Systems and Models What is a system? What is a model? Feedback Mechanisms Transfer vs. Transform Laws of Thermodynamics

Systems A system is a collection of well-organised and well-integrated elements with perceptible attributes which establish relationships among them within a defined space delimited by a boundary which necessarily transforms energy for its own functioning.

A Natural System - Ecosytem

An ecosystem is a system whose organized and integrated elements (parts) transform (change) energy which is used in the transformation process and recycling of matter in an attempt to preserve its structure and guarantee the survival of all its biotic and abiotic characteristics. Although we tend to isolate systems by deleting/merging the boundaries, in reality such boundaries may not be exact or even real. Furthermore, one systems is always in connection with another system with which it exchanges both matter and energy. Question: How does this hold true for the universe?

It exchanges neither energy nor matter Types of Systems There are three types of systems based on whether they exchange energy and/or matter: Isolated System System It exchanges neither energy nor matter

It only exchanges energy. Closed System Energy System Energy It only exchanges energy.

It exchanges both energy and matter. Open System Energy Energy System Matter Matter It exchanges both energy and matter.

Equilibria The steady state is a common property of most open systems in nature whereby the system state fluctuates around a certain point without much change of its fundamental identity. Static equilibrium = no change at all. Dynamic equilibrium = a continuous move from one point to another with the same magnitude, so no net change really happens. Living systems (e.g. the human body, a plant, a population of termites, a community of plants, animals and decomposers in the Tropical Rainforest) neither remain static nor undergo harmonic fluctuations, instead living systems fluctuate almost unpredictably but always around a mid value which is called the “steady state”.

Feedback Mechanisms (+/-) The reaction of particular component elements of the systems againts disturbing agents is consider a feedback mechanism. Two Types of Feedback Mechanisms: Positive and Negative

Positive Feedback Positive feedback leads to increasing change in a system. Positive feedback amplifies or increases change; it leads to exponential deviation away from an equilibrium. For example, due to Global Warming high temperatures increase evaporation leading to more water vapour in the atmosphere. Water vapour is a greenhouse gas which traps more heat worsening Global Warming. In positive feedback, changes are reinforced. This takes ecosystems to new positions.

Negative Feedback Negative feedback is a self-regulating method of control leading to the maintenance of a steady state equilibrium. Negative feedback counteracts deviations from the steady state equilibrium point. Negative feedback tends to damp down, neutralise or counteract any deviation from an equilibrium, and promotes stability. In this example, when the Hare population increases, the Lynx population increases too in response to the increase in food offer which illustrates both Bottom-Up regulation and Positive Feedback. However, when the Lynx population increases too much, the large number of lynxes will pray more hares reducing the number of hares. As hares become fewer, some lynxes will die of starvation regulating the number of lynx in the population. This illustrates both Top-Down and negative Feedback regulation.

Transfer vs. Transformations Transfers normally flow through a system from one compartment to another and involve a change in location. For example, precipitation involves the change in location of water from clouds to sea or ground. Similarly, liquid water in the soil is transferred into the plant body through roots in the same liquid form.

Transformations lead to an interaction within a system in the formation of a new end product, or involve a change of state. For example, the evaporation of sea water involves the absorption of heat energy from the air so it can change into water vapour. In cell respiration, carbon in glucose changes to carbon in carbon dioxide. Ammonia (NH3) in the soil are absorbed by plant roots and in the plant nitrates are transformed into Amino acids. During photosynthesis carbon in the form of CO2 is changed into carbon in the form of Glucose (C6H12O6).These are just some example of transformations.

Laws of Thermodynamics Two laws: 1st – Energy is neither created nor destroyed. ie. The amount of energy in the universe is constant. It is cycled through environmental systems. example: The food chain: energy enters the chain through the sun, where photosynthesis turns it into food (chemical energy) and then passed through the food chain.

Laws of Thermodynamics 2nd Law – The entropy of an isolated system not in equilibrium will increase over time. ie. The amount of energy passed through a system will decrease. example: in the food chain energy is lost through waste heat. Heat given off as organisms live and die. That energy is then released back into the environment. Heat Heat Heat Heat

Limitations of Models Models are simplifications of real systems. They can be used as tools to better understand a system and to make predictions of what will happen to all of the system components following a disturbance or a change in any one of them. The human brain cannot keep track of an array of complex interactions all at one time, but it can easily understand individual interactions one at a time. Models are proposed representations of how a system is structured, which can be rejected in light of contradictory evidence. (hypothesis) No model is a 'perfect' representation of the system because, as mentioned above, all models are simplifications and in some cases over simplified. human subjectivity may lead to models that are biased based on prior knowledge and educational background/ or lack of, and a disregard of the relevance of some components or simply by a limited perception or understanding of the reality which is to be modeled.

Models assignment In groups of 3 Read over the worksheet and answer the questions at the end. Due: 8/30/11 Also: Read chapter 1 of the companion book: answer the ‘to think about’ on page 9, ‘to research’ on page 15 and ‘Earth days’ on page 16. Then read chapter 4 and answer the ‘Review’ on pages 86,87