1.2 Systems and models

Significant ideas:

  • A systems approach can help in the study of complex environmental issues.
  • The use of systems and models simplifies interactions but may provide a more holistic view without reducing issues to single processes.

Knowledge and understanding:

  1. A systems approach is a way of visualizing a complex set of interactions which may be ecological or societal.
  2. These interactions produce the emergent properties of the system.
  3. The concept of a system can be applied at a range of scales.
  4. A system is comprised of storages and flows.
  5. The flows provide inputs and outputs of energy and matter.
  6. The flows are processes that may be either transfers (a change in location) or transformations (a change in the chemical nature, a change in state or a change in energy).
  7. In system diagrams, storages are usually represented as rectangular boxes and flows as arrows, with the direction of each arrow indicating the direction of each flow. The size of the boxes and the arrows may be representative of the size/magnitude of the storage or flow.
  8. An open system exchanges both energy and matter across its boundary while a closed system exchanges only energy across its boundary.
  9. An isolated system is a hypothetical concept in which neither energy nor matter is exchanged across the boundary.
  10. Ecosystems are open systems; closed systems only exist experimentally, although the global geochemical cycles approximate to closed systems.
  11. A model is a simplified version of reality and can be used to understand how a system works and to predict how it will respond to change.
  12. A model inevitably involves some approximation and therefore loss of accuracy.

Applications and skills:

  • Construct a system diagram or a model from a given set of information.
  • Evaluate the use of models as a tool in a given situation, for example, climate change predictions.


  • The use of models facilitates international collaboration in science by removing language barriers that may exist.

Theory of knowledge:

  • Models are simplified constructions of reality – in the construction of a model, how can we know which aspects of the world to include and which to ignore?


  • Introduction to water systems (4.1)
  • Introduction to soil systems (5.1)
  • Terrestrial food production systems and food choices (5.2)
  • Introduction to the atmosphere (6.1)