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TOPIC 1. SYSTEMS AND MODELS (5 Hours). IB Material Calculations TOK Link ICT Link. 1.1.1 Concept and characteristics of a system.

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topic 1



(5 Hours)

1 1 1 concept and characteristics of a system
1.1.1 Concept and characteristics of a system
  • 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 boundarywhich necessarilytransforms energyfor its own functioning.
  • An ecosystem is a dynamic unit whose organised and integrated elements transform energy which is used in the transformation and recycling of matter in an attempt to preserve its structure and guarantee the survival of all its component elements.
  • Although we tend to isolate systems by delimiting 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.
  • TOK Link: Does this hold true for the Universe?

System B



E 3

E 1

E 2

System C

Systems A


1 1 2 types of systems 1
1.1.2 Types of systems (1)

There are three types of systems based on

whether they exchange energy and/or matter:

Isolated System


It exchanges neither energy nor matter

Do isolated systems exist? If not, why then we have thought about them?

1 1 2 types of systems 2
1.1.2 Types of systems (2)

Closed System


It only exchanges energy.

1 1 2 types of systems 3
1.1.2 Types of systems (3)

Open System

Energy Energy


Matter Matter

It exchanges both energy and matter.

1 1 4 laws of thermodynamics
1.1.4 Laws of Thermodynamics
  • 1st Law of Thermodynamics
  • The first law is concerned with the conservation of energy and states that “energy can not be created nor destroyed but it is transformed from one form into another”.

* In any process where work is done, there has been an energy transformation.

  • With no energy transformation there is no way to perform any type of work.
  • All systems carry out work, therefore all systems need to transform energy to work and be functional.
first law of thermodynamics
First Law of Thermodynamics





photosynthesis and the first law of thermodynamics
Photosynthesis and the First Law of Thermodynamics

Heat Energy

Light Energy

Chemical Energy


the 2nd law of thermodynamics
The 2nd Law of Thermodynamics
  • The second law explains the dissipation of energy (as heat energy) that is then not available to do work, bringing about disorder.
  • The Second Law is most simply stated as, “in any isolated system entropy tends to increase spontaneously”. This means that energy and materials go from a concentrated to a dispersed form (the capacity to do work diminishes) and the system becomes increasingly disordered.
life and entropy
Life and Entropy

Life, in any of its forms or levels of organization, is the continuous fight against entropy. In order to fight against entropy and keep order, organization and functionality, living organisms must used energy and transform it so as to get the energy form most needed.

Living organisms use energy continuously in order to maintain everything working properly. If something is not working properly, living organisms must make adjustments so as to put things back to normal. This is done by negative feedback mechanism.

What is really life? What do we live for? What is out purpose?





The Second Law of Thermodynamics can also be stated in the following way:

  • In any spontaneous process the energy transformation is not 100 % efficient, part of it is lost (dissipated) as heat which, can not be used to do work (within the system) to fight against entropy.
  • In fact, for most ecosystems, processes are on average only 10% efficient (10% Principle), this means that for every energy passage (transformation) 90% is lost in the form of heat energy, only 10% passes to the next element in the system.
  • Most biological processes are very inefficient in their transformation of energy which is lost as heat.
  • As energy is transformed or passed along longer chains, less and less energy gets to the end. This posts the need of elements at the end of the chain to be every time more efficient since they must operate with a very limited amount of energy.
  • In ecological systems this problem is solved by reducing the number of individuals in higher trophic levels.
combustion cell respiration two examples that illustrate the 1st and the 2nd laws of thermodynamics
Combustion & Cell Respiration: two examples that illustrate the 1st and the 2nd laws of Thermodynamics

Chemical Energy


Chemical Energy


100 J

100 J




20 J


Cell Respiration

40 J

Heat Energy

60 J

Heat Energy

80 J


The Second Law of Thermodynamics in numbers: The 10% LawFor most ecological process, theamount of energy that is passed from one trophic level to the next is on average 10%.

Heat Heat Heat

900 J 90 J 9 J

Energy 1 Process 1 Process 2 Process 3

1000 J 100 J 10 J 1 J

J = Joule SI Unit of Energy

1kJ = 1 Kilo Joule = 1000 Joules

(d) Calculate the percentage (%) of the solar energy received by plants which remain available for herbivores? [2]




(e) Which energy transformation chain is more efficient? Support your answer with relevant calculations. [3]




photosynthesis and the 2 nd law of thermodynamics
Photosynthesis and the 2nd law of Thermodynamics

What is the efficiency of photosynthesis?

consumers and the 2 nd law of thermodynamics



10% for growth


Urine and Faeces


Food Intake

How efficient is the cow

in the use of the food it

takes daily?

Consumers and the 2nd law of Thermodynamics
the ecosystem and the 2 nd law of thermodynamics






What determines that some ecosystems are more efficient than others?

