Excretion January 2023

Q1.

Answer the question with a cross in the box you think is correct . If you change your mind
about an answer, put a line through the box and then mark your new answer with a cross .

Homeostasis is the state maintained by living systems.

(a) Feedback mechanisms are involved in maintaining homeostasis.

Describe the difference between a negative feedback mechanism and a positive feedback
mechanism.
(2)
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(b) Which statement about the homeostasis of thermoregulation when the human body temperature is 37
°C is correct?
(1)
A thermoregulation is no longer required
B the body no longer generates any heat
C the body will be generating more heat than it can lose
D the body temperature is maintained in a dynamic equilibrium

(c) The health of a kidney can be determined by measuring the glomerular filtration rate (GFR).
This method measures the rate at which a small molecule called creatinine is filtered from the blood.
(i) Explain how small molecules like creatinine are filtered from the blood in the glomerulus.
(3)
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(ii) In 15 hours, a person excreted 1960 mg of creatinine in the urine.
Calculate the GFR for this person.
Give your answer to 3 significant figures.
(1)

Answer ...........................................................

(d) In type II diabetes, body cells take up less glucose in response to insulin.
Many people with type II diabetes are overweight or obese.
Some of these individuals have been given surgery to help weight loss.
A clinical trial investigated the effect of surgery on the uptake of glucose by body cells in the presence
of insulin.
This trial used groups of people who were non-diabetic, people in the early stage of diabetes
(pre-diabetic) and people who were type II diabetics.

(i) Comment on the results of this trial.

(3)
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 (ii) Calculate the difference that surgery makes to the mean uptake of glucose in the non-diabetic
group and the type II diabetic group.
(2)

Answer ...........................................................

(Total for question = 12 marks)

Q2.

The kidney is involved in osmoregulation and the production of urine.

(a) (i) Which substances are filtered from the blood in the renal capsule?
(1)
A glucose and fibrinogen
B glucose, fibrinogen and urea
C glucose and urea
D urea and prothrombin

(ii) Which structure is acting as the filter in the renal capsule?

(1)
A basement membrane
B cells lining the renal capsule
C endothelial cells in the walls of the capillaries
D podocytes

(iii) Which transport mechanism is responsible for the uptake of glucose into the cells of the wall of the
proximal tubule?
(1)
A diffusion
B endocytosis
C sodium co-transport
D osmosis

(iv) Explain why some urea is reabsorbed in the proximal tubule.

(2)

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(b) In an investigation, salt solution was injected into the carotid artery of a mammal.
The carotid artery carries blood to the head.
The rate of urine production was measured after the injection.
The table shows the results.

(i) Calculate the percentage decrease in the rate of urine production 10 minutes after the injection.
Give your answer to 2 decimal places.
(2)

Answer ........................................................... %
(ii) At what times should more measurements be taken to find the lowest rate of urine production?
(1)
A at 1-minute intervals between 5 minutes and 10 minutes
B at 1-minute intervals between 5 minutes and 15 minutes
C at 1-minute intervals between 10 minutes and 15 minutes
D at 5 minutes, 10 minutes and 15 minutes, two more times

(iii) Explain the results of this investigation. Use the information in the table to support your answer.
(4)
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(Total for question = 12 marks)

Q3.

Ecstasy (MDMA) is a recreational drug that can have serious toxic effects.

(a) The effect of MDMA on ADH concentration in blood has been studied.
In one study, each person in a group of volunteers was given MDMA. The MDMA and ADH
concentrations in the blood were
measured.
The graph shows the results of this study.

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 (i) Estimate how long it takes the MDMA concentration in the blood to become 0.0 μg dm−3.
(1)

Answer ........................................................... hours

(ii) Calculate the rate of removal of ADH from the blood between 4 and 8 hours.
(2)

Answer ...........................................................

*(b) Taking MDMA causes a person to be very thirsty. This can lead to swelling of the brain, which can
be fatal.
The table shows some laboratory results for one case in which a person suffered swelling of the
brain.

Comment on the role of ADH in MDMA-induced brain swelling.

Use the information in the graph and table as well as your own knowledge to support your answer.
(6)
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(Total for question = 9 marks)