3.6 Responding to changes in environment

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  • A stimulus is a change in the internal or external environment. A receptor detects a stimulus. A coordinator formulates a suitable response to a stimulus. An effector produces a response.
  • Receptors are specific to one type of stimulus.
  • Nerve cells pass electrical impulses along their length. A nerve impulse is specific to a target cell only because it releases a chemical messenger directly onto it, producing a response that is usually rapid, short-lived and localised.
  • In contrast, mammalian hormones stimulate their target cells via the blood system. They are specific to the tertiary structure of receptors on their target cells and produce responses that are usually slow, long-lasting and widespread.
  • Plants control their response using hormone-like growth substances.

Source: AQA Spec

Included in this download

ModuleTitle
3.6.1Stimuli, both internal and external, are detected and lead to a response
3.6.2Nervous coordination
3.6.3Skeletal muscles are stimulated to contract by nerves and act as effectors
3.6.4Homeostasis is the maintenance of a stable internal environment