Cambridge O Level Biology · Syllabus 5090 · Coordination and Control
Effector
What is Effector?
A muscle or a gland that carries out a response after receiving information from a coordinator. A muscle responds by contracting; a gland responds by secreting a substance. No other type of structure counts as an effector in the Cambridge O Level Biology syllabus.
This definition is part of the Coordination and Control chapter in Cambridge O Level Biology.
Effector 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.
Questions students ask about Effector
What is the order of a reflex arc?
Stimulus, receptor, sensory neurone, relay neurone in the central nervous system, motor neurone, effector, response. The effector is a muscle or a gland, and the impulse never travels backwards along this pathway.
What is the difference between nervous and hormonal control?
Nervous control uses electrical impulses travelling along neurones, is rapid, is usually short-lived, and acts on the effectors that those neurones connect to. Hormonal control uses chemical hormones carried in the blood, is generally slower to begin, is often longer-lasting, and acts on any cells carrying complementary receptors.