Cambridge IGCSE Environmental
Management (0680)
Exam notes — syllabus for 2027, 2028, 2029 exams
Contents
Exam framework — structure & AOs · command words · marking principles · maths & data skills ·
fieldwork skills
Topic 1 — Natural resources — 1.1 Rock formation · 1.2 Extraction of rocks, ores & minerals · 1.3
Sustainable management of rocks, ores & minerals · 1.4 Energy resources · 1.5 Conservation of energy
resources · 1.6 Fracking
Topic 2 — Land — 2.1 Soils & crop growth · 2.2 Food production & crop yield · 2.3 Soil erosion
Topic 3 — Water — 3.1 Water sources & supply · 3.2 Water pollution · 3.3 Water-related diseases · 3.4
Marine aquaculture · 3.5 Oil pollution · 3.6 Plastic pollution
Topic 4 — The atmosphere and human activities — 4.1 The atmosphere · 4.2 Climate change · 4.3
Acid rain · 4.4 Ozone depletion
Topic 5 — Ecosystems, biodiversity and fieldwork — 5.1 Ecosystems · 5.2 Forest ecosystems · 5.3
Managing biodiversity · 5.4 Fieldwork investigations
Topic 6 — Natural hazards — 6.1 Earthquakes & volcanoes · 6.2 Tropical cyclones · 6.3 Flooding · 6.4
Drought
Topic 7 — Human population — 7.1 Population density, distribution & structure · 7.2 Human
population size · 7.3 Managing human population size
Exam structure
Paper 1: Principles of Environmental
Management
Paper 2: Environmental Management in
Context
Length
1h 45 min
1h 45 min
Marks
80
80
Weight
50%
50%
Format
Short-answer + structured questions +
extended response based on source material
Short-answer + data processing/analysis +
extended response based on source material
Answer
All questions
All questions
Both papers test AO1, AO2, AO3. Paper 2 leans on source material (graphs/tables/maps/photos) to
illustrate environmental management issues and fieldwork investigations. Practical-method questions
appear on Paper 2 only.
Assessment objectives (AO) — weighting
Page 1 of 41
AO
Covers
% of
qualification
%
Paper
1
%
Paper
2
AO1
Knowledge with understanding: facts, definitions, concepts,
theories, terminology, management strategies
43
55
30
AO2
Handling information & problem-solving: locate/select/present
info, translate between forms, manipulate data, interpret
patterns, solve quantitative problems
30
30
30
AO3
Investigation skills & making judgements: plan/evaluate
fieldwork, suggest explanations, reasoned conclusions
27
15
40
AO1 tests both familiar and unfamiliar contexts — expect the exam to apply syllabus knowledge to a
scenario never taught explicitly. Cambridge deliberately excludes named case-study examples from the
syllabus, so any named country/example in a question is scene-setting, not memorised content.
Command words (use the exact word to decide the shape of
your answer)
Word
Means
Answer shape
Calculate
Work out from given facts/figures
Method → substitution → answer with units
Compare
Identify/comment on similarities and/or
differences
Each point must reference both things
compared
Define
Give precise meaning
One precise statement
Describe
State the points of a topic / give characteristics
and features
Facts or steps, no reasoning needed
Determine
Establish an answer using the information
available
Show working
Discuss
Write about issue(s) in depth, in a structured
way
Balanced points (see below)
Explain
Set out reasons / relationships / say why or how,
with evidence
Fact + reason ("X, because Y")
Give
Produce an answer from a source or recall
Direct, no elaboration
Identify
Name/select/recognise
Direct, no elaboration
Justify
Support a case with evidence/argument
Choice + explicit reasoning
Plot
Mark point(s) on a graph
Not a text answer — use the grid
Predict
Suggest what may happen based on available
info
Specific forecast, not vague possibility
Show
(that)
Provide structured evidence leading to a given
result
Full working — the answer alone proves
nothing
Sketch
Simple freehand drawing, careful proportions
Not a text answer — describe key features if
no grid available
Page 2 of 41
Word
Means
Answer shape
State
Express in clear terms
Bare fact
Suggest
Apply knowledge to a scenario with several valid
answers
Ground it in the specifics given
One marking point per mark. If a question is worth [n] , write exactly n distinct, independentlymarkable points — no more, no fewer. For "state/give/suggest two X [2] ", use a numbered list (1, 2); if
marks exceed the item count (e.g. "explain two reasons [4] "), give each item its own fact+reason substructure so 4 separate points still exist on the page.
"Discuss the benefits and limitations of X" is the dominant multi-mark question type — it follows
almost every strategy the syllabus introduces. Split points roughly evenly across both sides (e.g. 3+3 for
six marks); do not spend a mark on an unrequired "overall verdict" sentence — 0680 does not credit
synthesis the way Evaluate/Assess does at A Level.
Extended (level-of-response) questions — usually the final, essay-style question on a paper, worth
5–6 marks — are marked in bands, not by tallying points:
Level
Marks
What's expected
3
5–6
Clear, detailed response covering multiple relevant strands (causes/impacts/management,
as relevant); reaches a conclusion; balanced argument; specific examples or well-developed
ideas
2
3–4
Response covers some strands but lacks full detail or structure; may or may not reach a
conclusion
1
1–2
Brief description or list; may lack a conclusion; may include irrelevant material or
contradictions
—
0
No creditable response
To hit Level 3: cover more than one strand of the issue, use the specific data/scenario given, write in
connected paragraphs (not a bare list), and reach an explicit conclusion.
The final question on Paper 1 is typically this level-of-response style (worth 5–6 marks),
usually responding to a given statement rather than just "benefits and limitations." Recent
mark schemes reward a coherent response that develops and supports a conclusion
with relevant details/examples, precise subject vocabulary, and — for full marks — a
balanced evaluation of the statement (i.e. this question does want an explicit, justified
verdict, unlike shorter "discuss" questions). Cambridge has stated the style of this last
question is changing under the 2027–2029 syllabus, so treat "developed, evidence-based,
concluding answer in full sentences" as the transferable skill rather than an exact template.
Marking principles that work in your favour: marks are awarded positively (never deducted for
wrong/extra content); whole marks only; correct answers reached by an unclear or wrong method still
score if the question didn't demand "show your working"; an error carried forward from an earlier wrong
answer still earns later marks if used correctly afterwards; contradictory statements within the same
answer earn nothing for that point.
Page 3 of 41
Maths & data skills (examinable on both papers, calculators
allowed)
Arithmetic, decimals, fractions, ratios; percentages and percentage change; mean and range;
standard form; significant figures / decimal places as specified; sensible rounding and estimation.
Substituting values into a given formula.
Units of time, mass, length, volume, area, concentration; area of a rectangle, volume of a rectangular
block; scale diagrams.
Reading/plotting: population pyramids, line graphs, scatter graphs, bar charts, divided bar charts, pie
charts, histograms; determining gradient and intercept; recognising direct/inverse proportion and
positive/negative correlation.
Map skills: 8-point compass direction, latitude and longitude in degrees.
Data types: qualitative (descriptive, not measured) vs quantitative (numerical); quantitative splits into
discrete (whole-number counts) and continuous (any value, e.g. temperature, time); primary data
(collected by you — experiments, surveys, interviews) vs secondary data (already collected by others —
internet, past studies, government data).
Worked calculation templates
Percentage of an amount: % ÷ 100 × amount . E.g. 11% of 226 million → (11÷100)×226 = 24.9 million.
One quantity as a % of another: second quantity ÷ first quantity × 100 . E.g. 10.3 of 30.37 million
km² → (10.3÷30.37)×100 = 33.92%.
% increase/decrease: (new − original) ÷ original × 100 (swap order for a decrease). E.g. GDP $90m
→ $120m: (120−90)÷90×100 = 33.3% increase.
Reverse percentage (find the original): subtract the % change from 100, divide the given value by that
to get 1%, then ×100. E.g. 320 km² is post a 15% loss → 100−15=85; 320÷85=3.76 (=1%); ×100 =
376 km² original.
Ratio, splitting a total: add the ratio parts → divide total by that sum (=1 part) → multiply by the parts
needed. E.g. split 99 seeds 2:3:4 → 9 parts → 11/part → field A (2 parts) = 22.
Ratio, reducing to 1:n: divide both sides by the smaller number. E.g. 5:8 → 1:1.6.
Significant figures: count digits from the first non-zero digit (0.001 = 1 s.f.; 54 649 = 5 s.f.). Round using
the next digit along (≥5 rounds up).
Gradient: pick two points well apart on the line, form a right triangle, gradient = Δy ÷ Δx. Interpolation
reads a value between two known data points; extrapolation extends the line beyond the data
collected — flag extrapolated answers as less certain.
Correlation: positive (both variables rise together), negative (one rises as the other falls), none (no
relationship). Correlation ≠ causation. Directly proportional = constant ratio, straight line through the
origin; inversely proportional = one doubles as the other halves.
Data presentation conventions (easy marks lost here — check every time):
Unit goes in the column heading / axis label with a solidus, e.g. time / s — never in the body of a
table, never repeated on every row.
Independent variable → x-axis; dependent variable → y-axis (unless told otherwise).
Scale axes to use more than half the grid in both directions, in sensible steps (e.g. 2 cm = 1, 2 or 5
units).
Plot points as neat crosses (×) or encircled dots; plot to within half a small square.
Best-fit line: one single, smooth, thin line or curve — does not need to pass through every point,
ignore anomalies, only draw a curve if intermediate values are genuinely predictable.
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Pie charts: sectors in rank order (largest first) starting at 12 o'clock, clockwise; "other" ranked too;
max 6 sectors.
Bar charts (categorical/discrete data): equal-width bars that do not touch.
Histograms (continuous data): start at zero; bars do touch.
Fieldwork (heavily examined on Paper 2 — AO3 is 40% of that
paper)
Required apparatus: hand lens · humidity/moisture meter · light meter · metre ruler · pH meter ·
pitfall trap · pooter · quadrat (open frame and grid) · 30 cm ruler · sweep net · transect (tape
measure/string) · tray for hand-sorting.
Sampling strategies: random sampling; systematic sampling. Sampling techniques: pitfall traps;
pooters; sweep nets; quadrats; transects; aerial photography/drones; automated sampling.
Skills to have ready for any fieldwork question:
Suggest a testable aim/hypothesis; identify independent, dependent and control variables; explain
why a variable is controlled.
Suggest an appropriate range/number of values for the independent variable.
Select/suggest AND justify the most appropriate apparatus, sampling technique and sampling
strategy (Justify = give the reason the choice is better than the alternatives, not just name it).
Identify risks and safety precautions; identify/label apparatus from diagrams.
