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 – usually energy or materials or both Outputs – usually energy, materials or both – may be useful – ex. a crop – may be a problem –ex. pollution

When a system is in equilibrium: inputs = outputs Ex. 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 typeEnergyMaterialsExamples openInputs and outputs Most common type of system - includes most ecosystems, food production systems and many others closedInputs and outputsCycle around within system Earth is almost a closed system; aquarium with sealed lid; biosphere domes isolatedNo inputs or outputs 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”.

Systems and the Laws of Thermodynamics 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.

Positive Feedback examples 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. – 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.

Positive or negative feedback? 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...

Feedback mechanisms in systems 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.

Negative Feedback Examples Ex. as a population of mice increases, there is less food to go around, so some animals starve, reducing population back to sustainable levels – 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

Negative Feedback Examples Ex. A student fails a test and as a result hates the teacher and the class. The student decides to attend tutorial sessions and makes an A on the next test and as a result enjoys the class again. – 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.

NEGATIVE FEEDBACK MECHANISMS - push a system back to its original equilibrium position Example: Imagine you are out walking in the country. As you walk, the sun rises higher in the sky and the air temperature increases. Your body senses that your internal temperature is rising above 37 0 C and you start to sweat, which reduces your body temperature by evaporating water from your skin, returning your temperature to normal

POSITIVE FEEDBACK MECHANISMS - push a system to a new state of equilibrium Example: Imagine you are lost on a high snowy mountain. When your body senses that it is cooling below 37 0 C, various mechanisms such as shivering help to raise your internal temperature again, but if these are insufficient to restore normal body temperature, your metabolic processes start to slow down, as, like most chemical reactions, they happen more slowly at lower temperatures. As a result you become lethargic and sleepy and move around less and less, allowing your body to cool even further. Unless you are rescued at this point, your body will reach a new equilibrium – you will die of hypothermia.

Both natural and human systems are influenced by feedback mechanisms. Generally, we wish to preserve the environment in its original state, so negative feedback is usually helpful and positive feedback is usually undesirable. However there are other situations where change is needed and positive feedback is advantageous. For example, if students enjoy their Environmental Systems lessons, they want to learn more, so attend classes regularly and complete assignments. Consequently they move to a new equilibrium of being better educated about the environment.

On the following slides there are a number of examples of how both positive and negative feedback mechanisms might operate in the physical environment. No one can be sure which of these effects is likely to be most influential, and consequently we cannot know whether or not the Earth will manage to regulate its temperature, despite human interference with many natural processes.

+– + or – feedback? As carbon dioxide levels in the atmosphere rise: Temperature of Earth rises As Earth warms: the rate of photosynthesis in plants increases more carbon dioxide is therefore removed from the atmosphere by plants, reducing the greenhouse effect and reducing global temperatures

+– + or – feedback? As Earth warms: Ice cover melts, exposing soil or water Planetary albedo decreases More energy is absorbed by Earth’s surface Global temperature rises More ice melts

+– + or – feedback? As Earth warms, upper layers of permafrost melt, producing waterlogged soil above frozen ground: Methane gas is released in anoxic environment Greenhouse effect is enhanced Earth warms, melting more permafrost

+– + or – feedback? As Earth warms, increased evaporation: Produces more clouds Clouds increase albedo, reflecting more light away from Earth Temperature falls Rates of evaporation fall

+– + or – feedback? As Earth warms, organic matter in soil is decomposed faster: More carbon dioxide is released Enhanced greenhouse effect occurs Earth warms further Rates of decomposition increase

+– + or – feedback? As Earth warms, evaporation increases: Snowfall at high latitudes increases Icecaps enlarge More energy is reflected by increased albedo of ice cover Earth cools Rates of evaporation fall

+– + or – feedback? As Earth warms, polar icecaps melt releasing large numbers of icebergs into oceans: Warm ocean currents such as Gulf stream are disrupted by additional fresh water input into ocean Reduced transfer of energy to poles reduces temperature at high latitudes Icesheets reform and icebergs retreat Warm currents are re-established

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.

On your own paper… Draw diagrams of one example of positive feedback and one example of negative feedback using the examples given, to show how feedback affects a system. Include feedback loops on your diagrams.