Control of blood water potentialAQA A-Level Biology: Subtopic test

1. 1
   A marathon runner sweats heavily during a race in hot weather and drinks nothing for two hours. Her blood water potential falls, and her body responds by changing the volume and concentration of her urine.

   (a)

   Which structure detects the fall in the water potential of the runner's blood?

   [1 mark]

   • AThe posterior pituitary gland
   • BOsmoreceptors in the hypothalamus
   • CThe glomerulus of the nephron
   • DCells of the distal convoluted tubule

   (b)

   Where is the ADH that acts on her kidneys released into the blood?

   [1 mark]

   • AThe hypothalamus
   • BThe anterior pituitary gland
   • CThe posterior pituitary gland
   • DThe adrenal cortex

   (c)

   Explain how the release of ADH changes the volume and concentration of the runner's urine.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A physiologist is studying filtration in the kidney of a mammal. In each nephron, blood flows from an afferent arteriole into a knot of capillaries called the glomerulus, and leaves in an efferent arteriole. Fluid is forced out of the capillaries into the lumen of the Bowman's capsule.

   (a)

   What maintains the high hydrostatic pressure of the blood in the glomerulus?

   [1 mark]

   • AThe afferent arteriole is wider than the efferent arteriole
   • BThe efferent arteriole is wider than the afferent arteriole
   • CThe capillary walls of the glomerulus are thick
   • DBlood flows in the glomerulus against the flow in the nephron

   (b)

   Which of these would NOT normally be found in the filtrate in the Bowman's capsule?

   [1 mark]

   • AGlucose
   • BUrea
   • CSodium ions
   • DPlasma proteins such as albumin

   (c)

   Describe how glucose in the filtrate is reabsorbed into the blood in the proximal convoluted tubule.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   The kangaroo rat lives in deserts and produces urine far more concentrated than that of a beaver, which lives by rivers. Anatomical studies show that the kangaroo rat has nephrons with much longer loops of Henle than the beaver, which has nephrons with short loops.

   (a)

   Describe how the loop of Henle maintains a gradient of sodium ions in the tissue fluid of the medulla.

   [3 marks]

   (b)

   Explain why the kangaroo rat can produce more concentrated urine than the beaver.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Two patients each produce abnormally large volumes of urine. Patient X has a tumour of the posterior pituitary gland that stops it releasing antidiuretic hormone (ADH). Patient Y has untreated diabetes mellitus, and the concentration of glucose in her blood is far above normal.

   (a)

   Explain why Patient X produces a large volume of dilute urine and feels intense thirst.

   [6 marks]

   (b)

   Explain why Patient Y has glucose in her urine and produces a large volume of urine.

   [6 marks]

   Total for question 4: 12 marks

End of questions