OSMOREGULATION

Question 1

Q2.In a mammal, urea is removed from the blood by the kidneys and concentrated in the filtrate.
(a) Describe how urea is removed from the blood. (2)

Answer 1

Hydrostatic pressure / description of pressure / description of how pressure
generated;

Causes ultrafiltration (Allow description of ultrafiltration) at Bowman’s capsule /
glomeruli / renal capsule;

Through basement membrane;

Enabled by small size urea molecule;

Question 2

(b) Explain how urea is concentrated in the filtrate. (3)

Answer 2

Reabsorption of water / by osmosis;

At the PCT / descending LoH;

At the DCT / CD;

Active transport of ions / glucose creates gradient (in context);

Ignore references to facilitated diffusion or to selective
re absorption.

Question 3

(a) Describe how ultrafiltration produces glomerular filtrate.
(5)

Answer 3

1. Blood pressure / hydrostatic pressure;
2. Small molecules / named example;
3. Pass through basement membrane / basement membrane acts as filter;
4. Protein too large to go through / large so stays behind;
5. Presence of pores in capillaries / presence of podocytes;

Question 4

(b) Some people who have diabetes do not secrete insulin.

Explain how a lack of
insulin affects reabsorption of glucose in the kidneys of a person who does not
secrete insulin. (4)

Answer 4

1. High concentration of glucose in blood;
2. High concentration in tubule / in filtrate;
3. Reabsorbed by facilitated diffusion / active transport;
4. Requires proteins / carriers;
5. These are working at maximum rate / are saturated;
6. Not all glucose is reabsorbed / some is lost in urine;