01 · How topics are classified and ordered

What this resource is

This framework re-presents the Diploma Programme Environmental Systems and Societies Higher Level course as a single, prerequisite-ordered teaching sequence — not eight syllabus topics plus three HL lenses taught in numerical order. It is built on three convictions: that topics should be taught in the order their dependencies require, that each should be taught to its full depth rather than its minimum, and that the connections between topics should be made explicit so that students see ESS as one connected discipline rather than thirty separate ones.

ESS is unusual among Diploma subjects in that the syllabus already tells you what the connective tissue is. Perspectives, systems and sustainability are not three topics in Chapter 1 — they are the three unifying concepts the whole course is built from. At Higher Level a fourth demand is added on top: students are required to synthesise core content, HL extension material and the HL lenses into a single argument. That is a sequencing problem before it is a teaching problem, and it is what this framework is designed to solve.

Inside this document

01The design principle — how topics are classified and ordered
02The Teaching Spine — the full 30-topic flow, at a glance
03Why the Syntheses Come Last — the prerequisite feeder map
04The Sequence at a Glance — every topic with syllabus code, role and hours
05The 30 Topics in Depth — depth, interconnection and inquiry angle for each
06Time Allocation & Pacing — reconciled to 240 hours, finishing by end of January

The design principle

Every topic is classified by the role it plays in the sequence:

Foundational — self-contained, and a prerequisite for later topics.
Developmental — extends one or more foundations.
Synthesis — teachable at depth only once several strands are mature. Succession and stability, climate intervention, conservation and regeneration, environmental economics and ethics, sustainable harvesting, water quality, food security, energy security and sustainable urban design all sit here, and all are placed late by design.

The synthesis topics are scattered across all eight syllabus topics, yet their feeders cut straight across topic boundaries. Eutrophication and sewage treatment sit in the water chapter but are unteachable without the nitrogen cycle from the ecology chapter. Food security sits in the land chapter but needs trophic efficiency, water access, soil processes and climate impacts simultaneously. Ocean acidification appears in the water chapter and again in the climate chapter and makes sense in neither until the carbon cycle is secure. Fish stock assessment and maximum sustainable yield are population dynamics problems filed three chapters away from population dynamics.

Three further principles govern the order. Climate change is taught early, not sixth. Placed straight after ecology, where the carbon cycle, Milankovitch forcing and feedback mechanisms are still fresh, it becomes a lens available for the whole second half of the course rather than a late arrival that has to be retrofitted onto biodiversity, water, food and energy.

The HL lenses are taught as a block in the middle, not appended at the end. Environmental law, environmental and ecological economics and environmental ethics are analytical instruments, and an instrument delivered in the final weeks can only be applied retrospectively. Taught after the foundation, ecology, climate and biodiversity — which supply the treaties, the valuation problems and the ethical dilemmas the lenses need to work on — they are then available for every remaining topic. Water, land, resources, energy and urban systems are each written here to be analysed through all three.

And the foundation topic is never finished. Perspectives, systems and sustainability are taught first because nothing else makes sense without them, but each subsequent topic names which of the three it is exercising. A student who can draw a systems diagram in week three and cannot draw one for a fishery in week thirty has not learned systems thinking; they have learned a diagram.

02 · The full 30-topic flow, at a glance

IB DEMYSTIFIEDExaminers · Moderators · Mentors

The Teaching Spine

Prerequisite-ordered flow · 30 topics · ESS HL

Teach top to bottom — each phase is a prerequisite for the next. Colour shows each topic’s role; the pill shows the phase’s teaching hours.

PHASE A16 teaching hours

1Perspectives

2Systems

3Sustainability

▼

PHASE B35 teaching hours

4Populations & Niches

5Energy & Productivity

6Nutrient Cycles

7Climate Systems

8Succession

▼

PHASE C23 teaching hours

9Atmospheric Systems

10Climate Drivers

11Mitigation & Intervention

12Ozone Protection

▼

PHASE D26 teaching hours

13Biodiversity & Evolution

14Human Pressures

15Conservation

▼

PHASE E17 teaching hours

16Environmental Law

17Environmental Economics

18Environmental Ethics

▼

PHASE F40 teaching hours

19Water & Oceans

20Water Security

21Sustainable Harvesting

22Water Quality

23Soil Processes

24Food Security

▼

PHASE G33 teaching hours

25Natural Capital

26Energy Security

27Waste Management

28Population Dynamics

29Urban Systems

30Urban Air Quality

Role: Foundational Developmental Synthesis — taught late

Total taught content: 190 h · + 50 h experimental programme = 240 h

The full 30-topic sequence. Teach top to bottom; each phase is a prerequisite for the next.

03 · The prerequisite feeder map

IB DEMYSTIFIEDExaminers · Moderators · Mentors

Why the Syntheses Come Last

How the applied topics build on the foundations

Each synthesis topic (right) can only be taught at depth once its feeders (left) are in place. A gold arrow means ‘is a prerequisite for’.

8. Succession & Stability

2 · Systems — feedback & tipping points4 · Populations — r and K strategies5 · Productivity — GPP:NPP through the sere6 · Nutrient cycles — soil development

➤

8 · Succession & Stability

Placed fifth in the syllabus, but it is the culmination of the ecology topic.

11. Mitigation & Intervention

3 · Sustainability — frameworks & justice6 · Nutrient cycles — carbon stores & fluxes9 · Atmospheric systems — the mechanism10 · Drivers & impacts — thresholds

➤

11 · Mitigation & Intervention

Geoengineering cannot be evaluated before the system it would alter.

15. Conservation & Regeneration

1 · Perspectives — competing value systems8 · Resilience — what makes recovery possible13 · Biodiversity — what is being protected14 · Human pressures — what it is protected from

➤

15 · Conservation & Regeneration

Reserve design is an ecological argument with an ethical premise.

24. Agriculture & Food Security

5 · Productivity — trophic efficiency18 · Environmental ethics — diet & justice20 · Water access — irrigation limits23 · Soil processes — the productive base

➤

24 · Agriculture & Food Security

Four strands converge on one question: can we be fed sustainably?

26. Energy Resources & Security

11 · Mitigation — decarbonisation pathways16 · Environmental law — treaty obligations17 · Environmental economics — externalities25 · Natural capital — income vs capital

➤

26 · Energy Resources & Security

The clearest topic in the course for applying all three HL lenses at once.

