1. Feedback & homeostasis
Pages 36-37
Life Processes Packet

2. Why is an organism’s homeostasis constantly threatened?
Because an organism’s internal and external environment is constantly changing.

3. How does an organism maintain stability, or homeostasis?
Living things constantly monitor and respond to changes in their environment.

4. What can happen if an organism’s control mechanisms fail?
Disease or Death can occur!

5. What are some adjustments you body makes throughout the day to maintain homeostasis?
* Body temperature adjusts throughout the day
* Heart rate & breathing rate are altered
* Blood flow can either increase or decrease

6. RESPONSE Change (STIMULUS) ORGANISM Species of Bacteria
Temperature falls below a certain point
Produces a chemical that acts an antifreeze
Many Plants
Air is hot and dry
Leaf closes to conserve water
Monarch Butterflies
Seasons change
Butterflies migrate
Humans
Person hears a loud noise
The person becomes alert
Heart rate increases in case “fight or flight” is necessary

7. Dynamic equilibrium
How is the term Dynamic Equilibrium related to the term homeostasis?
How can microorganisms or diseases interfere with homeostasis?
Dynamic Equilibrium is essentially the same as homeostasis.
It means that small changes constantly occur in order to maintain homeostasis.
Both microbes and disease interfere with homeostasis.

8. Look at the graphs on page 30
Look at the graphs on page 30. How do these graphs illustrate the concept of homeostasis and dynamic equilibrium?
Graph A
This graph shows that body temperature can fluctuate though out the day, but always remains within a certain range
Graph B
This graph shows that blood sugar levels in the blood will increase after a meal, but then drop due to the effects of insulin. After awhile, blood sugar levels return to “normal” but fluctuate slightly through the day.

9. What is a feedback mechanism?
A cycle in which the output of one system “feeds back” to another organ or system to modify or reinforce the action taken by the system.
WHAT IS MEANT BY THE TERM STIMULI?
A stimulus is any change in the environment

10. Contractions during childbirth Fruit ripening
TWO TYPES OF FEEDBACK
POSITIVE FEEDBACK
NEGATIVE FEEDBACK
This type of feedback occurs when a change in the environment prompts System 1 to send a message to System 2 As a result, HOMEOSTASIS is restored.
This is the most common type of Feedback.
Examples include:
* How a THERMOSTAT works
* Maintaining body temperature
* Maintaining blood sugar levels
This type of feedback occurs when a change prompts a GREATER change and/or response.
Some examples are:
Contractions during childbirth Fruit ripening
Blood clotting

11. Explain how the body maintains a steady level of blood glucose levels
Explain how the body maintains a steady level of blood glucose levels. Is this positive or negative feedback?
When glucose levels are high, the PANCREAS releases INSULIN which lowers the blood sugar level and returns it to normal.
This is NEGATIVE FEEDBACK.

12. Explain how guard cells on a leaf help to maintain water levels within a plant.
When a leaf detects a shortage of water the GUARD CELLS close to prevent evaporation. The guard cells will open when conditions become better and more stable.