Cambridge O Level Biology · Syllabus 5090 · Coordination and Control
Homeostasis
What is Homeostasis?
The maintenance of a constant internal environment. Conditions such as body temperature and blood glucose concentration are held within narrow limits around a set point rather than at a fixed unchanging value, because enzyme-controlled reactions in cells work properly only across a narrow range of conditions.
This definition is part of the Coordination and Control chapter in Cambridge O Level Biology.
Homeostasis in context
Coordination is how an organism detects a change and produces a useful response to it. Every example in this chapter — pulling a hand off a hot pan, narrowing a pupil, sweating on a hot afternoon, storing glucose after a meal — runs through the same five stages: stimulus → receptor → coordinator → effector → response. Mammals run that chain two ways. Nervous control sends electrical impulses along neurones: fast, precisely targeted, usually short-lived. Hormonal control sends chemicals dissolved in blood plasma: generally slower, more widespread, often longer-lasting. Homeostasis is the job both systems do together — holding internal conditions within narrow limits by negative feedback, in which every correction opposes the change that triggered it.
Homeostasis is the maintenance of a constant internal environment. "Constant" means kept within narrow limits around a set point, not held at a single unchanging value: the variable fluctuates continually, and each deviation triggers a response that returns it towards the set point.
Questions students ask about Homeostasis
What is homeostasis?
Homeostasis is the maintenance of a constant internal environment. "Constant" means held within narrow limits around a set point rather than perfectly unchanging: the variable fluctuates, and each deviation triggers a response that returns it towards the set point.