How to read this

Right-hand boxes are the five synthesis topics that draw the most strands together.
Left-hand chips are the topics they depend on, including the HL lenses.
A gold arrow means ‘is a prerequisite for’.
Every feeder sits earlier in the spine, so by the time the topic is taught its feeders are done.
The whole argument for the order in one image: sequence by dependency, not by chapter number.

Each synthesis topic can be taught at depth only once its feeders are in place.

04 · Every topic with syllabus code, role and hours

The sequence at a glance

Every topic in teaching order, with its syllabus code, its role and its teaching hours. The suggested Year 1 / Year 2 boundary falls at the end of Phase E and is adjustable.

#	Topic	Syllabus	Role	Hours
Phase A — Foundation: Perspectives, Systems, Sustainability (16 h)
1	Environmental Perspectives and Values	1.1	Foundational	3 h
2	Understanding Environmental Systems	1.2	Foundational	5 h
3	Sustainability and Sustainable Development	1.3	Developmental	8 h
Phase B — How Ecosystems Work (35 h)
4	Organisms, Populations and Ecological Communities	2.1	Foundational	9 h
5	Energy Flow, Biomass and Productivity	2.2	Foundational	9 h
6	Biogeochemical and Nutrient Cycles	2.3	Developmental	6 h
7	Climate Systems and Global Biomes	2.4	Developmental	6 h
8	Ecosystem Succession, Stability and Change	2.5	Synthesis	5 h
Phase C — The Atmosphere and a Changing Climate (23 h)
9	Atmospheric Systems and Processes	6.1	Foundational	5 h
10	Drivers and Impacts of Climate Change	6.2	Developmental	7 h
11	Climate Mitigation, Adaptation and Intervention	6.3	Synthesis	7 h
12	Stratospheric Ozone and Atmospheric Protection	6.4	Developmental	4 h
Phase D — Biodiversity, Evolution and Conservation (26 h)
13	Biodiversity and Evolutionary Processes	3.1	Developmental	9 h
14	Human Pressures on Biodiversity	3.2	Developmental	8 h
15	Conservation, Restoration and Regeneration	3.3	Synthesis	9 h
Phase E — The HL Lenses: Law, Economics and Ethics (17 h)
16	Environmental Law	HL.a	Developmental	5 h
17	Environmental and Ecological Economics	HL.b	Synthesis	7 h
18	Environmental Ethics	HL.c	Synthesis	5 h
Phase F — Water, Soil and Food (40 h)
19	Water Systems and Ocean Processes	4.1	Foundational	7 h
20	Water Access, Use and Security	4.2	Developmental	6 h
21	Aquatic Food Production and Sustainable Harvesting	4.3	Synthesis	7 h
22	Water Pollution and Water Quality	4.4	Synthesis	5 h
23	Soil Systems and Soil Processes	5.1	Foundational	6 h
24	Agriculture, Food Production and Food Security	5.2	Synthesis	9 h
Phase G — Resources, People and Cities (33 h)
25	Natural Capital and Resource Management	7.1	Developmental	6 h
26	Energy Resources and Energy Security	7.2	Synthesis	7 h
27	Solid Waste and Waste Management	7.3	Developmental	5 h
28	Population Dynamics and Environmental Pressure	8.1	Developmental	6 h
29	Urban Systems and Sustainable City Planning	8.2	Synthesis	5 h
30	Urban Air Pollution and Atmospheric Quality	8.3	Synthesis	4 h
	Total taught content			190 h

Scroll the table sideways on narrow screens.

05 · Depth, interconnection and inquiry angle for each

The 30 topics in depth

Each topic carries its teaching depth, its interconnections with other topics, and the practical and inquiry angle through which it prepares a student for the individual investigation and for Papers 1 and 2. HL extension content is taught inside the topic it belongs to rather than appended to it.

Showing all 30 topics in teaching order.

Phase A — Foundation: Perspectives, Systems, Sustainability

The three unifying concepts of the course, taught first because every later topic is an application of them. The order within the phase matters: perspectives first, because a student who has not yet examined their own value system will mistake it for neutrality; then systems, because it supplies the analytical apparatus; then sustainability, the largest topic in the foundation, which depends on both and previews the economics lens to come.

1. Environmental Perspectives and Values

1.1 · Foundational · 3 h

Teach to this depth: The factors that shape an environmental viewpoint — cultural, religious, economic, socio-political, education, media, personal experience — identified in real people rather than described in the abstract. Environmental value systems taught as inputs, processing and outputs, so the concept arrives already in systems form. Ecocentric, anthropocentric and technocentric worldviews placed on a spectrum rather than in three boxes, with real actors, policies and campaigns located on it. Then the historical development of environmental movements through the events that shifted public perspective. The essential move is that students identify and defend their own position and then argue the opposing one credibly — the precise skill the ethics lens will formalise later.
Connects to: Perspectives is one of the three unifying concepts, so it recurs everywhere: conservation priorities, geoengineering, energy choices, food ethics, climate justice and urban planning are all disagreements between value systems before they are disagreements about evidence. It is the direct precursor of the environmental ethics lens in Phase E.
Practical & inquiry angle: A structured worldview survey of the class or the wider school, analysed for pattern. Perspectives is the criterion most often thinly handled in the individual investigation, and it begins here.

2. Understanding Environmental Systems

1.2 · Foundational · 5 h

Teach to this depth: Systems thinking as a way of seeing, then the technical apparatus built carefully: storages and flows, inputs, outputs and transfers against transformations. Open, closed and isolated systems distinguished with examples that are genuinely each. Negative feedback as the mechanism of stability and positive feedback as the mechanism of runaway change, both traced through real loops rather than described. Steady-state equilibrium, tipping points and resilience defined precisely, since these are the terms that make the second half of the course intelligible. Then models — their construction, usefulness and limitations — including the first and second laws of thermodynamics as constraints on every system that follows.
Connects to: The analytical spine of the entire course. Every subsequent topic is a system: an ecosystem, the carbon cycle, a fishery, a watershed, a city, the climate. Feedback and tipping points return decisively in climate change, in ecosystem stability and in the planetary boundaries framework.
Practical & inquiry angle: Building and critiquing a systems diagram for a local system, with storages quantified where possible. Every strong individual investigation begins by defining the system boundary, and that skill is taught here or nowhere.

