TOPIC 1TOPIC 1SYSTEMS AND MODELSSYSTEMS AND MODELS

(5 Hours)(5 Hours)

HIRAM BINGHAMHIRAM BINGHAMThe British International School of LimaThe British International School of Lima

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IB Material Calculations TOK Link ICT Link

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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 boundary which necessarily transforms energy for 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 LinkTOK Link:: Does this hold true for the Universe? Does this hold true for the Universe?

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E 1E 1

E 2E 2

E 3E 3

Boundary

Elements

Relationships

Systems ASystems A

System BSystem B

Sys

tem

CS

yste

m C

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A natural system = Ecosystem

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1.1.2 Types of systems (1)

There are three types of systems based on

whether they exchange energy and/or matter:

Isolated System

SystemSystem

It exchanges neither energy nor matterIt exchanges neither energy nor matter

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

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1.1.2 Types of systems (2)

Closed System

EnergyEnergy SystemSystem EnergyEnergy

It only exchanges energy.It only exchanges energy.

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1.1.2 Types of systems (3)

Open System

Energy EnergyEnergy Energy

SystemSystem

Matter MatterMatter Matter

It exchanges both energy and matter.It exchanges both energy and matter.

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1.1.4 Laws of Thermodynamics

• 11stst Law of Law of ThermodynamicsThermodynamics

• The first law is concerned with the conservation of energyconservation 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.

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First Law of ThermodynamicsFirst Law of Thermodynamics

ENERGY 2

PROCESS

ENERGY 1 (WORK)

ENERGY 3

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Photosynthesis:Photosynthesis: an example of the First Law of an example of the First Law of Thermodynamics: Thermodynamics: Energy TransformationEnergy Transformation

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PhotosynthesisPhotosynthesis and the First Law of and the First Law of ThermodynamicsThermodynamics

Heat Energy

Light Energy

Chemical Energy

Photosynthesis

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• The 2nd Law of The 2nd Law of ThermodynamicsThermodynamics

• 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.

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Life and EntropyLife 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?

Entrop

yLifeEn

ergy

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• 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.

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

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Combustion & Cell Respiration: two examples that illustrate the 1st and the 2nd laws of Thermodynamics

Heat EnergyHeat Energy

Heat EnergyHeat Energy

ATPATP

Chemical Energy(petrol)

Chemical Energy(sugar)

PROCESSCombustion

20 J

PROCESSCell Respiration

40 J

100 J100 J

80 J

60 J

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

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

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

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Photosynthesis and the 2nd law of Thermodynamics

What is the efficiency of photosynthesis?

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Primary Producers and the 2nd law of Thermodynamics

(Output)(Output)

(Output)(Output)

(Output)(Output)

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Consumers and the 2nd law of Thermodynamics

10% for growth

2850 kJ.day-1

Food Intake

Respiration2000 kJ.day-1

565 kJ.day-1

Urine and Faeces

How efficient is the cowin the use of the food it takes daily?

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The Ecosystem and the 2nd law of Thermodynamics

Heat

Heat

Heat

Heat

Heat

What determines that some ecosystems are more efficient than others?

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IB Question

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IB Question

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IB Question

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IB Question

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1.1.5 The Steady State1.1.5 The Steady State• The steady statesteady 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”.

Population Growth - Logistic Model

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1000

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0 5 10 15Time / month

Num

ber o

f ind

ividu

als

Nt1(actual) Nt1(sim) Nt2(sim) Nt3(sim) N4(sim)38

ST

AT

E O

F T

HE

S

YS

TE

M

TIME

Static Equilibrium

Dynamic Equilibrium

Steady State

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1.1.6 Positive and Negative 1.1.6 Positive and Negative Feedback MechanismsFeedback Mechanisms

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!

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Positive Feedback• Positive feedbackPositive feedback leads to

increasing change in a system. • Positive feedbackPositive 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.

AtmosphereAtmosphere

OceansOceans

SunSun

Water Vapour

++

++

++

++

Global

Warming

Heat Heat EnergyEnergy

EvaporationEvaporation

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Negative Feedback

• Negative feedbackNegative feedback is a self-regulating method of control leading to the maintenance of a steady state equilibrium.

• Negative feedbackNegative feedback counteracts deviations from the steady state equilibrium point.

• Negative feedbackNegative feedback tends to damp down, neutralise or counteract any deviation from an equilibrium, and promotes stability.

Population ofHare

Population ofLynx

++ --

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.

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Negative feedback: an example of population control

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Positive & Negative Feedback

Population 1

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Climate Food Population 2

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Population 3

+

+ +

-

-

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Positive & Negative Feedback

Food Population

Positive feedbackPositive feedback

Negative feedbackNegative feedback46

Negative or Positive ?

Climate

Disease

Food

P1 P 2 P3

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Bottom-Up & Top-Down ControlIn 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.

Plants

Nutrient pool of the Soil48

Ocean Food Webs - Bottom Up vs Top Down.flvFood Web Bottom-Up Top-Down & Middle Control Worksheet.doc

Positive and Negative FeedbackS

tate

of

the

Eco

syst

em

Time

+

- +

-

S1S2

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?

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1.1.7 Transfer and Transformation Processes1.1.7 Transfer and Transformation Processes• Transfers 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.

• TransformationsTransformations 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.

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1.1.8 Flows and Storages• FlowsFlows are the inputsinputs and outputsoutputs 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).

• StoragesStorages or stocksstocks are the quantities that remain in the system or in any of its component elements called reservoirsreservoirs.

• 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.

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53• http://bcs.whfreeman.com/thelifewire/content/chp58/5802004.html

IB Question

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WaterWater

OO22

COCO22

OO22

COCO22

NONO33

NONO33

LightLight

Aq Plant 1

Aq Plant 2

Phytoplankton

Algae

MudMud

DecomposersDecomposers

AirAir

DOMDOM

COCO22

COCO22

OO22

SnailSnail

FleaFlea

CarnivorousCarnivorousanimalanimal

Herbivorous animalsHerbivorous animalsPrimary ProducersPrimary Producers

HeatHeat

O2

HeatHeat

A simple modelA simple modelof an aquariumof an aquarium

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Transfer, transformation, flows and storages(A qualitative model)

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Transfer, transformation, flows and storages

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Transfer, transformation, flows and storages

59• http://bcs.whfreeman.com/thelifewire/content/chp58/5802001.html

What can you identify in aWhat can you identify in a

plant?plant?

• Transfer:Transfer:

• TransformationTransformation

• FlowsFlows

• Storage:Storage:60

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1.1.9 Quantitative Models

• A modelmodel 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 modelmodel 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.

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A quantitative model(The Carbon Cycle)

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• http://bcs.whfreeman.com/thelifewire/content/chp58/5802002.html

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: outputsinputs

The Steady State condition:The Steady State condition:

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IB Question

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

MODEL MAKING PASTORAL SYSTEM IN ANGOLA.ppt

Models can be used to make predictionsModels can be used to make predictions

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

MODELLING SYSTEMS Handout.doc

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.

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