Systems

1. Systems The parts and their interactions……………..

2. definition • A system can be defined as ‘an assemblage of parts and their relationships forming a functioning entity or whole’.

3. An Ecosystem

4. System Notation • Boxes which are STORES of energy and matter. • a boundary line representing the edge of the system. • arrows which show how things FLOW through systems. This could either be energy or matter. • Arrows entering the system boundary or stores are INPUTS • Arrows leaving the system boundary or stores are OUTPUTS. • PROCESSES in the store areas which can TRANSFORM or TRANSFER energy and matter.

5. Open, closed and isolated systems • Open System: Both energy and matter may enter or leave the system. • Closed system: Only energy can enter or leave the system. • Isolated system: Nothing can enter or leave the system.

7. Open, Closed or isolated? • Match the above names to the following definitions: • A ___________ system exchanges matter and energy with its surroundings (e.g. an ecosystem). • A ­­__________ system exchanges energy but not matter; (the “Biosphere II” experiment was an attempt to model this. These systems do not occur naturally on Earth, although the biosphere (or Gaia) itself can be considered a ________ system). • A __________ system exchanges neither matter nor energy. (No such systems exist, with the possible exception of the entire cosmos). • All ecosystems are ________ systems, because of the input of _______ energy and the exchange of ________ with other ecosystems.

8. Static equilibrium • Most non-living systems like a pile of rocks or a building are in a state of static equilibrium. • This means that they do not change their position or state, i.e. they just look the same for long periods of time and the rocks or bricks stay in the same place.

9. Steady – State Equilibrium Ecosystems are steady-state systems. From a distance a forest just looks the same for long periods of time (=equilibrium). At the individual level each tree is growing, dying and being replaced by young ones, as is every other organism.

10. Stability • The more complex an ecosystem is, the more negative feedback cycles will exist. This will make the ecosystem stable. • Monocultures are not complex, they lack negative feedback cycles and are vulnerable.

11. Feedback cycles • Negative feedback keeps the system in a steady state. When you exercise you heat up, so you sweat. This cools you down. The more you exercise, the more you sweat, and you stay cool enough! • Positive feedback loops cause the system to continue to change away from the normal state. • Positive feedback loops are often called vicious circles.

12. Feedback

13. Positive or negative feedback? • With the warming of the oceans and the air above them, evaporation would increase, increasing the amount of water vapour in the air. Water vapour is in fact the most potent natural greenhouse gas, and the increase in water vapour concentrations, would further trap heat.

14. Positive or Negative Feedback? • There is the possibility that vegetation covered by permafrost in the northern hemisphere could be laid bare as ice melts due to global warming. This decomposing matter forms a carbon store estimated at as much as 450 billion tonnes, which could release enormous quantities of carbon dioxide and methane into the atmosphere.

15. Positive or negative feedback? Trees store carbon and draw it down to produce food, but dead, burnt or cleared forests turn from being carbon sinks to carbon sources. When forests are burnt, will the temperature increase or decrease? Is this positive or negative feedback?

17. Draw a diagram(s) of the water (hydrological) cycle, showing as many energy and material transfers and transformations as you can. • Use boxes for storages and arrows for flows. • Use a different colour or a different diagram for energy and for materials. • Indicate clearly which are transfer and which are transformation processes on your diagram Assignment using the previous slide • Draw a diagram(s) of the water (hydrological) cycle, showing as many energy and material transfers and transformations as you can. • Use boxes for storages and arrows for flows. • Use a different colour or a different diagram for energy and for materials. • Indicate clearly which are transfer and which are transformation processes on your diagram

18. Limiting factors and Carrying Capacity • The carrying capacity (K) is the maximum number of individuals of a species that the habitat can hold. • Limiting factors are the abiotic and biotic factors that keep the population from continuing to increase. • Does this demonstrate positive or negative feedback?

19. Limiting factors control a population Biotic (living factors) • Food – both quantity and quality of food are important. • Predators – refer back to predator prey relationships. • Competitors – other organisms may require the same resources from an environment. • Parasites – may cause disease and slow down the growth of an organism.

20. Limiting factors limit population growth Abiotic (nonliving factors) Temperature – higher temperatures speed up enzyme-catalyzed reactions and increase growth. Oxygen Availability – affect the rate of energy production by respiration. Light Availability – for photosynthesis and breeding cycles in animals and plants. Toxins and pollutants – tissue growth may be reduced.

22. Density dependant factors External factors that are density dependant • Disease transmission • Vulnerability to predators Internal Factors that are density dependant • Over crowding (habitat, nesting space) • Food supply • Do density dependant factors show negative or positive feedback?

23. Gypsy moth • Intraspecific competition • Limited food • Limited Space

25. Density Independent Factors • The following factors are classed as density-independent factors: • Drought • Freezes • Hurricanes • Floods • Forest Fires • r-strategists are often controlled by density independent factors

26. A drought caused the Darwin Finches to decline • Density dependent or density independent?

28. Density dependant or independent?Positive or negative feedback?

29. First law of Thermodynamics • Energy can neither be created nor destroyed, it can only be converted from one form into another. • A simple example here would be that energy arrives on earth as solar energy (mainly as visible light); some of this is converted into heat, some absorbed by plants, some is reflected. The light absorbed by plants can be converted into stored energy through photosynthesis. Animals can eat the plants to obtain energy.

30. Second Law of Thermodynamics • In any isolated system, entropy tends to increase” • You may be familiar with the idea that as soon as your own room is tidy, it automatically begins to become dirty, disorganised and difficult to find things except old socks. • What the 2nd law is saying really is this- that in a system, whenever energy (or some material) is converted from one form to another, you don’t get a 100% ‘pure’ transfer, say of electricity into light- some energy is ‘spilt’ or lost in various ways, eg as heat. • So in any isolated system, the energy available goes from being in a ‘concentrated’ to a more diffuse or diluted form.

31. Photosynthesis example • Use a plant as a system • Consider the storage of carbon in this system • Label inputs • Label outputs • Which inputs and outputs are matter and which are energy? • Where do the first and second laws of thermodynamics come into play in this example?

32. Model • A model is a representation of part or the totality of a reality made by human beings. • Models represent the structural complexity of the reality in a simpler way eliminating unnecessary elements that create confusions • Models help us understand processes which are difficult to work out with the complexity of the real world. • They predict the behavour of a system within the limitations imposed by the simplification accepted as necessary for the sake of the understanding.

33. Models are not perfect • No model is a 'perfect' representation of the system because all models are simplifications and in some cases needed over simplifications. • Human subjectivity may lead to humans to make models biased by scholar background, disregard of the relevance of some components or simply by a limited perception or understanding of the reality which is to be modeled.