3. Sustainability and Sustainable Development

1.3 · Developmental · 8 h

Teach to this depth: The largest topic in the foundation, and it earns the hours. Sustainability defined through the relationship between use and regeneration, then sustainable development as the contested political project it actually is, with the tension between the two named rather than smoothed over. Environmental justice taught with cases in which the people bearing the cost are not the people receiving the benefit. Sustainability indicators — ecological footprint, biocapacity, carbon and water footprints — calculated and then criticised for what they leave out. The UN Sustainable Development Goals and planetary boundaries as two competing frameworks with different logics. Citizen science as a genuine data source with genuine limitations. Then alternative economic models — circular economy, doughnut economics, degrowth — taught as arguments to be evaluated, which is exactly what the economics lens will do formally.
Connects to: Builds on both preceding topics: sustainability is a systems property judged from a perspective. It supplies the evaluative criteria for every management strategy the course later proposes, and it is the direct foundation for the environmental economics lens and for natural capital.
Practical & inquiry angle: Calculating and interrogating a personal or school ecological footprint; comparing two countries against the same indicator set and explaining the divergence. A common and productive individual investigation context.

Phase B — How Ecosystems Work

The scientific engine room of the course and, at 35 hours, its largest topic. Populations first, because carrying capacity and life-cycle strategy recur in fisheries, demography and urban systems alike; then energy and productivity, which explain why trophic efficiency constrains food production and why sustainable yield has a ceiling; then nutrient cycling, the prerequisite for both climate change and eutrophication; then climate and biomes; and finally succession, the synthesis of all four.

4. Organisms, Populations and Ecological Communities

2.1 · Foundational · 9 h

Teach to this depth: Species, populations, communities, habitats and ecosystems distinguished precisely, and the abiotic–biotic distinction applied to a real site. Classification and taxonomy taught as a working tool, with dichotomous keys used rather than described, and the HL extension into modern phylogenetic classification and the reasons traditional groupings have been revised. Population dynamics done properly: limiting factors, carrying capacity, density-dependent and density-independent controls, and the S and J curves derived from what the organisms are doing. The fundamental and realised niche taught as the outcome of competition, with real displacement examples. Life-cycle strategies — r and K selection and survivorship curves — connected to succession and to fishery recovery before either is met. Field methods for estimating abundance taught to competent use.
Connects to: Carrying capacity and limiting factors recur in maximum sustainable yield and fish stock assessment, in human demography and in urban carrying capacity. r and K strategies are the mechanism behind both succession and the recovery of depleted populations. The field methods here are the methods most individual investigations actually use.
Practical & inquiry angle: A quadrat or transect survey with abundance, percentage cover and a diversity index calculated, plus capture–mark–recapture where feasible, and the sampling limitations stated by the students. The single highest-value practical of Year 1.

5. Energy Flow, Biomass and Productivity

2.2 · Foundational · 9 h

Teach to this depth: Photosynthesis and respiration at the level ESS needs, with the link to the carbon cycle flagged before it is taught. Autotrophs, heterotrophs, and the full set of consumer categories. Trophic levels, food chains and webs constructed from real ecosystems. Then the quantitative core taken to HL depth: energy losses between trophic levels and the reasons for them; gross and net primary productivity and gross and net secondary productivity, each calculated from real figures; ecological efficiency computed and compared between systems; and maximum sustainable yield derived here from net productivity, which is what makes the fisheries topic tractable later. Pyramids of numbers, biomass and productivity drawn to scale, with inverted cases explained. Finally, human impacts on flows of energy and matter.
Connects to: Trophic efficiency is the argument behind lower-trophic-level diets in food security and behind fishery collapse in sustainable harvesting. Sustainable yield introduced here is applied in Phase F. Productivity returns in succession, in soil systems and in ocean upwelling.
Practical & inquiry angle: Measuring productivity in a bottle ecosystem or by light–dark bottle method; computing ecological efficiency from published data for a terrestrial and an aquatic system. Reliably quantitative and reliably examined.

6. Biogeochemical and Nutrient Cycles

2.3 · Developmental · 6 h

Teach to this depth: Biogeochemical cycles taught as systems diagrams with storages and flows — the vocabulary from topic 2 applied for the first time to something planetary. The carbon cycle in full: the atmospheric, oceanic, terrestrial and lithospheric stores, the fluxes between them, and the residence time of each, with the sizes quantified so that later claims about sinks and emissions can be checked rather than believed. Human disruption traced through combustion, deforestation and land-use change. Then the nitrogen cycle at HL depth — fixation, nitrification, assimilation, ammonification and denitrification — with the Haber process and fertiliser use identified as the largest single human alteration of a global cycle, which is the direct cause of the eutrophication taught in Phase F.
Connects to: The direct prerequisite for the whole atmosphere and climate phase, for ocean acidification and carbon sequestration, for soil carbon release, and for eutrophication. Placing it immediately before the climate topics is the central sequencing decision of this framework.
Practical & inquiry angle: Quantifying a carbon store — a tree, a plot, a school ground — and comparing it against a published flux; measuring soil nitrate across contrasting land uses. Systems diagrams with real numbers attached are what separate a strong Paper 2 answer from a labelled sketch.

7. Climate Systems and Global Biomes

2.4 · Developmental · 6 h

Teach to this depth: Weather distinguished from climate with the timescales explicit. Atmospheric circulation built from the ground up — differential heating, Hadley, Ferrel and polar cells, and the resulting pressure belts — so that the global distribution of deserts and rainforests is derived rather than memorised. Ocean currents and thermohaline circulation as the second distributor of heat. Major biomes characterised by temperature, precipitation, productivity and structure and mapped onto the circulation pattern. Then the HL extension: climate classification systems, the El Niño–Southern Oscillation as a coupled ocean–atmosphere oscillation with its teleconnections traced, and the mechanism linking sea surface temperature to tropical cyclone frequency and intensity under a warming climate.
Connects to: Explains biome distribution, which explains where productivity is highest, which explains where agriculture and biodiversity are concentrated. ENSO connects forward to fisheries and upwelling; circulation returns in the atmosphere phase and in urban air pollution.
Practical & inquiry angle: Constructing climographs from real station data and inferring biome; correlating an ENSO index against a regional rainfall or fishery series and interpreting the lag.

