1.3 Energy and equilibria

Significant ideas:

  • The laws of thermodynamics govern the flow of energy in a system and the ability to do work.
  • Systems can exist in alternative stable states or as equilibria between which there are tipping points.
  • Destabilizing positive feedback mechanisms will drive systems toward these tipping points, whereas stabilizing negative feedback mechanisms will resist such changes.

Knowledge and understanding:

  1. The first law of thermodynamics is the principle of conservation of energy, which states that energy in an isolated system can be transformed but cannot be created or destroyed.
  2. The principle of conservation of energy can be modelled by the energy transformations along food chains and energy production systems.
  3. The second law of thermodynamics states that the entropy of a system increases over time. Entropy is a measure of the amount of disorder in a system. An increase in entropy arising from energy transformations reduces the energy available to do work.
  4. The second law of thermodynamics explains the inefficiency and decrease in available energy along a food chain and energy generation systems.
  5. As an open system, an ecosystem will normally exist in a stable equilibrium, either in a steady-state equilibrium or in one developing over time (for example, succession), and maintained by stabilizing negative feedback loops.
  6. Negative feedback loops (stabilizing) occur when the output of a process inhibits or reverses the operation of the same process in such a way as to reduce change—it counteracts deviation.
  7. Positive feedback loops (destabilizing) will tend to amplify changes and drive the system toward a tipping point where a new equilibrium is adopted.
  8. The resilience of a system, ecological or social, refers to its tendency to avoid such tipping points and maintain stability.
  9. Diversity and the size of storages within systems can contribute to their resilience and affect their speed of response to change (time lags).
  10. Humans can affect the resilience of systems through reducing these storages and diversity.
  11. The delays involved in feedback loops make it difficult to predict tipping points and add to the complexity of modelling systems.

Applications and skills:

  • Explain the implications of the laws of thermodynamics to ecological systems.
  • Discuss resilience in a variety of systems.
  • Evaluate the possible consequences of tipping points.


  • The use of energy in one part of the globe may lead to a tipping point or time lag that influences the entire planet’s ecological equilibrium.

Theory of knowledge:

  • The laws of thermodynamics are examples of scientific laws—in which ways do scientific laws differ from the laws of human science subjects, such as economics?


  • Systems and models (1.2)
  • Communities and ecosystems (2.2)
  • Terrestrial food production systems and food choices (5.2)
  • Energy choices and security (7.1)