The Ecosystem and the 2nd law of Thermodynamics
1 1 5 the steady state
1.1.5 TheSteadyState
  • The steady state is a common property of most open systems in nature whereby the system state fluctates around a certain point without much change of its fundamental identity.
  • Static equilibrium means no change at all.
  • Dynamic equilibrium means 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”.


Static Equilibrium

Dynamic Equilibrium

Steady State


1 1 6 positive and negative feedback mechanisms
1.1.6 Positive and NegativeFeedbackMechanisms

Natural systems should be understood as “super-organisms” whose component elements react against disturbing agents in order to preserve the steady state that guarantees the integrity of the whole system.

The reaction of particular component elements of the systems againts disturbing agents is consider a feedback mechanism.

Feedback links involve time lags since responses in ecosystems are not immediate!

positive feedback
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.


Water Vapour











negative feedback

Population of


Negative Feedback




  • Negativefeedbackis a self-regulatingmethod of control leadingtothemaintenance of a steadystateequilibrium.
  • Negativefeedbackcounteractsdeviationsfromthesteadystateequilibriumpoint.
  • Negativefeedbacktendstodampdown, neutraliseorcounteractanydeviationfromanequilibrium, and promotesstability.

Population of


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.

positive negative feedback
Positive & Negative Feedback

Population 1


Climate Food Population 2


Population 3






positive negative feedback1
Positive & Negative Feedback

Food Population

Positive feedback

Negative feedback

negative or positive
Negative or Positive ?




P1 P 2 P3

bottom up top down control
Bottom-Up & Top-Down Control

In reality, ecosystems are controlled all the time by the combined action of Bottom-Up and Top-Down mechanisms of regulation.

In Bottom-Up regulation the availability of soil nutrients regulate what happens upwards in the food web.

In Top-Down regulation the population size (number of individuals) of the top carnivores determines the size of the other populations down the food web in an alternating way.


Ocean Food Webs - Bottom Up vs Top Down.flv

Food Web Bottom-Up Top-Down & Middle Control Worksheet.doc

Nutrient pool of the Soil

positive and negative feedback
Positive and Negative Feedback




State of the Ecosystem






1 1 7 transfer and transformation processes
1.1.7 Transfer and Transformation Processes
  • 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.
1 1 8 flows and storages
1.1.8 Flows and Storages
  • Flows are the inputs and outputs that come in and out between component elements in a system. This inputs and outputs can be of energy or quantities of specific substances (e.g. CO2 or H2O).
  • Storages or stocks are the quantities that remain in the system or in any of its component elements called reservoirs.
  • For example, in the Nitrogen Cycle, the soil stores nitrates (stock) (NO3-) however some nitrates are taken away as such by run-off water and absorbed by plant roots (output flows) but at the same time rainfall brings about nitrates, human fertilization and the transformation of ammonia (NH3) in to nitrates maintain the nitrate stock in soil constant under ideal conditions.


A simple model

of an aquarium









Primary Producers

Herbivorous animals

Aq Plant 1

Aq Plant 2

















transfer transformation flows and storages1
Transfer, transformation, flows and storages
What can you identify in a


  • Transfer:
  • Transformation
  • Flows
  • Storage:
1 1 9 quantitative models
1.1.9 Quantitative Models
  • A model is an artificial construction designed to represent the properties, behaviour or relationships between individual parts of the real entity being studied y order to study it under controlled conditions and to make predictions about its functioning when one or more elements and /or conditions are changed.
  • A model is a representation of a part of the real world which helps us in ex situ studies.
  • For example, the Carbon Cycle on the next slide is a quantitative model showing how carbon flows from one compartment to another in our planet. The width of the arrows are associated to the amount of carbon that is flowing. Figures next or on top of arrows indicate the amount of carbon in the flow. Similarly, figures inside boxes of compartments show the stocks or storages of carbon in each compartment.
a quantitative model the carbon cycle
A quantitative model(The Carbon Cycle)
a simplified model on how the ecosystem works
A simplified model on how the ecosystem works
  • For an entire ecosystem to be in steady state, or for one of its components to be in steady state, the following must be achieved:

The Steady State condition:


ES-Practice-Model Making Pastoral System in Angola.pdf

IB Question


models can be used to make predictions
Models can be used to make predictions

The following model tries to explain the ecological behaviour of a human communities.


1 10 strengths and limitations of models
1.10 Strengths and Limitations of Models
  • A model is a representation of part or the totality of a reality made by human beings with the hope that models can help us (i) represent the structural complexity of the reality in a simpler way eliminating unnecessary elements that create confusions, (ii) understand processes which are difficult to work out with the complexity of the real world, (iii) assess multiple interaction individually and as a whole (iv) predict the behaviour of a system within the limitations imposed by the simplification accepted as necessary for the sake of the understanding.
  • 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. By adding components to a model one by one, we develop an ability to consider the whole system together, not just one interaction at a time. Models are hypotheses. They are proposed representations of how a system is structured, which can be rejected in light of contradictory evidence.
  • No model is a \'perfect\' representation of the system because, as mentioned above, all models are simplifications and in some cases needed over simplifications. Moreover, 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.