8. Ecosystem Succession, Stability and Change

2.5 · Synthesis · 5 h

Teach to this depth: Zonation distinguished from succession by whether the variable is space or time. Primary and secondary succession traced through a real sere, with soil depth, productivity, biomass, diversity and complexity tracked at each stage. At HL the productivity argument is made quantitative: gross productivity, net productivity and the GPP-to-respiration ratio change predictably through the sere, and students should be able to explain why net productivity peaks in mid-succession and approaches zero at climax. Reproductive strategies from topic 4 explain who colonises when. Then resilience and stability: what allows an ecosystem to absorb disturbance and return, where the tipping points sit, and the reasons a climax community is better understood as a contested idea than a fixed endpoint.
Connects to: The synthesis of the ecology phase: it needs population dynamics, energy and productivity, nutrient cycling and the feedback vocabulary from the foundation. Resilience is then the organising idea for conservation, restoration and rewilding in Phase D.
Practical & inquiry angle: A transect across a real successional or zonation gradient — a dune, a wall, an abandoned plot — with diversity and, where possible, productivity measured at intervals. A classic and very defensible individual investigation.

Phase C — The Atmosphere and a Changing Climate

Moved forward from sixth in the syllabus to third in the teaching order. The carbon cycle and the feedback vocabulary are still fresh from Phase B, so the greenhouse mechanism, Milankovitch forcing and hothouse states can be built rather than asserted — and once climate change is in place, it is available as a driver for biodiversity loss, ocean acidification, water scarcity, food insecurity, energy choice and migration, all of which the course goes on to teach.

9. Atmospheric Systems and Processes

6.1 · Foundational · 5 h

Teach to this depth: Atmospheric composition and the functions the atmosphere performs. The energy budget handled honestly: incoming shortwave radiation, albedo, surface absorption, outgoing longwave radiation, and the greenhouse gases that intercept it. The natural greenhouse effect established as a precondition for life before the enhanced effect is mentioned, since the confusion between the two is the most damaging misconception in the topic. Vertical structure and how temperature, pressure and density change with altitude. Then the HL extension, which is where the topic becomes genuinely interesting: Milankovitch cycles as the orbital pacemaker of glacial cycles, hothouse Earth conditions in the geological record, and the co-evolution of atmospheric composition and life — the Great Oxidation Event as the original example of organisms remaking their own atmosphere.
Connects to: Sits on the carbon cycle from topic 6 and the circulation from topic 7. It is the mechanism the next two topics diagnose and treat, it returns in ozone chemistry and urban air quality, and the deep-time material supplies the strongest available context for judging the current rate of change.
Practical & inquiry angle: A comparative albedo or heat-retention experiment; interpreting ice-core CO₂ and temperature series against orbital forcing and identifying what the orbital explanation cannot account for.

10. Drivers and Impacts of Climate Change

6.2 · Developmental · 7 h

Teach to this depth: Natural drivers separated from anthropogenic ones, with attribution examined rather than assumed — students should be able to say why the current change is not explained by the natural drivers established in the previous topic. Greenhouse gases compared on source, concentration, lifetime and global warming potential. Feedback mechanisms that decide severity: ice–albedo, permafrost methane, water vapour, and weakening ocean and forest sinks. Consequences in both registers, ecological and socio-economic. Then the HL extension: how climate data are actually collected, from ice cores and proxies to satellites and the instrumental record; how global climate models are constructed, what an ensemble is, and what a projection is not; critical thresholds and tipping elements; and the asymmetry between responsibility for emissions and vulnerability to effects, which sets up the ethics and law lenses directly.
Connects to: Positive feedback and tipping points from the foundation reach their most important application here. The consequences become driving pressures in biodiversity, water, food and population topics later. The responsibility–vulnerability asymmetry is the core case for the environmental ethics lens.
Practical & inquiry angle: Working with real temperature, CO₂ or sea-level series; comparing two emissions scenarios from a published model ensemble and stating precisely what the spread represents. Paper 1 case studies lean heavily on this skill.

11. Climate Mitigation, Adaptation and Intervention

6.3 · Synthesis · 7 h

Teach to this depth: Mitigation and adaptation distinguished by what they target, then a full spread of strategies under each, evaluated on effectiveness, cost, timescale, equity and feasibility. Decarbonisation treated concretely across energy, transport, industry, buildings and land use, with the scale of change made honest. International agreements assessed on what they actually bind parties to and what enforcement exists. Then the HL extension, which is the most demanding evaluative material in the course: emission scenarios and their assumptions, carbon capture and storage, solar radiation management and other geoengineering proposals, each assessed for efficacy, cost, reversibility, governance and moral hazard — the argument that a plausible technical fix reduces the pressure to cut emissions. Stakeholder perspectives from topic 1 are put to work throughout.
Connects to: Needs the greenhouse mechanism, the carbon cycle, the impacts of the previous topic and the sustainability frameworks from Phase A. It is the direct precursor to energy security in Phase G, and geoengineering is the case study the ethics lens is most useful on.
Practical & inquiry angle: Costing and evaluating a school or local decarbonisation measure against the emissions it avoids; a structured evaluation of one geoengineering proposal against a stated criteria set.

12. Stratospheric Ozone and Atmospheric Protection

6.4 · Developmental · 4 h

Teach to this depth: Ultraviolet radiation and its biological effects, then the ozone–oxygen cycle taught as a dynamic steady state rather than a layer. Halogenated organic gases as catalysts, with the catalytic nature emphasised because it explains the disproportion between quantity released and damage done. At HL, the polar mechanism in full: the vortex, polar stratospheric clouds, the heterogeneous chemistry that liberates reactive chlorine, and why depletion is therefore seasonal and regional. Chlorofluorocarbons and their hydrofluorocarbon replacements evaluated on both ozone and climate criteria — the replacements solved one problem and created another, which is the clearest case in the course of a solution with a displaced cost. The Montreal Protocol assessed as the benchmark against which climate agreements are judged.
Connects to: Shares atmospheric structure with topic 9 and offers the sharpest available contrast with topic 11 on why one international agreement worked and another has struggled — a contrast the environmental law lens then formalises.
Practical & inquiry angle: Interpreting ozone-column and halocarbon time series together and using the lag between them to argue about policy effectiveness and atmospheric residence time.

Phase D — Biodiversity, Evolution and Conservation

Placed after climate because climate change is one of the principal threats the phase evaluates, and after succession because resilience is what conservation is trying to preserve. The internal order is diagnostic: what biodiversity is and how it arose, what is destroying it, and only then what can be done. The phase also supplies the richest material the HL lenses will work on — CITES and the Convention on Biological Diversity for law, ecosystem service valuation for economics, and intrinsic value for ethics.

