The kidney and osmoregulationEdexcel A-Level Biology B: Subtopic test

1. 1
   In a hospital laboratory, samples of blood plasma, glomerular filtrate and urine from a healthy adult are compared. The plasma contains water, glucose, amino acids, urea, mineral ions and large proteins such as albumin. The filtrate is collected from the Bowman's capsule.

   (a)

   Where is the urea in the plasma made, and from what?

   [1 mark]

   • AIn the kidney, from the breakdown of glucose
   • BIn the pancreas, from the breakdown of fatty acids
   • CIn the liver, from the deamination of excess amino acids
   • DIn the liver, from the breakdown of excess glucose

   (b)

   What produces the high hydrostatic pressure in the glomerulus that drives ultrafiltration?

   [1 mark]

   • AThe afferent arteriole is wider than the efferent arteriole
   • BThe efferent arteriole is wider than the afferent arteriole
   • CThe glomerular capillary wall is very thick
   • DADH constricts the glomerular capillaries

   (c)

   Explain why red blood cells and albumin are found in the plasma but not in the glomerular filtrate.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A scientist follows the glucose concentration along the nephron of a healthy person after a meal. The filtrate entering the proximal convoluted tubule has the same glucose concentration as plasma, but none is detectable by the end of the tubule. The cells lining the tubule have microvilli and many mitochondria.

   (a)

   How is glucose reabsorbed from the filtrate into the cells of the proximal convoluted tubule?

   [1 mark]

   • ABy simple diffusion through the phospholipid bilayer
   • BBy a glucose pump that uses ATP directly
   • CBy osmosis through aquaporins
   • DBy co-transport with sodium ions through carrier proteins

   (b)

   What is the main role of the many mitochondria in the proximal convoluted tubule cells?

   [1 mark]

   • ATo carry out ultrafiltration
   • BTo supply ATP for the sodium-potassium pumps that maintain the sodium gradient
   • CTo digest proteins in the filtrate
   • DTo make urea from amino acids

   (c)

   A person with untreated diabetes mellitus has glucose in their urine, although their kidneys are healthy. Explain why.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A researcher compares the kidneys of a beaver, which lives in water, with those of a kangaroo rat (Dipodomys sp.), which lives in desert and rarely drinks. The beaver has short loops of Henle. The kangaroo rat has very long loops of Henle for its body size and a thick medulla, and it produces very little urine.

   (a)

   Explain how the loop of Henle produces a low water potential in the tissue fluid of the medulla.

   [3 marks]

   (b)

   Explain how the kidney of the kangaroo rat is adapted to conserve water, compared with the kidney of the beaver.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student runs a 10 km race on a hot day without drinking. During the race her urine output falls and her urine is dark and concentrated. Later that evening she drinks several glasses of an alcoholic drink, which inhibits the release of ADH, and her urine volume rises sharply.

   (a)

   Explain how the student's body brings about the change in her urine during the race.

   [6 marks]

   (b)

   Explain, in terms of the nephron, why the alcohol increases her urine volume, and why it may leave her dehydrated.

   [6 marks]

   Total for question 4: 12 marks

End of questions