Homeostasis — AQA GCSE Combined Science: Trilogy
Homeostasis keeps conditions in the body at the optimum for enzymes and cells, using receptors, coordination centres and effectors.
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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 keeps conditions close to the optimum for enzyme action and all cell functions. In humans it controls blood glucose concentration, body temperature and water levels, using automatic nervous or chemical responses.
A control system keeps a condition in the body at its optimum level using three types of component. Receptors are cells that detect stimuli. Coordination centres, such as the brain, the spinal cord and the pancreas, receive and process the information. Effectors are muscles or glands that bring about responses which restore optimum levels.
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Quick check questions
Define homeostasis.
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The regulation of the internal conditions of a cell or organism to maintain optimum conditions for function, in response to internal and external changes.
Name three things controlled by homeostasis in the human body.
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Blood glucose concentration, body temperature and water levels.
What do receptors do?
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They detect stimuli (changes in the environment).
Name the two types of effector.
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Muscles and glands.
Frequently asked questions
Why is homeostasis important?
Homeostasis is important because cells can only survive within narrow limits, and enzymes work best at optimum conditions. If temperature, pH, glucose or water levels drift too far from the optimum, enzymes work more slowly or stop working, and cells cannot carry out their reactions. Automatic control systems keep conditions close to the optimum.
What are the three main parts of a control system?
A control system has receptors, coordination centres and effectors. Receptors are cells that detect stimuli. Coordination centres, such as the brain, spinal cord and pancreas, receive and process the information. Effectors are muscles or glands that bring about responses to restore optimum levels. The receptors then detect the new level again.
Does homeostasis keep conditions exactly the same?
No. Homeostasis does not keep conditions exactly the same all the time; it keeps them close to the optimum. Control systems constantly monitor and adjust the composition of the blood and tissues, so blood glucose concentration, body temperature and water levels stay near the levels at which enzymes and cells work best.
Is homeostasis controlled by nerves or hormones?
Homeostasis can be controlled by either. The control systems are automatic and may involve nervous responses, carried as electrical impulses along neurones, or chemical responses, using hormones carried in the blood. For example, the pancreas controls blood glucose concentration by releasing the hormone insulin when the concentration is too high.
Written and checked against the AQA GCSE Combined Science (8464) specification · Updated October 2026