AQA A-Level Biology: Homeostasis
6 exam-style questions with full mark schemes and model answers. Write your own answer and the AI examiner marks it against the mark scheme.
Describe and explain how the concentration of glucose in the blood is controlled by negative feedback.
In your answer you should refer to:
- detection of changes in blood glucose concentration by the islets of Langerhans
- the actions of insulin and glucagon
- the role of the liver
- the principle of negative feedback.
In a glucose tolerance test, a person drinks a measured glucose solution at time 0. Their blood glucose concentration is then measured every 30 minutes. The table shows the results for a healthy (non-diabetic) person and for a person with untreated type 1 diabetes.
| Time / min | Non-diabetic / mmol dm⁻³ | Untreated type 1 diabetic / mmol dm⁻³ |
|---|---|---|
| 0 | 5.0 | 9.0 |
| 30 | 8.0 | 13.0 |
| 60 | 7.0 | 16.0 |
| 90 | 6.0 | 15.0 |
| 120 | 5.0 | 14.0 |
(a) Describe two ways in which the response of the type 1 diabetic differs from that of the non-diabetic person. (2 marks)
(b) Calculate the percentage increase in the non-diabetic person's blood glucose concentration between 0 and 30 minutes. Show your working. (2 marks)
(c) Explain the change in the non-diabetic person's blood glucose concentration between 30 and 120 minutes. (2 marks)
The table shows the concentration of three substances in the blood plasma, the glomerular filtrate and the urine of a healthy person.
| Substance | Blood plasma / g dm⁻³ | Glomerular filtrate / g dm⁻³ | Urine / g dm⁻³ |
|---|---|---|---|
| Protein | 75.0 | 0.0 | 0.0 |
| Glucose | 1.0 | 1.0 | 0.0 |
| Urea | 0.30 | 0.30 | 18.0 |
(a) Using the data, explain why protein is absent from the glomerular filtrate and why glucose is present in the filtrate but absent from the urine. (3 marks)
(b) Calculate how many times more concentrated urea is in the urine than in the blood plasma. Show your working. (2 marks)
A person has a rare mutation. They produce normal amounts of antidiuretic hormone (ADH), but the mutation means the ADH receptors in the cells of their collecting duct do not work and cannot bind ADH.
Suggest and explain the effect of this mutation on:
- the volume and concentration of the urine this person produces
- the water potential of their blood.
(5 marks)
Some people with high blood pressure are given a diuretic drug. This drug blocks the reabsorption of sodium ions (Na⁺) from the filtrate in the nephron (in the loop of Henle).
Explain how this drug affects the water potential of the filtrate and therefore the volume of urine produced.
(4 marks)
A mammal becomes too hot on a warm day.
Explain how negative feedback returns its core body temperature to normal. In your answer refer to thermoreceptors, the hypothalamus, and two named effector responses.
(3 marks)