IBESS - Topic 1 Review: Chapter 4
Topic 1: Systems and Models (5 hours)
Obj.
1.1.1
Assessment Statement
Outline the concept and characteristics of systems.
1.1.2
Apply the systems concept on a range of scales.
1.1.3
Define the terms open system, closed system and isolated
system.
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
1.1.6
Define and explain the principles of positive feedback and
negative feedback.
10 Review Points
Notes
The emphasis will be on ecosystems but some mention should
be made of economic, social and value systems.
The range must include a small-scale local ecosystem, a large
ecosystem such as a biome, and Gaia as an example of a global
ecosystem.
These terms should be applied when characterizing real
systems.
• An open system exchanges matter and energy with its
surroundings (for 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).
The first law concerns the conservation of energy.
The second law explains the dissipation of 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 into a dispersed form (the
availability of energy to do work diminishes) and the system
becomes increasingly disordered.
Both laws should be examined in relation to the energy
transformations and maintenance of order in living systems.
A steady-state equilibrium should be understood as the common
property of most open systems in nature. A static equilibrium, in
which there is no change, should be appreciated as a condition
to which natural systems can be compared. (Since there is
disagreement in the literature regarding the definition of
dynamic equilibrium, this term should be avoided.) Students
should appreciate, however, that some systems may undergo
long‑term changes to their equilibrium while retaining an
integrity to the system (for example, succession). The relative
stability of an equilibrium—the tendency of the system to return
to that original equilibrium following disturbance, rather than
adopting a new one— should also be understood.
The self-regulation of natural systems is achieved by the
attainment of equilibrium through feedback systems.
• Negative feedback is a self-regulating method of control
leading to the maintenance of a steady-state equilibrium—it
counteracts deviation, for example, predator–prey relationships.
• Positive feedback leads to increasing change in a system—it
accelerates deviation, for example, the exponential phase of
population growth.
1.1.7
Describe transfer and transformation processes.
Feedback links involve time lags.
Transfers normally flow through a system and involve a change
in location.
Transformations lead to an interaction within a system in the
formation of a new end product, or involve a change of state.
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.
Distinguish between flows (inputs and outputs) and storages
(stock) in relation to systems.
Construct and analyse quantitative models involving flows and
storages in a system.
Evaluate the strengths and limitations of models.
1.1.8
1.1.9
1.1.10
Identify flows through systems and describe their direction and
magnitude.
Storages, yields and outputs should be included in the form of
clearly constructed diagrammatic and graphical models.
A model is a simplified description designed to show the
structure or workings of an object, system or concept. In
practice, some models require approximation techniques to be
used. For example, predictive models of climate change may
give very different results. In contrast, an aquarium may be a
relatively simple ecosystem but demonstrates many ecological
concepts.
Multiple Choice (1/4 point each)
1. A system may best be defined as
A. a set of components that function predictably.
B. an assemblage of parts and their relationships forming a whole.
C. a set of components that function unpredictably.
D. an assemblage of functioning parts without inputs or outputs.
2.
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
3.
What do outputs from an open system consist of?
A. Energy only
B. Matter only
C. Energy and matter
D. Neither energy nor matter
4.
Which system represents a herd of elephants living on the African grassland?
A. An open system
B. A closed system
C. An isolated system
D. An autotrophic system
5.
A desert with very low precipitation and little vegetation is an example of which type of system?
A. Open
B. Closed
C. Isolated
D. Closed and isolated
6.
What does the first law of thermodynamics tell us?
A. Doing work always creates heat.
B. Entropy tends to increase.
C. Energy cannot be recycled.
D. All energy comes from other energy.
7.
Over a long period of time, energy input to a system is
A. always equal to energy output.
B. usually greater than energy output.
C. always greater than energy output.
D. always less than energy output.
8.
Which statement best illustrates the second law of thermodynamics?
A.
Potential energy increases as energy moves through a system.
B.
The amount of energy is unchanged as matter moves through a system.
C.
Potential energy decreases as energy and matter move through a system.
D.
Energy cannot leave a system.
9.
Consider these statements concerning the flow of energy through ecosystems:
Statement 1:
Statement 2:
The amount of energy that is available to living things decreases as it is transformed
and passed along food chains.
As energy is transformed along food chains, no energy is destroyed.
Which is a correct evaluation of these statements?
Choice
A
B
C
D
Statement 1
Demonstrates the first law of
thermodynamics
Is unrelated to the laws of
thermodynamics
Demonstrates the second law of
thermodynamics
Demonstrates the second law of
thermodynamics
Statement 2
Demonstrates the second law of
thermodynamics
Demonstrates the second law of
thermodynamics
Demonstrates the first law of
thermodynamics
Is unrelated to the laws of
thermodynamics
10. As disease spreads through a population, numbers fall. As the result of a reduction in contact
between individuals, the rate of spread of the disease is reduced. This is followed by a recovery in
numbers. This is an example of
A. positive feedback
B. negative feedback
C. demographic transition
D. entropy
11. Which row correctly gives examples of transfer and transformation processes?
Transfer
Transformation
A.
