Here's a breakdown:

* Stimulus: A change in the environment that triggers a reaction in an organism. This could be anything from light, sound, temperature, touch, or even chemicals.

* Response: The organism's reaction to the stimulus. This can be a behavioral change (like moving away from a hot surface) or a physiological change (like sweating to cool down).

Example:

* Stimulus: A loud noise.

* Response: A dog might jump or bark.

Let me know if you'd like more examples or explanations!