1. Mechanisms of Homeostasis

2. Control Systems in Organisms
External and internal factors can challenge the stability of an organism
Must maintain stability despite changes in its environment
Homeostasis: the regulation and maintenance of the internal environment
Stimulus: anything that causes an imbalance in the internal conditions of a cell, organ, organ system, or organism

3. How Control Systems Work

4. How Control Systems Work
Homeostasis depends on communication between the receptors, the control center, and the effectors
This communication/interaction is called a feedback loop
EX: Nervous System and Endocrine System

5. We’re going to take a look at a feedback loop
Find A Partner!
We’re going to take a look at a feedback loop

6. Balance
Have you ever lost your balance? Did you “recover” from it? If so… you’ve experienced a feedback loop between your center of balance and your skeletal muscles. In this activity, you will balance a book on your head while walking.

7. Predict
How would you need to adjust your balance to keep a book balanced on your head?

8. Procedure Balance the textbook on your head.
Walk 7 steps forward and backward with your eyes open.
Walk 7 steps forward and backward but this time with your eyes closed (make sure your path is clear before closing your eyes)!

9. Analyze
What type of receptors provided information about the position of the book while you walked? (HINT: Think of the five senses!)
How did you respond whenever the book changed position? Did you find it more or less difficult to maintain balance with your eyes closed? Explain!!!!

10. Clean Up
Please place the books back in the cabinet and return to your seats 

11. Good Morning! Good Morning!
Welcome back to Biology! Please do the following to prepare for class today.
Grab the first two pages off the front table and staple them together
Grab a study guide off the front table and put it in your binder
Get your notes sheet out from last class to finish our homeostasis notes.

12. Negative Feedback Loop
Consider what happened in the book balancing activity….
You responded to a change in the book’s position by changing your speed, or posture until the book returned to balance
What you experienced is a result of a negative feedback loop

13. Negative Feedback Loop
A stimulus causes an imbalance in one direction
Imbalance detected by receptors and send info to the control center
Control center evaluates and sends signal to the effectors to make adjustments that are in opposite direction of the imbalance

14. Negative Feedback Loop

15. Positive Feedback Loop
Makes adjustments in the same direction as the stimulus
These amplify the stimulus instead of stopping it
EX: when you get a cut

16. Positive Feedback Loop