Decomposition
Organic matter entering the ocean
B.
Evaporation
Decomposition
C.
Evaporation
Organic matter entering the ocean
D.
Organic matter entering the ocean
Evaporation
12. 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
Paper 1 Response Practice (7 points total)
13. A) Define the term feedback.
the return of part of an output of a system (or subsystem) as an input, so as to
affect succeeding outputs/OWTTE;
(1)
B) Explain, with the help of an example, the term negative feedback in relation to an ecosystem.
Answers must have a definition, some explanation of negative feedback and an example
(which need not be as detailed as that below) to achieve full marks.
negative feedback:
feedback that tends to damp down, neutralize or counteract any
deviation from an equilibrium and promotes stability/OWTTE;
example:
increase in number of predators (e.g. owls) → decrease in small
mammals (e.g. mice, voles, shrews) → increase in small
mammals → increase in predators;
explanation:
understanding of ecological relationships/processes;
For the final mark the answer must show some understanding of
ecological relationships or processes, such as predation, disease,
breeding success. This material may be incorporated in the
example. Some or all of the information may be given in the
form of a diagram.
14. A)
3 max
A tree can be thought of as a system. Draw and label a systems diagram of a tree that shows
inputs, outputs and storages of matter and energy.
(a)
Heat
Heat
Light
H2O
CO 2
O2
Tissue to other
trophic levels
TREE
Litter to soil
Nutrients
Water
3 max
Award [1] for tree in box, [1] for two matter flows and [1] for two
energy flows.
(3)
Long Response Practice (NO POINTS AWARDED!!!!)
15. The Gaia Hypothesis proposes that our planet functions as a single organism that maintains
conditions necessary for its survival by feedback mechanisms. It was formulated by James Lovelock
in the mid-1960s. In his recent book The revenge of Gaia, he suggests that we have passed the
“tipping point” on global warming and that feedback mechanisms will speed up the rate of global
warming.
(a)
State what type of system the Earth is and what the inputs and outputs are
(3)
Earth is a closed system;
inputs – solar radiation/Sun’s energy/light and output – heat energy;
materials recycled within the system/matter recycled (may discuss
space ships and meteorites moving a small amount of matter in and out);
(b)
Using positive and negative feedback models explain the process of climate change.
climate change is a significant shift in climatic conditions;
may be warming or cooling;
positive feedback allows for movement away from equilibrium and
decreases stability;
negative feedback dampens down deviation from equilibrium
and increases stability;
example model:
ice caps melting leads to reducing albedo/more dark sea to
absorb heat/temperature increase leading to more ice cap melting
thus positive feedback;
ice caps melting leads to more evaporation more clouds/albedo
effect of clouds stop energy reaching Earth’s surface/decrease
warming thus negative feedback;
in short term, positive feedback model appears to operate e.g.
temperature change over industrial period/in the long-term, negative
feedback appears to operate e.g. glacial cycles;
(7)
(c)
Scientists use computer simulations to model the effects of changes in the temperature of the
Earth. Discuss the advantages and disadvantages of this modelling.
advantages: [2 max]
allows us to predict;
simplifies complex systems;
can change inputs and see what happens;
can show them to others;
Accept any other reasonable suggestions.
disadvantages: [2 max]
not accurate;
rely on the expertise of the people making them;
on validity of input data;
different people interpret them differently;
can be hijacked politically;
Accept any other reasonable suggestions.
4 max
(4)
(d)
Describe your personal viewpoint on the global warming issue and justify your position based
on the evidence.
Responses to this question will depend on the candidate’s own
personal viewpoint but examples could be:
example 1:
stating viewpoint: [1 max]
global warming is the biggest threat to life on Earth ever and we
are heading for catastrophe;
evidence: [3 max]
evidence for heating of the Earth is overwhelming;
evidence from increasing greenhouse gases caused by human activities;
ice caps retreating;
glaciers retreating;
sea levels rising;
more floods;
hurricanes increase in severity;
example 2:
stating viewpoint: [1 max]
global warming may be occurring but has throughout the life of
the Earth and will bring benefits to many people;
evidence: [3 max]
shift of biomass towards the poles will mean
crops can grow where they could not before;
more rainfall in some areas is a good thing;
if the Arctic ice melts, we can mine for minerals and oil under
the Arctic Sea;
large areas of Siberia and Canada will be warmer and easier to
live in;
4 max
Award up to [3 max] for any three pieces of evidence. Accept
any other reasonable suggestions.
(4)
Expression of ideas (2)
(Total 20 marks)