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Stimulus and Response. Year 9 Science . Any change in an organism’s environment that causes the organism to react. (“cause”) Stimuli (singular) can be: External Internal. Stimulus. Response. How an organism reacts to a stimulus (“effect”) Responses can be: Voluntary Involuntary.

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Stimulus and response

Stimulus and Response

Year 9 Science

Stimulus and response



  • How an organism reacts to a stimulus

  • (“effect”)

  • Responses can be:

  • Voluntary

  • Involuntary

Stimulus and response

Response organism to react.


Touch a hot surface...

Hear a loud bang...

Raise your body temp...

Feel cold...

...pull back your hand

...flinch/yell out

...start to sweat

...put on something warm

Stimulus response model
Stimulus-Response Model organism to react.

Stimulus response example
Stimulus-Response Example organism to react.

Learned responses
Learned Responses organism to react.

Some responses are instinctual (we are born with them)

Other responses can be learned.

  • A famous demonstration of learned response is known as “Pavlov’s Dog”

  • A dog is given an external stimulus (the bell) during meals

  • The dog learns to associate the bell with food and gives the same response

Involuntary responses
Involuntary responses organism to react.

Some responses happen without any thought whatsoever.

These are known as involuntary responses.

Can you think of others?

Reflex arc fast
Reflex arc – fast! organism to react.

A reflex arc is a fast response that occurs automatically, without any thought. These are the fastest responses in your body

For example, when you touch something hot, you pull your hand away before you “think” about it being hot.

The stimulus (heat) is relayed along the sensory neuron through the spinal cord to the effector which makes you move your hand.

Homeostasis organism to react.

Homeostasis: the maintenance of a stable internal environment in spite of external or internal environmental changes.

The body is constantly working to maintain homeostasis inside us by coordination of our body systems.

Blood Glucose Maintenance

Feedback loops
Feedback loops organism to react.

  • The body maintains homeostasis by responding in one of two ways:

    • Positive feedback – a response that enhances the effect of a stimulus

    • (rare – production of oxytocin during labour to increase contractions)

    • Negative feedback – a response that counteracts the effect of a stimulus

    • (these are the most common in the body)