1.3 energy and equilibria
TRANSCRIPT
1.3 Energy and equilibria
Wednesday, May 3, 2023Scott Lucas
Dwight School London, 2015
Assessment statementsSignificant ideas• The laws of thermodynamics govern the flow of
energy in a system and the ability to do work.• Systems can exist in alternative stable states or as
equilibria between which there are tipping points.• Destabilizing positive feedback mechanisms will
drive systems toward these tipping points, whereas stabilizing negative feedback mechanisms will resist such changes.
Assessment statementsKnowledge and understanding [The use of examples in this sub-topic is particularly important so that the abstract concepts have a context in which to be understood.]• The first law of thermodynamics is the principle of conservation of energy,
which states that energy in an isolated system can be transformed but cannot be created or destroyed.
• The principle of conservation of energy can be modelled by the energy transformations along food chains and energy production systems.
• The second law of thermodynamics states that the entropy of a system increases over time. Entropy is a measure of the amount of disorder in a system. An increase in entropy arising from energy transformations reduces the energy available to do work.
• The second law of thermodynamics explains the inefficiency and decrease in available energy along a food chain and energy generation systems.
Assessment statementsKnowledge and understanding• As an open system, an ecosystem will normally exist in a stable equilibrium,
either in a steady-state equilibrium or in one developing over time (for example, succession), and maintained by stabilizing negative feedback loops. [A stable equilibrium is the condition of a system in which there is a tendency for it to return to the previous equilibrium following disturbance.] [A steady-state equilibrium is the condition of an open system in which there are no changes over the longer term, but in which there may be oscillations in the very short term.]
• Negative feedback loops (stabilizing) occur when the output of a process inhibits or reverses the operation of the same process in such a way as to reduce change—it counteracts deviation.
• Positive feedback loops (destabilizing) will tend to amplify changes and drive thesystem toward a tipping point where a new equilibrium is adopted.
Assessment statementsKnowledge and understanding• The resilience of a system, ecological or social, refers to its tendency to avoid
such tipping points and maintain stability. [Emphasis should be placed on the relationships between resilience, stability, equilibria and diversity.]
• Diversity and the size of storages within systems can contribute to their resilience and affect their speed of response to change (time lags)
• Humans can affect the resilience of systems through reducing these storages and diversity.
• The delays involved in feedback loops make it difficult to predict tipping points and add to the complexity of modelling systems. [A tipping point is the minimum amount of change within a system that will destabilize it, causing it to reach a new equilibrium or stable state.] [Examples of human impacts and possible tipping points should be explored.]
Assessment statementsApplications and skills• Explain the implications of the laws of thermodynamics to
ecological systems.• Discuss resilience in a variety of systems.• Evaluate the possible consequences of tipping points.International-mindedness• The use of energy in one part of the globe may lead to a
tipping point or timelag that influences the entire planet’s ecological equilibrium.
Vocabulary• First law of thermodynamics: energy in an isolated system can be transformed but cannot
be created or destroyed• Second law of thermodynamics: energy is transformed through energy transfers which
increases entropy that reduces the energy available to do work• Entropy: a measure of the amount of disorder in a system• Equilibrium: the tendency of a system to return to an original state following a disturbance• Static (stable) equilibrium: no change over time; will adopt a new equilibrium if disturbed –
non-living systems• Steady-state (dynamic) equilibrium: the system as a whole remains more-or-less constant,
even with continuous inputs and outputs of matter and energy• Stable: system returns to the same equilibrium after a disturbance• Unstable: system returns to a new equilibrium after a disturbance• Negative feedback loop: when the output of a process inhibits/reverses the process to
reduce change – it counteracts deviation “stabilizing”• Positive feedback loop: tends to amplify change toward a tipping point where a new
equilibrium is adopted – destabilizing• Resilience: the ability of a system to return to its initial state after a disturbance• Tipping point: the critical point in a situation, process, or system beyond which a significant
and often unstoppable effect or change takes place
SI1.3.1 The laws of thermodynamics govern the flow of energy in a system and the ability to do work• Energy in all systems is subject to the laws of
thermodynamics
U1.3.1 The first law of thermodynamics is a principle of conservation of energy, which states that energy in an isolated system can be transformed but cannot be created or destroyed• Total energy of an isolated system, i.e. the universe,
is constant• The form of energy can change though• Light (sunlight) energy to heat (radiation) energy• Chemical energy (fossil fuels) to electrical energy
U1.3.1 The first law of thermodynamics is a principle of conservation of energy, which states that energy in an isolated system can be transformed but cannot be created or destroyed
U1.3.2 The principle of conservation of energy can be modelled by the energy transformations along food chains and energy production systems
Learn the specific organisms in this example of a food chain
U1.3.3 The second law of thermodynamics states that the entropy of a system increase over time. Entropy is a measure of the amount of disorder in a system. An increase in entropy arising from energy transformations reduces the energy available to do work.• More entropy = less order• Over time the thermal death of the universe will be
reached, energy differences will be evened out until nothing can change• Energy conversions are never 100% efficient• When energy is used to do work, some energy is
always lost as heat
Entropy• High quality energy such as light (via photons) and
chemical energy (via bonds between atoms) can be used to do work = ordered = low entropy• Low-quality energy, heat cannot be used to do work
(or very little) = disordered = high entropy• Over time high-quality energy (low entropy)
degrades to low-quality energy (high entropy) = entropy increases• Ex. light chemical mechanical heat
U1.3.4 The second law of thermodynamics explains the inefficiency and decrease in available energy along a food chain and energy generation systems.
