Cambridge OCR A Level · Biology A - H420

Excretion as an example of homeostatic control: Practice Questions

5 multiple-choice questions marked as you go, and 4 written questions with worked solutions. All on Excretion as an example of homeostatic control.

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Question 1

1 mark

A patient is undergoing treatment for kidney failure. During haemodialysis, which principle is primarily responsible for the removal of urea from the patient's blood into the dialysis fluid?

Question 2

1 mark

Antidiuretic hormone (ADH) plays a crucial role in osmoregulation. Which of the following correctly describes the mechanism by which ADH increases the reabsorption of water in the kidney?

Question 3

1 mark

The Glomerular Filtration Rate (GFR) is a key indicator used to assess kidney function. If a patient's GFR decreases significantly, which of the following physiological changes is most likely to be observed?

Question 4

1 mark

In the mammalian liver, ammonia is converted into urea through a series of biochemical reactions. Which molecule reacts with ammonia to initiate the ornithine cycle?

Question 5

1 mark

Which row in the table below correctly identifies the site of osmoreceptor cells and the gland that releases ADH into the blood?

\(\begin{array}{|l|c|c|} \hline & \text{Location of Osmoreceptors} & \text{Gland Releasing ADH} \\ \hline \text{A} & \text{Posterior pituitary gland} & \text{Hypothalamus} \\ \hline \text{B} & \text{Hypothalamus} & \text{Anterior pituitary gland} \\ \hline \text{C} & \text{Hypothalamus} & \text{Posterior pituitary gland} \\ \hline \text{D} & \text{Collecting duct} & \text{Adrenal cortex} \\ \hline \end{array}\)

Question 6

2 marks

Define the term excretion and explain its physiological importance in maintaining homeostasis within a mammalian body.

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Question 7

3 marks

In the process of urine production, explain how the basement membrane of the Bowman's capsule acts as a selective barrier during ultrafiltration.

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Question 8

6 marks

A patient presents with a significantly reduced Glomerular Filtration Rate (GFR). Explain why this condition often leads to an electrolyte imbalance and discuss how haemodialysis can be used to manage this specific homeostatic failure.

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Question 9

8 marks

(a) Explain the role of the loop of Henle in the mammalian kidney and how its length relates to the environment in which an animal lives. [3]

(b) Anti-diuretic hormone (ADH) plays a crucial role in osmoregulation. Describe the mechanism by which ADH increases the permeability of the collecting duct to water, including the cellular signalling involved. [3]

(c) A patient is diagnosed with central diabetes insipidus, a condition where the posterior pituitary gland fails to secrete sufficient ADH. Predict the effect of this condition on the volume and concentration of the patient’s urine, and explain why this occurs with reference to water potential gradients. [2]

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