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

2

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 (we`ll discuss this later).

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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17

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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

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IB Question

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IB Question

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