IB ESS Subject Guide (2026 Syllabus) – Master Checklist

IB ESS Subject Guide (2026 Syllabus) – Master Checklist

How to use:

For every box below, tick it when you can do it. Use the Confidence Check at the end of each topic to track your level:

Explain(I know the definition/idea)
→
Apply(I can use it in an example)
→
Evaluate(I can debate its strengths/weaknesses)
1Topic 1: Foundation (SL: 16 hrs | HL: 16 hrs)
Big Question:

How do our viewpoints, systems thinking, and sustainability limits shape environmental decisions?

✓Core Concepts (Master these for both SL & HL):

  • Perspectives: Ecocentric (nature has rights), Anthropocentric (nature serves humans), Technocentric (technology fixes everything).
  • Systems: Open vs Closed. Positive feedback (amplifies change) vs Negative (damps change). Tipping points.
  • Sustainability: Triple bottom line (Environment + Society + Economy). Ecological footprint. Carrying capacity.

↗Practical Skills:

  • Draw a systems diagram (inputs, outputs, energy flows).

⌕Key Terms (Define them):

  • Intrinsic value / Throughput / Equilibrium / Steady-state economy
✓Confidence Check:
2Topic 2: Ecology (SL: 22 hrs | HL: 35 hrs)
Big Question:

How does energy move and matter cycle through living communities, and what disrupts them?

✓Core Concepts (Master these for both SL & HL):

  • Energy flow: Sun → Producers → Consumers. Energy transfer between trophic levels is inefficient and varies; the 10% figure is a useful approximation, not a fixed rule.
  • Matter cycles: Carbon, Nitrogen, and Phosphorus cycles. Human disruptions (fossil fuels, farming, deforestation).
  • Species roles: Predation, Competition, Mutualism, Parasitism.
  • Populations: Carrying capacity. r-strategists (fast breeders) vs K-strategists (slow breeders).
  • Succession: Primary (new land) vs Secondary (recovery after disturbance).

↗Practical Skills:

  • Calculate population growth rate.
  • Construct and interpret a food web.

HLHL Only (Extra Depth):

  • Apply the 3 HL lenses (Law, Economics, Ethics) to ecological case studies (e.g., overfishing).

⌕Key Terms (Define them):

  • Biomass / GPP & NPP / Keystone species / Limiting factors
✓Confidence Check:
3Topic 3: Biodiversity and Conservation (SL: 13 hrs | HL: 26 hrs)
Big Question:

Why does variety of life matter, and what are the best ways to protect it?

✓Core Concepts (Master these for both SL & HL):

  • 3 Levels: Genetic, Species, and Ecosystem diversity.
  • Major threats (HIPPO): Habitat loss, Invasive species, Pollution, Population (human growth), Over-exploitation.
  • Conservation types: In-situ (protected parks) vs Ex-situ (zoos, seed banks).
  • Global efforts: CITES (trade control), IUCN Red List (threat categories).

↗Practical Skills:

  • Calculate Simpson’s Diversity Index from given data.
  • Evaluate a real conservation case study (e.g., rhino protection).

HLHL Only (Extra Depth):

  • Apply economic valuation methods (e.g., cost-benefit) to conservation decisions.

⌕Key Terms (Define them):

  • Endemism / Simpson’s Diversity Index / Flagship / Umbrella species
✓Confidence Check:
4Topic 4: Water (SL: 12 hrs | HL: 25 hrs)
Big Question:

How do we manage and protect our limited freshwater supplies fairly?

✓Core Concepts (Master these for both SL & HL):

  • The Water Cycle: Evaporation → Condensation → Precipitation → Runoff → Infiltration.
  • Pollution sources: Agricultural (fertilisers), Industrial (heavy metals), Domestic (sewage, plastics).
  • Eutrophication: Excess nutrients → algal blooms → oxygen drop (dead zones).
  • Management options: Dams, Desalination, Wastewater treatment, Efficient irrigation.

↗Practical Skills:

  • Measure/interpret water quality indicators (DO, pH, temperature, turbidity).

HLHL Only (Extra Depth):

  • Evaluate international water conflict case studies (e.g., transboundary rivers) using HL lenses.

⌕Key Terms (Define them):

  • BOD (Biochemical Oxygen Demand) / Turbidity / Aquifer / Water scarcity
✓Confidence Check:
5Topic 5: Land (SL: 8 hrs | HL: 15 hrs)
Big Question:

How does human land use affect soil health and long-term food production?

