index above 30 and fasting blood glucose slightly above the normal range. At the start, their mean fasting insulin concentration was 2.3 times that of adults with normal blood glucose. Participants were randomly allocated to two groups. The control group received a leaflet on healthy eating. The lifestyle group had coaching aimed at losing 7% of body mass and doing 150 minutes of brisk exercise per week. After three years, 28% of the control group and 14% of the lifestyle group had developed type 2 diabetes.

   (a)

   Explain why the participants had raised fasting blood glucose even though their insulin concentration was high.

   [3 marks]

   (b)

   Evaluate the evidence from this trial that type 2 diabetes can be prevented by changes in lifestyle.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A hiker's core body temperature is logged by a sensor during one day in the mountains. At dawn she sits still in air at −2 °C; later she climbs a steep slope in bright sunshine with the air at 30 °C. Throughout the day her core temperature stays between 36.8 °C and 37.4 °C, while her skin temperature varies between 24 °C and 35 °C.

   (a)

   Explain how negative feedback maintained the hiker's core temperature while she sat in the cold at dawn.

   [6 marks]

   (b)

   Using the data, discuss why negative feedback rather than positive feedback is used to control body temperature.

   [6 marks]

   Total for question 4: 12 marks

End of questions