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.