Systems+and+models

toc =Important vocabulary= [|Systems], [|Ecosystem], [|Biome], [|Gaia], [|Open] [|Closed] and [|Isolated] systems, [|The Biosphere II project], The [|first] and [|second] laws of thermodynamics,  [|Entropy] ([|introductory article to entropy]), Equilibrium,  [|Positive] and [|negative] feedback.

=Course content= From the IB course guide

Introduction
It is essential that the systems approach is used throughout this course. This approach identifies the elements of the systems, and examines the relationships and processes that link these elements into a functioning entity. This topic may be best viewed therefore as a theme to be used in the delivery of the other topics, rather than as an isolated teaching topic.

The topic identifies some of the underlying principles that can be applied to living systems, from the level of the individual up to that of the whole biosphere. It would therefore be helpful to describe and analyse the systems addressed in the terms laid out in this topic (wherever possible). The systems approach also emphasizes the similarities between environmental systems, biological systems and artificial entities such as transport and communication systems. This approach stresses that there are concepts, techniques and terms that can be transferred from one discipline (such as ecology) to another (such as engineering).

TOK: How does a systems approach compare to the reductionist approach of conventional science? How does methodology compare between these two approaches? What are the benefits of using an approach that is common to other disciplines such as economics and sociology?

Content

 * Outline the concept and characteristics of systems.**

The emphasis will be on ecosystems but some mention should be made of economic, social and value systems.

The range must include a small-scale local ecosystem, a large ecosystem such as a [|biome], and [|Gaia] as an example of a global ecosystem.
 * Apply the systems concept on a range of scales.**


 * Define the terms open system, closed system and isolated system.**

These terms should be applied when characterizing real systems.
 * An [|open system] exchanges matter and energy with its surroundings (for example, an ecosystem).
 * A [|closed system] exchanges energy but not matter; the [|Biosphere II] experiment was an attempt to model this. Strictly, closed systems do not occur naturally on Earth, but all the global cycles of matter, for example, the water and nitrogen cycles, approximate to closed systems.
 * An [|isolated system] exchanges neither matter nor energy. No such systems exist (with the possible exception of the entire cosmos).


 * Describe how the first and second laws of thermodynamics are relevant to environmental systems.**

The [|first law] concerns the conservation of energy.

The [|second law] explains the dissipation of energy that is then not available to do work, bringing about disorder. The second law is most simply stated as: “In any isolated system entropy tends to increase spontaneously.” This means that energy and materials go from a concentrated into a dispersed form (the availability of energy to do work diminishes) and the system becomes increasingly disordered.

Both laws should be examined in relation to the energy transformations and maintenance of order in living systems.


 * Explain the nature of equilibria.**

A [|steady-state equilibrium] should be understood as the common property of most open systems in nature. A static equilibrium, in which there is no change, should be appreciated as a condition to which natural systems can be compared. (Since there is disagreement in the literature regarding the definition of dynamic equilibrium, this term should be avoided.) Students should appreciate, however, that some systems may undergo long-term changes to their equilibrium while retaining an integrity to the system (for example, succession). The relative stability of an equilibrium—the tendency of the system to return to that original equilibrium following disturbance, rather than adopting a new one—should also be understood.


 * Define and explain the principles of positive feedback and negative feedback.**

The self-regulation of natural systems is achieved by the attainment of equilibrium through feedback systems.
 * [|Negative feedback] is a self-regulating method of control leading to the maintenance of a steady-state equilibrium—it counteracts deviation, for example, predator–prey relationships.
 * [|Positive feedback] leads to increasing change in a system—it accelerates deviation, for example, the exponential phase of population growth.

Feedback links involve time lags.


 * Describe transfer and transformation processes.**

Transfers normally flow through a system and involve a change in location.

Transformations lead to an interaction within a system in the formation of a new end product, or involve a change of state. Using water as an example, run-off is a transfer process and evaporation is a transformation process. Dead organic matter entering a lake is an example of a transfer process; decomposition of this material is a transformation process.


 * Distinguish between flows (inputs and outputs) and storages (stock) in relation to systems.**

Identify flows through systems and describe their direction and magnitude.


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

Storages, yields and outputs should be included in the form of clearly constructed diagrammatic and graphical models.


 * Evaluate the strengths and limitations of models.**

A model is a simplified description designed to show the structure or workings of an object, system or concept. In practice, some models require approximation techniques to be used. For example, predictive models of climate change may give very different results. In contrast, an aquarium may be a relatively simple ecosystem but demonstrates many ecological concepts.

=Practical work=