Record results in a suitable table with correct units and appropriate significant figures; use
repeats/replicates.
Process data (calculations, graphs); interpolate/extrapolate for a gradient or intercept.
Form a conclusion with explanation and justification, referencing the actual data.
Evaluate data quality, identify anomalies, evaluate the sampling technique/strategy (including
whether a control was used), identify sources of error, suggest improvements.
Page 5 of 41
Topic 1 — Natural resources
1.1 Formation of rocks
Three rock types, by formation:
Type
Forms from
Examples
Crystals?
Fossils?
Igneous
Magma (below surface)
or lava (at surface)
cooling and solidifying
Granite, basalt
Yes — size depends on cooling
speed (slow/deep cooling →
large crystals, e.g. granite;
fast/surface cooling → small
crystals, e.g. basalt)
No
Sedimentary
Weathered rock
fragments (or dead
organic material)
compacted and
cemented in layers
Limestone,
sandstone,
shale
Sometimes absent
Yes, may
be
present
Metamorphic
Existing rock (any type)
changed by heat +
pressure, usually from
tectonic plate
movement
Marble (from
limestone),
slate (from
shale)
Mineral crystals present
No
Rock cycle (know the full sequence and be able to label a diagram): weathering (rock broken down in
place — biological/chemical/physical) → erosion (fragments removed) → transportation (moved by
wind/water/ice) → deposition (dropped when wind/water slows) → sedimentation (layers accumulate) →
compaction (pressure from layers above squeezes out space) → cementation (dissolved minerals bind
particles = sedimentary rock). Separately: crystallisation = magma cooling to form igneous rock. Heat +
pressure on any rock = metamorphic rock. All three types can re-melt back to magma, restarting the
cycle.
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Permeability = the ability of water to pass through the pore spaces of rock or soil. - Permeable: most
sedimentary rocks — limestone, sandstone. - Impermeable: igneous, metamorphic, and some
sedimentary rock — shale.
⚠️ Exam trap: permeability does not follow rock-type group. Shale is sedimentary but impermeable,
while limestone/sandstone (also sedimentary) are permeable. Never write "sedimentary = permeable" as
a blanket rule.
1.2 Extraction of rocks, ores and minerals
Ore = rock containing minerals and metals (that can be extracted).
Extraction methods: - Surface: opencast/open-pit/open-cut mining (overburden stripped off, mined in
stepped "benches"); strip mining (overburden removed, then horizontal seams cut out — common for
shallow coal). - Subsurface: deep mining (sloping tunnels to deep deposits); shaft mining (vertical shaft
+ horizontal galleries — most expensive/technical, only for high-value deposits). - Biological:
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phytomining (plants absorb metal through roots, concentrate it, then are harvested and burned to
recover it — bioaccumulation in action); bioleaching (bacteria break down low-grade ore into an acidic
metal-ion solution that is chemically processed). Both are slow but low-impact — useful when
concentration is too low for conventional mining.
Factors affecting the decision to extract — exploration (finding deposits is unlikely: ~1 in 100 for
common metals, as low as 1 in 1000 for rare ones like gold) → geology (rock type/structure decides
mining method) → accessibility & terrain (remote/difficult land raises cost) → quantity & quality of
deposit (ore grade — low-grade ore costs the same to transport/process as high-grade but yields far less
profit) → climate (extreme heat/cold raises cost, e.g. permafrost) → environmental impact assessment
(required by many governments before permission is granted) → supply and demand (price fluctuates;
falling demand can pause extraction until scarcity pushes prices back up) → cost and profit.
Impacts of extraction: - Environmental: habitat/biodiversity loss (vegetation clearance, waste heaps);
air pollution (dust — blocks light, cuts photosynthesis; can be toxic); land pollution (waste
rock/tailings and chemical spills contaminate the ground); noise pollution (surface mining
explosives/machinery > deep mining); water pollution (acidic runoff dissolves toxic metal ions →
bioaccumulation in individual organisms → biomagnification up the food chain, killing top
consumers); visual pollution (often temporary — reversible by restoration); water usage; waste
management. - Economic: jobs (fewer than expected — mining is mechanised; more jobs if refining also
happens locally); tax revenue; infrastructure investment (roads, utilities) — but loss of livelihoods (e.g.
farmers displaced) and volatile local economy tied to one industry. - Social: better
roads/schools/healthcare from mine investment vs. housing shortages, community relocation, loss of
cultural/religious sites, loss of community cohesion from incoming workers.
Managing damaged landscapes: - Land restoration: replace overburden to reshape land → import
topsoil → bioremediation (organisms break down toxins in contaminated ground) → replant trees (roots
stabilise soil, rebuild habitat). Slow, but returns land closest to its original state. - Repurposing: landfill
(waste + soil cover + planting); flooded pits → lakes/reservoirs (irrigation, drinking water) if the rock is
impermeable; nature reserves (raises biodiversity even if terrain has changed); recreation/tourism.
Faster than restoration, but doesn't recreate the original ecosystem — e.g. landfill can generate
methane and water-pollution risk.
1.2.6 Discuss benefits/limitations of these strategies — balance restoration [slow, thorough, high
monitoring cost] against repurposing [fast, useful, but not a true restoration] using the points above.
1.3 Sustainable management of rocks, ores and minerals
Finite resource = a natural resource used up at a faster rate than it is replaced. Sustainable
management of resources = using strategies that meet present needs without compromising the
ability of future generations to meet their own needs.
Strategies: - Reduce and reuse — less material per product (same-strength but lighter designs),
process near the extraction site (less transport fuel), reuse containers/items instead of buying new. Recycling — accessibility (enough collection points/facilities), ease (simple sorting/process), education
(people must know how to recycle correctly — lack of knowledge and inconvenience are major reasons
people don't). Recycled metal uses far less energy than refining new ore. - Increased efficiency of
extraction — better technology recovers more from a deposit (underground coal mining, for
comparison, typically recovers only 55–70% of a reserve) and processes mine waste a second time. Avoiding resource depletion — careful monitoring; not always simple, since some finite-resource
uses (e.g. lithium for EV batteries) reduce a bigger problem (fossil fuel dependency). - Legislation (laws
forcing take-back/recycling schemes, tracked waste disposal, fines for illegal dumping, taxes on excess
waste) + enforcement (spot checks; legislation alone fails without it — compliance still needs
monitoring and penalties). - Alternative materials — substituting an abundant material for a scarce
one (may perform worse, or open a new use for former waste, e.g. recycled plastic in concrete).
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1.3.4 Discuss — balance: recycling saves energy and delays exhaustion, but not all materials/people
participate; legislation drives change but is hard to enforce; alternative materials conserve resources but
may underperform.
1.4 Energy resources
Fossil fuel formation (coal, petroleum, natural gas): dead plant/animal matter buried under layers of
sediment → millions of years of heat + pressure → organic matter transformed. Coal: vegetation → peat
→ (compression) → lignite → (further compression) → coal. Petroleum/natural gas: buried marine
organisms transformed similarly, then migrate into and are trapped within porous sedimentary rock
beneath an impermeable cap rock — this is why they're accessed by drilling.
Classification: - Renewable (non-finite): biofuels (bioethanol, biomass, biogas, wood), geothermal,
hydro-electric, tidal, wave, solar, wind. - Non-renewable (finite): fossil fuels, nuclear (uranium).
Generating electricity — the common mechanism: a turbine (blades turned by a moving
gas/liquid/steam) drives a generator (turns kinetic energy into electrical energy via electromagnetic
induction — a magnet + rotating coil of conductor). - Fossil fuels, biofuels, nuclear, geothermal:
heat source → boils water → steam drives the turbine. (Geothermal: cold water pumped onto hot
underground rocks → heated water/steam raised, heats a second water supply via a heat exchanger →
that steam drives the turbine.) - Hydro-electric: flowing/stored (dammed) water directly turns the
turbine — no boiling needed. - Wind: moving air turns the turbine directly (via a gearbox). - Tidal: a
tidal barrage (small dam) releases water at changing tide height through a turbine. - Wave: turbine
driven by wave motion at sea, not tied to the tide cycle, but stops in calm weather. - Solar (the
exception — no turbine): photovoltaic cells generate a small electric charge directly from light;
panels/arrays combine many cells.
Benefits/limitations — the recurring axis: fossil fuels/biofuels/nuclear release energy on demand
(dispatchable) but fossil fuels emit CO₂ (+ other pollutants) and are finite; nuclear is energy-dense and
carbon-free but carries radiation risk and waste that stays radioactive for centuries; biofuels are
renewable but need land (competing with food crops) and still emit CO₂/pollutants when burned.
Solar/wind/wave/tidal are carbon-free and inexhaustible but intermittent (weather/time-of-day
dependent), geographically limited, and have upfront cost + visual impact. Hydro-electric and
geothermal are reliable and carbon-free but hydro floods land/displaces communities/ecosystems, and
geothermal only suits certain locations.
Factors affecting energy demand: - Transport — global shipping/air freight has risen sharply;
cheaper manufacturing abroad trades off against higher transport-fuel use. - Personal & national
wealth — richer people/countries buy and run more energy-using goods; a weak economy means less
manufacturing, less transport, and less capacity to import energy. - Climate — colder climates use more
heating energy; more extreme weather (climate change) raises demand for heating/cooling. - Human
population size — the single biggest driver; more people means more of everything that uses energy,
including food and water supply. - Industry — industrialised/manufacturing-heavy economies use far
more energy per person than agricultural ones (e.g. steel production needs very high, sustained heat). Disruption to supply and unreliable supply — infrastructure damage or inconsistent access changes
both how much is used and how much is demanded once supply improves. - Scarcity of resources —
geopolitical conflict or poor weather (low wind/sun) restricts how much can be generated/imported.
1.5 Conservation and management of energy resources
Strategies: - Reducing consumption — e.g. avoiding standby power (devices left on standby can
collectively use as much energy as a light left on). Low-cost but hard to enforce (behaviour change, not
easily monitored). - Insulation — the biggest shares of heat loss in a typical uninsulated house are
Page 9 of 41
through the roof (~30–35%), windows (~21–31%) and walls (~18–25%), with the rest lost to air
leakage; loft insulation, cavity wall insulation, and double/triple glazing (trapped air/gas layer as
insulator) all cut heat loss. Long-term savings but high install cost, harder to retrofit older/historic
buildings. - Energy-efficient devices (including EVs) — better technology (e.g. car fuel efficiency more
than doubled 1975→2021, roughly 6 km/litre to over 13 km/litre) cuts energy per use; scrappage
schemes speed uptake, but not everyone can afford to upgrade, and replaced devices add to waste. Exploiting existing energy resources — anaerobic digestion (bacteria break down organic waste in a
sealed container → biogas, mostly methane, + a compost by-product improving soil); incineration of
household waste for heat/electricity (small ash volume, but produces air pollutants); waste cooking oil
recycled into biofuel. - Education on energy conservation — raises awareness, but stated willingness
to act (e.g. survey responses) often doesn't match real buying behaviour; energy-efficiency labelling
supports comparison. - Transport policies — fuel-efficiency/emissions regulation, congestion charges
(e.g. low-emission zones), better public transport/cycling infrastructure, restricted vehicle access days,
grants for efficient/electric vehicles. - Battery storage — stores excess renewable generation for use
when demand is high but generation is low; limited by finite battery-mineral supply, cost, and local
objections (fire risk, visual impact). - Development of new energy resources (below).
