B Environmental Systems
opic 1: System and Models
ystecollection of interrelated parts that work together by way of some driving process.
urroundings – everything around the system being studied
pen system – exchanges energy and matter with surroundings. Most ecosystems are open.
losed system – exchanges energy but not matter with surroundings. Our planet is [usually] closed.
solated system – exchanges neither energy nor matter with surroundings. Laboratory experiments are usually isolated.
rst Law of Thermodynamics: Conservation of energy.
nergy cannot be created or destroyed, only transformed from one form to another. There is a fixed amount of energy in the universe. Therefore 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.
hen 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.
ntropy 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.
quilibriustate of balance among the components of a system
table equilibrium - The condition of a system in which there is a tendency for it to return to a previous equilibrial condition following disturbance
teady-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.
ynamic 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.