(a) Compare the ureter and the urethra in terms of their functions in adult humans. [4] (b) Explain how the process of dialysis maintains the correct chemical composition of the blood for a person with kidney disease. [6]

Mark scheme

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

1. [1] both carry + urine / urea ;
2. [1] ureter from kidney ;
3. [1] ureter to bladder ;
4. [1] urethra from bladder ;
5. [1] urethra out of body ;
6. [1] male / penis / testis + urethra carries + semen / sperm ;
7. [1] selectively / partially / semi + permeable ;
8. [1] large surface area ;
9. [1] fluid / dialysate ;
10. [1] counter-current / continuously changed ;
11. [1] urea / toxins / poisons / harmful substances + from blood / to fluid ;
12. [1] water / salts / ions + between blood and fluid ;
13. [1] diffusion / osmosis ;
14. [1] high to low concentration / down concentration gradient ;
15. [1] large molecules / proteins + stay in blood / do not enter fluid ;