Describe the roles of ADH and the collecting ducts in osmoregulation.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2021). The mark or mark type is shown in brackets.

1. [1] (a) hypothalamus / osmoreceptors, detects changes in water potential of blood ;
2. [1] (a) (causes) posterior pituitary gland;
3. [1] (a) (to) release ADH into blood ;
4. [1] (a) ADH binds to receptors ;
5. [1] (a) on cell surface membrane of collecting duct (cells);
6. [1] (a) stimulates enzyme cascade / phosphorylase enzyme produced ;
7. [1] (a) vesicles, move towards / fuse with, cell surface membrane ;
8. [1] (a) (vesicles have) aquaporins ;
9. [1] (a) collecting duct, membranes / cells / walls, more permeable to water ;
10. [1] (a) water moves, down water potential gradient / by osmosis;
11. [1] (a) into, (collecting duct) cells / tissue fluid / blood;
12. [1] (a) water potential (of blood) returns to set point ;
13. [1] (b) dendrites attached to cell body;
14. [1] (b) nucleus in, cell body / soma ;
15. [1] (b) many mitochondria ;
16. [1] (b) much rough endoplasmic reticulum / Nissl's granules (in cell body);
17. [1] (b) long axon;
18. [1] (b) synaptic knobs / synaptic bulbs / terminal branches / axon terminals ;
19. [1] (b) Schwann cells / myelin sheath / myelinated ;
20. [1] (b) nodes of Ranvier ;
21. [1] (b) cell body in, CNS / brain and spinal cord ;
22. [1] (b) accept from labelled diagram
23. [1] (b) if sensory neurone described max 5