13. Biodiversity and Evolutionary Processes

3.1 · Developmental · 9 h

Teach to this depth: Biodiversity separated into species, genetic and habitat diversity, and the diversity–resilience relationship argued from the succession work rather than asserted. Evolution by natural selection, speciation, and the role of geographic and reproductive isolation, with genetic diversity treated as the raw material that determines whether a population can respond to change at all. Diversity indices calculated by hand at least once, and the reasons two sites with identical richness can differ in diversity. Then the HL extension: biodiversity hotspots and the criteria that define them; human influence on evolutionary processes through selective breeding, fragmentation, pollution and antibiotic and pesticide resistance; the geological timescale; the five mass extinction events and what distinguishes them; and the Anthropocene as a proposal to be evaluated on evidence rather than adopted as a slogan.
Connects to: Rests on population dynamics, energy flow and succession from Phase B. Genetic diversity underpins minimum viable population in conservation; the extinction record supplies the comparator for current rates; hotspots drive the prioritisation debate two topics later.
Practical & inquiry angle: Calculating and comparing a diversity index across two habitats with a defensible account of what the difference does and does not show; plotting current extinction rates against background rates from the fossil record.

14. Human Pressures on Biodiversity

3.2 · Developmental · 8 h

Teach to this depth: The major threats — habitat loss and fragmentation, overexploitation, invasive species, pollution and climate change — with their relative importance argued from evidence. Conservation status assessed using real criteria, and listings traced back to mechanism. At least one extinction and one recovery examined for the specific cause of the outcome. The tragedy of the commons taught as a structural explanation for overuse — a property of the incentive arrangement rather than a failure of character — which is what makes it transferable to fisheries, water and the atmosphere. Then the HL extension: threats to specific hotspots, key biodiversity areas and how they are designated, Indigenous land-management approaches and the evidence on their outcomes, conservation as an environmental justice problem when protection displaces people, and loss of biosphere integrity as a breached planetary boundary.
Connects to: Climate change from Phase C is among the threats evaluated. The commons problem returns in sustainable harvesting, water security and natural capital. The environmental justice material is the direct bridge into the ethics lens.
Practical & inquiry angle: Building an evidence-based threat profile for one local species; a common-pool resource simulation with the institutional rules that prevent collapse tested rather than described.

15. Conservation, Restoration and Regeneration

3.3 · Synthesis · 9 h

Teach to this depth: The arguments for preserving biodiversity set out in full — ecological, economic, cultural, aesthetic and ethical — with the point made that they are different arguments supporting the same action for incompatible reasons. In-situ and ex-situ approaches compared on what each can achieve. Protected-area design as an applied ecological problem: size, shape, edge effects, corridors, buffer zones and minimum viable population, each justified from the ecology already taught. Then the HL extension: the roles of intergovernmental and non-governmental conservation organisations and how their funding shapes their priorities; habitat restoration and regeneration techniques; rewilding and trophic cascades evaluated against real reintroductions; how conservation success is actually measured and why most projects are not measured well; and ecotourism assessed on both sides, including the cases where it becomes the pressure it was meant to relieve.
Connects to: Draws together perspectives, resilience, biodiversity measurement and threat analysis. Reserve design is only teachable once succession, edge effects and population viability are secure, and the funding and valuation questions here run directly into the economics lens taught next.
Practical & inquiry angle: Designing a reserve for a real landscape on a real map and defending every boundary decision; evaluating a named protected area or reintroduction against its stated objectives and its published monitoring data.

Phase E — The HL Lenses: Law, Economics and Ethics

The three lenses are the defining feature of Higher Level, and they are placed here on purpose. Taught at the end of the course they could only be applied backwards; taught here, after the foundation, ecology, climate and biodiversity have supplied the treaties, the valuation problems and the ethical dilemmas they need to work on, they become instruments available for the whole second half. Every topic in Phases F and G is written to be analysed through all three. The order within the phase runs from the most concrete to the most abstract: law, then economics, then ethics — which is also the order in which each depends on the last.

16. Environmental Law

HL.a · Developmental · 5 h

Teach to this depth: How environmental law is actually made and at what levels it operates — local ordinance, national statute, regional directive, international treaty — and the difference between hard law that binds and soft law that signals. Key principles taught as operative tests rather than slogans: the polluter pays principle, the precautionary principle, common but differentiated responsibilities, and the public trust doctrine, each applied to a case where it changed an outcome. Then the enforcement problem, which is where the topic earns its place: sovereignty, monitoring, verification, dispute resolution and sanction, and the reasons transboundary harm is the hardest category to regulate. The Montreal Protocol and the climate agreements compared directly on design, and the comparison used to derive what makes an environmental treaty work.
Connects to: Draws its cases from every topic already taught — ozone, climate, CITES and the Convention on Biological Diversity, marine protected areas — and is then applied forward to water rights, fishing quotas, emissions regulation and urban air standards. The transboundary problem is the tragedy of the commons from topic 14 in legal form.
Practical & inquiry angle: Evaluating one treaty against the design features derived in the topic and predicting where it will fail; tracing a single pollutant from source to regulation across two jurisdictions.

17. Environmental and Ecological Economics

HL.b · Synthesis · 7 h

Teach to this depth: The largest of the three lenses. Environmental economics and ecological economics distinguished by a genuine disagreement — whether the economy is a subsystem of the biosphere or the biosphere an input to the economy — because everything else in the topic follows from which view is taken. Externalities defined and then found in real prices, with market failure explained as the mechanism rather than named as a label. Valuation methods for ecosystem services attempted and criticised, including the objection that some things should not be priced at all. Policy instruments compared on efficiency, equity and enforceability: taxes, subsidies, cap-and-trade, standards and liability. Cost–benefit analysis performed and then interrogated on its two most contested inputs, the discount rate and the value placed on lives and species. Then GDP set against alternative welfare measures, and the growth debate — green growth, steady-state, degrowth — argued to a genuine standstill rather than resolved.
Connects to: Formalises the alternative economic models from topic 3 and the valuation problem raised in conservation. It is the direct prerequisite for natural capital in Phase G, and it supplies the cost–benefit apparatus used to evaluate energy, water, waste and urban policy for the rest of the course.
Practical & inquiry angle: A full cost–benefit analysis of a real local proposal with the discount rate varied and the conclusion shown to flip; valuing an ecosystem service on the school site and stating what the valuation omits.

