A-LevelBiologyHomeostasis9700/43 · Oct/Nov 2022 · Q811 Marks

(a) Fig. 8.1 is a diagram of a kidney nephron. [Figure 8.1] [Figure 8.2]

(a)With reference to Fig. 8.1, name A, B and C.[3]
(b)Antidiuretic hormone (ADH) is involved in the maintenance of the water potential of the blood. Fig. 8.2 shows the relationship between blood ADH concentration, urine concentration and the flow rate of urine. The flow rate of urine is the rate of production of urine by the kidneys. Describe the relationships shown in Fig. 8.2.[3]
(c)Describe and explain the action of ADH on the cells of the collecting duct when the water potential of the blood decreases.[5]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2022). The mark or mark type is shown in brackets.

[3] (a) A - distal convoluted tub(ul)e ; B - cortex; C - loop of Henlé ;
[3] (b) any three from: 1 as ADH concentration increases urine concentration increases ; 2 as ADH concentration increases urine flow rate decreases ; 3 as urine flow rate decreases urine concentration increases ; 4 data quote with units ; 5 AVP;
[5] (c) any five from: 1 ADH binds to cell, surface / membrane, receptor (of collecting duct cells) ; 2 ref. G protein / adenyl(ate) cyclase; 3 second messenger / cAMP; 4 protein kinase activated; 5 vesicles, move towards / fuse with, cell (surface) membrane ; 6 correct ref. aquaporins; 7 collecting duct / cells / membrane, (more) permeable to water ; 8 more water, leaves, lumen / nephron or more water enters, blood / medulla ;

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