Three times a week
339 words over 31 numbered lines, then 8 parts worth 16 marks (Linear Paper 2 (4BI1/2B) style, 14–18 marks). Read the article, answer each part, then open its mark scheme and set your mark.
Illustrative article written for Scholar Lab, not a Pearson text. The biology is real; the studies, people and figures are invented or rounded for practice.
Three times a week
Three times a week, Samir spends four hours in a hospital chair
connected to a machine. His kidneys stopped working properly two years
ago, after a long illness. Without the machine, waste substances such
as urea would build up in his blood, and the water and salt content of
his body would change until his cells could no longer work.
Healthy kidneys filter the blood all the time. In each nephron, small
molecules are forced out of the blood in the glomerulus. Useful
substances such as glucose are then reabsorbed, together with as much
water as the body needs. The rest leaves the body as urine.
In dialysis, blood is taken from a vein in Samir’s arm and pumped
through the machine. Inside, the blood flows through thousands of thin
tubes made of a partially permeable membrane. Dialysis fluid flows
past the outside of the tubes in the opposite direction. The fluid
contains glucose and salts at the same concentrations as normal blood
plasma, but it contains no urea.
Urea diffuses out of the blood into the dialysis fluid, which is
replaced constantly. Blood cells and proteins are too large to pass
through the membrane, so they stay in the blood. Patients on dialysis
must limit how much salt, protein and liquid they take in between
sessions.
The best long-term treatment is a kidney transplant. A healthy kidney
can come from a person who has died, or from a living donor, because
people can live normally with only one kidney. The donor must have a
similar tissue type to the patient. Even so, patients must take drugs
for the rest of their lives to stop their immune system from rejecting
the new kidney.
There are not enough donated kidneys for everyone who needs one. In an
illustrative region, 2 400 people were waiting for a kidney, and 900
transplants were carried out in one year. Some countries now use an
opt-out system, in which everyone is a donor unless they have recorded
that they do not wish to be.
Read the article. Use the information in the article and your own knowledge to answer the questions. The lines in brackets show where to look; select them to highlight the text.
Use the information in the article and your own knowledge to answer the questions. The lines in brackets show you where to look; select them to highlight the text.
Name the organ that produces urea.
(1)State what is meant by the term excretion.
(1)Explain why glucose is not normally found in the urine of a healthy person.
(2)Explain how urea is removed from the blood during dialysis.
(3)Suggest why the dialysis fluid contains glucose and salts at the same concentrations as normal blood plasma.
(2)Explain why a transplanted kidney may be rejected.
(3)Calculate the percentage of people waiting who received a transplant in that year.
(2)Suggest one advantage and one disadvantage of an opt-out system of organ donation.
(2)Total for this question: 16 marks
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