Topic 1- Systems and Models

Content and Notes

Assessment 1.1.1: Outline the concept and characteristics of systems

System: an entity with at least two components (parts) that are linked and interact in some way.

System consist of:
  • storages ( of matter and energy )
  • flows ( inputs into the system, output from the system )
  • processes (which transfer or transform energy or matter )
  • feedback mechanisms that maintain stability and equilibrium


Assessment 1.1.2: Apply the systems concept on a range of scales

An example of ecosystem: Amazon Rainforest

In economics term: a national banking system
In biology term: the digestive system

Assessment 1.1.3: Define the terms open system, closed system and isolated system

  • Open System: Allow energy or matter to enter or leave the boundaries of the system, e.g. human body

  • Closed System: Allow energy to enter or leave but matter is contained within the boundaries, e.g. Earth (Earth is an imperfect example for the system as there are still matter entering and leaving it)

  • Isolated System: Do not allow either matter or energy to enter, e.g. universe (this system is a theoretical concept with the only possible example of the universe)

Assessment 1.1.4: Describe how the first and second laws of thermodynamics are relevant to environmental systems

First Law of thermodynamics: energy can neither be created nor destroyed ; the total energy of the universe or any isolated part of it will be the same before and after matter is moved or transformed
  • The total amount of energy in the world remain the same, merely changed from one form to another

Second Law of thermodynamic: in an isolated system the total amount of entropy will tend to increase
  • When energy is transformed there is a loss of order or complexity
  • The amount of usable energy in the universe would decrease over time
  • Heat energy is the least ordered type of energy
  • All energy stored in chemicals will be finally released as heat energy radiating out to space

Earth import energy from outside to allow organisms to survive and work against the second law of thermodynamic

Assessment 1.1.5: Explain the nature of equilibria

Equilibrium: the state of balance of the components of a system
  • Steady State: might be small change but in long term it's stable
external image steadystate.gif
  • Static: all time constant
external image static.gif
  • Stable: would self-regulate if faced a change (negative feedback mechanism)
external image stable.gif
  • Unstable: when a disturbance is introduced, it move to a new state of equilibrium
external image unstable.gif

Assessment 1.1.6: Define and explain the principles of positive feedback and negative feedback.

Positive Feedback: an initial change in the system would trigger a cycle that amplifies that change.

Negative Feedback: an initial change in the system would lead to a cycle that returns to and reduces that change

external image feedbacks-schematic.png

Assessment 1.1.7: Describe transfer and transformation processes

Transfer: a movement/flow in an ecosystem, which does not involve a change of form or state of the energy or matter, e.g. water flowing from river to the sea
Transfers can involve:
  • The movement of material through living organisms (carnivores eating other animals)
  • The movement of material in a non-living process (water being carried by a stream)
  • The movement of energy (ocean currents transferring heat)

Transformation: a movement/flow in an ecosystem, which involves a change of form or state of the energy or matter, e.g. ice changing to water
Transformations can involve:

  • Matter (glucose converted to starch in plants)
  • Energy (Light converted to heat by radiating surfaces)
  • Matter to energy (burning fossil fuels)
  • Energy to matter (photosynthesis)

Assessment 1.1.8: Distinguish between flows (inputs and outputs) and storages (stock) in relation to systems.

Inputs and outputs from systems are called flows and represented by arrows in system diagrams. The stock held within a system is called the storage and is represented through boxes.

Energy flow
Energy flow

Assessment 1.1.9: Construct and analyse quantitative models involving flows and storages in a system.*

Assessment 1.1.10: Evaluate the strengths and limitations of models.

Some question to consider when evaluating models:
  • What are the limitations of knowledge? (The data may not be known or not available)
  • Is the data a representative sample of the whole system? Is the data reliable
  • Is it an evidence based model that makes logical sense?
  • Are there feedback with possible tipping points
  • Are there potential influences on the model that are missing?
  • Is the model a useful tool for analyzing the situation?

*Most of these notes come from the internet and reference books*