Instant Access to A Level Biology Revision

Sign up now to get access to the entire library of A Level Biology resources for all exam boards

Join now

If you're ready to pass your AQA A-Level Biology exams, become a member now to get complete access to our entire library of revision materials.

Join over 22,000 learners who have passed their exams thanks to us!

Join now →

Or try a sample...

Not ready to purchase the revision kit yet? No problem. If you want to see what we offer before purchasing, we have a free membership with sample revision materials.

Signup as a free member below and you'll be brought back to this page to try the sample materials before you buy.

Download the samples →

3.6 Responding to changes in environment

  • 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

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