Homeostasis - AQA GCSE Biology Exam Questions

Practise 33 exam-style questions on Homeostasis for AQA GCSE Biology. Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with an AI tutor on hand if you get stuck.

33 questions
2–6 marks each
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20 questions, marked as you go

Sample questions with model answers

Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.

Question 1

3 marks

Explain how vasodilation and vasoconstriction at the skin surface help regulate body temperature.

Model answer

Vasodilation widens skin blood vessels increasing blood flow to skin so more heat is lost to the environment. Vasoconstriction narrows vessels reducing blood flow at skin to conserve heat.

Explanation

Widening or narrowing skin blood vessels changes skin blood flow; more flow (vasodilation) increases heat loss, while less flow (vasoconstriction) conserves heat.

Mark scheme

1 mark
vasodilation increases blood flow to skin
1 mark
increased heat loss (to environment) via skin
1 mark
vasoconstriction decreases blood flow to skin and reduces heat loss

Question 2

4 marks

A student records the following for one volunteer: fasting blood glucose 3.0 mmol/L; after meal 8.5 mmol/L. Which samples indicate hypoglycaemia and hyperglycaemia? Give thresholds and the volunteer's status.

Model answer

Hypoglycaemia: blood glucose < ~4.0 mmol/L (fasting 3.0 mmol/L = hypoglycaemia). Hyperglycaemia: blood glucose > ~7.8–8.0 mmol/L after meal (postprandial 8.5 mmol/L = hyperglycaemia).

Explanation

Typical fasting hypoglycaemia is below about 4 mmol/L. Post-meal levels above about 7.8–8.0 mmol/L are considered high; thus the volunteer shows both low fasting and high post-meal glucose.

Mark scheme

1 mark
hypoglycaemia threshold ~ <4.0 mmol/L (fasting 3.0 mmol/L is low)
Accept 3.5–4.0 mmol/L thresholds
1 mark
fasting 3.0 mmol/L = hypoglycaemia
1 mark
hyperglycaemia threshold roughly >7.8–8.0 mmol/L after meal
Accept 7.8, 8.0 or >8.0 as post-meal threshold
1 mark
after-meal 8.5 mmol/L = hyperglycaemia

Question 3

5 marks

A person exercises intensely and becomes dehydrated. Explain three homeostatic responses the body makes to maintain water balance.

Model answer

Osmoreceptors detect increased blood osmolarity ? hypothalamus triggers thirst ? person drinks. Pituitary releases more ADH ? kidney tubules reabsorb more water ? less urine produced and more concentrated.

Explanation

Dehydration increases blood osmolarity; osmoreceptors and hypothalamus trigger thirst and ADH release. ADH increases kidney water reabsorption so urine is small in volume and concentrated, aiding water conservation.

Mark scheme

1 mark
osmoreceptors detect increased osmolarity / low water
1 mark
thirst triggered (drink more water)
Accept drinking behavior
1 mark
pituitary releases more ADH
1 mark
ADH makes kidneys reabsorb more water
1 mark
urine becomes more concentrated and volume decreases

Question 4

6 marks

Explain how the kidney filters blood and then selectively reabsorbs useful substances. Mention three specific substances and what happens to them.

Model answer

Blood is filtered in glomerulus; small molecules (water, glucose, ions, urea) pass into filtrate. Glucose is all reabsorbed by active transport in proximal tubule; most water is reabsorbed in tubules/collecting duct under ADH control; excess ions are reabsorbed or secreted to maintain balance; urea is not reabsorbed (or only partly) so is excreted.

Explanation

The kidney filters blood in the glomerulus producing filtrate. Useful substances like glucose and many ions are reabsorbed back into the blood (glucose by active transport) and water is reabsorbed under hormonal control, while urea is excreted.

Mark scheme

1 mark
filtration at glomerulus / kidney filters blood and forms filtrate
1 mark
small molecules (water, glucose, ions, urea) enter filtrate
1 mark
glucose is reabsorbed completely (by active transport) into blood
1 mark
water is reabsorbed (in tubules/collecting duct) controlled by ADH
1 mark
ions (sodium, chloride) are selectively reabsorbed or secreted to balance levels
1 mark
urea largely remains in filtrate / is excreted in urine (only partly reabsorbed)

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