TOPIC 1
Systems and Models
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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 Link: Does this hold true for the Universe?
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Boundary
Relationships
System B
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
It exchanges neither energy nor matter
Do isolated systems exist?
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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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Understanding of 1st & 2nd laws of
thermodynamics
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1.1.4 Laws of
Thermodynamics
 1st Law of Thermodynamics
conservation of energy and states that
“energy can not be created nor destroyed but it is transformed from one
form into another”.
 The first law is concerned with the
 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.
* In any process where work is done, there has been an energy transformation.
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First Law of Thermodynamics
ENERGY 2
ENERGY 1
PROCESS
(WORK)
ENERGY 3
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Photosynthesis: an example of the First Law of
Thermodynamics: Energy Transformation
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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. To keep order,
organization and functionality, living
organisms must used energy and
transform energy.
 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
(sugar)
100 J
100 J
Chemical Energy
(petrol)
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
Heat
900 J
Energy 1
1000 J
Heat
90 J
Process 1
100 J
Process 2
10 J
Heat
9J
Process 3
1J
J = Joule SI Unit of Energy
1kJ = 1 Kilo Joule = 1000 Joules
For most ecological process, theamount of energy that is
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passed from one trophic level to the next is on average 10%.
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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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Systems
1. Which row contains correct statements about exchanges between
open and closed systems and their surroundings?
Open system
A. Exchanges matter but not energy
B. Exchanges matter but not energy
C. Exchanges energy but not matter
D. Exchanges matter and energy
Closed system
Exchanges neither matter nor energy
Exchanges energy but not matter
Exchanges neither matter nor energy
Exchanges energy but not matter
Thermodynamics
2. “The change in a system’s internal energy is equal to the energy
absorbed by the system minus the energy released into its surroundings.”
This statement best illustrates
A. the law of conservation of mass.
B. the first law of thermodynamics.
C. the second law of thermodynamics.
D. the third law of thermodynamics.
Negative Feedback
3. Which is an example of negative feedback?
A. An increase in air temperature increases the rate of melting of the Earth’s ice
caps, thus decreasing the reflection of solar radiation.
B. An increase in a herbivore population, leading to overgrazing and thus to a
decline in the herbivore population.
C. An increase in human birth rate compared with death rate leading to
exponential increase in the human population.
D. A loss of vegetation leads to soil erosion and thus further loss of vegetation
occurs.
Transfer Process
4. Which of the following is a transfer process / are transfer processes?
I. Deposition of sand by waves on beaches
II. Organic matter entering the ocean
III. Decomposition of organic matter at the bottom of a lake
IV. Run-off of water from land to rivers
A. I and IV only
B. III only
C. I, II and IV only
D. I, II, III and IV
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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Consumers and the
2nd law of Thermodynamics
Respiration
2000 kJ.day-1
10% for growth
2850 kJ.day-1
Food Intake
How efficient is the cow
in the use of the food it
takes daily?
565
kJ.day-1
Urine and
Faeces
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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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500
10,000
1000
0.75
100
15
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11.25
Sealevel Changes
The graph below shows changes in the sea level on
the island of Oahu in the Hawaiian Islands, Pacific
Ocean, over the last century. Zero represents the
mean sea level in 1950.
(a) Describe and discuss possible explanations for the shape of the
curve in the graph.
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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
Number of individuals
Population Growth - Logistic Model
nature whereby the system state fluctates
around a certain point
without much change of its fundamental
identity.
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 Static equilibrium means no change at all.
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 Dynamic equilibrium means a continuous move from one point
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to another with the same magnitude,
so no net change really
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happens.
 Living systems (e.g. the human body,
a plant, a population of
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termites, a community of plants, animals and decomposers in the
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Tropical Rainforest) neither remain static nor undergo harmonic
fluctuations, instead living systems 0fluctuate almost unpredictably
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but always around a mid value which0 is called 5the
“steady
state”.
Time / month
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Nt1(actual)
Nt1(sim)
Nt2(sim)
Nt3(sim)
N4(sim)
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 “superorganisms” 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 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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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.
Population of
Lynx
-
-
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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. 49
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 & 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.
Plants
Ocean Food Webs - Bottom Up vs Top Down.flv
Food Web Bottom-Up Top-Down & Middle
Control Worksheet.doc
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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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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