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Question
Explain how high biodiversity in a UK oak woodland helps the community remain stable if one species of caterpillar declines. (4 marks)
Solution
Many bird species (blue tit, great tit, treecreeper) feed on a range of caterpillar species, not just one.
If one caterpillar species declines, birds switch to alternative caterpillars or insects.
Bird numbers remain roughly constant; food web doesn't collapse.
High biodiversity = many alternative pathways → community absorbs change → stable.
Answer
Many bird species feed on a range of caterpillar species (1). If one caterpillar species declines, birds switch to alternatives (1). Bird populations stay roughly constant and the food web absorbs the change (1). Multiple feeding pathways from high biodiversity make the ecosystem more stable (1).
Question
Explain why a field planted with a single variety of wheat is more vulnerable to disease than a meadow with many species. (3 marks)
Solution
All wheat plants have identical (or near-identical) genes — low genetic diversity.
If a pathogen can infect one plant, it can infect all of them — disease spreads through the whole field.
A diverse meadow has many species with varied resistance — most are unaffected by any one disease.
Answer
All wheat plants have nearly identical genes (low genetic diversity) (1). A pathogen that infects one can infect all, so disease spreads through the entire crop (1). A diverse meadow has many species with different disease resistance, so any single disease affects only a few species (1).
Question
Fertiliser runoff into a UK river leads to dead fish downstream. Explain the steps. (5 marks)
Solution
Fertiliser adds nitrate and phosphate to the water.
Algae grow rapidly using the extra nutrients — an algal bloom forms on the surface.
Algae block light → submerged plants die.
Bacteria decompose dead algae and plants, respiring aerobically and using up dissolved oxygen.
Dissolved O₂ falls below the level fish need → fish suffocate and die.
Answer
Fertiliser adds nitrate/phosphate (1). Algae bloom using the extra nutrients (1). Algae block light, killing plants below (1). Bacteria decompose dead material, using up dissolved O₂ (1). Fish suffocate as O₂ falls too low (1).
Question
Explain how the pesticide DDT almost wiped out UK peregrine falcons in the 1960s. (3 marks)
Solution
DDT was sprayed on crops; it washed into water and was eaten by small organisms.
DDT BIOACCUMULATED up the food chain — small fish, then larger fish, then bird-eating peregrines had the highest concentrations.
DDT thinned the eggshells of peregrines, so eggs broke before chicks hatched — population crashed.
Answer
DDT washed into water and entered food chains (1). It bioaccumulated, reaching highest levels in top predators like peregrines (1). DDT thinned the falcons' eggshells, so eggs broke and chicks died, crashing the population (1).
Question
List four ways humans reduce the land available for plants and animals. (4 marks)
Solution
Recall the AQA-specified four uses.
Building (housing, roads, factories) covers ground; quarrying removes rock and topsoil; farming replaces wild habitat with monocultures; dumping waste in landfill buries habitat and leaches pollutants.
Answer
(1) Building (e.g. houses, roads) (2) Quarrying for stone or sand (3) Farming / agriculture (4) Dumping waste / landfill.
Examiner note
AQA mark schemes accept these four. 'Cutting down trees' alone is NOT one — that's deforestation (4.7.3.4), a separate topic.
Question
Explain why the destruction of peat bogs to produce compost is harmful to the environment. (4 marks)
Solution
Identify habitat loss — peat bogs are home to specialised plants and animals.
Identify biodiversity decrease — rare species are lost.
Identify the CO₂ release — drained peat is exposed to air and decomposes, releasing carbon dioxide.
Link CO₂ release to global warming / climate change.
Answer
Peat bogs are habitats for rare specialised species (1), so destroying them reduces biodiversity (1). When peat is removed and exposed to air, it decomposes and releases stored CO₂ (1), which contributes to global warming (1).
Question
Give three reasons why large areas of tropical forest are cleared. (3 marks)
Solution
Recall the AQA-listed drivers.
Pick three distinct ones — e.g. cattle ranching, palm oil plantations, biofuel crops (or rice paddies, or timber).
Answer
(1) To create grazing land for cattle (2) To grow crops for biofuels such as sugar cane (3) To create palm oil plantations.
Question
Explain TWO different ways in which deforestation increases atmospheric carbon dioxide. (4 marks)
Solution
First way — burning or decay of the cut wood releases stored carbon as CO₂.