New energy resources:
Resource
How it works
Key limitation
Blue hydrogen
Hydrogen split from natural gas (steam
methane reforming); CO₂ by-product is
captured, not released
Still depends on a finite fossil fuel
Green
hydrogen
Hydrogen split from water via
electrolysis, powered by renewable
electricity
Electrolysis itself is energy-intensive
Ground source
heat pump
Heat exchanger extracts heat from the
ground
Ground temperature too low to raise steam
— heats buildings/water directly, cannot
generate electricity
Air source
heat pump
Heat exchanger extracts heat from
outside air (works like a reversed
fridge/AC unit)
Same limitation as ground source —
space/water heating only
1.5.3 Discuss — behavioural strategies (reducing consumption, education) are free/cheap but hard to
enforce and slow to change habits; physical measures (insulation, efficient devices, battery storage, new
resources) cost more upfront but save energy reliably once installed; balance ease/cost against how
much energy each strategy actually saves.
1.6 Fracking
Fracking = extraction of natural gas or petroleum from shale rock by hydraulic fracturing. Process: drill
vertically (often 2–3 km) into shale → pump water + sand + chemicals under high pressure → rock
fractures, releasing gas/oil, forced back up and collected. Water = carrier (cheap, available); sand =
"proppant" (holds fractures open); chemicals = prevent pipe blockage.
1.6.2 Discuss — benefits: accesses otherwise-unreachable reserves, natural gas burns cleaner than coal,
cuts import dependence, creates local jobs; limitations: risk of toxin/chemical contamination of
groundwater, very high water use, noise and land disturbance at drill sites, risk of triggering earth
tremors, long-term impacts still not fully known.
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Topic 2 — Land
2.1 Soils and crop growth
Composition: mineral particles (sand, silt, clay) + organic content (living organisms + decomposed
matter) + gases (in pore spaces) + water (in pore spaces). (% composition not required.)
Mineral particles by size (largest → smallest):
Size
Feel
Drainage / air
Sand
0.02–2.0 mm
Gritty
Large pores — drains freely, good air spaces
Silt
0.002–0.02 mm
Silky/soapy
Intermediate
Clay
<0.002 mm
Sticky when wet, hard when dry
Tiny pores — holds water, poor drainage/air
Why composition matters for crop growth: - Mineral particles — size decides drainage,
water/nutrient retention, cultivation ease (above table). - Nutrient content = organic content + inorganic
ions: nitrogen as nitrate (NO₃⁻), phosphorus as phosphate (PO₄³⁻), potassium as potassium
ions (K⁺). Deficiency signs: N → slow growth, yellowing of oldest leaves; P → dull blue-green leaves,
early leaf fall; K → poor fruit/seed quality, brown leaf edges. - pH (acidic/neutral/alkaline) — affects how
easily roots take up ions; at high (alkaline) pH, nitrate and phosphate uptake fall sharply, but potassium
uptake is largely unaffected. Most soils sit within pH 4–9. - Pore spaces — need to be large enough for
drainage/gas exchange but numerous enough to retain some moisture. - Gas content — roots need O₂
for respiration; waterlogged pores exclude O₂ and roots die. - Water content and drainage — sandy soils
drain fast (drought risk); clay soils hold water (waterlogging risk). - Ease of cultivation — sandy soils are
light/easy to work; clay is dense and harder to cultivate, especially wet.
Loam = ideal medium because it combines sand+silt+clay: enough pore space to drain excess water
and retain moisture + air for roots; holds organic content/ions well; drains excess water; easy to
cultivate.
Weather = day-to-day atmospheric conditions in a location (cf. climate = weather over many years,
Topic 4). Some regions have distinct wet/dry seasons that dictate planting/harvest timing.
Optimum photosynthesis/crop growth conditions: - Word equation: carbon dioxide + water -(light energy, chlorophyll)--> glucose + oxygen. - Length of growing season — longer near the
equator (less seasonal variation) can allow more than one harvest per year; short growing seasons limit
which crops mature in time. - Optimum weather conditions — temperature and light intensity need
to sit in the range each crop is suited to; too hot/cold or too dull/intense slows growth or damages the
plant. - Daylight hours — more light = more photosynthesis; some crops need a minimum day length
to flower/ripen at all.
2.2 Food production and crop yield
Types of agriculture (classifications combine — e.g. an intensive commercial arable farm): - Arable
(crops for humans) / pastoral (livestock/livestock products) / mixed (both). - Subsistence (grows to
feed the farmer's own family, little/no surplus) / commercial (grows to sell for profit). - Intensive (high
yield per unit area via heavy inputs of labour/fertiliser/machinery). - Monoculture (one crop/animal
type only — efficient and allows specialised expertise + large machinery, but the whole crop is
vulnerable to one pest/disease and reduces local biodiversity).
Sustainable food production = producing enough food for the present generation using methods that
let future generations grow food from the same land.
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Strategies to increase yield: - Mixed cropping / intercropping / crop rotation — growing >1
crop together (different heights/root depths reduce competition; one crop can support another) or in
planned sequence. Crop rotation prevents the pest/disease build-up, one-sided nutrient depletion that
comes from growing the same crop repeatedly; legumes (pea/bean family) fix nitrogen via root-nodule
bacteria, replenishing soil nitrate for the crop that follows. - Improved irrigation — trickle/drip (pipes
deliver water straight to the root zone: efficient and automatable, but costly to install and tubes can
block); rainwater harvesting (stored for dry periods, but open storage loses water to evaporation and
can breed disease-carrying mosquitoes); automated watering (sensors trigger irrigation only when
needed). - Mechanisation — tractors etc. let one person cultivate more land, apply fertiliser/pesticide
efficiently, but favour large uniform fields (natural vegetation removed → biodiversity loss). - GMOs —
genes inserted from one organism to another for disease/pest resistance, higher nutritional value,
herbicide resistance, higher yield, longer storage life. Concerns: unknown long-term health effects,
"unnatural", risk of the modified gene spreading to wild plants, knock-on effects on non-target insects. Controlled environments — greenhouses (light passes through the transparent material, converts to
heat, heat is trapped inside — same "trapping" principle as the greenhouse effect in Topic 4) let growers
manage temperature/light/humidity/day length/water; polytunnels are a cheaper but less effective
version. Hydroponics = growing in nutrient-dissolved water with no soil (roots in circulating, aerated
nutrient solution) — very efficient/no soil pests, but expensive, technical, and disease spreads fast
through the shared water. Aeroponics = roots suspended in air and misted with nutrient solution —
even better root aeration, but nozzles can block. - Managed grazing (livestock rotation) — lets grazed
land recover, preventing the vegetation loss/compaction of overgrazing. - Urban farming — uses city
space/vertical facilities (often with hydroponics) to grow food close to consumers. - Agroforestry —
crops grown among trees; canopy shelters crops from weather, roots + ground cover reduce soil
erosion, uses vertical space efficiently. - Fertilisers: organic (manure, crop residue, mulch — bulky,
improves soil structure/water-holding as well as supplying nutrients, but variable composition and harder
to transport) vs. inorganic/NPK (factory-made, precise/consistent nutrient ratio, easy to store/apply, but
costly and no soil-structure benefit). - Pest control: chemical — insecticide/herbicide/fungicide, fast
and effective but risks non-target species, resistance (repeated use selects for resistant survivors, who
breed a resistant population) and pest resurgence (killing a pest's natural predators lets the pest
rebound even higher). Biological control — introduce a natural predator/pathogen of the pest: no
chemical residue, self-sustaining once established, but slower-acting, and the control agent itself can
escape and disrupt the wider ecosystem.
Impacts of unsustainable practices: - Overproduction → food wastage (also wastes storage,
transport, quality, labour). - Food shortages — commercial cash crops (coffee, cotton, soybeans,
palm oil) or biofuel crops grown instead of food crops on the best land. - Mismanaged irrigation → soil
erosion (excess run-off), salinisation (water evaporates, leaves salts behind; ~20% of irrigated land
has become saline over the last 20 years — impairs water uptake by osmosis), waterlogging (excludes
O₂ from roots, soil capping/compaction). - Pesticide overuse → resistance, pest resurgence, harm to
pollinators (fewer bees → reduced pollination) and wider food-web effects. - Fertiliser overuse →
leaching into water → nutrient enrichment → eutrophication (see Topic 3). - Nutrient exhaustion —
repeated cropping with no replenishment strips inorganic ions and organic content. - Removal of
natural vegetation — deforestation, overcultivation (breaks down soil structure, reduces pore spaces),
overgrazing (compaction, vegetation loss). - Monoculture/intensification → soil/water pollution,
biodiversity loss (removal of "competing" wild species). - Soil erosion — loss of topsoil and its nutrients
(detailed next).
2.3 Soil erosion
Soil profile (top → bottom): topsoil (most fertile — organic matter, most root growth) → subsoil → parent
material → bedrock.
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Causes: unsustainable agricultural practices (cultivation breaks soil into smaller, more erodible
particles) · deforestation (roots no longer bind soil or slow run-off) · farming on steep slopes (gravity +
removed vegetation) · bare soil (overgrazing removes cover; compacted, exposed) · wind erosion (dry,
loose soil particles blown away) · water erosion (heavy rain dislodges particles; run-off carries them;
fast-flowing gullies cut deeper channels).
Impacts: - Silting of rivers — deposited soil reduces channel capacity (→ flood risk), creates
mosquito-breeding pools, reduces light/oxygen for aquatic life. - Desertification — topsoil gone →
subsoil can't support growth → even less organic matter returned → self-worsening cycle. - Mass
movement — landslides, rockslides, mudslides (saturated soil layer, or surface soil carried in run-off,
moves downslope). - Loss of habitats and biodiversity — topsoil itself is a habitat; knock-on loss of
shelter/food up the food web. - Reduced crop yield, malnutrition and famine, displacement of
people (forced relocation to find cultivable land, potential conflict with existing communities).
