1. 2-5 What Are Systems and How Do They Respond to Change?
Concept 2-5 Systems have inputs, flows, and outputs of matter and energy, and feedback can affect their behavior.

2. Systems Have Inputs, Flows, and Outputs
interact
A System is set of components that _________________ in a regular way
Examples: Human body, a river, the economy, the planet
Most systems have the following key components…
________________ from the environment
Flows or _________________ of matter and energy
___________________ to the environment
Inputs
throughputs
Outputs

3. Inputs, Throughput, and Outputs of an Economic System
Aluminum ore
Mining &
Manufacturing
Aluminum can
Figure 2.17: This diagram illustrates a greatly simplified model of a system. Most systems depend on inputs of matter and energy resources, and outputs of wastes, pollutants, and heat to the environment. A system can become unsustainable if the throughputs of matter and energy resources exceed the abilities of the system’s environment to provide the required resource inputs and to absorb or dilute the resulting wastes, pollutants, and heat.
Fig. 2-17, p. 48

4. Systems Respond to Change through Feedback Loops
Most systems are affected in one way or another by ________________...any process that increases or decreases a change to a system
Positive feedback loop
Causes system to change further in the ______________ direction
Can cause major environmental problems
Negative, or corrective, feedback loop
Causes system to change in the _______________ direction
feedback
same
opposite

5. Positive Feedback Loop
Core Case
Study
Decreasing
Vegetation
erosion &
Nutrient loss
Figure 2.18: This diagram represents a positive feedback loop. Decreasing vegetation in a valley causes increasing erosion and nutrient losses that in turn cause more vegetation to die, resulting in more erosion and nutrient losses. Question: Can you think of another positive feedback loop in nature?
more
decreasing
vegetation
Fig. 2-18, p. 49

6. Negative Feedback Loop
Figure 2.19: This diagram illustrates a negative feedback loop. When a house being heated by a furnace gets to a certain temperature, its thermostat is set to turn off the furnace, and the house begins to cool instead of continuing to get warmer. When the house temperature drops below the set point, this information is fed back to turn the furnace on until the desired temperature is reached again.
Fig. 2-19, p. 50

7. Environmental Example of Negative Feedback
Recycling Aluminum Cans!
Aluminum ore must be ____________ and then manufactured for use…likely causing environmental ______________
Recycling our current supply of aluminum will…
______________ the need for ______________, manufacturing, ______________ and ______________ associated with the product
mined
degradation
Reduce
mining
pollution
waste

8. Time Delays Can Allow a System to Reach a Tipping Point
A complex system will often show a ________ __________ or lack of response between the input of a feedback ________________ and the response to it
Time delays can allow an environmental problem to build slowly until it reaches a tipping point or ________________ level
Melting of polar ice
Population growth
Depletion of fish populations due to overfishing
time
delay
stimulus
threshold

9. System Effects Can Be Amplified through Synergy
A synergistic interaction, also called ________________ occurs when…
Two or more processes combine in such a way that combined effect is _______________ than the two ________________ effects
Helpful
Studying with a partner
Harmful
E.g., Smoking and inhaling asbestos particles…increased risk of lung cancer is fivefold
synergy
greater
separate

10. Three Big Ideas of This Chapter
There is ______________…we cannot do away with matter
2. You ___________________get something for nothing…during energy changes we cannot get more energy than we put in
You ___________________________…we always end up with lower-quality energy during a transfer
These laws place limits on what we can do with matter and energy resources
no away
Law of Conservation of Matter
cannot
1st law of thermodynamics
cannot break even
2nd law of thermodynamics

11. Review Questions What are the three key components of most systems?
What is the difference between a positive and negative feedback loop?
What is another term for synergistic interaction?
inputs
throughputs
outputs
positive – change continues in the same direction
negative – change moves in the opposite direction
synergy