A person whose kidneys have stopped working properly can be kept healthy by a treatment called dialysis, in which a machine does some of the work normally d...
Question 1 Report
A person whose kidneys have stopped working properly can be kept healthy by a treatment called dialysis, in which a machine does some of the work normally done by the kidneys. The diagram shows part of a dialysis machine, in which the patient's blood flows close to a fresh dialysis fluid. The table shows the concentration of several substances in the blood before dialysis and in the fresh dialysis fluid.
| Substance | Blood before dialysis / g per dm3 | Fresh dialysis fluid / g per dm3 |
|---|---|---|
| Glucose | 1.0 | 1.0 |
| Urea | 1.8 | 0.0 |
| Salts | 3.6 | 3.6 |
| Protein | 7.2 | 0.0 |
(a) State the name of the organ that has failed in this person. [1]
(b) Name the process by which urea passes from the blood into the dialysis fluid and, using the table, explain why it moves in this direction. [3]
(c) Explain why the dialysis fluid contains glucose at the same concentration as normal blood. [2]
(d) Explain why the plasma proteins are not lost into the dialysis fluid. [2]
(e) Explain why the used dialysis fluid is continually replaced with fresh fluid. [2]
(f) State one other treatment for kidney failure and give one advantage of it. [3]
Answer Details
(a) The organ that has failed is the kidney. [1]
(b) Urea passes into the fluid by diffusion [1]. From the table it is at a higher concentration in the blood (1.8 g per dm\(^3\)) than in the fresh fluid (0.0 g per dm\(^3\)) [1], so it diffuses down the concentration gradient across the partially permeable membrane into the fluid [1]. [3]
(c) The fluid has glucose at the same concentration as blood (both 1.0), so there is no concentration gradient for glucose [1]; this means glucose is not lost from the blood by diffusion, keeping the patient's blood sugar normal [1]. [2]
(d) The plasma protein molecules are too large [1] to pass through the tiny pores of the partially permeable membrane, so they stay in the blood [1]. The table confirms protein remains at 7.2 in the blood. [2]
(e) Replacing the used fluid keeps it free of urea, which maintains a steep concentration gradient for urea [1]; so urea keeps diffusing out of the blood until enough has been removed [1]. [2]
(f) One other treatment: a kidney transplant [1]; an advantage is that the person no longer needs regular dialysis sessions [1] and can eat a more normal diet / live more freely [1]. [3]
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