Principles of Homeostasis
Recap Principles of Homeostasis for GCSE Biology with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Homeostasis keeps internal conditions constant using receptors, coordination centres and effectors working together.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
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 change.
It matters because enzymes work best within narrow ranges of temperature and pH, and cells need the right water and glucose concentrations. In humans, homeostasis controls blood glucose concentration, body temperature and water levels.
All control systems have the same three components: receptors that detect a stimulus, coordination centres such as the brain, spinal cord or pancreas that process the information, and effectors — muscles or glands — that bring about a response restoring the optimum level.
Revision notes
What homeostasis maintains
In humans, homeostasis controls blood glucose concentration, body temperature and water levels.
It maintains optimum conditions for enzyme action and for all cell functions, which is why the internal environment must be kept within narrow limits.
The three components
Receptors detect a change, or stimulus. Coordination centres — the brain, spinal cord or pancreas — receive and process the information.
Effectors, which are muscles or glands, bring about the response. Every control system in the specification follows this same structure.
Automatic control systems
Control systems may involve nervous responses, which are fast and short-lived, or chemical responses using hormones, which are slower and longer-lasting.
Identifying which type a question describes is often the first step to answering it.
Key points
- Homeostasis maintains optimum internal conditions.
- It controls blood glucose, body temperature and water levels.
- Receptors detect the stimulus.
- Coordination centres process the information.
- Effectors are muscles or glands that bring about a response.
- Control may be nervous or hormonal.
Worked examples
Example 1
Define homeostasis. [2 marks]
Model answer
Homeostasis is the regulation of the internal conditions of a cell or organism (1 mark) to maintain optimum conditions for function, in response to internal and external changes (1 mark).
Example 2
Name the three components of a control system and give the role of each. [3 marks]
Model answer
Receptors, which detect the stimulus or change (1 mark). Coordination centres such as the brain, spinal cord or pancreas, which process the information (1 mark). Effectors, which are muscles or glands that bring about the response (1 mark).
Example 3
Explain why homeostasis is important for enzyme-controlled reactions. [2 marks]
Model answer
Enzymes work best within narrow ranges of temperature and pH (1 mark), so homeostasis keeps these conditions at the optimum and prevents the enzymes being denatured (1 mark).
Common mistakes
Saying homeostasis keeps everything constant.
It maintains conditions within narrow limits around an optimum, not perfectly constant.
Confusing receptors with effectors.
Receptors detect; effectors respond. Muscles and glands are effectors.
Naming only the brain as a coordination centre.
The spinal cord and pancreas are also coordination centres.
Forgetting to mention optimum conditions.
The purpose of homeostasis is to maintain optimum conditions for function.
Exam tips
- Learn the three components as a sequence you can apply to any example.
- Use the word optimum in your definition.
- Name muscles or glands when asked what an effector is.
- Identify whether a response is nervous or hormonal.
Key terms
- Homeostasis
- Regulation of internal conditions to maintain optimum function.
- Receptor
- A cell that detects a stimulus.
- Coordination centre
- A structure that processes information from receptors.
- Effector
- A muscle or gland that brings about a response.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.