Strategies to reduce soil erosion:
Strategy
How it works
Terracing
Steps cut into a slope hold rainwater in flat sections instead of letting it run
downhill, reducing speed/volume of run-off and soil movement
Contour ploughing
Furrows follow the land's contours (not up/down the slope), so each furrow holds
back water rather than channelling it downhill
Bunds
Earth banks around a plot hold back water (and any soil it carries), reduce run-off,
and reduce wind speed/erosion
Wind breaks
Vegetation (or artificial barriers) slows wind speed at ground level; roots also bind
soil against water run-off
Maintaining
vegetation cover
Roots physically bind soil; cover crops/no-dig methods keep roots in the ground
between main crops
Adding organic
matter
Improves soil structure — larger, irregular particles bind others together, hold
water, resist wind/water loss
Page 13 of 41
Topic 3 — Water
3.1 Water sources and supply
Water cycle — stores: salt water (oceans) + fresh water (ice sheets/glaciers, groundwater, atmosphere,
lakes/rivers). Transfers: precipitation (rain/snow falls) · interception (plants catch precipitation before
ground) · surface run-off (flows over ground into rivers) · infiltration (seeps into ground) · throughflow (moves through soil) · groundwater flow (moves through rock) · transpiration (water loss from
plants, draws water up through them) · evaporation (liquid → vapour) · condensation (vapour →
liquid, forms clouds).
Freshwater sources: atmosphere (rain, snow) · surface water (rivers, lakes, reservoirs — some behind
dams) · groundwater (aquifers = water stored in porous rock, reached by wells; if under pressure =
artesian aquifer, water rises unaided) · oceans (via desalination).
World's oceans: Pacific, Atlantic, Indian, Southern, Arctic.
Potable water = safe to drink. Treatment stages: screening (removes large debris) → sedimentation
(chemicals added make particles clump and sink) → filtration (through sand, removes remaining
particles) → chlorination (kills pathogens).
Comparing potable water availability: - Water-rich vs water-poor regions — depends on rainfall and
population size relative to supply (a country can have high rainfall but still be water-stressed if demand
is high). - Urban vs rural — urban areas typically get better piped water/sanitation (cheaper to install per
person, more political pressure); rural areas often rely on unimproved sources; but dense urban slums
can have very poor sanitation despite city wealth. - Global inequalities — depend on both sanitation
systems (keeping sewage away from drinking water) and treatment infrastructure; economic water
scarcity (can't afford to extract/treat available water) is distinct from physical water scarcity (not enough
water to begin with).
Desalination:
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Method
Process
Efficiency
Distillation
Water heated to boiling; salt stays in the liquid; steam
(pure water) is cooled and condensed back to liquid
~10–30% — energy-intensive, so
mainly used by energy-rich
countries
Reverse
osmosis
Water forced under high pressure through a fine
membrane that lets water molecules through but blocks
salt ions/other molecules
~30–50% — less energy than
distillation; most new plants use
this
3.1.8 Discuss — benefit: creates potable water where none exists; limitations: high energy use/cost, and
both methods produce concentrated brine by-product that is often pumped back to sea, harming marine
life/causing local acidification.
Multipurpose dam uses: flood control · hydro-electric power · irrigation · water storage · transport
(navigable water level) · recreation · tourism · fish farming.
3.1.10 Discuss — benefits as above, carbon-free power; limitations: high cost, displacement of people,
loss of land, disrupts fish migration/breeding, reduces silt/fertility downstream, siltation reduces the
reservoir's own storage capacity over time, structural failure risk.
3.2 Water pollution
Sources: domestic waste (greywater — detergents/phosphates) · sewage (urine/faeces — pathogens +
organic matter) · plastic waste · industrial processes (toxic chemicals, heavy metals) · agricultural
practices (fertiliser/pesticide run-off).
Impacts: - Infectious bacterial disease risk — e.g. cholera, spread via contaminated water. Accumulation of toxic substances from industry (heavy metals etc.). - Bioaccumulation — build-up
of a substance within a single organism over time. - Biomagnification — that substance's
concentration increases at each step up a food chain (highest in top predators). - Acid rain effects on
aquatic organisms — see Topic 4; lowers pH, fish lay fewer/malformed eggs, leaches toxic metals (e.g.
aluminium) from soil into water. - Leaching and nutrient enrichment → eutrophication: nutrients
(nitrate/phosphate) enter water → algal bloom (rapid algae growth) → algae die → bacteria decompose
them, consuming dissolved oxygen → oxygen levels fall → fish and other aquatic animals die from lack
of oxygen.
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Strategies for improving water quality: - Improved sanitation — toilets that separate human
waste from contact/water supply (flush, pit latrine, composting toilet). - Treatment of sewage —
screening (remove large objects) → primary settling (solids settle as sludge) → secondary/oxidation
(aerated to grow bacteria that break down dissolved organic matter, lowering biological oxygen
demand) → second settling (more bacteria/sludge settle out) → effluent released; sludge separately
broken down anaerobically (releases methane) and can be dried for use as fertiliser. - Pollution control
and legislation — monitored emission limits, fines/prosecution for exceeding them, incentives
(grants/tax relief) for compliance.
3.3 Water-related diseases
Malaria — caused by the parasite Plasmodium, carried by the female Anopheles mosquito (the
vector, not the cause). Mosquito bites an infected human → picks up parasite → parasite multiplies in the
mosquito → transmitted to the next person it bites. Water-related because the mosquito breeds in still
water. - Control — personal protection: insecticide-treated bed nets, insect repellent, protective
clothing, antimalarial drugs, vaccination. - Control — vector control: cover/drain breeding sites (still
water), insecticide spraying, sterilising male mosquitoes (breed but produce no offspring), biological
control (e.g. fish that eat larvae), oil on water surfaces (stops larvae breathing/adults laying eggs).
Cholera — bacterial infection, spread via water contaminated with human faeces; causes
vomiting/diarrhoea → dehydration → can be fatal without treatment (rehydration). - Control:
handwashing, adequate sanitation and sewage treatment (kept separate from drinking water), potable
supply (boiling/chlorination), vaccination.
3.3.4 Discuss — vector control for malaria is cheap and can be done by individuals but only reduces, not
eliminates, transmission; drug/parasite-targeting treatment is more effective long-term but expensive,
and both the mosquito and the parasite are developing resistance. For water-related disease control
generally: individual actions (handwashing, boiling water) are low-cost, while sanitation infrastructure
and treatment need government investment but give more complete, lasting protection — any lapse
quickly allows disease to return.
3.4 Marine aquaculture
Impacts of exploiting marine species: - Overfishing/overharvesting — catching faster than
stocks can reproduce; fish also caught progressively smaller/younger as stocks decline. - Target and
bycatch species — non-target/wrong-size/wrong-species individuals caught and usually discarded
(dead); large unselective nets worsen this. - Food chains — removing one species disrupts predators
and prey linked to it through the food web.
Marine aquaculture = farming marine species in captivity: fish, crustaceans, seaweeds. (No named
species required.)
Impacts: reduces pressure on wild fisheries + increases food supply (benefits) vs. risk of farmed
organisms escaping and disrupting wild ecosystems, disease spreading (more easily than in the wild) to
natural populations, local food web disruption, nutrient enrichment from waste/feed, energy use
(maintaining conditions), and the farmed stock itself needs feeding — sourced from elsewhere
(limitations).
Managing harvesting of marine species:
Strategy
Effect
Limits on boat/net
size
Restricts how much can be caught/processed at once
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Strategy
Effect
Increased mesh
size
Lets juvenile/undersized fish escape, so they can breed
Sustainable
methods (pole and
line)
Highly selective — minimal bycatch
Quotas
Legal catch limits based on stock science — fisheries with quotas are about half as
likely to collapse as unmanaged ones
Closed seasons
No fishing during breeding periods
Limited fishing
days
Restricts total effort
Protected areas
No fishing where species breed/is vulnerable
Conservation laws
National legal protection
International
agreements
Needed beyond national waters (exclusive economic zones extend 200 nautical miles;
open ocean needs shared agreement); implementation and monitoring are the hard
part — the ocean is vast and hard to police, so enforcement (not just the rule)
determines success
3.4.5 Discuss — these measures work when monitored/enforced, but illegal, unreported, unregulated
fishing is easy to get away with in practice; balance "protects future stocks/livelihoods" against "hard to
enforce, costly, restricts income now."
3.5 Oil pollution
Causes: off-shore and on-shore extraction (leaks) · pipelines · shipping (collisions/damage) · cleaning of
tanks at sea · refineries.
Impacts (mechanism: oil floats, blocks light and gas exchange at the surface): - Birds — feathers
coated in oil lose waterproofing/buoyancy/flight ability; ingest oil while feeding. - Marine mammals —
food source depleted; ingest oil while feeding; skin/fur coated. - Fish — oil blocks gas exchange at the
surface and affects gills directly → oxygen shortage; food shortage as phytoplankton die back. Crustaceans — smothered, affected by toxic chemicals (can move away, unlike sessile species). Seaweeds — smothered, unable to photosynthesise. - Coral reefs — oil blocks light to symbiotic
algae/phytoplankton → reduced photosynthesis and oxygen → wider reef community affected. Beaches — oil washed in by tides coats rocks/organisms in shallow pools.
(Note: the amount of oil spilt doesn't necessarily predict environmental damage — spread, location, and
clean-up difficulty matter more.)
Spill prevention: - MARPOL (International Convention for the Prevention of Pollution from Ships) —
international regulations on oil/sewage/rubbish/toxic-liquid discharge from ships. - Double-hulled
tankers — a second inner hull keeps cargo contained if the outer hull is breached. - Risk assessments
— identify hazards → assess likelihood → assess consequences → decide mitigating measures. - Regular
maintenance — of extraction/transport equipment (e.g. blowout preventers on wells).
Minimising spill impact:
Page 18 of 41
Method
How / limitation
Improved navigation
systems
Prevents collision-caused spills in the first place
Booms
Floating barriers contain/corral the slick — work best in calm seas, small spills
Sorbents
Materials that absorb oil (peat, clay, synthetics) — best for smaller spills/final cleanup
Detergent sprays
Break the slick into smaller droplets to disperse — least effective/most damaging in
sensitive habitats (e.g. coral)
Skimmers
Mechanically drag oil off the water surface — need calm conditions
Controlled burning
Removes oil quickly by burning it off — produces air pollution
3.6 Plastic pollution
Conventional plastics = made from fossil fuels, generally non-biodegradable (take a very long
time to break down).
Bioplastics = made fully/partly from biological material instead of fossil fuels — may or may not be
biodegradable (roughly half of bioplastics are not biodegradable in practice, since composting
conditions aren't present where they end up, and processing can make the material harder to break
down).