• Energy is lost between each trophic level in a food chain/web• Plants are 1-2% efficient converting insolation (solar
energy) into sugar (chemical energy)• Herbivores assimilate (turn into animal matter) ~10% of
the total energy they consume• The rest is metabolism (respiration), movement, heat, fecal
matter, • Carnivores is ~10% efficient
• Used for respiration, movement, heat• Shed skin/antlers & bones aren’t consumed typically so aren’t
passed from the herbivore trophic level
Calculating efficiency• Efficiency: amount of useful energy/work/output
divided by the amount of energy consumed/input into the process
• * 100%
Summary of second law
S1.3.1 Explain the implications of the laws of thermodynamics to ecological systems• First?• Second?
S1.3.1 Explain the implications of the laws of thermodynamics to ecological systems• First
• Energy is transferred/transformed but not destroyed• Energy is converted from one form to another, eventually
ending up as heat• Second
• Living systems tend to disorder• Energy is required to maintain or increase order• This requires a source of energy, the sun or food, to continue
to remain ordered• Energy transfer is never 100% efficient so some energy is lost
as heat• Energy transfer is about 10% efficient between trophic levels
SI1.3.2 Systems can exist in alternative stable states or as equilibria between which there are tipping points• More complex systems are more likely to be stable
and withstand stress/change better• Ecosystems follow this; more complex ones i.e. more
organisms at each trophic level result in a more stable system, it can withstand stress and change better• Analogy: a road network with one road connecting
two points• If that road gets blocked then you cannot reach your
destination• If there are other roads then you can take another route
SI1.3.2 Systems can exist in alternative stable states or as equilibria between which there are tipping points• Tundra is a simple ecosystem; if something happens
populations can vary widely e.g lemmings• Monocultures; farm only one crop, if disease/pests
attack they destroy the whole crop• Ex. potato blight in Ireland 1845-8
Equilibrium• The tendency of a system to return to an original state
following a disturbance• Equilibriums moderate changes in a system, preventing
sudden drastic changes; keeping change between limits• Can think of systems in terms of
• Activity• Steady-state (dynamic): the system as a whole remains more-or-less
constant, even with continuous inputs and outputs of matter and energy – living systems
• Static (stable): no change over time; will adopt a new equilibrium if disturbed – non-living systems
• Stability• Stable: system returns to the same equilibrium after a disturbance• Unstable: system returns to a new equilbirum after a disturbance
Activity: Steady-state examples• Water tank that fills and empties at the same rate; there is
activity but no change in the overall water level• Economics, stable market even with flows of capital in and
out• Ecology, population size may stay the same even with births
and deaths occurring, no net change• Body temperature, fluctuates but remains around 37 °C;
cold – shiver to warm up, hot – sweat to cool down
Activity: Static examples• A pile of books will remain until knocked over, the
new equilibrium• Buildings remain the same for a long time i.e. don’t
move/change position
StabilityStable
Unstable
Feedback loops• Systems receive information from outside and inside the
system• The system reacts to this information and either stabilizes
(negative feedback) or changes (positive feedback) the system
• Ex. You feel cold (information) so you but a sweater on or turn up the heat (reaction)Ex. You feel hungry (information) so you eat food (reaction) or get hungrier (increasing in information strength)
• Negative: returns to original state by counteracting change• Positive: changes system to new state by
destabilizing/increasing change
U1.3.5 As an open system, an ecosystem, will normally exist in a stable equilibrium, either a steady-state or one developing over time (eg succession), and maintained by stabilizing negative feedback loopsU1.3.6 Negative feedback loops (stabilizing) occur when the output of a process inhibits or reverses the operation of the same process in such a wat to reduce change – it counteracts deviation• Negative feedback loop: when the output of a process
inhibits/reverses the process to reduce change – it counteracts deviation “stabilizing”• Negative feedback prevents change which helps maintain
ecosystem’s steady-state equilibria• Systems are self-regulated by negative feedback
mechanisms• Short term changes may happen but long term the
system is steady-state• Succession is development of an ecosystem’s stability
over time
Negative feedback examples
Negative feedback examples• Body temperature: you are exercising, your body
temperature rises, detectors in you body sense the increase, your body starts to sweat and blood flow to the surface of you skin increases, these help cool you down
Simple predator prey interactions: prey increase, more food for predators; predators increase, eat more prey; prey numbers drop, due to more predators; predator numbers drop due to less prey (food), etc
Predator-prey negative feedback
