By the end of this lesson
- Identify stimulus, receptor and effector.
- Order a response pathway.
- Distinguish detection from action.
BIG QUESTION
What minimum components turn information into action?
A receptor detects change and a communication pathway activates an effector that produces the response.
Receptors transduce stimuli
A receptorA cell or group of cells that detects a specific stimulus and converts it into a signal, such as electrical impulses. detects a specific stimulus and converts it into a biological signal. Receptors may be specialised cells, nerve endings or molecular sensors.
The receptor does not necessarily carry out the final response.
Communication coordinates the pathway
Signals travel through nervous, hormonal or local chemical pathways. A coordination centre may process inputs before directing an effector.
The specification’s minimum sequence is stimulus → receptor → effector → response.
Effectors create the change
Animal effectors include muscles, which contract, and glands, which secrete. Plant effectors include growth regions whose elongation changes direction.
The response should be matched to the original stimulus and biological context.
Parts of a response pathway
Each component has a distinct job.
| Component | Question it answers | Example |
|---|---|---|
| Stimulus | What changed? | High temperature. |
| Receptor | What detected it? | Thermoreceptor. |
| Coordination/communication | How is information processed/transmitted? | CNS or hormone pathway. |
| Effector | What acts? | Sweat gland. |
| Response | What changes? | More evaporative cooling. |
Language that earns precision
- transduction
- Conversion of stimulus energy or chemistry into a biological signal.
- effector
- Muscle, gland or other tissue that produces a response.
- coordinated response
- Linked detection, communication and action caused by a stimulus.
Common misconceptions
Claim: A receptor carries out the response.
Correction: It detects; an effector acts.
Claim: An effector is always a muscle.
Correction: Glands and plant growth tissues can also be effectors.
Claim: Every pathway must involve conscious brain processing.
Correction: Reflex, hormonal and plant responses can occur without conscious awareness.
Match the answer to the command word
Stimulus → receptor → coordinator/communication → effector → response.
Name the particular receptor and effector where the context allows.
Recall, apply, then justify
Describe a coordinated response to high body temperature.
Hint
Use the full pathway.
Suggested marking points
- High body temperature is the stimulus.
- Thermoreceptors detect the rise.
- A coordination centre processes the signal.
- Sweat glands/skin blood vessels act as effectors.
- Sweating/vasodilation increases heat loss.
Distinguish a receptor from an effector.
Hint
Detect versus act.
Suggested marking points
- A receptor detects a stimulus and generates a signal.
- An effector carries out the response.
Explain how failure at three different points in one response pathway could produce the same absent response.
Planning hint
Detection, transmission and action can each fail.
What a strong design includes
- A damaged receptor may not detect the stimulus.
- A communication pathway may fail to transmit the signal.
- A coordination centre may fail to process/direct output.
- An effector may fail to respond despite receiving a signal.
- Each failure prevents the final action.
- Testing intermediate signals can distinguish the location of failure.