Topic 1 Systems and Models

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)

storage

Energy or matter in(INPUT)

Energy or matter out(OUTPUT)

TRANSFORMATION

(Feedback mechanism to control input – and maintain EQUILIBRIUM)

Try to Produce a System Diagram

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

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)

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)

A ClimographM

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Rainfall (mm/year)

-15

-10

-5

-0

5

10

15

20

25

1000 2000 3000 4000 5000 6000

dese

rt

gras

slan

dsh

rubl

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tundra

taiga

Tropical rainforest

temperate

deciduous fo

rest

temperate

evergreen forest

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)

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

Static Equilibrium

time

State of the system

Note: this is not realistic – it could only occur in an isolated system

Steady State Equilibrium

time

State of the system

Stable Equilibrium

time

State of the system

disturbance

Weebles wobble but they don’t fall down!

Unstable Equilibrium

time

State of the system

disturbance

He’s going down!

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

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

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

Case Studiespredator-prey equilibria