2. 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)
5. 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
6. 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)
7. 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)
9. 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)
10. 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
15. 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
16. 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
17. 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
