Biodiversity & Waste management & Land use & Deforestation & Maintaining biodiversity

SPEC 4.7.3.1–7.3.6 (excl. 7.3.5) • PAPER 2

⭐ HIGH PRIORITY

Biodiversity & Human Impact

Five interlinked sub-topics — biodiversity, waste & pollution, land use, deforestation, and maintaining biodiversity. Tested every series, often as 6-mark Level-marked questions spanning the whole topic group.

The Big Idea

The human population is large and growing — that drives most of the pressure on ecosystems. This lesson covers the pressures (waste, land use, deforestation) and what people do to fight back (maintaining biodiversity).

Spec-Verbatim Definition

Biodiversity is the variety of all the different species of organisms on Earth, or within an ecosystem.

What This Lesson Covers

4.7.3.1 Biodiversity — definition and why it matters.

4.7.3.2 Waste management — pollution in water, air and land.

4.7.3.3 Land use — building, quarrying, farming, dumping waste; peat bogs.

4.7.3.4 Deforestation — large-scale tropical loss.

4.7.3.6 Maintaining biodiversity — five named conservation methods.

Not Here

4.7.3.5 Global warming is its own lesson (7.10), but we'll note where the topics overlap (peat bogs, deforestation → CO₂).

Biodiversity & Stability [4.7.3.1]

Why High Biodiversity Matters (Spec)

A great biodiversity ensures the stability of ecosystems by reducing the dependence of one species on another for food, shelter, and the maintenance of the physical environment.

High Biodiversity

Many species → many niches filled.

If one species declines, others can fulfil similar roles.

Ecosystem is resilient to disturbance.

Stable food webs, intact shelter and nutrient cycles.

Low Biodiversity

Few species → ecosystem depends heavily on each one.

Loss of any species can collapse food webs.

Ecosystem is fragile — small changes have big effects.

Often the result of human pressure.

Spec Statement

"The future of the human species on Earth relies on us maintaining a good level of biodiversity. Many human activities are reducing biodiversity and only recently have measures been taken to try to stop this reduction."

Waste & Pollution [4.7.3.2]

Why is there more pollution? Rapid growth in the human population plus an increase in the standard of living means more resources are used and more waste is produced.

WherePollution Sources (Spec)Effect

In waterSewage; fertiliser; toxic chemicalsKills aquatic plants and animals; fertiliser run-off → algal bloom → low O₂ in water

In airSmoke; acidic gases (e.g. SO₂)Damages plants and sensitive species; acid rain harms forests and lakes

On landLandfill; toxic chemicalsReduces habitat; chemicals can enter food chains

Spec Statement

"Pollution kills plants and animals which can reduce biodiversity." — Always include this final link in your answers.

Land Use [4.7.3.3]

The spec names four ways humans reduce the land available for other animals and plants:

1 — Building

Houses, factories, roads, urban sprawl. Replaces natural habitat with surfaces unsuitable for most species.

2 — Quarrying

Extracting rock, stone, sand and minerals. Removes the surface layer; habitat permanently disturbed.

3 — Farming

Crops and livestock require huge areas. Monocultures replace mixed ecosystems → fewer species supported.

4 — Dumping Waste

Landfill sites take up large areas; toxic chemicals leak into surrounding soil and water.

Synoptic Link

The underlying driver of all four is population growth: more people → more housing + more food + more resources extracted + more waste. The peat-bog issue on the next slide is a specific example.

Peat Bogs [4.7.3.3]

Peat bogs are wetland habitats where waterlogged, acidic, low-oxygen conditions prevent dead plants from fully decaying. The partly-decayed plant matter — peat — stores huge amounts of carbon.

Two Linked Problems When Peat Is Destroyed

Biodiversity loss — peat bog destruction reduces the area of habitat and thus the variety of plant, animal and microorganism species that live there.

CO₂ AND methane released — the spec specifies that decay or burning of peat releases CO₂. Peat layers also store methane (CH₄), which is released when the bog is dug up. Both are greenhouse gases (→ lesson 7.10).

Mark Scheme Alert (Jun 2024 P2 Q2.5)

For 4-mark "explain how peat destruction affects atmospheric temperature" questions, mark schemes award separate marks for: temperature increase; CO₂ released; CO₂ from decay/burning; methane released. Skipping methane = lose 1 mark out of 4.

The Conflict (WS 1.5)

Gardeners and farmers want cheap available compost (peat is excellent for this). But conserving peat bogs maintains a unique habitat AND keeps carbon locked away. The spec asks you to evaluate this conflict.

Deforestation [4.7.3.4]

The spec is very specific. Large-scale deforestation in tropical areas has occurred for two named reasons:

Reason 1

To provide land for cattle and rice fields — food production for a growing global population. Cattle ranching has been a major driver in South America.

