Topic 1 – systems and models
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Topic 1 – systems and models

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Topic 1 – systems and models Topic 1 – systems and models Presentation Transcript

  • 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 Climograph Meanannualtemperature(oC) Rainfall (mm/year) -15 -10 -5 -0 5 10 15 20 25 1000 2000 3000 4000 5000 6000 desert grassland Tropical rainforest
  • 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 Studies predator-prey equilibria