TOPIC 1
SYSTEMS AND MODELS
(5 Hours)
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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.
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• TOK Link: Does this hold true for the Universe?
System B
Boundary
Relationships
E3
E1
Systems A
E2
Elements
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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
System
It exchanges neither energy nor matter
Do isolated systems exist? If not, why then we have
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thought about them?
1.1.2 Types of systems (2)
Closed System
Energy
System
Energy
It only exchanges energy.
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1.1.2 Types of systems (3)
Open System
Energy
Energy
System
Matter
Matter
It exchanges both energy and matter.
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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.
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First Law of Thermodynamics
ENERGY 2
ENERGY 1
PROCESS
(WORK)
ENERGY 3
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Photosynthesis and the First Law of
Thermodynamics
Heat Energy
Light Energy
Photosynthesis
Chemical Energy
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• 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.
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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?
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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.
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Combustion & Cell Respiration: two examples that
illustrate the 1st and the 2nd laws of Thermodynamics
Chemical Energy
Chemical Energy
(petrol)
(sugar)
100 J
100 J
ATP
PROCESS
Combustion
20 J
PROCESS
Cell Respiration
40 J
Heat Energy
60 J
Heat Energy
80 J
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The Second Law of Thermodynamics
in numbers: The 10% Law
For most ecological process, theamount of energy that is passed from one
trophic level to the next is on average 10%.
Heat
900 J
Energy 1
1000 J
Heat
90 J
Process 1
100 J
Heat
9J
Process 2
10 J
Process 3
1J
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]
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
(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)
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How efficient is the cow
Consumers and the
2nd law of Thermodynamics in the use of the food it
takes daily?
Respiration
2000 kJ.day-1
10% for growth
2850 kJ.day-1
Food Intake
565
kJ.day-1
Urine and
Faeces
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The Ecosystem and the 2nd
law of Thermodynamics
What determines
that some ecosystems
are more efficient
than others?
Heat
Heat
Heat
Heat
Heat
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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 State
•
•
•
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”.
Population Growth - Logistic Model
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Number of individuals
•
1000
800
600
400
200
0
0
5
10
15
Time / month
Nt1(actual)
Nt1(sim)
Nt2(sim)
Nt3(sim)
N4(sim)
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Static Equilibrium
Dynamic Equilibrium
Steady State
TIME
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1.1.6 Positive and Negative
Feedback 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! 36
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.
Sun
Atmosphere
Water Vapour
+
+
Global
Evaporation
+
Heat
Energy
Warming
+
Oceans
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Population of
Lynx
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.
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-
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Population of
Hare
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. 38
Negative feedback: an example of
population control
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Positive & Negative Feedback
Population 1
+
+
+
-
Climate
Food
-
Population 2
+
-
Population 3
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Positive & Negative Feedback
Positive feedback
Food
Population
Negative feedback
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Negative or Positive ?
Climate
Disease
Food
P1
P2
P3
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Bottom-Up & TopDown 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
Plants
Nutrient pool of the Soil
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State of the Ecosystem
Positive and Negative Feedback
?
+
-
-
+
S2
S1
Time
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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.
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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.
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• http://bcs.whfreeman.com/thelifewire/content/chp58/5802004.html
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IB Question
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A simple model
of an aquarium
CO2
O2
CO2
O2
CO2
O2
Heat
Air
Primary Producers
Herbivorous animals
Aq Plant 1
Aq Plant 2
Carnivorous
animal
Snail
Light
Algae
Flea
Phytoplankton
Heat
NO3
CO2
NO3
O2
DOM
Water
Decomposers
Mud
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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
• http://bcs.whfreeman.com/thelifewire/content/chp58/5802001.html
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What can you identify in a
plant?
• Transfer:
• Transformation
• Flows
• Storage:
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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.
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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:
The Steady State condition:
 inputs   outputs
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IB Question
ES-Practice-Model Making Pastoral System in Angola.pdf
MODEL MAKING PASTORAL SYSTEM IN ANGOLA.ppt
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Models can be used to make predictions
The following model tries to explain the ecological behaviour of a human communities.
MODELLING SYSTEMS Handout.doc
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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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