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Work through the notes, try the practice questions, then take the quiz. The report tells you exactly what to revise next. (2026)
Question
Define homeostasis and give two conditions controlled in the human body. (3 marks)
Solution
Definition: regulation of internal conditions to keep them within narrow limits / maintain optimum function.
Examples (any two): body temperature, blood glucose, water/ion balance.
Answer
Homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function, in response to internal and external changes (1). Examples include body temperature (1) and blood glucose concentration (1).
Question
Describe how negative feedback returns body temperature to normal after it has risen above 37 °C. (5 marks)
Solution
Thermoreceptors in the skin and hypothalamus detect the rise in temperature.
The hypothalamus (coordination centre) processes the information.
It sends nervous signals to effectors: sweat glands release sweat which evaporates and cools the skin.
Blood vessels in the skin dilate (vasodilation), so more heat is lost from the surface.
These responses reduce body temperature back towards 37 °C — the opposite of the change.
Answer
Thermoreceptors detect the rise in temperature (1). The hypothalamus (coordination centre) processes the signal (1). It signals sweat glands to release sweat that evaporates and cools the skin (1). Blood vessels to the skin dilate, increasing heat loss (vasodilation) (1). These responses are opposite to the change (negative feedback) and return temperature to 37 °C (1).
Examiner note
Mention the words 'negative feedback' and 'opposite' to secure the final mark.
Question
Describe how the level of thyroxine in the blood is controlled by negative feedback. (4 marks)
Solution
If thyroxine falls below the set point, the pituitary releases TSH (thyroid-stimulating hormone).
TSH travels in the blood to the thyroid gland and stimulates it to release thyroxine.
Thyroxine level rises back towards the set point.
High thyroxine then inhibits release of TSH from the pituitary, so thyroxine stops rising. This is negative feedback.
Answer
When thyroxine falls, the pituitary releases more TSH (1). TSH stimulates the thyroid gland to release thyroxine (1), raising the blood thyroxine level back to the set point (1). High thyroxine then inhibits TSH release from the pituitary — this is negative feedback (1).
Examiner note
Use the words 'pituitary', 'TSH', 'thyroid', 'thyroxine' and 'negative feedback' explicitly.
Question
Explain how adrenaline prepares the body for vigorous physical activity. (3 marks)
Solution
Adrenaline increases heart rate so more blood is pumped per minute.
It increases breathing rate so more oxygen is taken in.
It causes the liver to release glucose / blood vessels to muscles to dilate — delivering more oxygen and glucose for respiration in muscles.
Answer
Adrenaline increases heart rate, so more blood is pumped to muscles (1). It increases breathing rate, so more oxygen is taken into the blood (1). It causes the liver to release glucose into the blood and dilates blood vessels to muscles, so muscle cells get more glucose and oxygen for respiration (1).
The regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes.
A specialised cell that detects a stimulus (a change in the environment).
A muscle or gland that carries out a response to a stimulus.
Part of the body (brain, spinal cord or pancreas) that processes information from receptors and decides on a response.
A control mechanism in which a deviation from the set point triggers an opposite response, restoring the original level.
A hormone released by the thyroid gland that controls the basal metabolic rate and is needed for growth and development.
A hormone released by the pituitary gland that stimulates the thyroid gland to release thyroxine. Part of the thyroxine negative-feedback loop.
A control mechanism in which a change away from the set point triggers a response that opposes the change, restoring the set point. Used to regulate thyroxine, body temperature, blood glucose, water balance.
A hormone released by the adrenal glands in response to fear, stress or excitement. It prepares the body for fight-or-flight by increasing heart rate, breathing rate and blood glucose.
The body's rapid response to perceived threat, triggered by adrenaline. Prepares for vigorous action.
Mistake
Listing the brain or a nerve as an effector.
Why it happens
Confusing parts of the pathway.
How to avoid it
Effectors are ALWAYS muscles or glands — they DO the response, not the processing.
Mistake
Thinking 'negative feedback' means a bad thing happens.
Why it happens
Misreading 'negative' as 'harmful'.
How to avoid it
Negative = OPPOSITE. The response is the opposite of the change, not harmful.
Mistake
Saying 'the brain detects temperature change'.
Why it happens
Skipping the receptor step.
How to avoid it
Thermoreceptors (in skin and hypothalamus) detect change; the brain processes the signal afterwards.
Mistake
Saying the thyroid 'detects' low thyroxine.
Why it happens
Confusing the receptor with the effector.
How to avoid it
The pituitary (and hypothalamus) detects and decides; the thyroid responds to TSH.
Mistake
Saying adrenaline is controlled by negative feedback.
Why it happens
Assuming all hormones use the same control mechanism.
How to avoid it
Only thyroxine (in this topic) uses negative feedback. Adrenaline is released directly in response to a stimulus.
Mistake
Mixing up TSH and thyroxine.
Why it happens
Similar-sounding names.
How to avoid it
TSH = made by pituitary; STIMULATES thyroid. Thyroxine = made BY thyroid; controls metabolism.