Topic 1 systems and models

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?

1 4/14/2013 Guru/ESS/System & Models-Chapter

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E 1

E 2

E 3

Boundary

Elements

Relationships

Systems A

System B


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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

thought about them? 4 4/14/2013 Guru/ESS/System & Models-Chapter

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Closed System

Energy System Energy

It only exchanges energy.


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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

PROCESS

ENERGY 1 (WORK)

ENERGY 3


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4/14/2013 Guru/ESS/System & Models-Chapter

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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

Chemical Energy

Photosynthesis


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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. 12 4/14/2013 Guru/ESS/System & Models-Chapter

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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 (we`ll discuss this later).


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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 Energy

Heat Energy

ATP

Chemical Energy

(petrol) Chemical Energy

(sugar)

PROCESS

Combustion

20 J

PROCESS

Cell Respiration

40 J

100 J 100 J

80 J

60 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 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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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

10% for growth

2850 kJ.day-1

Food Intake

Respiration

2000 kJ.day-1

565

kJ.day-1

Urine and

Faeces

How efficient is the cow

in 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


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IB Question


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IB Question


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Education

Topic 1 systems and models