Unit 1 Systems and Models “Nautre Does nothing uselessly” Aristotle (384 – 322 BC) Assessment statement
1.1.1 Outline the concept and characteristics of systems. Apply the systems concept on a range of scales.
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.
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).
The first law concerns the conservation of energy. The second law explains the second laws of thermodynamics 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 are relevant to environmental to increase spontaneously.” This means that energy and materials go from a systems. concentrated into a dispersed form (the availability of energy to do work diminishes) and the system becomes increasingly disordered. Describe how the first and
Both laws should be examined in relation to the energy transformations and maintenance of order in living systems.
Assessment statement 1.1.5 Explain the nature of equilibria.
Teacher’s notes 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. 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.
Define and explain the principles of positive feedback and negative feedback.
Feedback links involve time lags. 1.1.7 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. 1.1.8 Distinguish between flows (inputs and Identify flows through systems and describe their direction and outputs) and storages (stock) in relation magnitude. to systems. Construct and analyse quantitative models involving flows...