A receptor detects a stimulus, an effector carries out the response, and the response is what the effector does. Name each part separately to avoid losing marks.
This lesson closes the SPM Biology coordination and response chapter. It builds on tracing a reflex arc.
How do the terms fit together?
The chain runs: stimulus, receptor, coordination (nerves or hormones), effector, response.
- The stimulus is the change detected.
- The receptor is what detects it.
- The effector is the muscle or gland that acts.
- The response is the action itself.
Worked example: four scenarios
| Scenario | Stimulus | Receptor | Effector | Response |
|---|---|---|---|---|
| Bright light shines in the eye | Bright light | Retina of the eye | Iris muscles | Pupil gets smaller |
| A loud noise startles you | Sound | Ear | Muscles in the body | You jump |
| Smelling nasi lemak | Chemicals in the air | Nose | Salivary glands | Saliva is released |
| Touching a hot pan | Heat | Skin | Arm muscle | The hand is pulled away |
Notice that in the saliva example the effector is a gland, not a muscle.
The mistake that costs marks
The common slip is to write the response as the effector. Saying “the effector is the pupil getting smaller” gives the action, not the organ.
| Wrong | Right | |
|---|---|---|
| Effector | Pupil gets smaller | Iris muscles |
| Response | Iris muscles | Pupil gets smaller |
| Receptor | The brain | The retina of the eye |
Test yourself with “what detects?” for the receptor, “what acts?” for the effector, and “what happens?” for the response.
Check yourself
The smell of frying chicken makes your mouth water. Name the stimulus, receptor, effector and response.
Answer
Stimulus: chemicals from the food in the air.
Receptor: the nose. Effector: the salivary glands.
Response: saliva is released.
What to study next
Test the whole chapter in the coordination and response practice set. Practise with the biological data interpretation trainer, and log slips in the mistake log and paper-error review.
If you would like a teacher to test your labelling on new scenarios, see online one-to-one Biology tuition.