Second way — fewer trees remain to absorb CO₂ by photosynthesis, so future CO₂ removal is reduced.
Both increase the net CO₂ in the atmosphere, enhancing the greenhouse effect.
Answer
(1) Burning or decomposing trees releases stored carbon as CO₂ (2 marks). (2) Fewer trees remain to absorb CO₂ during photosynthesis, so CO₂ uptake is reduced (2 marks).
Question
Name two greenhouse gases that humans are increasing in the atmosphere, and give ONE human source for each. (4 marks)
Solution
Recall the two AQA-specified gases.
Match each to a clear human source.
Answer
(1) Carbon dioxide — from burning fossil fuels (e.g. coal power stations). (2) Methane — from cattle (digestion) or rice paddies or landfill.
Question
Explain TWO ways that global warming causes sea levels to rise. (4 marks)
Solution
Identify thermal expansion — water expands when heated, so warmer oceans take up more volume.
Identify melting of land-based ice (Greenland ice sheet, Antarctic ice, mountain glaciers) — this adds new water to oceans.
Note that sea ice melting does NOT raise sea level (it was already floating).
Answer
(1) Thermal expansion — warm water has greater volume than cold water, so oceans expand as they warm (2). (2) Melting of land ice — ice on Greenland, Antarctica and mountain glaciers melts and flows into the oceans, adding water and raising the sea level (2).
Examiner note
Mention land ice specifically — confusing sea ice with land ice is a common error.
Question
Define the term 'biodiversity' and explain why it is important. (3 marks)
Solution
Define biodiversity as the variety of species.
Explain importance — stable ecosystems, less dependence on one species.
Answer
Biodiversity is the variety of different species in an ecosystem or on Earth (1). It is important because ecosystems with high biodiversity are more stable (1), since they are less dependent on any one species for food, shelter or to maintain the environment (1).
Question
Describe THREE different conservation programmes used to maintain biodiversity. For each, give one specific UK example. (6 marks)
Solution
Pick three distinct strategies from the AQA list.
Match each to a specific UK example for the 'application' mark.
Answer
(1) Breeding programmes — captive breeding of endangered species and reintroduction, e.g. red kites reintroduced to the Chilterns. (2) Protected reserves — legally protected areas, e.g. UK Sites of Special Scientific Interest (SSSIs). (3) Hedgerow planting and field margins — farmers leave hedgerows and wildflower strips, e.g. funded under the Countryside Stewardship scheme.
The variety of all the different species of organisms on Earth or within an ecosystem.
An ecosystem where biotic and abiotic factors are in balance so populations remain roughly constant.
The benefits humans get from healthy ecosystems — pollination, clean water, carbon storage, soil formation, flood control.
Planting a large area with a single species (often a single variety) of crop — has very low biodiversity.
The release of harmful substances into the environment — water, air or land — that damage organisms.
Excess nutrients (nitrate, phosphate) cause algal blooms; decomposing algae deoxygenate water; fish die.
Precipitation made acidic by SO₂ and NOₓ from burning fossil fuels — damages forests and freshwater life.
Build-up of persistent toxic chemicals at progressively higher levels through a food chain.
Disposal of solid waste by burying it in the ground — uses land and releases methane and leachate.
The way humans modify or manage areas of land — including building, quarrying, farming and dumping waste.
Partly decomposed plant material built up over thousands of years in waterlogged, acidic bog conditions; a major store of carbon.
Extracting rock, sand or other materials from the ground, usually for construction; destroys habitats and topsoil.
The variety of all the different species of organisms on Earth, or within an ecosystem.
The large-scale cutting down of forests, especially in tropical regions, usually to clear land for farming, biofuels or timber.
A fuel produced from living or recently living biological material, such as ethanol from sugar cane or biodiesel from palm oil.
A natural store that absorbs more carbon dioxide than it releases — e.g. forests and oceans.
A process where the result of a change further amplifies that change — e.g. deforestation → more CO₂ → more warming → more forest stress.
The long-term increase in Earth's average surface temperature caused by rising levels of greenhouse gases in the atmosphere.
An atmospheric gas (e.g. CO₂, methane, water vapour) that absorbs infrared radiation and traps heat in the atmosphere.
