1) A system is a collection of organized elements that transform energy and exchange both energy and matter with its environment. 2) There are three types of systems - isolated (exchanges neither energy nor matter), closed (exchanges only energy), and open (exchanges both energy and matter). 3) Feedback mechanisms in systems can be positive, amplifying changes from equilibrium, or negative, counteracting changes to maintain stability.

1. Systems and
Models
What is a system? What is a model?
Feedback Mechanisms
Transfer vs. Transform
Laws of Thermodynamics

2. Systems
• 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.

3. A Natural System - Ecosytem

4. • An ecosystem is a system whose organized and integrated
elements (parts) transform (change) energy which is used
in the transformation process and recycling of matter in an
attempt to preserve its structure and guarantee the survival
of all its biotic and abiotic characteristics.
• Although we tend to isolate systems by deleting/merging
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.
• Question: How does this hold true for the universe?

5. Types of Systems
There are three types of systems based on
whether they exchange energy and/or matter:
Isolated System
System
It exchanges neither energy nor matter

6. Closed System
Energy System Energy
It only exchanges energy.

7. Open System
Energy Energy
System
Matter Matter
It exchanges both energy and matter.

8. Equilibria
• The steady state is a common property of most open systems in
nature whereby the system state fluctuates around a certain point
without much change of its fundamental identity.
• Static equilibrium = no change at all.
• Dynamic equilibrium = 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”.

9. 6
5
4
State of the System
3
static
equilibrium
2 Dynamic
Equilibriu,
1 Steady State
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Time

10. Feedback Mechanisms (+/-)
The reaction of particular component elements
of the systems againts disturbing agents is
consider a feedback mechanism.
Two Types of Feedback Mechanisms:
Positive and Negative

11. 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.

12. 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.
– 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.

13. Transfer vs. Transformations
• 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.

16. • 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.

18. Laws of Thermodynamics
Two laws:
1st -

19. Models
• A model is an artificial construction designed
to represent the properties, behavior or
relationships between individual parts of the
whole being studied or the order in which 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 understand
complexities large and small.

20. Limitations of Models
• 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.
– Models are proposed representations of how a system is structured, which can
be rejected in light of contradictory evidence. (hypothesis)
• No model is a 'perfect' representation of the system because, as mentioned
above, all models are simplifications and in some cases over simplified.
– 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.