Internal and External Stimuli

Internal and External Stimuli

My AP Biology Thoughts

Unit 8 Episode #17

Welcome to My AP Biology Thoughts podcast, my name is Arthur and I am your host for episode 17 called Internal and External Stimuli. Today we will be discussing the different kinds of stresses induced upon organisms that evoke different responses.

Segment 1: Introduction to Internal and External Stimuli

Important Definitions:

  • Internal stimulus:
  • A stress that comes from within the organism to provoke a response.
  • External stimulus:
  • A stress from the outside environment induced upon an organism.  
  • Homeostasis:
  • The state of stability where all essential biological functions can optimally be carried out.  

Segment 2: Example of Internal and External Stimuli

Internal Stimuli:

  • Hunger:
  • Obtain glucose to carry out cellular respiration.
  • Thirst
  • Obtain water to allow for breathing and the transportation of oxygen throughout the body.  

External Stimuli: 

  • Temperature:
  • Endotherms need to maintain their core body temperature so if the outside environment is too hot or too cold, the organism will respond in a way to maintain the core temperature.
  • Ectotherms need certain temperatures in order to maintain their metabolism, so they will either move to warmer or colder locations.  
  • Sunlight:
  • Plants when hit with sunlight will experience phototropism in order to allow them to get the maximum amount possible. 

Segment 3: Digging Deeper Internal and External Stimuli

The existence of food webs and chains is dependent on organisms consuming one another. In order for this to happen, the consumers need the stimulus of hunger.  

Thank you for listening to this episode of My AP Biology Thoughts. For more student-ran podcasts and digital content, make sure that you visit See you next time!

Music Credits:

  • “Ice Flow” Kevin MacLeod (
  • Licensed under Creative Commons: By Attribution 4.0 License

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