HomeostasisAQA A-Level Biology: Topic test

20 questions, 54 marks

AQA A-Level Biology

Homeostasis topic test

Total 54 marks

Name

Class

Date

1
In an experiment on an anaesthetised mammal, the concentration of carbon dioxide in the air it breathes is raised. Dissolved carbon dioxide lowers the pH of the blood slightly. Chemoreceptors detect the change and the breathing rate increases until the blood pH returns to about 7.4.
(a)
Which statement describes this response?
[1 mark]
APositive feedback, because the breathing rate increases as the pH falls.
BPositive feedback, because the response is rapid.
CA feedforward response, because breathing changes before the pH changes.
DNegative feedback, because the response reverses the departure of the pH from its normal level.
(b)
Why is it important that the pH of the blood is kept stable?
[1 mark]
AA change in pH alters the tertiary structure of enzymes, changing the shape of their active sites.
BA change in pH alters the water potential of the blood, so cells would shrink or burst.
CA change in pH alters the supply of respiratory substrate to cells.
DA change in pH alters the rate of diffusion of carbon dioxide only.
(c)
Explain why separate mechanisms that correct a rise and a fall in blood pH give better control than a single mechanism that corrects only a fall.
[2 marks]
Total for question 1: 4 marks
2
A volunteer has not eaten for several hours. She then eats a large meal rich in starch. Her blood glucose concentration rises from 4.5 mmol dm⁻³ to 7.0 mmol dm⁻³ within 40 minutes and then falls back towards 4.5 mmol dm⁻³ over the next hour. After a long fast later in the week, her liver glycogen stores are almost used up.
(a)
Which process occurs in her liver cells when her blood glucose concentration rises after the meal?
[1 mark]
AGlycogenolysis
BGluconeogenesis
CGlycogenesis
DHydrolysis of starch to maltose
(b)
How does insulin increase the uptake of glucose by her muscle cells?
[1 mark]
ABy diffusing through the cell surface membrane into the cytoplasm
BBy increasing the number of glucose channel proteins in the cell surface membrane
CBy activating adenylate cyclase, which converts glycogen to glucose
DBy hydrolysing glycogen inside the cells
(c)
Name the process by which her liver makes glucose when the glycogen is almost used up, and name two types of molecule that it uses as the starting material.
[2 marks]
Total for question 2: 4 marks
3
In a healthy adult the kidneys produce 180 dm³ of glomerular filtrate per day, but only 1.5 dm³ of urine per day. The glucose concentration in the blood plasma is 5 mmol dm⁻³ and is the same in the glomerular filtrate. Almost all of the glucose in the filtrate is reabsorbed in the proximal convoluted tubule, so healthy urine contains none.
(a)
Calculate the percentage of the glomerular filtrate that is reabsorbed, and the amount of glucose, in mmol, that is filtered per day. Show your working.
[3 marks]
(b)
Explain how glucose is reabsorbed from the filtrate in the proximal convoluted tubule, and why water is reabsorbed there as well.
[4 marks]
Total for question 3: 7 marks
4
A 15-year-old boy drinks large volumes of water, urinates frequently and feels very tired. A urine test shows that his urine contains glucose, and his blood glucose concentration is 18 mmol dm⁻³. He is diagnosed with type I diabetes.
(a)
Explain why his urine contains glucose and why he produces a large volume of urine.
[6 marks]
(b)
Explain why negative feedback cannot control his blood glucose concentration after a meal, and how insulin injections and his diet can be used to control it.
[6 marks]
Total for question 4: 12 marks
5
Adrenaline is secreted by the adrenal glands into the blood when a person is frightened. It travels all round the body, but only some cells, such as liver cells and heart muscle cells, respond. The effects, such as a faster heart rate, last for several minutes after the fright has passed.
(a)
Why do only some cells respond to adrenaline?
[1 mark]
AOnly these cells have receptors with a tertiary structure complementary to adrenaline.
BAdrenaline is carried in the blood only to these cells.
CThe membranes of other cells are impermeable to adrenaline.
DOther cells contain enzymes that destroy adrenaline.
(b)
Which row correctly compares a hormonal response with a nervous response?
[1 mark]
AHormonal: rapid, short-lived, localised. Nervous: slow, long-lasting, widespread.
BHormonal: rapid, long-lasting, localised. Nervous: slow, short-lived, widespread.
CHormonal: slow, short-lived, widespread. Nervous: rapid, long-lasting, localised.
DHormonal: slow, long-lasting, widespread. Nervous: rapid, short-lived, localised.
(c)
Explain why the effects of adrenaline last for minutes rather than milliseconds.
[2 marks]
Total for question 5: 4 marks
6
A 52-year-old man with a body mass index of 34 is diagnosed with type II diabetes. His blood contains a high concentration of insulin, but his blood glucose concentration remains high after meals. His doctor advises him on his diet.
(a)
Which statement is the most likely explanation of his condition?
[1 mark]
AHis β cells have been destroyed by his immune system.
BHis target cells have lost responsiveness to insulin, so less glucose is taken up.
CHis liver cells cannot make glucagon.
DHis pancreas does not secrete insulin.
(b)
Which advice is most appropriate for him?
[1 mark]
AEat large meals less often, choosing foods that are digested quickly.
BEat more refined sugar to supply his cells with glucose.
CReduce total energy intake and replace simple sugars with foods that release glucose slowly.
DStop eating all protein, because it is converted into glucose.
(c)
Explain why insulin injections are essential for a patient with type I diabetes but are not usually the first treatment for this man.
[2 marks]
Total for question 6: 4 marks
7
A volunteer who had gone for 12 hours without drinking produced 0.8 cm³ of concentrated urine per minute. After drinking 1.0 dm³ of water in 10 minutes, her urine output rose to 12 cm³ per minute within an hour, and her urine became very dilute.
(a)
Describe how drinking the water leads to the production of a larger volume of dilute urine.
[3 marks]
(b)
Explain how the loop of Henle and ADH enabled her kidneys to produce concentrated urine before she drank.
[4 marks]
Total for question 7: 7 marks
8
A mountaineer spends eight hours climbing in cold, dry air. She breathes rapidly and loses water vapour in her exhaled air. She eats nothing and drinks no water during the climb. Her core temperature stays at 37 °C.
(a)
Explain how her blood glucose concentration is maintained during the climb.
[6 marks]
(b)
Explain how her kidneys respond to the loss of water so that the water potential of her blood returns towards normal.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).