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Systems and Models. Objective 1.1. The Gaia Hypothesis. In the 1960’s, James Lovelock first suggested the Gaia hypothesis. He proposed that the Earth can be regarded as a single functioning ecosystem. In the 1970’s, Lynn Margulis further develop the hypothesis.

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Systems and Models

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Systems and models

Systems and Models

Objective 1.1

The gaia hypothesis

The Gaia Hypothesis

  • In the 1960’s, James Lovelock first suggested the Gaia hypothesis.

  • He proposed that the Earth can be regarded as a single functioning ecosystem.

  • In the 1970’s, Lynn Margulis further develop the hypothesis.

  • They suggested that all living things and their non-living environments are closely integrated to form one system which is self-regulating and maintains the conditions for life.

Types of systems

Types of systems

Open System

Closed Systems

  • An open system exchanges both matter and energy.

  • Most living systems and all ecosystems are open.

  • They exchange energy, new matter, and waste.

  • Even remote ecosystems in Antarctica and isolated ecosystems are open.

  • A closed system exchanges energy but NOT matter across its boundaries.

  • These systems are extremely rare in nature.

  • Most examples are used in experiments and are artificial.

  • A bottle system is an example.

Isolated systems

Isolated Systems

  • Isolated systems exchange neither matter nor energy with its environment.

  • No such systems exist.

  • Some people do regard the universe as an isolated system.

Self assessment questions

Self-assessment questions

  • Outline the difference between the systems approach and the conventional approach to the study of an ecosystem.

  • Construct a table to compare the exchange of matter and energy in an open, closed, and isolated system.

  • Discussion:

    a. What are the benefits and drawbacks of using the systems approach in other fields like economics and engineering?

    b. Do you think that it is useful to have the concept of an isolated system which does not exchange energy or matter with its surroundings?

Laws of thermodynamics

Laws of Thermodynamics

What is their relevance to environmental systems?

First law of thermodynamics

First law of thermodynamics

  • Energy cannot be created or destroyed but can be converted from one form to another.

  • Energy exists in the form of light, heat, chemical energy, electrical energy, sound, and kinetic energy.

  • Different forms of energy are interconvertible, BUT, in a living system, heat energy cannot be converted to other forms.

Systems and models

  • In an ecosystem, useful energy enters the system in the form of sunlight.

  • This is converted into chemical energy during photosynthesis.

  • This energy builds the bonds used to form biomass.

  • This energy is then passed along the food chain in a series of transfers as organisms eat plant and then are eaten themselves.

  • At each stage, some energy is passed along and transformed to other forms, including heat energy, as organisms respire and use it for other life processes.

Systems and models

  • Energy leaves the system as heat energy because heat cannot be transformed in a living process.

  • In living systems, NO new energy has been created.

  • Although the amount of energy in the system does not change, the amount available reduces as energy is used for life processes (STERNGRR).

  • Energy transfer and transformation are not very efficient in living systems, as only 10% of useable energy is passed from one organism to another.

Second law of thermodynamics

Second law of thermodynamics

  • This law states that in an isolated system entropy tends to increase.

  • Entropy is a measure of the evenness of energy distribution in a system.

  • Energy is used to create order and hold molecules together.

  • This means that if less energy is available, entropy, or disorder, increases.

  • The availability of energy becomes reduced and the system becomes less orderly.



  • Equilibrium is a state of balance which exists between the different parts of any system.

  • Most systems tend to return to their steady, balanced state after any disturbance.

Dynamic or steady state equilibrium

Dynamic or Steady-stateEquilibrium

A stable form of equilibrium which allows a system to return to its steady state after a disturbance.

Static equilibrium

Static Equilibrium

Type of equilibrium in which there are no changes over time because there are no inputs or outputs to the systems.

Stable equilibrium

Stable Equilibrium

In a stable equilibrium, the system tends

to return to the same stable state after

a disturbance.

Unstable equilibrium

Unstable Equilibrium

In an unstable equilibrium, a new

equilibrium is formed after a disturbance.

