A-LevelBiologyHomeostasis9700/41 · Oct/Nov 2019 · Q18 Marks

ADH is a hormone that is released into the blood of a mammal when changes occur in the internal environment.

(a)(i)State one change in the internal environment of a mammal that leads to the release of ADH.[1]
(a)(ii)Name the part of the body that releases ADH into the blood.[1]
(b)Fig. 1.1 shows a cell of one of the collecting ducts of the kidney. [Figure 1.1] Name membrane protein A and cell structure B. A .............................................................................................................................. B ..............................................................................................................................[2]
(c)The phosphorylase enzyme stimulates structure B. Describe the response of structure B to this stimulation and describe the consequences of this response.[4]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2019). The mark or mark type is shown in brackets.

[1] any one from: 1 decrease in water potential (of the blood) ; I low water potential 2 lower blood volume ; 3 increase in, ion / salt, concentrations (of the blood);
[1] posterior pituitary (gland);
[2] A - receptor; I G-protein B - vesicle; I aquaporin
[4] any four from: 1 (B/vesicles) moves towards / fuses with, cell surface membrane ; Ignore aquaporins 2 aquaporins added to cell surface membrane ; A water channels 3 cell surface membrane more permeable to water; 4 water moves from, collecting duct/lumen / filtrate, into, cell / blood / tissue fluid; 5 by osmosis / down water potential gradient ; 6 water potential of blood, rises / returns to set point; 7 less water lost (in urine / from body) ; A urine, more concentrated / lower volume

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