Practise 38 exam-style questions on Feedback systems (HT only) 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.
38 questions
2–4 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
2 marks
Explain why someone with hyperthyroidism often feels hot and loses weight despite increased appetite.
Model answer
Excess thyroxine raises basal metabolic rate, producing more heat (feels hot) and burning more calories; increased energy use leads to weight loss even though appetite may be increased.
Explanation
Thyroxine speeds up cellular processes so more energy is consumed and heat produced; sustained high metabolism can cause weight loss despite increased food intake.
Increased metabolism burns more energy causing weight loss even with increased appetite
Question 2
3 marks
A patient has low thyroxine. Explain why a doctor might prescribe levothyroxine (synthetic thyroxine) and how the doctor would avoid giving too high a dose.
Model answer
Levothyroxine replaces low thyroxine, restoring metabolic rate and aiding growth/energy. Doctor starts with low dose and monitors blood thyroxine and TSH — adjust dose so levels are normal (negative feedback), avoiding symptoms of hyperthyroidism.
Explanation
Replacement therapy corrects the hormone deficit. Because thyroxine participates in negative feedback via TSH, doctors monitor blood hormone levels and clinical signs to adjust dosing and prevent iatrogenic hyperthyroidism.
Mark scheme
1 mark
Levothyroxine replaces the missing thyroxine / restores basal metabolic rate
1 mark
Doctor adjusts dose based on blood tests (measure thyroxine / TSH) / starts low and titrates
Any correct monitoring strategy allowed.
1 mark
Adjusting prevents excess thyroxine which would suppress TSH / cause hyperthyroid symptoms (so use negative feedback monitoring)
Question 3
3 marks
Describe how you would explain to a patient the difference between a blood test showing 'low TSH, high thyroxine' and 'high TSH, low thyroxine'.
Model answer
'Low TSH, high thyroxine' = primary hyperthyroidism (thyroid overactive); 'High TSH, low thyroxine' = primary hypothyroidism (thyroid underactive). Explain that TSH is the pituitary signal: low TSH means pituitary is suppressing because thyroxine is high; high TSH means pituitary is trying to stimulate an underactive thyroid.
Explanation
TSH and thyroxine together show whether the problem is in the thyroid itself (primary) because TSH responds inversely to circulating thyroxine via feedback.
Mark scheme
1 mark
Low TSH & high thyroxine indicates hyperthyroidism (overactive thyroid)
1 mark
High TSH & low thyroxine indicates hypothyroidism (underactive thyroid)
1 mark
Explain TSH is pituitary signal: low when thyroxine high (suppressed), high when thyroxine low (stimulate thyroid)
Question 4
4 marks
Explain how adrenaline and thyroxine together prepare the body differently for immediate action and for longer-term metabolic adaptation.
Model answer
Adrenaline triggers immediate responses (increased heart rate, breathing, blood glucose) via sympathetic nervous system for fight/flight. Thyroxine increases basal metabolic rate over hours to days, altering enzyme levels and metabolism to raise overall energy turnover and support sustained increased activity and growth. Adrenaline is quick and short-lived; thyroxine is slower but longer-lasting.
Explanation
Adrenaline readies the body instantly for immediate action while thyroxine adjusts the body’s metabolic machinery for sustained increased demand or developmental needs over longer timeframes.
Mark scheme
1 mark
Adrenaline produces immediate cardiovascular and respiratory changes and rapid glucose mobilization
1 mark
Adrenaline acts via sympathetic nervous system / adrenal medulla and is short-lived
1 mark
Thyroxine increases basal metabolic rate by upregulating metabolism/enzymes and affects growth/long-term energy use
1 mark
Thyroxine acts more slowly and lasts longer — supports longer-term metabolic adaptation
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