Biodegradable plastics — designed to decompose in water or soil; broken down by bacteria/fungi
into water, biomass, and gases (CO₂, methane); rate depends on biotic (which organisms are
present) and abiotic (temperature, light, O₂) factors.
Microplastics — <5 mm; formed either when larger plastics break down, or manufactured directly
for use in commercial products (e.g. microbeads).
Impacts on marine ecosystems: - Visual pollution. - Entanglement — trapped in bags/nets/rings;
can be fatal. - Mistaken for food — fills the stomach without providing nutrition (so the animal can't
eat real food), and can physically damage the digestive tract. - Bioaccumulation and
biomagnification — builds up in tissues and up the food chain; plastics also bind to other toxic
chemicals in the environment, which can then biomagnify too.
Managing plastic pollution: alternative packaging (e.g. plant-based/biodegradable materials) ·
avoiding single-use plastics · safe disposal (vs. landfill/uncontrolled burning) · recycling (complicated by
many different plastic types with different properties) · legislation and enforcement (e.g. bans on
specific single-use items).
Page 19 of 41
Topic 4 — The atmosphere and human activities
4.1 The atmosphere
Structure (4 layers, by temperature trend):
Layer
Height
Temperature
trend
Why
Upper boundary
Troposphere
0 – ~8 km
(poles) to
~17 km
(tropics)
Decreases with
height (~6–
6.4°C/1000 m)
Surface heats this layer by
conduction/convection; effect
weakens with altitude
Tropopause —
marks the limit of
weather/climate
Stratosphere
up to ~50
km
Increases with
height
(temperature
inversion)
Ozone layer (in the lower
stratosphere) absorbs
incoming UV radiation
Stratopause
Mesosphere
50–80 km
Falls rapidly (to
below –80°C)
No ozone/water vapour/dust
here to absorb radiation
Mesopause
Thermosphere
80–1000 km
Rises rapidly (to
~1500°C)
Atomic oxygen absorbs UV
radiation directly
Thermopause
Page 20 of 41
Composition of clean, dry air:
Gas
%
Notes
Nitrogen (N₂)
78
Needed for plant growth
Oxygen (O₂)
21
Product of photosynthesis; used in respiration
Argon
0.9
Inert/noble gas
Carbon dioxide (CO₂)
0.04
Variable gas; used in photosynthesis, released in respiration
Water vapour (H₂O)
0.2–4.0, variable
Source of precipitation
Ozone (O₃)
trace (~0.00006%)
Found in lower stratosphere; absorbs UV
Page 21 of 41
⚠️ Exam trap: "clean, dry air" excludes water vapour — that's why nitrogen/oxygen/argon/CO₂
percentages are quoted for dry air specifically.
Climate = the weather conditions in a location based on the weather over many years (contrast with
day-to-day weather, Topic 2).
Natural greenhouse effect — the mechanism that keeps Earth warm enough for life: 1. Solar (shortwave) radiation passes through the atmosphere. 2. Some is absorbed by land/oceans, heating Earth's
surface. 3. Some is reflected straight back into space (by clouds/surface). 4. The warmed surface emits
long-wave radiation back out; greenhouse gases and clouds absorb some of this and re-emit it back to
the surface. 5. This natural process keeps Earth roughly 34°C warmer than it would otherwise be —
enough to support life.
4.2 Climate change
Greenhouse gas = a gas that absorbs radiation and emits the energy as thermal (heat) energy. Named
greenhouse gases (syllabus): carbon dioxide (CO₂), water vapour (H₂O), methane (CH₄). (CFCs
and nitrous oxides also act as greenhouse gases and appear in mark schemes as extra credit, but the
three above are the core named list.)
Causes of increased greenhouse gas concentrations:
Cause
Gas released
Mechanism
Combustion of fossil fuels
CO₂
Direct release on burning
Agriculture
CH₄
Cattle digestion, manure decomposition, rice fields
Page 22 of 41
Cause
Gas released
Mechanism
Deforestation
CO₂
Fewer plants to remove CO₂ via photosynthesis
Land-use change
CH₄
Wetland drainage
Cement manufacture
CO₂
Limestone (CaCO₃) heated → lime (CaO) + CO₂
Rising population & energy use
CO₂
More combustion overall
(Pre-industrial CO₂ ≈ 280 ppm; 2023 measured ≈ 424 ppm — highest ever recorded. Global transport =
15% of global greenhouse gas emissions (2023). Global cement manufacture = 8% of world CO₂
emissions (2023).)
Enhanced greenhouse effect: greenhouse gases absorb (extra) solar/outgoing radiation, causing
global warming, which can result in climate change. CO₂ is the single largest contributor.
Impacts of climate change (ENSO/El Niño/La Niña mechanisms are explicitly not required — don't
spend time on them): - Increased Earth surface temperature. - Increased ocean surface temperature. Melting ice sheets, glaciers and permafrost → sea-level rise (also rises from thermal expansion of
warmer water). - Ocean acidification (more dissolved CO₂) → organisms like coral struggle to build
calcium carbonate skeletons → coral bleaching. - Disruption to food chains. - Change in biodiversity. Loss of habitat. - Forced migration of humans and other animals. - Increased frequency/severity of
extreme weather → flooding and loss of land, drought, wildfires. - Change in crop yields (can rise —
longer growing season — or fall — more drought). - Increased pest outbreaks and invasive species. Food shortages.
(Not all impacts are negative for everyone — e.g. some regions gain longer growing seasons or newly
ice-free shipping routes — but the balance of impacts is negative.)
Strategies to reduce carbon footprint (mitigation — tackles the cause):
Strategy
Limitation
Reduced fossil fuel use (more renewables/nuclear)
Existing infrastructure makes fossil fuels cheap;
renewables/nuclear need investment; nuclear is costly
and produces radioactive waste
Sustainable food choices (plant-based, seasonal,
local)
People act only if changes are easy, accessible,
affordable
Reduced livestock farming
Reduces methane but affects farmers'
livelihoods/production
Reduction in children per woman
Reduces long-term footprint, but birth rate is very hard
to change
Increased energy efficiency
Individuals may feel their actions won't make a
difference; upfront cost
Reforestation & afforestation (carbon sinks)
Needs a very large global effort to have a sizeable
impact
Carbon sequestration (CCS: capture, remove and
store CO₂ underground)
Expensive technology; limited storage capacity in some
countries; leakage risk (groundwater contamination,
triggers small earthquakes)
Transport policies (public transport, electric/hybrid
vehicles, car-sharing)
Hard to decarbonise aviation/shipping; behaviour
change is slow; can be costly
Page 23 of 41
Strategy
Limitation
International agreements & policies (e.g. 2015
Paris Agreement — 195 countries agreed to limit
warming to 2°C)
Countries wanting to industrialise resist cuts; poorer
countries lack funds
Taxation (carbon tax on fossil fuels)
Hits poorer people harder; politically difficult; only
targets CO₂, not other gases
Research & climate modelling
Not all models are reliable; extreme events are hard to
predict
Artificial intelligence (predicting impacts, tracking
deforestation/emissions)
AI itself has a carbon footprint and a manufacturing
impact
4.2.9 Discuss — balance ease/cost/effectiveness against who bears the cost and how enforceable each
strategy is; no single strategy is sufficient alone.
Climate change adaptation = altering behaviour, practices and infrastructure to adapt to (cope with)
the impacts of climate change — usually local/national scale, not global.
Adaptation strategies:
Strategy
Benefit
Limitation
Crops resistant to warmer/drier/wetter
conditions
Reduces crop failure, food
insecurity
Cost; farmers in LICs need outside
help
Improved flood defences (sea walls,
storm-surge barriers, houses on stilts)
Reduces flood/erosion
damage, no relocation
needed
Expensive to build/maintain; may
disturb coastal habitats
Legislation on building near
coasts/floodplains
Reduces flood risk to
homes, industry, key
buildings
Hard to control urban growth; some
accept the risk
Building design/materials (insulation,
cooling systems, reflective roofing)
Protects against heat
exposure
Expensive; LIC self-built settlements
often lack access to new materials
4.3 Acid rain
Acid rain = precipitation/atmospheric deposits more acidic than natural rainwater (natural rain is
already slightly acidic, ~pH 5.6, from dissolved CO₂; acid rain is more acidic still — figures in past papers
have used both "<5" and "<5.6", so quote whichever the question gives you).
Formation: 1. Sulfur dioxide (SO₂) released from combustion of fossil fuels containing sulfur
compounds. 2. SO₂ also released from volcanic gases (natural source). 3. Oxides of nitrogen (NOₓ)
form when nitrogen from the atmosphere reacts with oxygen at the high temperature inside vehicle
engines. 4. SO₂ and NOₓ react with oxygen and water vapour in the atmosphere → weak nitric acid and
sulfuric acid → falls as acid rain.
Equation: sulfur dioxide + water + oxygen → sulfuric acid
(Acid rain can be carried hundreds of km by wind before falling as precipitation ("wet deposition"), so
impacts can occur far from the original source.)
Impacts: - Acidification of bodies of water (rivers, lakes). - Reduced fish populations. - Effects on
aquatic food webs. - Acidification of soils (leaches out nutrients, e.g. calcium). - Damage to crops and
vegetation: defoliation, reduced crop yields. - Damage to buildings (chemical weathering of
Page 24 of 41
limestone/marble).
Management strategies:
Strategy
Mechanism
Limitation
Flue-gas
desulfurisation
(scrubbers)
Spraying calcium carbonate/calcium oxide
into flue gas reacts with and removes SO₂
(up to ~95%)
Energy-intensive (needs high
temperatures); if water-based, the water
needs treating afterwards — leaks can
cause water pollution
Catalytic
converters
Catalyst speeds a reaction converting NOₓ
into less harmful gases before they leave
the exhaust
Expensive to replace; increase fuel
consumption (extra fuel keeps the
converter hot enough to work)
Transport policies
Subsidised public transport,
walking/cycling/car-sharing, more electric
vehicles — all cut NOₓ and SO₂ at the
source
Behaviour change is slow; infrastructure
investment needed
4.3.4 Discuss — both key technologies (scrubbers, catalytic converters) are effective and proven, but add
cost/energy demand; transport policy is cheaper per-person but slower to shift behaviour and requires
political will.
4.4 Ozone depletion
Cause: chlorofluorocarbons (CFCs) — from aerosols and refrigerants — released into the atmosphere
break down ozone in the ozone layer.
Impacts: - Higher levels of (harmful) solar UV radiation reaching Earth's surface. - Increased rates of
skin cancer (UV disrupts DNA, causes sunburn) and cataracts (clouding of the eye's lens). - Damage to
vegetation → reduced crop yields.
