Osmoregulation and ADHEdexcel International A Level Biology: Subtopic test

1. 1
   A student eats a very salty meal at lunchtime and drinks very little water for the rest of the afternoon. Later, a blood test shows that the water potential of her blood plasma has become more negative than normal.

   (a)

   Which part of the body contains the receptors that detect this change in the water potential of the blood?

   [1 mark]

   • APosterior pituitary gland
   • BCerebellum
   • CHypothalamus
   • DCollecting duct

   (b)

   What is the effect of the antidiuretic hormone (ADH) released in response to this change?

   [1 mark]

   • AThe walls of the collecting duct become more permeable to water
   • BThe walls of the collecting duct become less permeable to water
   • CThe proximal convoluted tubule actively transports more sodium ions
   • DThe rate of ultrafiltration in the glomerulus stops

   (c)

   Predict the effect on the urine that the student produces and explain how this restores her blood water potential.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A pharmacology student is studying a drug that stops the sodium-potassium pumps in the membranes on the blood side of the cells lining the proximal convoluted tubule. In a healthy kidney these cells have microvilli on the side facing the filtrate and contain many mitochondria.

   (a)

   By which process do glucose molecules normally move from the filtrate into the cells of the proximal convoluted tubule?

   [1 mark]

   • ASimple diffusion through the phospholipid bilayer
   • BActive transport directly powered by ATP at the surface facing the filtrate
   • COsmosis
   • DCo-transport with sodium ions

   (b)

   Which statement about the reabsorption of substances in the proximal convoluted tubule of a healthy person is correct?

   [1 mark]

   • AOnly half of the glucose is reabsorbed
   • BAll of the glucose and amino acids are reabsorbed
   • CNo water is reabsorbed
   • DAll of the sodium ions remain in the filtrate

   (c)

   Suggest why a person taking this drug would have glucose in the urine.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   The kangaroo rat lives in deserts and rarely drinks. Its kidneys have very long loops of Henle and it produces urine that is about four times more concentrated than human urine. The beaver, which lives in water, has short loops of Henle and produces dilute urine.

   (a)

   Describe how the ascending limb of the loop of Henle helps to produce a low water potential in the tissue fluid of the medulla.

   [3 marks]

   (b)

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

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A marathon runner loses about 2 dm³ of water as sweat during a race. Her blood volume falls and the water potential of her blood plasma falls. Shortly after the race she drinks 2 dm³ of water.

   (a)

   Explain how the body responds to the fall in water potential of the runner's blood during the race.

   [6 marks]

   (b)

   Explain how the runner's kidneys produce a different urine after she drinks 2 dm³ of water, and why the water reabsorbed in the proximal convoluted tubule is not controlled by ADH.

   [6 marks]

   Total for question 4: 12 marks

End of questions