topic 1 – systems and models
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Topic 1 Systems and Models
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What is a System?
• A system consists of:– Storages– Flows (inputs and outputs) (of energy or matter)– Processes (transfer or transformation)– Feedback mechanisms (to maintain stability)
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storage
Energy or matter in(INPUT)
Energy or matter out(OUTPUT)
TRANSFORMATION
(Feedback mechanism to control input – and maintain EQUILIBRIUM)
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Try to Produce a System Diagram
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Ecosystems
• Most of the systems we will look at are ecosystems (self contained communities of living things and their surrounding environment)
• Very large ecosystems which span a fairly stable climate are biomes
• Many biologists say the whole planet is a single ecosystem (eg Gaia theory). Some of them call it a CLOSED ecosytem
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Open, Closed and Isolated Ecosytems
• Open – matter and energy exchanged to suroundings• Closed – only energy exchanged to surroundings• Isolated – neither matter nor energy is exchanged to
surroundings
• Is the Earth really a closed ecosystem?• Do isolated ecosystems really exist? • Can closed ecosystems be created artificially? (eg
Biosphere 2 Project)
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Biomes and Biospheres
• Biome – An open ecosystem in a geographically defined area with similar climatic conditions throughout – eg, desert, grassland (savannah), tropical rainforest
• Biosphere – A closed ecosytem – generally made up of a range of biomes (i.e. the entire Earth)
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A ClimographM
ean
annu
al te
mpe
ratu
re (o C
)
Rainfall (mm/year)
-15
-10
-5
-0
5
10
15
20
25
1000 2000 3000 4000 5000 6000
dese
rt
gras
slan
dsh
rubl
and
tundra
taiga
Tropical rainforest
temperate
deciduous fo
rest
temperate
evergreen forest
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The Laws of Thermodynamics
• First Law – Energy can neither be created nor destroyed, but can only be transformed
• Second Law – Energy is always changed from a concentrated (useful) form, to a dispersed (less useful) form – we say that ENTROPY (disorder) always increases (this means an isolated system cannot exist – there must be an input of energy to keep entropy low)
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Equilibrium
• A system needs to be in equilibrium• If not, entropy will increase so much the
system will destroy itself by becoming too disordered
• There a 4 kinds of equilibrium:– Static– Steady State– Stable– unstable
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Static Equilibrium
time
State of the system
Note: this is not realistic – it could only occur in an isolated system
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Steady State Equilibrium
time
State of the system
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Stable Equilibrium
time
State of the system
disturbance
Weebles wobble but they don’t fall down!
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Unstable Equilibrium
time
State of the system
disturbance
He’s going down!
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Feedback Mechanisms
• This is a way that the INPUT is affected by the OUTPUT• In a stable equilibrium, feedback returns the
equilibrium to its original state• In an unstable equilibrium, feedback returns the
equilibrium to a different state• Feedback can be – POSITIVE – input changes to bring the system to a new
equilibrium– NEGATIVE – input changes in order to bring the system
back to its original equilibrium
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Negative Feedback
• Your (stable) equilibrium body temperature is 37oC
• Sensors in the skin detect your skin temperature is rising (you are in Cancún)
• Show what happens in a system diagram
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Positive Feedback
• Your (stable) equilibrium body temperature is 37oC
• Sensors in the skin detect your skin temperature is decreasing (you are locked in a freezer)
• Your body is unable to maintain its stable equibilibrium and therefore you enter a state of hypothermia
• Show what happens in a system diagram
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Case Studiespredator-prey equilibria