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SYSTEMS – A GUIDE TO TERMS Examples of systems: Ecosystems, weather systems, food production systems, sewage treatment systems, photosynthesis, education systems, information distribution systems, your body……… All systems have: Inputs o usually energy or materials or both Outputs o usually energy, materials or both o may be useful eg a crop o may be a problem eg pollution When a system is in equilibrium: inputs = outputs eg The temperature of our planet will remain constant, provided that energy inputs = energy outputs. If we reduce the outputs of energy by increasing levels of greenhouse gases which trap heat energy, the temperature rises (global warming). There are 3 main types of systems: System Energy Materials type Inputs and outputs Inputs and outputs open closed Inputs and outputs Cycle round within system isolated No inputs or outputs No inputs or outputs Examples Most common type of system - includes most ecosystems, food production systems and many others Earth is almost a closed system; aquarium with sealed lid; biosphere domes An abstract concept difficult to find real life examples – possibly the universe is an example Systems and the Laws of Thermodynamics The First Law of Thermodynamics tells us: “Energy is never created or destroyed, only changed from one form to another” This means that when energy flows through a system, the total amount of energy never changes. For example in an ecosystem light energy from the sun is changed to stored chemical energy and eventually it all turns to heat energy, but no energy is “lost”. The Second Law of Thermodynamics tells us that entropy, which is a measure of the amount of disorder or chaos in a system always increases. All energy changes release some energy as heat, and eventually all the energy in the universe will have turned to low grade heat energy. This spreading out of energy increases the amount of disorder and eventually (billions of years hence) we shall be left with a lukewarm universe and no way of doing any useful work Feedback mechanisms in systems feedback occurs when the output of a system influences the inputs and hence affects the state of the system positive feedback changes a system to a new state. In most natural systems it is considered a bad thing, but it is not always so! The term “vicious cycle” usually refers to positive feedback. o Ex. rising global temperatures melt frozen ground at high latitudes; waterlogged ground releases methane gas; methane adds to green house effect, increasing global warming further; more frozen ground melts releasing more methane. o Ex. teacher encourages student with positive feedback comments on his/her work; student associates learning with being praised so wants to learn more and produces a higher standard of work (a new state!). Student gains confidence from achievement, passes exams and leaves for university. negative feedback returns a system to its original state. In many natural systems homeostasis acts as a form of negative feedback . In most natural systems, negative feedback is considered a good thing, because it restores equilibrium. o Ex. as a population of mice increases, there is less food to go around, so some animals starve, reducing population back to sustainable levels o Ex. if global temperatures rise because of increased levels of greenhouse gases, evaporation rates from the sea surface will increase; clouds may increase and more snow may fall in high latitudes. This would increase the amount of sunlight reflected back to space, so the planet would cool down to its original temperature o Ex. a teacher writes only negative comments on a student’s work. The student feels they will never succeed, so puts less and less effort into studying, and eventually gives up and drops out of college and returns to an uneducated state, turns to a life of crime... o Most negative feedback mechanisms involving populations of organisms depend on density dependent factors ie with increasing population size, food and other resources are spread more thinly but diseases and parasites spread more readily, both of which tend to reduce population size. On your own sheet of paper: 1) Describe and then diagram a system of your choosing, including all inputs and out puts. 2) Explain the role of the first and second laws of thermodynamics in your system and their effects on your system – add them to your diagram. 3) Describe at least one positive and one negative feedback mechanism that influences your system – add them to your diagram.