ESS(System and Models)

The disadvantages of using models

1) they may not be accurate. 2)they rely on the expertise of the people making them. 3)different models may show different effects using the same data.

The advantages of using models

1)they allow scientists to predict and simplify complex systems. 2)inputs can be changed and outcomes examined without having to wait for real events.3)results can be shown to other scientists and to the public

Models and flow of storage

A model is simplified description designed to show the structure or working of an object system or concept. Models can be used to illustrate the flows, storages and linkages within ecosystems.

Flows and storage

Both energy and matter flows (inputs and outputs) through ecosystems but at times is also stored (stock) within the ecosystem.

Open System

Both matter and energy are exchanged across the boundaries of the system. Open system are organic and so must interact with their environment to take in energy and new matter, and to remove wastes.

Closed System

Energy but not matter is exchanged across the boundaries of the system. The Earth can be seen as a closed system: input=solar radiation (Sun energy or light), output=heat energy. Matter is recycled within the system.

First law of thermodynamics

Energy can not be created or destroyed, which means that the total energy in any isolated system, such as the entire universe is constant. All that can happen is that the form the energy takes changes. It also called law of conservation.

An Example of negative feedback

Increased release of carbon dioxide through the burning of fossil fuels leads to enhanced plant growth through increased photosynthesis.

An Example of positive feedback

Increased temperature through global warming melts more of the ice in the polar ice caps and glaciers, leading to a decrease in the Earth's albedo (reflection from the Earth's surface) - the Earth absorbs more of the Sun's energy which makes the temperature increase even more, melting more ice.

Second law of thermodynamics

It states that the entropy of an isolated system not in equilibrium will tend to increase over time, which means when energy is changed from one form to another, some useful energy is always lost to the environment as waste heat. As energy is dispersed to the environment, there will always be a reduction in the amount of energy passed on to the next trophic level.

Transfer

Matter and energy move through system. If the movement does not involve a change of form or state, it is transfer. Transfer normally flow through a system and involve a change in location, for example, water-flow from surface water to groundwater storage in the water cycle.

Negative feedback

Negative feedback mechanisms work by reducing the effect of one of the system's components. This is a self-regulating method of control leading to the maintenance of a steady-state equilibrium.

Isolated System

Neither energy nor matter is exchanged across the boundary of the system. These systems do not exist naturally, although it is possible to think of the entire universe as an isolated system.

Equilibrium

Open system tend to have a state of balance among the components of a system - they are in a state of equilibrium. Equilibrium avoids sudden changes in a system, though this does not mean that all systems are non-changing. If changes exists it tends to exist between limits.

Positive feedback

Positive feedback occurs when a change in the state of a system leads to additional and increase change. Thus, an increase in the size of one or more of the system's output feeds back into the system and results in self-sustained change that alters the state of a system away from its original equilibrium towards instability.

Unstable equilibrium

Systems that do not return to the same equilibrium but form a new equilibrium are describe as unstable. Scientists believe that the Earth's climate may reach a new equilibrium following the effects of global warming, with conditions on the planet dramatically altered.

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 as a whole remains in a more or less constant state (for example, a climax ecosystem).

Transformation

Transformations either lead to an interaction within a system in the formation of a new end product, or they involve a change of state. Using water as the example, run-off is a transfer process and evaporation is a transformation process.

Stable equilibrium

if a system returns to the original equilibrium after a disturbance, it is said to be stable equilibrium.

Static equilibrium

there are no inputs or outputs of matter of energy and no change in the system over time. For example, inanimate subject such as tables and chairs are in static equilibrium. No natural systems are in static equilibrium because all have inputs and outputs of energy and matter.