Antidiuretic hormone (ADH) is involved in the maintenance of a constant blood water potential. A student drank 0.5 dm³ of water and the concentration of ADH in their blood was measured every 30 minutes for 3 hours. Fig. 9.1 shows the results of this investigation. [Figure 9.1] Explain the results shown in Fig. 9.1.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2023). The mark or mark type is shown in brackets.

1. [1] (a) (drink of water causes) increase in blood water potential / AW ;
2. [1] (a) detected by, osmoreceptors / hypothalamus ;
3. [1] (a) causes decrease in release of ADH (into blood in first hour) ;
4. [1] (a) less water reabsorbed (from collecting ducts);
5. [1] (a) (so) decrease in blood water potential / blood water potential returns to set point ;
6. [1] (a) causes increase in release of ADH ;
7. [1] (a) negative feedback;
8. [1] (b) communication: nervous system: action potential / impulse and endocrine system: hormone ;
9. [1] (b) nature of communication: nervous system: electrical (and chemical) and endocrine system: chemical ;
10. [1] (b) mode of transmission: nervous system: neurone and endocrine system: blood ;
11. [1] (b) response destination: nervous system: muscle and endocrine system: target, organs / tissue / cells ;
12. [1] (b) transmission speed: nervous system: fast(er) and endocrine system: slow(er) ;
13. [1] (b) location of effect: nervous system: specific / localised and endocrine system: (can be) widespread ;
14. [1] (b) response speed: nervous system: fast(er) and endocrine system: slow(er) ;
15. [1] (b) duration of effect: nervous system: short-lived / temporary and endocrine system: can be long-lasting / permanent ;