O-LevelBiologyTransport in Humans5090/22 · Oct/Nov 2020 · Q710 Marks
The kidneys are organs of excretion.
- (a)Define the term excretion.[3]
- (b)A person with kidney damage requires the process of dialysis to take place several times each week. Dialysis is carried out using a kidney machine connected to the blood supply of the person. The diagram shows a section through the internal structure of a kidney machine. [Figure 7.1: Diagram showing a kidney machine with blood flow, dialysis fluid in/out, and dialysis membrane.]
- (b)(i)Describe the structure of the dialysis membrane and explain how it functions.[5]
- (b)(ii)Explain why the dialysis fluid in the kidney machine must be continuously replaced.[2]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2020). The mark or mark type is shown in brackets.
- [1] removal AW;
- [1] toxins/toxic;
- [1] waste products AW / urea / carbon dioxide;
- [1] multiple tubes / multiple sheets / coiled / folded / long;
- [1] large AW + surface area;
- [1] selectively / partially / semi + permeable ;
- [1] diffusion / osmosis ;
- [1] small/waste products AW/ urea / ions / water / toxins + do pass AW ;
- [1] large / protein / blood cells + do not pass AW ;
- [1] maintain gradient AW ;
- [1] prevent build up / ensure removal + waste products AW / urea / toxins ;
- [1] continued / more / maximum + diffusion / movement / exchange;
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