1. 1
   A 15-year-old is diagnosed with type 1 diabetes after losing weight and feeling constantly thirsty. Tests show antibodies against the cells of his pancreatic islets and almost no insulin in his blood. He now measures his blood glucose several times a day and injects insulin before meals. One morning he goes for a long run before breakfast and his blood glucose falls to 3.2 mmol L⁻¹.

   (a)

   Which response of his pancreas and liver would return his blood glucose towards the set point after the run?

   [1 mark]

   • Aβ cells secrete glucagon, which stimulates glycogen breakdown
   • Bβ cells secrete insulin, which stimulates liver cells to take up glucose
   • Cα cells secrete insulin, which stimulates glycogen synthesis
   • Dα cells secrete glucagon, which stimulates liver cells to break down glycogen

   (b)

   Why do only some cells in his body respond to the injected insulin, even though it circulates throughout the blood?

   [1 mark]

   • AInsulin can only pass through the walls of capillaries in the liver
   • BOnly target cells have receptors that bind insulin
   • CInsulin is broken down before it reaches most tissues
   • DOnly cells lacking glycogen can respond

   (c)

   Explain why he needs insulin injections, whereas many people with type 2 diabetes are first treated with changes to diet and exercise.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A cyclist rides for two hours in hot weather without drinking and loses about 2 litres of water as sweat. During the ride the osmotic concentration of her blood plasma rises from 0.285 osmol L⁻¹ to 0.300 osmol L⁻¹. Her urine becomes dark and small in volume, with an osmotic concentration of about 1.2 osmol L⁻¹.

   (a)

   Where are the receptors that detect the rise in her plasma osmotic concentration?

   [1 mark]

   • AIn the walls of the collecting ducts
   • BIn the posterior pituitary gland
   • CIn the hypothalamus
   • DIn the glomerulus

   (b)

   How does the increased secretion of antidiuretic hormone (ADH) cause her to produce a small volume of concentrated urine?

   [1 mark]

   • AAquaporins move from intracellular vesicles into the plasma membranes of collecting duct cells, so more water is reabsorbed
   • BAquaporins are removed from the plasma membranes of collecting duct cells, so less water is reabsorbed
   • CThe glomerulus filters less water from the blood
   • DThe loop of Henle actively pumps water out of the filtrate

   (c)

   Distinguish between excretion and osmoregulation, using her kidney function as an example.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Samples were taken from the blood plasma entering a glomerulus, from the filtrate in the Bowman's capsule, and from the urine of a healthy person. Protein: plasma 80 g L⁻¹, filtrate less than 0.1 g L⁻¹, urine 0 g L⁻¹. Glucose: plasma 1.0 g L⁻¹, filtrate 1.0 g L⁻¹, urine 0 g L⁻¹. Urea: plasma 0.3 g L⁻¹, filtrate 0.3 g L⁻¹, urine 20 g L⁻¹.

   (a)

   Explain the differences between the composition of the blood plasma and the filtrate in the Bowman's capsule.

   [3 marks]

   (b)

   Explain why glucose is absent from the urine but urea is about 67 times more concentrated than in the filtrate.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Blood flow to four organs was estimated for a healthy adult in three states. Wakeful rest (cardiac output 5.8 L min⁻¹): skeletal muscles 1.2, gut 1.4, kidneys 1.1 and brain 0.75 L min⁻¹. Vigorous physical activity (cardiac output 17.5 L min⁻¹): skeletal muscles 12.5, gut 0.6, kidneys 0.6 and brain 0.75 L min⁻¹. Sleep (cardiac output 5.0 L min⁻¹): skeletal muscles 0.7, gut 1.5, kidneys 1.1 and brain 0.75 L min⁻¹. During the vigorous activity the person's skin became flushed and they sweated heavily.

   (a)

   Analyse the changes in blood supply to the four organs during vigorous physical activity and sleep compared with wakeful rest, and explain their significance.

   [6 marks]

   (b)

   Explain how the body regulates core temperature during the vigorous activity, and why the flushed skin shows that blood supply is not controlled by muscle demand alone.

   [6 marks]

   Total for question 4: 12 marks

End of questions