IB ESS Study Guide
Topic 1: Systems and models
Assessment
1.1.1 Outline the
concept and
characteristics of
systems.
1.1.2 Apply the
systems concept on
the range of scales.
Notes
Define system: An assemblage of parts and the relationship between them, which together make a
whole.
 Given a system be able to identify storages (energy or matter), flows (inputs and outputs),
and processes (transfer or transformation of energy or matter)
Include
 a small-scale local ecosystem such as a pond
 a large ecosystem such as a deciduous forest (any biome)
 Gaia as an example of a global ecosystem. (idea that the whole earth is a living organism)
1.1.3 Define the
terms open system,
closed system and
isolated system.
These terms should be applied when characterizing real systems.
• An open system exchanges matter and energy with its surroundings (example, an ecosystem).
• A closed system exchanges energy but not matter; the “Biosphere II” experiment was
an attempt to model this. Strictly, closed systems do not occur naturally on Earth, but all the global
cycles of matter, for example, the water and nitrogen cycles, approximate to closed systems.
• An isolated system exchanges neither matter nor energy. No such systems exist (with the possible
exception of the entire cosmos).
1.1.4 Describe how
the first and second
laws of
thermodynamics are
relevant to
environmental
systems.
1.1.5 Explain the
nature of equilibria.
The First Law: energy is not created or destroyed (Energy is conserved).
1.1.6
Define and explain
the principles of
positive feedback and
negative feedback.
1.1.7
Describe transfer and
transformation
processes.
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The second law explains that as energy is transferred or transformed it becomes less ordered; there
is less energy available to do work (the availability of energy to do work is lost as heat)
(NOTE: disorder in thermal systems is entropy)
Steady-state equilibrium - the common property of most open systems in nature.
Static equilibrium, in which there is no change, is a condition to which natural systems can be
compared.
 Some systems may undergo long-term changes to their equilibrium but retain the integrity
of the system (example, succession).
 Stability is the tendency of the system to return to its original equilibrium following
disturbance, rather than adopting a new one.
The self-regulation of natural systems is achieved by the attainment of equilibrium through
feedback systems.
• Negative feedback (-) reduces change; a self-regulating method of control leading to the
maintenance of a steady-state equilibrium.
 example, predator–prey relationships.
• Positive feedback (+) leads to increasing change in a system—it accelerates deviation
 example, exponential population growth
Transfers flow through a system and involve a change in location (same state)
Transformations usually involve a change of state.
EXAMPLES
 Using water as an example, run-off is a transfer process and evaporation is a
transformation process.
 Dead organic matter entering a lake is an example of a transfer process; decomposition of
this material is a transformation process.
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1.1.8 Distinguish between flows (inputs and outputs) and storages (stock) in relation to systems.
 Identify flows through systems and describe their direction and magnitude.
1.1.9 Construct and analyze quantitative models involving flows and storages in a system.
 Storages, yields and outputs should be included in the form of clearly constructed diagrammatic and graphical
models.
PRACTICE
The diagram below shows storages (in percentage of total water) and flows in the global water cycle. The
rates of flow are given in 10
15
kg yr
–1
.
CLOUDS
0.001 %
Condensation
400
ATMOSPHERIC
WATER VAPOUR
0.001 %
Precipitation
100
Evaporation
64
SURFACE WATER 0.001 %
ICE
2%
GROUND WATER 1 %
(a)
(i)
Precipitation
300
Evaporation
336
Run-off/groundwater flow
OCEAN
97 %
What is the source of energy which drives the water cycle? ........................ .
(1)
(ii)
In which of the processes given in the diagram does this energy enter the cycle?
(1)
(b)
(i)
What percentage of all precipitation falls directly into the oceans?
(1)
(ii)
What percentage of all evaporated water comes from the oceans?
(1)
(c)
(i)
Assuming the cycle is in steady state, what mass of water flows into the oceans through run-off
and groundwater flow per year?
(2)
(ii)
Explain why this figure might increase in the future, as a result of burning fossil fuels.
(3)
(d)
Name a storage of water in the biosphere that is not shown in the diagram, and explain how water is
transferred in and out of this storage.
(3)
(e)
(i)
State briefly one way in which one of the other flows in the diagram might change if
evaporation rates were to increase.
(1)
(ii)
Describe how two changes in the flows shown on the diagram could lead to a fall in global
temperatures and reduce global warming.
(4)
(iii)
Name the type of feedback involved in this reduction in global warming.
(1)
(f)
Identify each of the different processes referred to on the diagram as either transfer or transformation
processes.
(2)
1.1.10 Evaluate the
strengths and
limitations of models.
A model is a simplified description of the structure or workings of an object, system or concept.
Examples:
model of climate change
an aquarium models a simple ecosystem
Strengths of Models
 allow scientists to simplify and communicate complex systems
 allow scientists to make predictions
 inputs can be changed and outcomes examined without having to wait for real events.
 results can be shown to scientists and the public
Limitations of Models
 might not be totally accurate
 rely on the expertise of people making them
 different people may interpret them in different ways
 model may be based on unreliable or incomplete data
 different models may show different effects using the same data
PRACTICE
1. Which of the following factors would prevent the ecosphere being classified as a closed system?
A. The input of solar energy
B. The re-radiation to space of heat energy
C. The arrival of rocks as meteorites from space
D. The unstable state of its equilibrium
2. Leaching of soil nutrients is an example of
A. transfer of materials.
B. transformation of materials.
C. transfer of energy.
D. transformation of energy.
3. Which of the following contributes most effectively to self-regulation within a system?
A. Rapid transfer of materials
B. Inputs of energy being greater than outputs
C. Negative feedback mechanisms
D. Positive feedback mechanisms
E.
4. A lake with a stream flowing into it, but with water lost only by evaporation, is an example of a system which is
A. isolated.
B. stable and closed.
C. unstable and closed.
D. open.
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