18. Environmental Ethics

HL.c · Synthesis · 5 h

Teach to this depth: Intrinsic and instrumental value distinguished, then the major ethical frameworks — consequentialist, deontological and virtue-based — applied to the same environmental dilemma so that students see them produce different answers from the same facts. Anthropocentric, biocentric and ecocentric ethics developed from the worldview spectrum of topic 1, now with argument rather than description. Intergenerational justice taken seriously, including the question of what is owed to people who do not yet exist and how discounting in the previous topic implicitly answers it. Environmental justice and the distribution of harm, using the responsibility–vulnerability asymmetry established in the climate topic. Then applied dilemmas worked through properly: geoengineering, rewilding and displacement, animal welfare in food systems, and the ethics of conservation triage.
Connects to: Completes the arc that began with perspectives in topic 1 and gives it analytical teeth. It supplies the evaluative move that the highest markbands reward, and it is applied directly to diet in food security, to fishing rights, to energy poverty and to urban planning in the phases that follow.
Practical & inquiry angle: A structured ethical analysis of one real decision from at least two frameworks, reaching a defended position rather than a survey of views. The move that most reliably separates a top-band extended response from a competent one.

Phase F — Water, Soil and Food

The two chapters that together answer whether humans can be fed, now with all three lenses available. Water comes first because irrigation, aquatic productivity and eutrophication all depend on it; soil follows as the other productive base; and food security closes the phase as the synthesis needing trophic efficiency, soil, water, climate and ethics simultaneously. Two topics here — eutrophication and ocean acidification — are the clearest evidence in the course that chapter order and teaching order should differ.

19. Water Systems and Ocean Processes

4.1 · Foundational · 7 h

Teach to this depth: The hydrological cycle drawn as a systems diagram with stores and flows, and the relative size and residence time of each store made explicit, since the fact that almost all fresh water is locked in ice and groundwater is the premise of the entire water security topic. Each process explained by what drives it, and human interference mapped onto the specific flow or store it alters. Then the HL extension into ocean processes: the physical and chemical properties of water that make all of this possible; thermal and salinity stratification; the thermohaline conveyor; upwelling and why the most productive fisheries sit where they do; and carbon sequestration by the ocean, with the acidification chemistry worked through properly — dissolution, carbonic acid, hydrogen ion concentration, carbonate availability and the consequences for calcifying organisms.
Connects to: Applies systems thinking directly and is the prerequisite for water security, water quality and irrigated agriculture. The acidification chemistry closes a loop opened in the carbon cycle and reopened in the climate impacts topic; upwelling explains the productivity that the fisheries topic then exploits.
Practical & inquiry angle: Comparing infiltration rates across land-use types on the school site; a stratification and density demonstration; measuring pH change in seawater or a carbonate system under elevated CO₂.

20. Water Access, Use and Security

4.2 · Developmental · 6 h

Teach to this depth: Why fresh water is unevenly available in space and time, and why availability and access are different problems — the second being political and economic rather than hydrological. Domestic, agricultural and industrial demand compared, with agriculture’s dominant share made explicit because it drives the food topics later. Supply-side responses evaluated on cost, energy, equity and sustainability, with demand-side responses given equal weight. Then the HL extension: water stress and scarcity defined against real thresholds and mapped; virtual water and the water footprint of traded goods; strategies for managing stress at catchment scale; and water equity as both a legal question, under the human right to water and transboundary treaty arrangements, and an ethical one — which is where the two lenses just taught do their first real work.
Connects to: Needs the hydrological cycle and the sustainability indicators from Phase A. Feeds irrigation constraints in food security, connects to climate through altered precipitation and glacial storage, and is the first topic in which law, economics and ethics are applied together to a single resource.
Practical & inquiry angle: Auditing school or household water use against a per-capita benchmark; calculating the virtual water content of a week’s diet; evaluating a real transboundary dispute from both parties’ legal positions.

21. Aquatic Food Production and Sustainable Harvesting

4.3 · Synthesis · 7 h

Teach to this depth: Aquatic food webs and the reasons marine productivity is concentrated where upwelling and nutrient supply allow. Rising demand set against the biology, and overexploitation explained through maximum sustainable yield and what happens when harvest exceeds recruitment — the productivity work from topic 5 doing real quantitative work. Mitigation approaches evaluated on enforceability as well as biology. Aquaculture assessed on both sides. Then the HL extension: ocean productivity and nutrient dynamics; fish stock assessment methods and their uncertainty; sustainable harvesting models; the biology of recovery in depleted populations, where the r and K strategies from topic 4 predict which stocks come back and which do not; and the regulation and ethics of marine harvesting, applying the law and ethics lenses to quotas, bycatch, high-seas governance and the rights of small-scale fishers.
Connects to: A five-way synthesis: population dynamics and productivity from Phase B, the commons problem from Phase D, ocean chemistry from topic 19, and both the law and ethics lenses. Taught in chapter order it would arrive before nearly all of these.
Practical & inquiry angle: Modelling a fish stock under different harvest rates using published landing data; evaluating a named fishery’s management against its stock trend and its governing legal instrument.

22. Water Pollution and Water Quality

4.4 · Synthesis · 5 h

Teach to this depth: Point and non-point sources distinguished because they demand different management. The main pollutant classes with a real source for each, and plastic pollution followed along the microplastic pathway to its ecological endpoint. Water quality assessed chemically and biologically — biochemical oxygen demand, dissolved oxygen, turbidity, nitrate and phosphate — with biotic indices actually used. Eutrophication in full as a positive feedback cascade, which makes it the best worked example of feedback in the course. Then the HL extension: drinking water standards and the difference between an ecological and a public health criterion; the stages of sewage treatment and what each removes; the strengths and limitations of individual water quality indicators; and management evaluated at the three levels of altering activity, treating discharge and remediating damage, with the polluter pays principle from the law lens applied directly.
Connects to: Eutrophication is unteachable without the nitrogen cycle from topic 6 and the feedback vocabulary from topic 2, and its principal cause is the fertiliser use taught two topics later. It is the strongest single argument in this framework for a dependency-ordered sequence.
Practical & inquiry angle: Sampling a local watercourse for dissolved oxygen, nitrate, phosphate, turbidity and invertebrate indicators, and relating results to upstream land use. Among the most commonly chosen and most successful individual investigations.

23. Soil Systems and Soil Processes

5.1 · Foundational · 6 h

Teach to this depth: Soil as a system with inputs, outputs, storages and transfers, and its composition quantified rather than listed. Texture, structure, porosity, permeability, pH and water-holding capacity taught as properties with agricultural consequences, using a texture triangle on real samples. The soil profile and its horizons interpreted rather than labelled. Then the HL extension: the factors of soil formation — parent material, climate, organisms, relief and time — used to explain why soils differ systematically across a landscape and across biomes, so that soil variation is derived rather than catalogued; and carbon release from soils through cultivation, drainage, warming and permafrost thaw, which returns the topic to the carbon cycle and to the feedback mechanisms from the climate phase.
Connects to: Depends on nutrient cycling and on the soil development stage of succession. It is the productive base for food security and a carbon store in the climate topics already taught — soil is the point at which the ecology, climate and food strands of the course physically meet.
Practical & inquiry angle: Measuring texture, pH, organic content and infiltration across contrasting land uses; comparing soil carbon under cultivated and uncultivated plots. Simple apparatus, genuinely quantitative, reliably successful.