Postive and negative feedback

Postive and Negative Feedback

Natural systems are able to regulate themselves through feedback systems. Information, which may come from inside or outside the system, starts a reaction which affects the processes within the system. Changes in these processes lead to changes in output, which also affect levels of input. This whole cycle is known as a feedback loop.

Positive feedback

Positive Feedback

  • Positive feedback results in a change in the system which leads to more and greater change. Information enhances the change and destabilizes the system.

  • Positive feedback leads to out of control growth of an organism which can overwhelm an ecosystem.

  • A system affected by positive feedback may reach a tipping point when it is unstable and a new equilibrium may form.

  • Examples: Hyacinth plant, locusts, global warming?

Negative feedback

Negative Feedback

  • Negative feedback works to counteract any deviation from the stable state.

  • Stabilizes a system and allows it to regulate itself.

  • Leads to stability

  • In organisms, negative feedback is vital to homeostasis

  • In ecosystems, negative feedback leads to the control of the relative number of species in food webs.

    • Deep vs. Wolf population

    • Global climate checks and balances?

      The more things change, the more they stay the same

Practice questions

Practice Questions

  • How does the first law of thermodynamics explain how energy moves through an ecosystem?

  • What is meant by ‘entropy’ and how does it relate to a natural system?

  • Outline the difference between a steady-state equilibrium and a static equilibrium.

  • Why does positive feedback lead to increasing change in a system?

  • Currently, the human population is growing at an exponential rate. What are the possible consequences of this example of positive feedback. Could this growth actually be part of a long-term negative feedback loop?

Transfers and transformations

Transfers and transformations



  • If matter and energy pass through a system without changing form, the movement is called a transfer.

  • A trophic level is a group of organisms which are all the same number of energy transfers from a producer in a food chain of food web.

  • Energy flows through an ecosystem as biomass, which is found in the bodies of organisms.



  • Transfer of matter through an ecosystem as one organism eats another.

  • Transfer of energy as wind carries heat energy from one part of the world to another.

  • Transfer of matter as water flows from a river to a sea.



  • A transformation occurs when a flow in a system involves a change of form or state.

  • In ecosystems, energy is transformed from sunlight to chemical energy during photosynthesis.

  • During respiration, chemical energy is transformed in to heat and kinetic energy.

More examples

More examples:

  • Energy to energy - Light energy to electrical energy in a solar panel (photovoltaic cell)

  • Matter to matter - Decomposition of leaf litter into organic materials

  • Matter to energy - Burning coal to produce heat and light

Flows and storages

Flows and Storages

  • Energy and matter and the inputs and outputs which flow through an ecosystem.

  • They are also stored within the system as storages (or stock)

  • Light enters an ecosystem, and it flows from part one part of an ecosystem to another as organisms eat each other.

  • Eventually, matter is recycled through decomposition.

  • In ecosystems, there are storages linked by flows.

  • Carbon and nitrogen are cycled around an ecosystem and pass between storages in different organisms, the atmosphere, and the soil.

Models of flows and storages

Models of flows and storages

  • Proportional sized arrows and boxes are used to indicate flows and storages.

  • The larger the arrow/box, the larger the flow/storage.

  • Arrows becomer wider the larger the flow.





  • Allows complex systems to be simplified

  • Allows predictions to be made about future events

  • Different scenarios can be considered by changing inputs and calculating outcomes

  • Can form the basis of discussion

  • May be oversimplified so that accuracy is lost

  • Depend on the skills and experience of the creators

  • May be interpreted differently by different scientists

  • Different models may predict different outcomes

  • Data may not be accurate and they can be manipulated for political or financial gain

Practice questions1

Practice Questions

  • What is the difference between transfer and transformation in an ecosystem?

  • Give an example of each of the following in an ecosystem: an input, an output, a storage

  • Give three advantages to drawing a model of climate change and suggest three weaknesses.

  • Why do you think that scientists are keen to use models to communicate their ideas to the general public and politicians? What are the merits of presenting information in this way?

Case study

Case Study

  • Read the handout with a partner

  • Construct your models on the paper provided

  • Be colorful and detailed!

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