Management strategies:
Strategy
Detail
International
agreement and
policies
Montreal Protocol (1987) — 43 countries initially agreed to phase out ozonedepleting substances by 1989; 131 more had joined by 2000; use of ozone-depleting
substances fell 99.7% by 2021 (vs 1986) — a widely-cited success story for
international cooperation
CFC ban and
alternatives
Pump-action sprays (no propellant needed); alternative chemicals such as HCFCs,
ammonia, water. Trade-off: alternatives are more expensive/less efficient, and HCFCs
are themselves potent, long-lived greenhouse gases (phasing them out too could cut
warming by ~0.5°C by 2100)
Safe disposal of
CFCs
Old fridges/AC units sent to facilities that break CFCs into harmless molecules
4.4.4 Discuss — the Montreal Protocol shows rapid, near-total success is possible, but alternatives carry
their own environmental costs (HCFCs as greenhouse gases), and safe disposal infrastructure is unevenly
available worldwide.
Ozone depletion vs enhanced greenhouse effect — don't mix these up:
Page 25 of 41
Ozone depletion
Enhanced greenhouse effect
Layer mainly
affected
Stratosphere (ozone layer)
Whole atmosphere/surface system
Radiation
direction
Incoming UV — less is blocked, so
more reaches the surface
Outgoing long-wave radiation — more is
trapped and returned to the surface
Pollutant gas
CFCs
CO₂, CH₄, H₂O (+ CFCs, N₂O)
Action of gas
Breaks down ozone molecules
Absorbs and re-emits long-wave radiation
International
agreement
Montreal Protocol (1987)
Paris Agreement (2015)
Page 26 of 41
Topic 5 — Ecosystems, biodiversity and fieldwork
5.1 Ecosystems
Core definitions:
Term
Definition
Habitat
The place within an ecosystem where an organism lives
Species
A group of organisms that can reproduce with one another to produce fertile offspring
Population
All the organisms of one species living in a defined area
Community
All the populations of different species living together in an area, interacting with each
other
Niche
The role of a species within its ecosystem (how/where it feeds, its interactions, its effect on
the environment)
Predator
An organism that kills and eats other organisms
Prey
An organism that is eaten by a predator
Apex
predator
A predator not normally killed and eaten by any other animal
Biotic (living) components:
Role
Definition
Producer
Carries out photosynthesis to make its own food
Primary consumer (herbivore)
Feeds on producers
Secondary consumer (carnivore)
Feeds on primary consumers
Tertiary consumer (carnivore)
Feeds on secondary consumers
Decomposer
Feeds on/breaks down dead plant or animal material
Abiotic (non-living) components: temperature · water · oxygen · carbon dioxide · salinity · light · pH
— each sets a range a species must tolerate (e.g. aquatic organisms need adaptations like gills, since
oxygen is far less soluble in water than air; saline-adapted plants like mangroves excrete excess salt).
Biotic interactions: - Native species — long-established in an area, adapted to local conditions.
Invasive species — arrive from elsewhere (often via human activity); can damage ecosystems
because native predators/prey have no evolutionary adaptation to them (e.g. no resistance to a toxin an
invasive species carries), and they compete with natives for resources. - Competition — more offspring
are produced than the environment can support, so organisms compete for limited resources; the least
well-adapted individuals die or fail to reproduce. - Predation — a predator kills and eats prey. Pollination — transfer of pollen from an anther to a stigma. Insect pollination: bright, scented petals +
nectar attract insects; pollen is sticky, heavier, less abundant. Wind pollination: anthers hang outside the
flower (no need for petals/scent/nectar); pollen is light and very abundant (main cause of hay fever).
Either route → pollen reaches a stigma → fertilisation → seed and fruit formation. (Naming/structure of
flower parts is not required.)
Photosynthesis: sunlight is the energy source; chlorophyll (in chloroplasts) captures the light energy,
which is used to synthesise glucose from carbon dioxide and water.
Word equation: carbon dioxide + water --(light energy, chlorophyll)--> glucose + oxygen
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Energy flow through food chains/webs: - Trophic (feeding) levels: producer → primary consumer →
secondary consumer → tertiary consumer. - Only about 10% of energy is passed on to the next
trophic level; ~90% is lost as heat through the life processes of the level below — movement,
respiration, digestion, excretion. - This is why food chains rarely exceed 4–5 links: too little energy
remains to support another level. - Pyramid of energy — bar width = energy at each trophic level (in
kJ); because of the 10% rule, this always forms a true pyramid shape (each level smaller than the one
below). - Pyramid of numbers — bar width = number of organisms at each level; this does not
always form a true pyramid shape — e.g. a single large tree (1 producer) can support hundreds of sapsucking insects, giving a narrow base with a wider level above it. (
Exam trap: if asked why a
pyramid of numbers isn't pyramid-shaped, the answer is about the size/energy content of
individual organisms, not about energy flow itself — the energy pyramid for the same food
chain is still a true pyramid.) - Energy vs minerals: energy flows through an ecosystem in one
direction and is ultimately lost as heat; minerals/nutrients cycle round an ecosystem — they are
released when organisms die and decompose, and taken up again by producers.
⚠️
Aerobic respiration (releases the energy consumers need for movement, digestion, excretion,
growth):
Word equation: glucose + oxygen → carbon dioxide + water (+ energy released; energy is not
written into the word equation itself)
Carbon cycle — same store/transfer pattern as any mineral cycle:
Stores
Transfers
Carbon dioxide in the atmosphere
Photosynthesis — fixes atmospheric CO₂ into plants (as
carbohydrates, fats, proteins)
Carbon in fossil fuels (coal, petroleum,
natural gas)
Respiration — returns CO₂ from living things to the
atmosphere
Carbon compounds in organic matter
(living/dead plants and animals)
Feeding — passes carbon compounds from one organism to
the next along a food chain
Decomposition — decomposers respire, releasing CO₂ from
dead matter back to the atmosphere
Fossilisation — dead organic matter converted, over
geological time, into fossil fuels
Combustion — burning fossil fuels or organic matter releases
stored carbon as CO₂
5.2 Forest ecosystems
Causes of deforestation:
Cause
Mechanism
Logging and timber
extraction
Trees felled for wood/paper; access roads built for logging open the forest to
further clearance
Subsistence and
commercial farming
Land cleared for crops/pasture — the single largest cause of deforestation
worldwide
Roads and settlements
Direct clearance, and roads enable other clearing activities to follow
Rock, ore and mineral
extraction
Land cleared to access mineral deposits found once an area is opened up
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Cause
Mechanism
Hydro-electric power
stations
Reservoir flooding submerges large forest areas
Climate change
Increases wildfire frequency/severity and storm/pest/invasive-species impacts,
which themselves destroy forest
Impacts of deforestation: - Habitat loss — tropical forests are centres of exceptional biodiversity, so
losses here are especially serious. - Loss of biodiversity (follows from habitat loss). - Soil erosion
and desertification — no roots to bind soil or canopy to soften rainfall impact; land can progressively
lose fertility until it resembles desert. - Silting and flooding — eroded soil washes into rivers/lakes,
reducing channel capacity and water quality; loss of the soil's water-holding capacity increases flood
frequency. - Global warming — fewer trees to remove CO₂ by photosynthesis; burning/decomposing
felled trees releases stored carbon. - Changes to rainfall patterns — less transpiration reduces local
cloud formation and precipitation, which can suppress tree growth further afield (a self-reinforcing
cycle). - Genetic depletion — species/genetic diversity lost before it can even be catalogued; wild
genetic material has potential value for medicine and future crop breeding.
Sustainable management of forests = balancing the needs of the environment, wildlife and humans
while conserving forests for future generations.
Why sustainable management is needed:
Reason
Mechanism
Climate regulation
Young/growing forest = carbon sink (takes in more CO₂ via photosynthesis than it
releases via respiration); mature forest = carbon store (intake ≈ output, carbon
stays locked in standing biomass)
Water cycle role
Interception, water uptake and transpiration add moisture to the atmosphere → cloud
formation → precipitation (can affect rainfall far from the forest itself)
Flood control
Reduces surface run-off, so rivers/lakes are less likely to be overwhelmed
Soil erosion
prevention
Canopy intercepts heavy rain; leaf litter slows run-off; roots bind soil; trees reduce
wind speed at ground level
Genetic resource
Wild genetic diversity may hold traits (e.g. disease resistance) valuable for future crop
breeding
Food, medicine, raw
materials
Direct livelihood source for people who depend on forests
Recreation,
ecotourism,
education
Sustainable income stream that also builds public support for conservation
5.3 Managing biodiversity
Conservation strategies — benefits and limitations:
Strategy
Benefit
Limitation
Sustainable harvesting
(wild plants/animals)
Meets present needs without
denying future generations;
guided by a management plan
(abundance, growth rate,
sustainable yield)
Requires reliable data on
population/reproductive biology; hard to
monitor and enforce
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Strategy
Benefit
Limitation
Sustainable forestry (e.g.
selective logging)
Only mature/valued trees
removed; forest can repair itself;
non-valued trees keep providing
habitat
Slower/less profitable than clear-felling;
priorities differ between economic and
environmental goals
National parks and reserves
Protects biodiversity by law;
supports recreation, education,
tourism income; can provide
climate-regulation services
Overcrowding; can exclude/displace local
communities; expensive infrastructure to
maintain; enforcement needs regular
inspection plus penalties
Wildlife corridors
Link fragmented habitats,
allowing movement/breeding
between populations (improves
gene flow); reduce human–wildlife
conflict
May help invasive species spread too; can
increase fire risk; may create predation
bottlenecks at pinch points
Seed banks
Preserve genetic diversity cheaply
(seeds need little space, are
dormant, need minimal care)
Cannot conserve all plant species; doesn't
protect the habitat itself
Zoos and captive breeding
Education, research, and a lastresort route to prevent extinction;
species reintroduced once habitat
is restored
Can harm animal welfare
(psychological/physical); genetic diversity
limited by small captive populations
(managed via studbooks, swapping
individuals between zoos)
Ecotourism
Sustainable income tied directly
to conservation; low-impact
compared to conventional tourism
Can still damage habitats if not carefully
managed; benefits to local people are
sometimes small
International cooperation
against animal trade
Needed because trade crosses
borders/exclusive economic zones
that no single country can police
Hard to monitor and enforce (vast areas,
corruption risk); influenced by politics
Regulation of trade in
vulnerable/endangered
species (CITES)
International agreement (since
1973) banning trade in species
facing imminent extinction, and
monitoring trade in others
Only a minority of member countries have
modern systems to track compliance;
illegal trade still occurs
Classifying organisms by
threat level (IUCN Red
List)
Directs conservation
effort/funding to the
species/habitats most at risk
Insufficient data exists to classify some
species at all
(IUCN threat categories, most to least severe: Extinct → Extinct in the Wild → Critically Endangered →
Endangered → Vulnerable [these three together = "threatened"] → Near Threatened → Least Concern.)