24. Agriculture, Food Production and Food Security

5.2 · Synthesis · 9 h

Teach to this depth: Agricultural systems compared as systems: inputs, outputs, energy efficiency and productivity per hectare and per unit of labour, across subsistence and commercial, extensive and intensive. Terrestrial compared with aquatic production on the same terms. Soil degradation traced to specific practices and conservation measures matched to cause. Food security taken apart into availability, access, utilisation and stability. Then the HL extension, which is substantial: the factors that actually determine farming choices; alternative and regenerative agriculture assessed on evidence rather than enthusiasm; technological innovation including genetic modification, precision agriculture and controlled-environment systems; the sustainability of different diets quantified through the trophic efficiency argument from topic 5; harvesting of wild species; lower-productivity food systems and why they persist; food distribution, loss and waste; and malnutrition in both its forms, with the ethics lens applied to diet, land use and the politics of hunger.
Connects to: The synthesis of the phase and the most connected topic in the course: energy flow, soil, water security, climate impacts, biodiversity loss from land conversion, eutrophication from fertiliser, and all three HL lenses converge here.
Practical & inquiry angle: Comparing the land, water and emissions footprint of two diets using published coefficients; a soil erosion or conservation trial on a real plot; evaluating a regenerative practice against a conventional control.

Phase G — Resources, People and Cities

The applied conclusion of the course. Natural capital formalises the economics lens into a resource framework; energy security is the choice on which climate mitigation depends and the clearest place in the course to apply all three lenses at once; waste is what the system does with what it has finished using; and the closing three topics turn the systems lens on the human population itself and on the cities most of it now lives in. Taught here, these can be taught as strategy rather than description.

25. Natural Capital and Resource Management

7.1 · Developmental · 6 h

Teach to this depth: Natural capital and natural income defined precisely, with the distinction between living off the income and consuming the capital as the organising idea — the same distinction sustainability rested on in topic 3, now with the economic apparatus from the lens behind it. Renewable, non-renewable and replenishable resources classified, with the awkward cases argued. Valuation of ecosystem services attempted and criticised. The dynamic nature of resource value illustrated with real reversals. Then the HL extension: the full range of uses of natural capital; environmental impact assessment as a procedure, including what it requires, where it is legally mandated and how it is routinely circumvented; unsustainable exploitation of renewable resources, where a renewable resource is destroyed precisely because it was assumed to be self-replenishing; and natural resource security as a strategic and geopolitical question.
Connects to: Formalises sustainability from Phase A and applies the economics lens from Phase E. It supplies the framework for evaluating energy, waste, fisheries, forests and soil, and the commons problem from topic 14 is its central failure mode.
Practical & inquiry angle: Valuing an ecosystem service on the school site and stating what the valuation omits; critiquing a real environmental impact assessment against what the topic says a good one contains.

26. Energy Resources and Energy Security

7.2 · Synthesis · 7 h

Teach to this depth: Every major energy source compared on a consistent criteria set — energy density, lifecycle emissions, land and water use, intermittency, waste, cost and social acceptability — so comparison is possible rather than anecdotal. Consumption patterns examined across countries and over time, with the inequality explicit. The choice treated as the multi-factor decision it is, so students can explain why two countries with the same resources choose differently. Then the HL extension: energy security defined and decomposed into availability, affordability, accessibility and reliability; fossil fuel reserves and the difference between resources, reserves and what is economically recoverable; nuclear power evaluated on the full lifecycle including waste and decommissioning; and battery and other storage technologies, with their material requirements and their own extraction footprint made part of the assessment rather than omitted from it.
Connects to: Needs natural capital, the carbon cycle, climate mitigation from Phase C, and all three HL lenses — treaty obligations and regulation from law, externalities and cost–benefit from economics, and energy poverty and intergenerational burden from ethics. It is the topic where the decarbonisation strategy proposed in topic 11 either becomes concrete or does not.
Practical & inquiry angle: A full comparison of two national energy mixes against a shared criteria set using real generation and emissions data; auditing and modelling school energy use with a costed intervention.

27. Solid Waste and Waste Management

7.3 · Developmental · 5 h

Teach to this depth: Waste types and sources quantified, with the differences in generation and composition between countries used as evidence of consumption patterns. Environmental and social impacts of disposal — leachate, methane, incineration emissions, marine plastic, and the export of waste to countries that did not generate it, which is an environmental justice case as much as a logistical one. Landfill, incineration with energy recovery, composting, anaerobic digestion and recycling compared on cost, emissions, energy and residual volume. Then the waste hierarchy applied as a decision rule, with the circular economy from topic 3 returning as the systemic alternative — designing waste out rather than managing it better — and extended producer responsibility examined as the legal instrument that makes it happen.
Connects to: Applies natural capital and the circular economy; connects to water quality through plastics and leachate and to climate through landfill methane. The waste export question applies the ethics and law lenses directly, and consumption patterns link it to the population topic that follows.
Practical & inquiry angle: A school waste audit by mass and category, with a costed intervention proposed and its diversion rate predicted and then measured.

28. Population Dynamics and Environmental Pressure

8.1 · Developmental · 6 h

Teach to this depth: Crude birth and death rates, fertility, natural increase and doubling time calculated, not merely defined. Age–sex pyramids read as predictions rather than descriptions. The demographic transition model taught with its limitations named, including the countries it does not describe. Population policies of both kinds evaluated on effectiveness and on ethics. Then the HL extension: dependency ratios calculated and their fiscal and social consequences traced; population momentum explained mechanistically, so students can say why a population keeps growing after fertility reaches replacement; regional population patterns and projections compared; and environmental migration examined as both a consequence of the climate impacts taught in Phase C and a category with no settled legal status — which returns the law lens to a live and unresolved problem.
Connects to: The human application of the population dynamics from topic 4 — carrying capacity, limiting factors and S-curves, now with the complication that humans change their own carrying capacity. Feeds urbanisation, and through consumption, energy and waste. Environmental migration closes a loop opened by the vulnerability asymmetry in topic 10.
Practical & inquiry angle: Constructing and interpreting pyramids for two contrasting countries from real census data and projecting the dependency burden forward; testing the demographic transition model against a country it fits badly.

