1. Topic: Feedback Mechanism.
Aim: How do organisms use the
feedback mechanism to maintain
homeostasis?
 Do now: Read P 150 & ans.
 Why do organisms use the feedback
mechanism?
 Organisms use the feedback mechanism to
detect changes from the normal conditions &
correct them returning the body to normal
state. (homeostasis).

2. What is the feedback mechanism ?
 Read p. 150 2nd Para.& ans.
What is the feedback mechanism?
It is a self- regulating system.
 Give an example to explain this system.
An increase in body temperature is sensed by the
brain.
The brain will send a message to the sweat glands
of the skin to produce sweat.
Evaporation of the sweat from the body will lower
body temperature.

3. Have you heard of the Negative
feedback mechanism?
 Read P150 3rd Para, & ans.
 Write two facts about the negative feedback
mechanism.
 The secretion of hormones by the
endocrine system is regulated by the negative
feedback mechanism.
 The level of one hormone in the blood stimulates or
inhibits the production of another.
 Study Fig. 17-5 summarize what you learned.

4. What are other examples of feedback
mechanisms that maintain
homeostasis? Check P150 3rd Para.
 Changes in heart rate or respiratory rate in
response to increased activity in muscle
cells.
 The maintenance of blood sugar levels by
insulin from the pancreas.

5. Do plants use the feedback
mechanisms?
Read P 151 1st Para.& ans.
 Howdo guard cells behave to change
stomates opening?
– Guard cells regulate the opening and closing of
the stomates.
– The change in stomates openings regulate water
loss and gas exchange .
This process maintains a balance of water
&gases in the plants.

6. GUARD CELLS IN ACTION