�　　IB Environmental Systems

　　Topic 1: System and Models

　　system – a collection of interrelated parts that work together by way of some driving process.

　　surroundings – everything around the system being studied

　　open system – exchanges energy and matter with surroundings. Most ecosystems are open.

　　closed system – exchanges energy but not matter with surroundings. Our planet is [usually] closed.

　　isolated system – exchanges neither energy nor matter with surroundings. Laboratory experiments are usually isolated.

　　- First Law of Thermodynamics: Conservation of energy.

　　Energy cannot be created or destroyed, only transformed from one form to another. There is a fixed amount of energy in the universe. Therore living organisms must get their required energy from their environment and surroundings.

　　-Second Law of Thermodynamics: In an isolated system entropy tends to increase spontaneously.

　　When energy is converted from one form to another, some of the energy is degraded into less-usable heat which disperses into the environment. Thus the amount of energy remains the same, but its usability decreases.

　　Entropy measures the amount of disorder in the universe – usable energy is more organized whereas less-usable energy is more diffuse/disorganized. Entropy increases naturally, or spontaneously.

　　Equilibrium – A state of balance among the components of a system

　　Stable equilibrium - The condition of a system in which there is a tendency for it to return to a previous equilibrial condition following disturbance

　　Steady-state equilibrium – The condition of an open system in which there are no changes over the longer term, but in which there may be oscillations in the very short term. There are continuing inputs and outputs of matter and energy, but the system as a whole remains in a more-or-less constant state.

　　Dynamic equilibrium – there is no specific ‘average’ state; the system has different average states at different times. After a disturbance, the system may move to a different ‘average’ state.

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