29. Urban Systems and Sustainable City Planning

8.2 · Synthesis · 5 h

Teach to this depth: The city analysed as a system with the vocabulary from topic 2 — inputs of food, water, energy and materials, outputs of waste, sewage, heat and emissions, and almost no internal cycling. Urbanisation and its drivers, and the forms urban expansion takes including informal settlement. The urban heat island explained mechanistically from albedo, thermal mass and reduced evapotranspiration. Then the HL extension: ecological approaches to city design; urban sustainability models and how a city’s metabolism can be measured; green architecture, green roofs and sustainable drainage assessed on what each does to a specific input or output rather than on how it sounds; and the equity question of who the sustainable city is actually built for, applying the ethics lens to gentrification and displacement.
Connects to: A systems synthesis drawing on the hydrological cycle for drainage and run-off, on energy and waste from earlier in the phase, on demography from the previous topic, and on the sustainability indicators from Phase A.
Practical & inquiry angle: Mapping the inputs and outputs of a real neighbourhood; measuring a heat island transect across a city with a thermometer and a route; assessing a green infrastructure installation against its stated purpose.

30. Urban Air Pollution and Atmospheric Quality

8.3 · Synthesis · 4 h

Teach to this depth: Primary and secondary pollutants distinguished, with the main urban pollutants traced to specific sources. Photochemical smog built as a chain of reactions rather than named, together with the meteorological and topographic conditions — temperature inversion, basin location, calm — that concentrate it. Tropospheric ozone treated properly at HL as a secondary pollutant with both health and crop-yield consequences, and the good-ozone–bad-ozone distinction made explicit against the stratospheric topic. Acid deposition in full: the sulphur and nitrogen chemistry, transboundary transport, effects on soils, water bodies and vegetation, and the reasons pollution and damage occur in different countries. Management evaluated at the three levels, with air quality standards and their enforcement analysed through the law lens.
Connects to: The final synthesis: atmospheric structure and circulation from Phases B and C, urban systems from the previous topic, energy choices from earlier in this phase, soil and water sensitivity from Phase F, and the law lens on standards and transboundary liability. Acid deposition returns to the commons problem in its most literal form.
Practical & inquiry angle: Measuring particulates or nitrogen dioxide along a traffic gradient with diffusion tubes or a low-cost sensor; using lichen distribution as a biological indicator; simulating acid deposition effects on seedling growth or on carbonate rock.

06 · Reconciled to 240 hours, finishing by end of January

Time allocation & two-year pacing

The IB recommends 240 teaching hours for ESS at Higher Level: 173 hours of syllabus content across the eight topics, 17 hours for the three HL lenses, and 50 hours for the experimental programme. The allocations in the sequence table above distribute those 190 content hours across all 30 topics; below they are reconciled topic by topic against the guide’s own figures and then paced so that teaching is complete by the end of January in Year 2.

Reconciliation to the official IB allocation

IB syllabus component	Topics	IB hours	Allocated here
Topic 1 — Foundation	3	16 h	16 h
Topic 2 — Ecology	5	35 h	35 h
Topic 3 — Biodiversity and conservation	3	26 h	26 h
Topic 4 — Water	4	25 h	25 h
Topic 5 — Land	2	15 h	15 h
Topic 6 — Atmosphere and climate change	4	23 h	23 h
Topic 7 — Natural resources	3	18 h	18 h
Topic 8 — Human populations and urban systems	3	15 h	15 h
HL lenses — law (5), economics (7), ethics (5)	3	17 h	17 h
Syllabus content subtotal	30	190 h	190 h
Experimental programme — practical work	—	30 h	30 h
Experimental programme — collaborative sciences project	—	10 h	10 h
Experimental programme — individual investigation	—	10 h	10 h
HL course total	30	240 h	240 h

Because this framework re-sequences topics across chapter boundaries, a phase’s hours will not match a syllabus topic’s. The reconciliation above proves that nothing has been added, lost or reweighted: every one of the eight syllabus topics and all three HL lenses receive exactly the hours the guide allocates them, and all 30 subtopics are present. Only the order has changed. The guide gives per-subtopic hours for the foundation topic (perspectives 3, systems 5, sustainability 8) and for the lenses (law 5, economics 7, ethics 5), which are used unaltered; within topics 2 to 8 the subtopic split is this framework’s.

The two-year pacing plan

Built on roughly four to four-and-a-half teaching hours per week across the two years, with practical work distributed through the phases rather than blocked. The cumulative column tracks progress toward the 240-hour total; the gold rows fall outside the teaching budget.

Period	Focus	Hours	Cumul.
YEAR 1
Autumn term	Phase A — Foundation · Phase B to nutrient cycles · fieldwork skills and the first practicals (10 h)	50	50
Spring term	Finish Phase B (climate systems, succession) · Phase C — atmosphere and climate in full · begin Phase D (biodiversity and evolution) · practical work (10 h)	53	103
Summer term	Finish Phase D (pressures, conservation) · Phase E — the three HL lenses · practical work (10 h) · collaborative sciences project (10 h)	54	157
YEAR 2 (to end January)
Autumn term	Phase F — water, oceans, soil and food, with all three lenses applied · individual investigation researched, written and submitted (10 h)	50	207
To end of January	Phase G — natural capital, energy security, waste, population, urban systems and air quality, taught as whole-course synthesis	33	240
FEBRUARY – APRIL	Dedicated revision: past papers, Paper 1 case-study drills and Paper 2 structured and extended response practice with explicit lens integration, and timed mocks (additional to the 240 teaching hours)	—	—
MAY	IB examinations	—	—

A note on the lenses and the investigation. Placing the three HL lenses at the end of Year 1 does two things at once. It gives students the legal, economic and ethical apparatus before the entire second year of applied content, so that every topic in Phases F and G can be analysed through all three as it is taught rather than revisited afterwards — which is what the Higher Level requirement to synthesise core, extension and lens material actually asks for. And it means that when the individual investigation is scoped in the autumn of Year 2, students can frame a research question with an economic or ethical dimension rather than a purely descriptive one. The 30 hours of practical work are deliberately front-loaded across Phases B, D and F so that by the start of Year 2 a student has already run every method they are likely to need and knows from experience which ones produce usable data.

Revision time (February–April) is deliberately additional to the 240 teaching hours, in line with the subject guide’s reminder that adequate time must be set aside for examination revision.