Reason 2

To grow crops for biofuels — e.g. palm oil, soya for biodiesel and ethanol production.

Effects To Evaluate (WS 1.4)

Biodiversity loss — tropical forests are among Earth's most species-rich habitats.

Atmospheric CO₂ rises — fewer trees photosynthesising (so less CO₂ removed) + burning trees releases stored carbon.

Soil erosion — tree roots no longer hold the soil; rainfall washes it away.

Water cycle disruption — less transpiration → less rainfall locally → drier climate.

Maintaining Biodiversity [4.7.3.6]

The spec lists five named conservation methods. Memorise them — they're high-frequency in mark schemes.

#Conservation Method (Spec)How It Helps

1Breeding programmes for endangered speciesCaptive breeding (often in zoos) increases population of endangered species; individuals can be reintroduced to the wild.

2Protection and regeneration of rare habitatsNational parks, nature reserves, reforestation. Preserves the conditions species need to survive.

3Reintroduction of field margins and hedgerows in agricultural areas where farmers grow only one type of cropProvides habitat & food for wild species (insects, birds, mammals) alongside farmland. Counters monoculture biodiversity loss.

4Reduction of deforestation and CO₂ emissions by some governmentsProtects forest habitats and slows climate change — protects biodiversity from both habitat loss and warming.

5Recycling resources rather than dumping waste in landfillLess land used for landfill; fewer raw materials extracted (less quarrying/mining); less pollution.

Use Spec Wording

When asked "name a way to maintain biodiversity", use the spec terms — e.g. "breeding programmes for endangered species" rather than vague "save the animals".

The Evaluation Skill: Conflicting Pressures

The spec asks students to "describe both positive and negative human interactions" and "explain and evaluate the conflicting pressures on maintaining biodiversity".

Negative Human Interactions

Deforestation (for cattle, biofuels)

Peat bog destruction (for compost, fuel)

Pollution (water, air, land)

Monoculture farming + hedgerow removal

Landfill and urban expansion

Overfishing (→ lesson 7.13)

Positive Human Interactions

Breeding programmes (zoos, sanctuaries)

Reforestation & habitat protection

Field margins & hedgerow reintroduction

Reducing CO₂ emissions (government policy)

Recycling instead of landfill

Sustainable fishing quotas

Worked Conflict: Peat Bogs

For peat extraction: peat makes cheap, effective garden compost — useful for food production and gardening.

Against peat extraction: destroys unique wetland habitat (reduces biodiversity); releases CO₂ → climate change.

Evaluation: conservation arguments are stronger — peat takes thousands of years to form and is effectively irreplaceable on human timescales. Alternative composts exist.

Common Errors

Wrong

"Biodiversity = the number of organisms in an ecosystem."

Right

"Biodiversity = the variety of different species. Counts species, not individuals." Mark scheme rejects "number of trees" — accepts "number of tree species".

Wrong

"Deforestation just means cutting down trees."

Right

Multiple effects: habitat & biodiversity loss + more atmospheric CO₂ (less photosynthesis + burning) + soil erosion + water cycle disruption.

Wrong

"Peat bogs are useless wetlands."

Right

Peat bogs are carbon stores AND unique habitats. Destruction releases CO₂ AND reduces biodiversity.

Wrong

"Air pollution = CO₂."

Right

Air pollution in 4.7.3.2 = smoke and acidic gases (e.g. SO₂). CO₂ is mainly a greenhouse gas (lesson 7.10), not classed as "pollution" in the spec.

Wrong

"Humans damage the environment."

Right

Name specific pressures from the spec: deforestation; peat destruction; monoculture; landfill; pollution. Generic answers score Level 1.

Examiner Alerts

Alert 1 — "Number of Species", Not "Number of Organisms"

The 2023 P2 examiner report flagged students "mistakenly referring to the number of trees rather than to the number of tree species". Mark schemes are strict: biodiversity = species count.

Alert 2 — Answer Both Halves Of A 6-Marker

Past 6-mark questions on this topic group split into TWO halves (e.g. "describe land use changes AND how they reduce biodiversity"). Mark schemes specify: "Answers referring to only [half 1] or only [half 2] are Level 1." Always answer both halves.

Alert 3 — Use Spec-Specific Conservation Terms

For maintaining biodiversity, the mark scheme rewards the spec's exact phrasings: "breeding programmes", "field margins and hedgerows", "protection and regeneration of habitats", "recycling". Generic "save habitats" loses precision marks.

