AQA GCSE Biology Foundation (8461), Foundation tier · Homeostasis and response
Practise Homeostasis. 7 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Homeostasis is how your body keeps its internal conditions steady so that cells and enzymes can work properly. It comes up as short definition questions and as 'name the part of the control system' questions, and it is the basis for every other subtopic in Homeostasis and response.
Key facts
Homeostasis = regulation of internal conditions to maintain optimum conditions for function
Controlled in humans: blood glucose concentration, body temperature, water levels
Why it matters: optimum conditions for enzyme action and all cell functions
Receptor = cell that detects a stimulus
Coordination centre (brain, spinal cord, pancreas) = receives and processes information
Effector = muscle or gland that brings about a response
Stimulus → receptor → coordination centre → effector → response
Control can be nervous, hormonal (chemical) or both
Notes
What homeostasis is
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.
It matters because enzymes and all cell functions work best in particular conditions. If conditions move too far from the optimum, reactions slow down and cells can be damaged (for example, a high temperature denatures enzymes).
In the human body, homeostasis controls blood glucose concentration, body temperature and water levels.
The control is automatic: you do not have to think about it. It can involve nervous responses, chemical (hormonal) responses, or both.
The parts of every control system
diagram
Receptors are cells that detect stimuli (changes in the internal or external environment).
Coordination centres, such as the brain, the spinal cord and the pancreas, receive and process information from receptors.
Effectors are muscles or glands. They bring about responses that restore optimum levels.
Muscles respond by contracting; glands respond by secreting (releasing) substances such as hormones.
The sequence is always: stimulus → receptor → coordination centre → effector → response.
Every control system: stimulus → receptor → coordination centre → effector → response (example in blue).
An example
On a hot day, temperature receptors in your skin detect the rise in temperature (stimulus and receptor).
Your brain processes the information (coordination centre).
Your sweat glands release more sweat (effector), which cools you down (response).
How to answer each type of question
Define homeostasis
1 to 2 marksGrade 4
Use the key words: regulation (or maintaining), internal conditions, optimum.
For a second mark, add 'in response to internal and external changes' or say what the optimum conditions are for (enzymes and cell functions).
Example. What is meant by the term homeostasis?
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Regulating / keeping the internal conditions of the body steady (1) at the optimum for enzymes and cells to function, despite internal and external changes (1).
Identify the receptor, coordination centre or effector
1 mark eachGrade 5
Receptors detect: find the cells that sense the change.
Coordination centres process: the brain, spinal cord or pancreas.
Effectors respond: a muscle that contracts or a gland that secretes.
Example. A person walks from a warm room out into the snow and starts to shiver. (a) Name the type of cell in the skin that detects the fall in temperature. (b) Name the coordination centre that processes this information. (c) Shivering happens when muscles contract. What part of the control system is a muscle?
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(a) Receptor (cells) / temperature receptors (1) (b) The brain (1) (c) An effector (1)
Explain why homeostasis is important
2 marksGrade 5
Link the condition to enzymes or cell functions.
Say what goes wrong if the condition is not controlled, using the context in the question.
Example. Explain why it is important that human body temperature is kept close to 37 °C.
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37 °C is the optimum temperature for the enzymes in the body (1). If the temperature rises too far, enzymes are denatured / if it falls, reactions become too slow, so cells cannot function properly (1).
Don’t lose marks
Leaving out 'internal'. Homeostasis controls conditions inside the body, not the surroundings.
Saying receptors 'detect the stimulus and respond'. Receptors only detect; effectors respond.
Calling the brain an effector or a muscle a receptor. Learn which part does which job.
Writing that enzymes are 'killed' when it is too hot. Enzymes are not alive: they are denatured.
More tips
Memory tricks
'Homeo' means 'same' and 'stasis' means 'staying still': homeostasis keeps things the same.
Learn the chain as SRCER: Stimulus, Receptor, Coordination centre, Effector, Response.
Effectors are only ever muscles or glands. If it is not one of those, it is not an effector.
The three things your body keeps steady: sugar (glucose), heat (temperature) and water.
Exam technique
Learn the definition closely: examiners look for 'internal conditions' and 'optimum'.
In a new context, work through stimulus, receptor, coordination centre, effector and response in order and label each one.
When asked why homeostasis matters, always mention enzymes or cell functions.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
Define homeostasisRegulating the internal conditions of a cell or organism to keep them at the optimum, in response to internal and external changes.
Grade 3
Name conditions controlled by homeostasisIn humans: blood glucose concentration, body temperature and water levels.
Grade 4
Name the three parts of a control systemReceptors, coordination centres and effectors.
Grade 5
Explain why homeostasis is importantIt keeps conditions at the optimum for enzyme action and all cell functions.
Grade 5
Describe the job of each partReceptors detect stimuli, coordination centres process the information, and effectors (muscles or glands) bring about a response.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Homeostasis maintains the optimum conditions for the molecules that control reactions in cells. Name these molecules.
Enzymes
All the automatic control systems in the body include receptors, coordination centres and effectors. Give the two types of effector.
Muscles and glands
These steps happen in one automatic control system in the body.
Body temperature increases.
Temperature receptors in the skin detect the change.
Nerve impulses travel to the brain.
The brain sends nerve impulses to the sweat glands.
The sweat glands produce more sweat.
Body temperature decreases.
Name the coordination centre.
The brain
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy6 marks
Homeostasis is important for the human body to work properly.
(a) What is meant by homeostasis?[2]
(b) Which three of these are controlled by homeostasis in the human body? Tick (✓) three boxes.[3]
Blood glucose concentration
Body temperature
Eye colour
Height
Water levels
(c) Homeostasis maintains the optimum conditions for the molecules that control reactions in cells. Name these molecules.[1]
Show the answer and mark scheme
(a)
the regulation of the internal conditions (of a cell or organism)
to maintain optimum conditions for function (in response to internal and external changes)
(b)Answer: Blood glucose concentration; Body temperature; Water levels
(c)Answer: Enzymes
enzymes
Question 2Medium7 marks
These steps happen in one automatic control system in the body.
Body temperature increases.
Temperature receptors in the skin detect the change.
Nerve impulses travel to the brain.
The brain sends nerve impulses to the sweat glands.
The sweat glands produce more sweat.
Body temperature decreases.
(a) Name the receptors in this control system.[1]
(b) Name the coordination centre.[1]
(c) Name the effectors.[1]
(d) Is this a nervous response or a chemical response? Give a reason for your answer.[2]
(e) Explain why step 6 is important.[2]
Show the answer and mark scheme
(a)
temperature receptors (in the skin)
(b)Answer: The brain
brain
(c)Answer: Sweat glands
sweat glands
(d)
nervous
it uses nerve impulses / neurones (not hormones)
(e)
it returns body temperature to the optimum
(so) enzymes work at their optimum rate / are not denatured
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