SI1.3.3 Destabilizing positive feedback mechanisms will drive systems toward these tipping points, whereas stabilizing negative feedback mechanisms will resist such changeU1.3.7 Positive feedback loops (destabilizing) will tend to amplify changes and drive the system toward a tipping point where a new equilibrium is adopted• Positive feedback loop: tends to amplify change
toward a tipping point where a new equilibrium is adopted – destabilizing• Amplifies the system output which leads to further
change• Eventually the deviation from equilibrium is too
much and a new equilibrium is established• A “vicious circle”
Examples of positive feedback
Examples of positive feedback• Body temperature: lost high up on a snowy
mountain, body shivers to warm up, doesn’t work so metabolism slows, you become lethargic and sleepy, move less, body cools more, hypothermia, death; unless you are saved
• Task: Feedback mechanism worksheet
U1.3.8 The resilience of a system, ecological or social, refers to its tendency to avoid such tipping points and maintain stability• Resilience: the ability of a
system to return to its initial state after a disturbance• High resilience = return to
equilibrium• Low resilience = enter a new
state/equilibrium• Resilience is usually good but
can be bad• Ex. antibiotic resistant
bacterial are resilient to antibiotics, good for them, bad for us
U1.3.9 Diversity and the size of storages within systems can contribute to their resilience and affect the speed of response to change (time lags)• Factors affecting ecosystem resilience
• High diversity/complex, more interactions between species = more resilience
• Greater species biodiversity, more likely one species can replace another = more resilience
• Greater genetic diversity within a species, allows different traits = more resilience
• Species with wider ranges = more resilience• Larger ecosystems, less edge effect, more space to move around
= more resilience• Climate; cold slows photosynthesis and growth = less resilience;
hot increases growth (condition dependent) = more resilience• Faster reproductive rate = more resilience
U1.3.10 Humans can affect the resilience of systems through reducing these storages and diversity• Factors affecting ecosystem resilience• Humans: can remove or mitigate the threat ex.
pollution, invasive species, etc = more resilience• Humans: can reduce size of storages by harvesting;
wood, fish, etc• Humans: can reduce diversity by species extinction =
less resilience
S1.3.2 Discuss resilience in a variety of systems
U1.3.11 The delays involved in feedback loops make it difficult to predict tipping points and add to the complexity of modelling systems• Within limits an ecosystem can recover and re-establish its
equilibrium• When the disturbance is too great, the ecosystem reaches a
tipping point• Tipping point: the critical point in a situation, process, or
system beyond which a significant and often unstoppable effect or change takes place (Merriam-Webster)• Past the tipping point the ecosystem cannot re-establish its
equilibrium• Positive feedback pushes the ecosystem to a new equilibrium
where there are significant changes to biodiversity and services it provides
U1.3.11 The delays involved in feedback loops make it difficult to predict tipping points and add to the complexity of modelling systems• Characteristics of a tipping point
• Involves positive feedback that leads to self-perpetuation eg. Deforestation reduces rainfall, increased fire risk, forest dieback• There is a threshold past which a fast shift of ecological
states occurs• The threshold point cannot be precisely predicted• Changes are hard to reverse• Significant lag time between the pressures driving the
change and the appearance of impacts, this creates great difficulties in ecological management (i.e. we can’t see the damage until it is far along)
U1.3.11 The delays involved in feedback loops make it difficult to predict tipping points and add to the complexity of modelling systems• Examples• Eutrophication: nutrients build up, plants flourish,
dissolved oxygen (DO) drops, animals die, bacteria decompose organic matter, reduces DO further• Keystone species extinction: keystone species is required
to maintain equilibrium otherwise an irreversible shift occurs to a new state, elephant in savannah• Coral reef death: ocean acidity rises, coral reef dies and
cannot regrow• Climate change: might be reaching a global tipping point
where our climate ends up to 8 °C warmer due to human activities
S1.3.3 Evaluate the possible consequences of tipping points• If there is a global tipping point consequnces could
include• Not being able to respond quick enough• Inaction or despair
• Precautionary may be best; we don’t know what will happen so we should prevent it from changing as much as possible
Visit ProjectEd for more resources
https://sites.google.com/a/dwightlondon.org/projected/
Works Cited• International Baccalaureate Organization. Diploma
Programme Environmental systems and societies guide. The Hague: IB Publishing Ltd, Feb. 2015. PDF.• Merriam-Webster. Merriam-Webster, n.d. Web. 15 Aug.
2015. <http://www.merriam-webster.com/dictionary/>.• "Modelling with Spreadsheets." BBC News. BBC, n.d.
Web. 13 Aug. 2015. <http://www.bbc.co.uk/schools/gcsebitesize/ict/modelling/0spreadsheetsrev5.shtml>.• Rutherford, Jill. Environmental Systems and Societies.
Oxford: OUP, 2015. Print.