Define the term excretion.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2015). The mark or mark type is shown in brackets.

1. [max. 3] (a) removal from organism/body;
2. [max. 3] (a) toxic/poisonous ;
3. [max. 3] (a) waste (products) ;
4. [max. 3] (a) from metabolism;
5. [max. 7] (b) 1 blood from patient to machine/returned to patient;
6. [max. 7] (b) 2 using partially permeable membrane/tubes AW ;
7. [max. 7] (b) 3 ref. dialysis fluid;
8. [max. 7] (b) 4 ref. relative concentrations AW;
9. [max. 7] (b) 5 filters/removes substances from + blood/unwanted out/wanted in ;
10. [max. 7] (b) 6 by diffusion;
11. [max. 7] (b) 7 urea/nitrogenous products/toxins/poisons ;
12. [max. 7] (b) 8 salt(s)/ions/small molecules ;
13. [max. 7] (b) 9 excess water/ref. osmoregulation;
14. [max. 7] (b) 10 large molecules/proteins stay in blood ;
15. [max. 7] (b) 11 practical aspect e.g. bubble trap/repetition/frequency/duration of procedure/dialysis fluid frequently changed/temperature ref/counter flow;