Edexcel A Level (IAL) Biology -8.9 Habituation- Study Notes- New Syllabus
Edexcel A Level (IAL) Biology -8.9 Habituation- Study Notes- New syllabus
Edexcel A Level (IAL) Biology -8.9 Habituation- Study Notes -Edexcel A level Biology – per latest Syllabus.
Key Concepts:
- 8.9 understand what is meant by the term habituation
Habituation
🌱 Introduction
Habituation is a basic form of non-associative learning. It occurs when an organism reduces or stops its response to a repeated, harmless stimulus over time.
- Helps organisms ignore irrelevant stimuli.
- Prevents wasting energy on unimportant events.
- Observed in both simple (invertebrates) and complex (vertebrates) animals.
🔍 Key Features of Habituation
- Stimulus-specific: Response decreases only to the repeated stimulus; other new stimuli still produce a reaction.
- Reversible: Response can return if stimulus stops for a while (spontaneous recovery).
- Not fatigue: Habituation is a learning process, not due to tired muscles or neurons.
- Energy-saving mechanism: Allows focus on important stimuli indicating danger or opportunity.
🔹 Examples
| Organism | Example of Habituation |
|---|---|
| Snail | Stops retracting into shell after repeated harmless touches |
| Humans | Ignore constant background noises (e.g., ticking clock) |
| Fish | Stops fleeing from a harmless repeated stimulus in a tank |
| Sea slug (Aplysia) | Reduced gill withdrawal after repeated harmless touch |
🔹 Mechanism
Repeated harmless stimulus → less neurotransmitter released at the synapse → smaller response in post-synaptic neurone → reduced action potential → weaker or no response.
Habituation = learning to ignore repeated harmless stimuli.
Key points: stimulus-specific, reversible, not due to fatigue.
Purpose: conserve energy and focus on important events.
Example: snail stops retracting after repeated harmless touches; humans ignore constant background noise.
Investigating Habituation to a Stimulus
🌱 Introduction
Habituation is a simple form of learning where an organism reduces its response to a repeated harmless stimulus. This practical demonstrates how organisms learn to ignore repeated stimuli.
🔍 Aim
To investigate habituation in response to a repeated stimulus.
⚙️ Materials Needed
- Small animal (e.g., snail, fish, or earthworm)
- Tweezers or soft brush (for tactile stimulus)
- Timer or stopwatch
- Observation sheet
🔹 Method (Step-by-Step)
- Place the organism in a quiet environment and allow it to acclimatise.
- Apply a harmless stimulus (e.g., touch the snail’s shell or fish’s tail) at regular intervals.
- Observe and record the organism’s response (e.g., retraction, movement, or escape behaviour).
- Repeat the stimulus several times at fixed intervals (e.g., every 30 seconds).
- Note if the response becomes weaker or stops over repeated trials.
- Record time taken for the response to disappear or reduce significantly.
🔹 Observations
| Trial Number | Stimulus Applied | Response Observed | Notes |
|---|---|---|---|
| 1 | Touch | Full retraction | Initial response |
| 2 | Touch | Slight retraction | Response reduced |
| 3 | Touch | Minimal retraction | Habituation begins |
| … | … | … | … |
🔹 Conclusion
A reduction in response with repeated harmless stimuli indicates habituation. This confirms the organism can learn to ignore irrelevant stimuli, conserving energy.
Stimulus-specific: other stimuli still cause response
Reversible: response can return after some time without stimulus (spontaneous recovery)
Not due to fatigue: organism can still respond to a new stimulus