Alert 4 — Tropical Deforestation Has Two Spec Causes

Only TWO causes are named in the spec: cattle and rice fields; crops for biofuels. Don't invent "logging for timber" as a primary cause in spec questions — although it happens, it's not in the spec wording for 4.7.3.4.

Alert 5 — Don't Over-Explain Global Warming

Jun 2024 examiner report warned: "the 'greenhouse effect' and 'climate change' are not equivalent to 'global warming'" and that descriptions of long/short-wave radiation, ozone, etc. are beyond the spec. The required chain is simple: gas released → atmospheric warming. Stay there — adding mechanism wastes time and risks errors.

Practice — Recall

(a) Define biodiversity. 1 mark

(b) Give the two reasons named in the AQA specification for large-scale tropical deforestation. 2 marks

(c) Name three ways humans can help to maintain biodiversity. 3 marks

(a)

The variety of all the different species of organisms on Earth or within an ecosystem. (1)

(b)

To provide land for cattle and rice fields (1); to grow crops for biofuels (1).

(c)

Any three from: breeding programmes for endangered species; protection and regeneration of rare habitats; reintroduction of field margins and hedgerows in agricultural areas; reduction of deforestation and CO₂ emissions; recycling resources rather than dumping in landfill. (1 mark each)

Practice — Explain

A gardener buys 80 bags of peat-based compost each year to enrich the soil in their vegetable patch. The peat is extracted from a peat bog in Ireland and burnt residues from compost production are released into the atmosphere.

Explain how the gardener's use of peat compost contributes to global warming.4 marks

Mark scheme structure (Jun 2024 P2 Q2.5): four distinct marking points.

1

The Earth's atmospheric temperature increases (allow: global warming / heat is trapped). (1)

2

Carbon dioxide is released from the peat bog into the atmosphere. (1)

3

CO₂ is produced specifically by burning or decay of the peat. (Allow alternative: fewer plants left in peat bog to take in CO₂ for photosynthesis.) (1)

4

Methane (CH₄) is also released from the peat bog (peat stores methane from past anaerobic decay). (1)

Examiner note (Jun 2024): "A significant number of students omitted any reference to methane, so were unable to gain marking point 4." Always include CH₄. Also: don't try to explain the greenhouse-effect mechanism — long-wave radiation, ozone, etc. are beyond the spec.

Practice — 6-Marker (Level)

A river flows through an area of intensive arable farmland. Recent studies show that:

fertiliser run-off has caused algal blooms in the river,

fish populations have fallen by 70 % since 1980,

hedgerows around the fields have been removed to enlarge the fields.

Evaluate the human impacts on this river ecosystem and suggest two conservation measures that could help restore biodiversity. 6 marks (Level marked)

Level 3 (5–6): coherent evaluation with named pressures, mechanism, and spec-named conservation methods.

A

Pollution: fertiliser run-off into water (named source from 4.7.3.2). Causes algal blooms → block light from underwater plants → algae die and decompose → microbial decay consumes O₂ → fish suffocate (link to 70 % decline).

B

Habitat loss: hedgerow removal reduces habitat for insects, birds and small mammals → biodiversity falls. Less food and shelter for species at multiple trophic levels.

C

Land use: intensive farming is one of the spec's four named ways humans reduce land for other species. The pressure also drives the hedgerow removal.

D

Conservation measure 1:reintroduction of field margins and hedgerows (spec 4.7.3.6) — provides habitat alongside crops; field margins also act as buffer strips, reducing fertiliser run-off into the river.

E

Conservation measure 2:protection and regeneration of rare habitats along the river bank, or reduction of CO₂ emissions / pollution through regulation of fertiliser use.

F

Judgement: the river ecosystem has been damaged by both pollution and habitat loss. Conservation measures that target both — like restored field margins — address multiple pressures at once and have the best chance of restoring biodiversity.

Level 2 answers identify the pressures but don't link to specific conservation methods. Level 1 answers describe one half (pressures OR conservation) but not both.

Recap & Next Up

5

Spec sub-topics

3

Pollution categories

5

Conservation methods

Three Things To Take Away

1

Biodiversity = variety of SPECIES. High biodiversity → stable ecosystems with reduced dependence. Mark scheme rejects "number of organisms".

2

Human pressures are named in the spec — water/air/land pollution; building/quarrying/farming/dumping waste; peat bog destruction; tropical deforestation (cattle/rice + biofuels). Be specific.

3

Five named conservation methods — breeding programmes; habitat protection; field margins/hedgerows; reducing deforestation/CO₂; recycling. Use spec wording for full marks.

Next: Lesson 7.10

Global warming (spec 4.7.3.5) — CO₂ and methane as named greenhouse gases; biological consequences. Pairs naturally with this lesson — peat and deforestation are key sources.