ENVIRONMENTAL SYSTEMS AND SOCIETIES ENVIRONMENTAL SCIENCE Subtopic 1.2. Systems and Models; Subtopic 1.3. Energy and Equilibria STUDY GUIDE 1. Provide the definitions of system, biome, open system, transfer, transformation, steady-state equilibrium, positive feedback, tipping points. System- An assemblage of parts and the relationship between them, which together constitute an entity or whole. Biome- Collection of ecosystems sharing similar climatic conditions. Open system- Both matter and energy are exchanged across the boundaries of the system. Transfer- cause a change in location Transformation- transformations refer to a change in the chemical nature, change in state or a change in energy. 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 remains in a more or less constant state. Positive feedback- Feedback that amplifies or increases change; it leads to exponential deviation away from equilibrium. Tipping points- The minimum amount of change within a system that will destabilize it and cause it to reach a new equilibrium or stable state. 2. Distinguish between a reductionist and a holistic approach. Reductionist approach- Divides systems into parts, or components, and each part is studied separately. Traditional scientific investigations. Holistic approach- System is studied as a whole, with patterns and processes described for the whole ecosystem. Modern ecological investigations. Way of visualizing a complex set of interactions, which can be applied across a range of different disciplines. 3. Draw a systems diagram of a producer (tree) and/or a consumer (fish). 4. Identify strengths and limitations of models. Strength: - Allow scientists to simplify complex systems and use them to predict what will happen if there are changes to inputs, outputs, and storages. - Allow inputs to be changed and outcomes examined faster. - Allow results to be shown to other scientists and public and are easier to understand. Limitations: - Doesn’t consider all variables. - May show different effects using the same data. - May be very complex and when oversimplified they may become less accurate. - Many assumptions must be made about complex facts, so models may not be accurate. - The complexity and oversimplification have led some people to criticize these models. - Different models use slightly different data to calculate predictions. - Any model is only as good as the data used. - Relies on the expertise of the people making them. - As they predict further into the future, they become uncertain. - Different people may interpret models in different ways and come to different conclusions. 5. Explain how the Gaia hypothesis can model a global ecosystem. The Gaia hypothesis proposes that all the organisms and the organisms' inorganic surroundings on Earth are tightly integrated to form a single and self-regulating complex system, while maintaining the conditions for life on the planet. The Gaia hypothesis can model a global system because it states that all the organisms and its surroundings, which is basically Earth itself, make the global system. 6. Contrast steady-state equilibrium with static equilibrium. In steady state equilibrium there are no changes over the longer term, but there may be oscillations in the very short term, there are continuing inputs and outputs of matter and energy, but the system remains in a constant state while in static equilibrium, there is no change in the system over time and no inputs or outputs of matter and energy. 7. Identify examples of steady-state and static equilibrium. 4Steady state: a bear Static equilibrium: a chair 8. Explain the first and second Laws of Thermodynamics. The first law of thermodynamics is the law of conservation of energy. Energy cannot be created or destroyed; it can only change form. The total energy in any system is constant. The available energy is reduced through inefficient energy conversions (total amount is the same, but less is available for work). Energy is lost as heat. The second law of thermodynamics is the entropy, which is disorder in a system. Energy goes from a concentrated form (e.g., the Sun) into a dispersed form (ultimately heat). The availability of energy decreases, and the system becomes increasingly disordered. Energy is needed to create order, disorder (entropy) increases over time as less energy is available. In isolated systems, without energy input, entropy increases spontaneously 9. Apply the Laws of Thermodynamics to ecosystems. According to he first law of thermodynamics, in ecosystems, energy enters the system as sunlight, is converted into biomass through photosynthesis, passes along food chains as biomass, is consumed, and leaves the ecosystem in the form of heat. Since heat is constantly loss and cannot be used again, the system becomes increasingly disordered (second law of thermodynamics), this way, for ecosystems to keep functioning they require a constant input of energy as sunlight. 10. Explain how the stability of an ecosystem depends on diversity and resilience. The resilience of a system refers to its tendency to maintain stability through steady-state equilibrium. Diversity and the size of storages within systems can contribute to their resilience and affect the speed of response to change. Rainforests have complex food webs which allow animal and plants to respond to disturbance of the ecosystem and thus maintaining stability. They also contain long-lived species and dormant seeds and seedlings that promote a steady-state equilibrium. 11. Represent a negative feedback loop by using a diagram. 12. Distinguish between stable and unstable equilibrium. If a system returns to the original equilibrium after a disturbance, it is a stable equilibrium. A system that does not return to the same equilibrium but forms a new equilibrium is an unstable equilibrium. 13. Explain how sea ice melting can be seen as an example of positive feedback. A system that does not return to the same equilibrium but forms a new equilibrium is an unstable equilibrium. Positive feedback mechanisms can lead to a system moving away from its original equilibrium. One example would be ice melting which may reach a new equilibrium following the effects of global warming, with conditions on the planet dramatically altered. As the earth experiences more and more heat, the ice melts in places it should be ice. As the ice melts the water also becomes warm (absorbs heat). Once the tipping point is reached, the system becomes destabilized, and a new equilibrium is reached. 14. Connect the concepts of unstable equilibrium, tipping points and positive feedback. Positive feedback is feedback that amplifies or increases change; it leads to exponential deviation away from equilibrium. Then the tipping point is the minimum amount of change within a system that will destabilize it and cause it to reach a new equilibrium or stable state, which will be an unstable equilibrium, a system that does not return to the same equilibrium but forms a new equilibrium. 15. Describe environmental issues associated with tipping points. Amazon Rainforest: Increased temperatures due to climate change and deforestation would reduce evapotranspiration. Drier conditions would lead to forest fires and reduced forest extent, causing the desertification of the Amazon basin.