✓Core Concepts (Master these for both SL & HL):

  • Soil composition: Minerals (sand/silt/clay), Organic matter, Water, Air.
  • Soil horizons: O (organic), A (topsoil), B (subsoil), C (parent material).
  • Degradation types: Deforestation, Desertification (overgrazing/drought), Salinization (salt build-up from irrigation).
  • Sustainable methods: Crop rotation, Contour ploughing, Terracing, Agroforestry.

↗Practical Skills:

  • Identify soil texture using the feel method or a soil texture triangle.

HLHL Only (Extra Depth):

  • Analyze the economic and ethical trade-offs of intensive agriculture vs conservation.

⌕Key Terms (Define them):

  • Erosion / Humus / Soil texture / Leaching
✓Confidence Check:
6Topic 6: Atmosphere and Climate Change (SL: 10 hrs | HL: 23 hrs)
Big Question:

How does the greenhouse effect work, and what can we do about rapid climate change?

✓Core Concepts (Master these for both SL & HL):

  • Layers: Troposphere (weather) & Stratosphere (ozone layer).
  • Greenhouse effect: Gases (CO₂, CH₄, N₂O) trap heat. Humans intensify it (fossil fuels, livestock, land use).
  • Feedback loops: Albedo effect (ice melts → less reflection → more warming). Methane release from permafrost.
  • Responses: Mitigation (cut emissions via renewables) vs Adaptation (flood barriers, drought crops).
  • Global pact: Paris Agreement (aims to hold warming well below 2°C and pursue efforts to limit warming to 1.5°C).

↗Practical Skills:

  • Interpret graphs of atmospheric CO₂ and global temperature over time.

HLHL Only (Extra Depth):

  • Evaluate climate policies using cost-benefit analysis and ethical arguments (e.g., climate justice).

⌕Key Terms (Define them):

  • Insolation / Carbon sink / Ocean acidification / Cap-and-trade
✓Confidence Check:
7Topic 7: Natural Resources (SL: 10 hrs | HL: 18 hrs)
Big Question:

How can we shift from wasteful extraction to a circular resource system?

✓Core Concepts (Master these for both SL & HL):

  • Renewables: Solar, Wind, Hydro, Biomass (replenish naturally, but have limits).
  • Non-renewables: Fossil fuels, Minerals (finite → depletion).
  • Extraction impacts: Mining (land destruction), Oil spills (ocean/coast damage), Fracking (water contamination).
  • Circular economy: Design out waste, keep materials in use, regenerate nature.
  • Footprint: Ecological footprint measures land/water needed for your lifestyle.

↗Practical Skills:

  • Calculate your own ecological footprint using an online tool or given data.

HLHL Only (Extra Depth):

  • Debate “peak resources” and energy transitions using economic models and ethical perspectives.

⌕Key Terms (Define them):

  • Peak (oil/coal) / Ore / Closed-loop recycling / Resource efficiency
✓Confidence Check:
8Topic 8: Human Populations and Urban Systems (SL: 9 hrs | HL: 15 hrs)
Big Question:

How can rapidly growing cities become sustainable and equitable?

✓Core Concepts (Master these for both SL & HL):

  • Demographic Transition Model (DTM): 5 stages describing changing birth and death rates through stages of development over time.
  • Population pyramids: Shape shows the age-sex structure and can indicate whether a population is growing, stable, or declining.
  • Urban metabolism: Cities take in energy, food, water, and materials and transform and output waste, heat, and pollution.
  • Urban challenges: Housing shortages, Traffic congestion, Air pollution, Waste piles.
  • Sustainable solutions: Green roofs, Public transit, Renewable grids, Waste-to-energy.

↗Practical Skills:

  • Analyse a demographic pyramid.
  • Evaluate the sustainability of a specific city’s design/plan.

HLHL Only (Extra Depth):

  • Apply HL lenses to urban issues (e.g., environmental law for emissions, ethics of displacement).

⌕Key Terms (Define them):

  • Megacity / Urban heat island / Gentrification / Smart city
✓Confidence Check:
HLHL Only – The Three Lenses (Apply to ALL Topics Above)

HL students, check these off as you integrate them into your case studies:

  • HL.a Environmental Law: International treaties vs national laws. The Polluter Pays Principle. Enforcement and loopholes.
  • HL.b Environmental & Ecological Economics: Cost-Benefit Analysis. Externalities. Natural capital. Is infinite growth possible?
  • HL.c Environmental Ethics: Anthropocentrism vs Biocentrism vs Ecocentrism. Rights of nature. Moral duties to future generations.
✓Confidence Check for Lenses:

Final Effective Tip for Students:

  1. Print it out and highlight anything you cannot instantly explain.
  2. Write out the Key Terms on flashcards (link to your Flashcards page).
  3. Practice the Skills with past data-based questions (link to your Question Bank).