5.3.2 Discuss — most strategies trade a conservation/education/income benefit against cost,
enforcement difficulty, or a knock-on ecological risk; ground your balance in the specific strategy named
by the question.
5.4 Fieldwork investigations
Applying the scientific method: 1. Make an observation → ask a question. 2. Suggest an aim or a
hypothesis — a testable prediction of cause and effect. A good hypothesis: is a statement, not a
question; predicts cause and effect; names the independent and dependent variables; is short. 3. Plan
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the method: choose a sampling strategy and technique (or a questionnaire/survey), decide on a pilot
study if useful, and identify variables. 4. Collect and record data (with repeats); analyse it; identify and
process anomalies; form a conclusion referring back to the original hypothesis.
Variables:
Variable
Definition
Independent variable (IV)
The one deliberately changed (or naturally varying) between samples/trials
Dependent variable (DV)
The one measured — it "depends on" the independent variable
Control variable
Kept constant so it cannot affect the result
Control (group/sample)
A comparison sample that does not receive the tested treatment
Repeats vs replicates: repetition = the same scientist runs the same investigation more than once;
replication = a different scientist repeats it independently. Both reveal the level of variability in results
and help identify anomalies (outlier results) — an anomaly can be discarded or, better, investigated for
a specific cause.
Sampling strategies:
Strategy
When to use
How
Systematic
sampling
Investigating change along an environmental
gradient (e.g. light intensity from woodland
into a field)
Samples placed at regular/irregular
intervals along a transect line
Random
sampling
Comparing two or more separate areas
Grid laid over each area; sampling point
coordinates chosen using random
numbers
5.4.3 Discuss — systematic sampling is fast and reveals a trend along a gradient but can miss variation
the transect line doesn't cross; random sampling avoids observer bias when comparing areas but needs
many samples to avoid being unrepresentative, and haphazard "by-eye" placement is not truly random
and tends to oversample the centre of an area.
Sampling techniques — benefits and limitations:
Technique
Best for
Limitation
Quadrat
Sedentary organisms
(plants, barnacles) —
counts or % cover
Quick/cheap/portable, but can be biased unless many
are used
Transect
Sampling along a
gradient
Only appropriate where a real gradient exists
Pitfall trap
Small ground-active
animals
Often kills specimens; catch reflects activity level
(e.g. warmer weather → more movement → more
caught) as well as true population
Sweep net
Insects in vegetation
Catch varies with time of day/weather; can damage
vegetation; only useful in tall-enough vegetation
Aerial
photography/drones
Large animals, large
areas, rapid coverage
Expensive; not suitable in forested/dense-canopy
areas
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Technique
Best for
Limitation
Automated sampling
(camera traps)
Unattended long-term
monitoring, minimal
labour to run
Generates huge volumes of data that are labourintensive to review
5.4.5 Discuss — quadrats/transects are cheap, simple and reusable but limited to slow-moving or
sedentary organisms; traps and nets reach mobile animals but disturb or kill some specimens and are
sensitive to weather/time of day; drones and camera traps scale to large areas/long periods with little
fieldwork labour but cost more up front and generate data that itself takes time to process.
Estimating population size from quadrat data: (1) count/estimate the number in each quadrat; (2)
find the mean number per quadrat; (3) find the total area of the site; (4) estimated total population
= mean per quadrat × (total area ÷ quadrat area).
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Topic 6 — Natural hazards
Natural hazard = a physical event with the potential to cause loss of life/injury and damage
property/infrastructure. Natural disaster = when a natural hazard actually causes damage and the
affected people are unable to cope effectively. Risk = the probability of a hazard occurring, combined
with the scale of losses/damage that might result.
6.1 Earthquakes and volcanoes
Structure of the Earth:
Layer
Detail
Crust
Oceanic: basalt, thin (~6 km), denser (3 g/cm³), younger, continually renewed/destroyed.
Continental: granite, thicker (~35 km, 100 km+ under mountains), lighter (2.6 g/cm³), older,
neither renewed nor destroyed
Mantle
>80% of Earth's volume; silicate minerals. Upper mantle is rigid and joins the crust to form the
lithosphere; the lower mantle (asthenosphere) is hot enough to flow slowly (plastic behaviour)
Core
Outer core: liquid iron/nickel. Inner core: solid iron/nickel (solid despite extreme heat, due to
immense pressure)
Continents (7): Africa, Antarctica, Asia, Europe, North America, Oceania, South America.
Cause of plate movement: heat from the core drives convection currents in the mantle — hot
material rises, cools, sinks, and repeats — dragging the rigid plates of the lithosphere above it.
Plate boundaries:
Type
Movement
Mechanism
Result
Divergent/constructive
Plates move
apart
Magma rises to fill the gap, cools
and solidifies as new crust
Volcanic activity
(typically nonexplosive) + (usually
minor) earthquakes
Convergent/destructive
Plates move
together
Denser oceanic plate is subducted
beneath the other; friction/heat
melts the descending plate into
magma, which rises and can erupt
Earthquakes (often
severe) + a line of
(often explosive)
volcanoes
Conservative
Plates slide
past each
other
No crust created or destroyed;
plates lock due to friction until
stress is suddenly released
Earthquakes only — no
volcanic activity
Hotspots: away from plate boundaries, a mantle plume (a narrow column of unusually hot mantle
material) can rise and melt the crust above it from below, forming a volcano.
Features of earthquakes: a sudden release of energy along a fault line generates seismic waves;
the focus is where the earthquake originates underground; the epicentre is the point on the surface
directly above the focus; magnitude (how much energy was released) is measured on the Moment
Magnitude Scale.
Features of volcanic eruptions: magma rises and reaches the surface as lava; ash and volcanic
bombs (large ejected fragments) are thrown out; gases are released (water vapour, carbon dioxide,
sulfur dioxide — SO₂ can go on to form acid rain, Topic 4); pyroclastic flows (a fast-moving,
superheated mix of gas, ash and rock fragments) can occur.
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Impacts of tectonic events (earthquakes and volcanic eruptions):
Impact
Mechanism
Damage to buildings/infrastructure
Ground shaking / ash and lava burial
Loss of crops, livestock, habitats
Ash blocks light (halts photosynthesis); lava burns/buries land
Evacuation of people and livestock
Needed to escape the immediate hazard zone
Fire
Ruptured gas pipes/electricity lines ignite
Tsunamis
Underwater or coastal earthquakes displace huge volumes of sea water
Landslides
Shaking destabilises slopes
Contamination of drinking water
Ruptured sewage/water pipes mix
Water-related disease
Contaminated water spreads disease (e.g. cholera — Topic 3)
Financial losses
Rebuilding costs, lost livelihoods, slowed economic growth
Human health
Injury, restricted access to food/medicine, poor mental health
Managing tectonic-event impacts (this toolkit reappears, with hazard-specific tweaks, for cyclones
and floods too):
Strategy
Mechanism
Limitation
Monitoring &
warning
Seismometers track tremors; groundwater/radon
changes can precede an earthquake;
satellites/tiltmeters/GPS track ground deformation and
gas emissions before an eruption
Precise time/location/magnitude
still can't be predicted reliably;
false alarms erode trust;
monitoring is expensive
Land-use
zoning
Hazard maps keep schools, hospitals and new housing
off the highest-risk land
Only effective where planning
laws are enforced; can't fix
existing settlements
Building
structure
Earthquake-resistant features: rubber shock absorbers at
the base, deep foundations into bedrock, cross-bracing
steel beams (lets the building flex as one rigid unit),
computer-controlled roof weights, fire-resistant
materials, flexible utility piping, avoiding brick/concrete
blocks. Volcano-adjacent buildings use sloped/reinforced
roofs against ashfall
Expensive to build or retrofit;
informal/self-built housing usually
can't comply
Disaster
preparation
Drills, education, stockpiled emergency supplies, trained
rescue teams
Costly; low engagement if people
see the risk as rare
Evacuation &
shelters
Removes people/livestock from danger to a supplied safe
location
People may refuse to leave (fear
of losing property/livestock);
enough shelters must exist
within reach
Rebuilding
Repairs/replaces damaged infrastructure, ideally to a
higher standard
Expensive and slow; poorer
countries depend on outside
funding
International
aid
Food, water, medicine, shelter, search-and-rescue teams,
funding
Slow to arrive; not a permanent
fix; needs working ports/airports
to be delivered
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6.1.9 Discuss — monitoring and building design save the most lives per event but cost the most upfront
and can't be retrofitted everywhere; aid and evacuation are cheaper to arrange but only address the
aftermath, not the risk itself.
Opportunities from volcanoes: fertile soils (weathered volcanic material is nutrient-rich, boosting
crop yields) · mineral extraction (sulfur, diamonds, gold) · building materials (igneous rock) · geothermal
power (cheap energy from underground heat) · tourism (hot springs, scenery, hiking).
6.2 Tropical cyclones
Tropical cyclones, hurricanes and typhoons are the same weather feature, named by region: cyclones
(Indian Ocean, Australia), hurricanes (Atlantic, eastern Pacific), typhoons (western Pacific). Wind
speeds exceed 119 km/hour.
Conditions needed to form: - Latitude 5°–30° north or south of the Equator (too close to the equator,
there's not enough Coriolis force — from Earth's rotation — to make the air spin; too far, the ocean is too
cold). - Ocean surface temperature of at least 27°C (fuels evaporation; the water vapour later
condenses and releases the energy that drives the storm). - Ocean depth of at least 60 m (a deep
enough reservoir of warm water).
Impacts on people and the environment:
Impact
Mechanism
Damage to
buildings/infrastructure
Strong winds
Loss of crops
Winds destroy/uproot; heavy rain damages
Livestock and habitat loss
Wind, flooding, storm surge
Evacuation of people/livestock
To escape wind, flood and surge risk
Flooding
Heavy rainfall + storm surge (low pressure raises sea level; winds push
waves inland)
Landslides
Heavy rainfall destabilises slopes
Contamination of drinking water
Flooding mixes sewage/waste into supplies
Water-related disease
Contaminated water spreads disease (e.g. cholera, diarrhoea)
Financial losses
Rebuilding, cancelled flights/closed ports disrupting trade and tourism
Human health
Injury, food shortages, disease
Managing the impacts (before/during/after) — same toolkit as 6.1 minus land-use zoning, with
cyclone-specific building features: storm shutters, buildings raised on stilts (against storm surge), singlestorey design, curved roofs (deflect wind). Monitoring uses satellites, coastal radar, balloon-borne
instruments and ground stations to track the storm and issue warnings.
