Classifying Feedback Loops
Oceanography
Name: ___________
Date: ___________
Learning Target
I can properly classify a feedback loop when given a description of it.
Directions
Read the description of each system. Decide what type of feedback loop (positive or negative) exists in the
situation. Write your decision in and explain why you think it is that type.
Reinforcing (positive) Feedback Loops
 Change is promoted or increased.
 Amplification occurs.
 A very different new state is
established for the system.
Balancing (negative) Feedback Loops
 Change is reduced or decreased.
 Stabilization occurs.
 The system hovers around the current
target point that already exists.
Letter
System Description
A
You get a rash from poison ivy. You know you
shouldn't scratch it, but it itches. So you scratch. But
scratching makes it itch more, and can even make the
rash spread to areas that didn't itch before. The more
you scratch, the more it itches.
B
Your internal body temperature needs to stay
constant. When you exercise or go outside on a hot
day, your temperature starts to increase. Your
nervous system sends information to your brain about
the change in temperature, and you brain in turn
sends signals to your skin to tell you to sweat. The
evaporation of the sweat helps keep your body
cooler. When you quit exercising or go back indoors,
your body cools back down to your normal
temperature. Signals are again sent to your brain, and
your brain tells your skin to quit sweating.
C
A farmer has insect pests on his crops, so he sprays a
pesticide to control the insects. After several seasons,
the insects start showing resistance to the pesticide,
so the farmer sprays even more pesticides and more
toxic pesticides. This further increases the selection
pressure on the insects, and after a few more seasons,
nothing seems to work against the pests. The more
the farmer sprays, the worse the problem becomes.
Type of
Feedback
Loop
Explanation
D
In nuclear fission, a neutron collides with an atom
causing its nucleus to split apart and release 2-3
neutrons. These neutrons go on to collide with other
atoms, which then release more neutrons. This cycle
continues, growing as increasingly more atoms are
split.
E
Your body’s cells need nutrients. It sends a message
to your brain saying this. Your brain tells you to eat.
You eat, and the food is digested. In your stomach, a
signal is created indicating that it is full and it sends
this to your brain. You stop eating, having provided
enough nutrients for your cells.
F
The thermostat attached to an air conditioner helps
maintain a constant temperature in your house.
During the summer, the sun heats the house and the
temperature goes up. When the temperature goes up,
the thermostat turns on the air conditioner, causing
the house to cool down. When the house is cool
again, the thermostat turns the air conditioner off.
G
The process of blood clotting occurs when injured
tissue releases signal chemicals that activate platelets
in the blood. An activated platelet releases chemicals
to activate more platelets, causing a rapid increase in
the number of platelets. This cascades and quickly
leads to the formation of a blood clot around the
injured tissue.
H
During the onset of contractions in childbirth
something occurs known as the Ferguson reflex.
When a contraction occurs, the hormone oxytocin
causes a nerve stimulus, which stimulates the
hypothalamus to produce more oxytocin, which
increases uterine contractions. This results in
contractions increasing in amplitude and frequency.
This continues to grow until the child is born.
Summary (3-4 sentences)
Describe what you key in on as you read the scenarios to help you figure out what type of feedback
loop is occurring.