A-LevelBiologyHomeostasis9700/41 · Oct/Nov 2024 · Q611 Marks

The mammalian kidney is responsible for: : the excretion of urea osmoregulation (the homeostatic control of the water potential of the blood).

(a)(i)Outline how and where the excretory product urea is made in the body.[2]
(a)(ii)Homeostatic control of the water potential of blood includes receptors, effectors and target cells. Identify the names and locations of these components of homeostatic control in osmoregulation.[3]
(b)The glomerulus and Bowman's capsule of the nephron are important in the formation of urine. Outline the role of the glomerulus and Bowman's capsule in the formation of urine.[3]
(c)Concentrated urine contains a high concentration of solutes and a small volume of water. Different species of mammals vary in their ability to produce urine with a high solute concentration. Table 6.1 compares the ratio of the solute concentration of urine (U) to the solute concentration of blood plasma (P) in some mammal species. The habitats of the mammal species are also shown. With reference to Table 6.1, suggest what the different values of U: P show about the ability of these mammal species to tolerate a shortage of water in their environment.[3]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2024). The mark or mark type is shown in brackets.

[2] 1 (excess) amino acids, deaminated / have amino group removed ;
2 in the liver;
[3] any three from:
1 osmoreceptors in hypothalamus (detect change / are receptors) ;
2 effector(s): collecting duct / distal convoluted tubule / nephron ;
3 target cells: collecting duct (cells);
[3] any three from:
1 ultrafiltration / forms glomerular filtrate;
2 high, hydrostatic / blood, pressure in, glomerulus / capillaries ;
3 so, water/ (named) solutes, move (out of glomerulus / into Bowman's capsule);
4 through two of: fenestrae / fenestrations
basement membrane
slit pores / filtration slits / between podocytes ;
5 AVP;
[3] any three from:
1 high(er/est), U:P / ratio → can tolerate water shortage;
2 high(er/est), U:P / ratio → much water reabsorbed / small volume of urine produced;
3 high(er/est), U:P / ratio → can, concentrate urine / conserve water OR high(er / est), U:P / ratio → (well) adapted to dry environment;
4 AVP;

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