6.2.4 Discuss — cyclones are the most predictable natural hazard (track and timing can be forecast),
which makes monitoring/evacuation especially effective, but the same strategies (storm-resistant
building, shelters) are still expensive and unevenly affordable.
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6.3 Flooding
Flooding occurs when a river overflows its banks and covers the floodplain (or when the sea floods lowlying coastal land).
Causes:
Cause
Mechanism
Land relief
Steep gradients cause fast surface run-off, leaving little time for infiltration
Saturated, compacted
or eroded soil
Reduces infiltration capacity (e.g. impermeable clay soils; machinery compaction);
eroded sediment fills river channels, reducing their capacity
Deforestation,
agriculture,
urbanisation
Less interception/infiltration without trees; overgrazing exposes soil; ploughing
down-slope channels water fast; impermeable urban surfaces + storm drains speed
run-off to rivers
Climate change
Rising sea levels; more frequent/intense extreme weather
Storm surges and
tsunamis
Coastal flooding triggered by tropical cyclones or tectonic events
Impacts:
Impact
Mechanism
Damage to buildings/infrastructure
Water damage; disrupted transport, electricity, gas
Loss of crops
Waterlogging/damage
Livestock and habitat loss
Drowning, injury, lost food supply
Evacuation of people/livestock
To reach safety
Landslides
Saturated slopes become unstable
Contamination of drinking water
Sewage, fuel and chemical pollutants mix into supplies
Water-related disease
e.g. diarrhoea, cholera
Financial losses
Property damage, lost employment/business, replacing possessions
Human health
Injury, disease, poor mental health after losing homes/businesses
Managing the impacts — same toolkit as 6.1 (this is the one hazard, alongside tectonic events, where
land-use zoning applies fully): building measures include raising buildings on stilts/extending
foundations, dry flood-proofing (reinforcing doors/windows/openings to keep water out entirely) vs
wet flood-proofing (water-resistant materials + raised electrical sockets, deliberately letting water in
without ruining the building), and flood barriers/walls. Disaster preparation adds hard engineering
(levees, flood barriers, flood-control channels, dams) vs soft engineering (afforestation, controlled
flooding of meadowland, storage basins); channel dredging/widening/straightening reduces flooding
locally but can worsen it downstream.
6.3.4 Discuss — hard engineering gives strong local protection but is expensive and can shift the flood
risk downstream; soft engineering is cheaper and more sustainable but offers less protection against a
severe event.
Opportunities from flooding: deposition of nutrient-rich silt on farmland (raises fertility and yields) ·
recharge of surface and groundwater stores (for drinking water and irrigation).
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6.4 Drought
Drought = a period of dry weather that is longer or more severe than normal.
Causes: lack of rain (disruption to normal atmospheric circulation/storm tracks, so evaporation exceeds
precipitation) · climate change (rising global temperatures and more extreme weather events alter
rainfall patterns in some regions).
Impacts:
Impact
Mechanism
Water sources dry up
Forces long-distance travel for water
Loss of crops, livestock,
habitats
Lack of water for growth/survival
Soil erosion
Vegetation dies back, leaving soil exposed
Desertification
Ongoing loss of vegetation and topsoil
Death of organisms
Along the food chain, as plants (and then the animals that depend on them)
die off
Famine
Crop/livestock failure cuts food supply
Increased wildfire risk
Dry vegetation ignites easily
Decreased air quality
Wildfire smoke adds particulates/carbon monoxide
Financial losses
Farmers lose income; unemployment rises
Human health
Malnutrition, dehydration, heatstroke (young/elderly most at risk),
stress/anxiety from income loss
Managing the impacts (a distinct toolkit — no land-use zoning, building design, or evacuation/shelters
here):
Strategy
Mechanism
Limitation
Monitoring &
warning
Tracks precipitation, groundwater levels,
river flow, reservoir stores, temperature
Onset/end of a drought still can't be
predicted precisely; warnings only help if
people can act on them (harder in LICs)
Emergency
water supplies
Water trucking, additional boreholes,
desalination, standpipes/rationing in urban
areas
Only works if a water source exists at all;
rising prices hit the poorest hardest
Water
conservation
Drought-resistant crops, drip/spray
irrigation, shelterbelts, bunds, controlled
grazing, education campaigns on efficient
use
Needs sustained behaviour change and,
often, upfront investment
Increasing
water supply
Dams and reservoirs, aquifers and wells,
desalination, rainwater harvesting
Large schemes are expensive; overusing
aquifers depletes groundwater long-term
International
aid
Emergency shelter, borehole drilling, microloans, immunisation/health programmes,
food/water distribution
Depends on continued external funding;
local maintenance/servicing capacity may
be lacking
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6.4.5 Discuss — supply-side strategies (dams, desalination) offer a lasting fix but are costly and slow to
build; conservation is cheap and can start immediately but only stretches existing supply rather than
growing it.
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Topic 7 — Human population
7.1 Population density, distribution and structure
Population density = the number of people living in an area, usually measured in people per km² (=
population ÷ area). Sparsely populated places contain few people; densely populated places contain
many.
Population distribution = how people are spread over an area (patterns are driven by factors such as
climate, relief, water/resource availability, and economic opportunity — e.g. coasts and river valleys are
typically denser than deserts, mountains or polar regions).
Population pyramids display structure — the age/sex composition of a population. Males are shown
on the left, females on the right; each horizontal bar is an age band (usually 5-year groups), and bar
length shows the number (or %) of people in that group. - Young dependent population: ages 0–14. Working (independent) population: roughly 15–65 — economically active, and (through taxation)
supports the dependent groups. - Elderly dependent population: over 65. - Three overall shapes:
expanding/young (wide base, narrowing sharply — high birth rate), stationary (roughly rectangular
until the oldest ages — birth and death rates are balanced and both relatively low),
contracting/declining (narrower base, top-heavy — low birth rate with an ageing population).
Income groups (World Bank): economies are classified by Gross National Income (GNI) per
capita into low-income countries (LICs), middle-income countries (MICs) and high-income
countries (HICs) (LIC < MIC < HIC; exact income thresholds are revised periodically, so focus on the
ranking and the classification basis, not a fixed figure).
Comparing population structure — typical LIC vs typical HIC:
Feature
Typical LIC
Typical HIC
Pyramid shape
Wide base, narrows quickly
(expanding)
Narrower base; more rectangular or top-heavy
(stationary/declining)
Birth rate
High
Low
Death rate (incl. infant
mortality)
Higher
Low
Life expectancy
Lower
Higher
Largest dependent
group
Young dependents
Elderly dependents
Government priority
this creates
More school places for a growing
youth population
More healthcare/care-home capacity for an
ageing population
7.2 Human population size
Birth rate (often expressed as fertility rate — children per woman) and death rate (closely linked to
life expectancy) drive natural population change:
Population growth = birth rate − death rate (rate of natural increase)
Adding migration gives the full picture: population growth = (birth rate + immigration) − (death
rate + emigration)
Migration: immigration = people entering an area; emigration = people leaving it. Movement is
driven by push factors (reasons to leave — e.g. drought, famine, poverty, conflict, poor services) and
pull factors (reasons to move to a place — e.g. jobs, better healthcare/education, food security,
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safety). Migration can be internal (within a country) or international.
Rural–urban migration and urbanisation: worldwide, the dominant pattern is movement from rural
to urban areas (though the reverse occurs too). Urbanisation = a rise in the percentage of people
living in urban areas — driven by rural push factors (fewer resources/services/opportunities) combined
with urban pull factors (perceived better jobs, healthcare, education).
Impacts of human population growth:
Impact
Mechanism
Informal urban
settlements
Housing shortages and poverty produce unplanned settlements
(slums/favelas/shantytowns) with poor sanitation and services
Megacities
Rapid urban growth produces cities of 10 million+ people, intensifying every other
impact below
Availability of
resources
More people compete for finite food, water, fuel and raw materials
Energy usage
Rising demand increases fossil fuel consumption and associated pollution
Sanitation
Sewage/waste volumes can outpace treatment capacity
Water supply
Growing demand strains sources and treatment infrastructure
Management of waste
Larger volumes of solid waste requiring safe disposal, reuse or recycling
Availability of land
Competition between housing, farming, industry and transport for finite land
Facilities and
infrastructure
Roads, bridges, utilities and telecommunications come under growing strain
Pollution (air, land,
light, noise, visual,
water)
More people generate more emissions, waste, artificial light, noise and water
contamination
Traffic congestion
More vehicles; building more roads often attracts further traffic rather than easing
congestion
Changes in
employment
opportunities
Not straightforward — more workers competing for jobs, but also more demand for
goods/services creating new jobs; the real-world relationship between population
growth and (un)employment is inconsistent
7.3 Managing human population size
Strategy
How it works
Limitation
Access to
contraception
Family planning lets couples choose family
size/timing; wider access lowers birth rates
Availability depends on government
policy, cost, belief systems and
tradition
Population
policies
Pro-natalist (used where population growth is
too slow/ageing too fast): financial incentives,
subsidised childcare, tax benefits for larger
families. Anti-natalist (used where growth is too
fast): family-planning provision, education, and
incentives or penalties tied to family size
Strict anti-natalist policies can leave
too few future workers to support the
elderly, weaken extended-family
support networks, and create
social/financial hardship for those
who exceed set limits
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Strategy
How it works
Limitation
Access to
education
Educates people (especially women) about family
planning; tends to delay marriage/childbearing
and open career opportunities, which — despite
the intuitive expectation that better education
raises population — is strongly linked to lower
birth rates over time
Benefits take a generation to appear;
resources for education may still be
allocated unequally (e.g. favouring
boys)
Access to
healthcare
Reducing infant/child mortality tends to lower
birth rates over time, as parents no longer need
"extra" children to offset expected child deaths
Access can be uneven in practice
even where nominally available (e.g.
long waiting times)
Control of
migration
Governments can restrict or permit entry (e.g. by
skill level); net migration = immigration −
emigration
Refugees/asylum seekers have
distinct legal protections (e.g. cannot
be returned to a country where they
face serious threats to life or
freedom), so this group falls outside
a single country's full control
7.3.2 Discuss — contraception/education/healthcare access address root causes and are broadly low-cost
per person, but take a generation to fully show their effect and depend on social acceptance; direct
population policies act faster but risk long-term demographic imbalance (too few workers to support the
elderly) and social/ethical costs; migration control changes distribution more readily than it changes
overall size, and is legally limited where refugees are involved.
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