The increase in volume of a substance when heated. Warmer oceans take up more space, contributing to sea-level rise.
The permanent disappearance of a species — no individuals remain anywhere on Earth.
The protection and careful management of living organisms and their habitats to maintain biodiversity.
A conservation programme where endangered species are bred in zoos or reserves with the aim of releasing offspring back into the wild.
An uncultivated strip of land around the edge of a farmer's field, planted with wildflowers or left wild to support biodiversity.
Mistake
Defining biodiversity as 'lots of animals'.
Why it happens
Forgetting plants, fungi, bacteria.
How to avoid it
Biodiversity = the variety of ALL species — plants, animals, fungi, bacteria. Don't forget the others.
Mistake
Saying 'biodiversity makes ecosystems unchanging'.
Why it happens
Overstating stability.
How to avoid it
Biodiversity REDUCES the impact of change. It doesn't stop change altogether.
Mistake
Assuming the UK is biodiversity-rich.
Why it happens
Pretty countryside.
How to avoid it
The UK is actually one of the most nature-depleted countries globally — half of wildlife has declined since 1970.
Mistake
Saying algae directly suffocate fish by using up oxygen.
Why it happens
Skipping the decomposer step.
How to avoid it
Algae actually MAKE O₂ during the day. It's the DECOMPOSER BACTERIA breaking down dead algae that use up O₂.
Mistake
Listing only CO₂ as an air pollutant.
Why it happens
Climate change focus.
How to avoid it
Add SO₂, NOₓ and particulates — they're the AQA-named pollutants for acid rain and respiratory illness.
Mistake
Writing 'pollution is bad' without naming a specific pollutant or effect.
Why it happens
Trying to be general.
How to avoid it
Name the pollutant, the source and the specific biological effect for full marks.
Mistake
Only mentioning 'building' when asked for ways humans use land.
Why it happens
It's the most obvious answer.
How to avoid it
Memorise all four: BUILDING, QUARRYING, FARMING, DUMPING WASTE — exam answers usually need 3+ of these.
Mistake
Forgetting the CO₂ angle on peat bogs.
Why it happens
Students focus on habitat loss but miss the climate impact.
How to avoid it
Peat = carbon store. When destroyed, the stored carbon is released as CO₂.
Mistake
Giving only one side in evaluation questions.
Why it happens
Wanting to sound decisive.
How to avoid it
Always give benefits AND costs, then conclude with reasoning. AQA evaluations require balance.
Mistake
Saying 'deforestation releases CO₂' but missing the loss of future uptake.
Why it happens
Students learn the release effect first.
How to avoid it
Always give BOTH carbon effects: (1) release of stored CO₂, (2) reduced future absorption.
Mistake
Talking about UK deforestation as the main issue.
Why it happens
Confusing this topic with land use (4.7.3.3).
How to avoid it
AQA spec specifies LARGE-SCALE TROPICAL deforestation — focus on Amazon, Borneo, Sumatra.
Mistake
Assuming biofuels are always good for the environment.
Why it happens
Biofuels are marketed as 'renewable'.
How to avoid it
Biofuels grown on CLEARED FOREST land cause huge net CO₂ release. Renewable ≠ environmentally good.
Mistake
Saying 'melting Arctic sea ice raises sea level'.
Why it happens
Students conflate sea ice and land ice.
How to avoid it
Sea ice is already in the water (Archimedes). Only LAND ice (Greenland, Antarctica, glaciers) melting raises sea level.
Mistake
Only listing CO₂ as a greenhouse gas.
Why it happens
CO₂ gets all the headlines.
How to avoid it
AQA names BOTH CO₂ AND methane. Mention sources of methane too: cattle, rice, landfill.
Mistake
Confusing weather with climate.
Why it happens
A cold winter feels like 'no global warming'.
How to avoid it
Weather = short-term local; climate = long-term average. Global warming is about decades of averages rising, not individual days.
Mistake
Defining biodiversity as 'lots of animals'.
Why it happens
Animal-focused thinking.
How to avoid it
Biodiversity = variety of all SPECIES (plants, animals, fungi, bacteria) in an ecosystem.
Mistake
Only mentioning zoos / breeding programmes.
Why it happens
Most famous strategy.
How to avoid it
AQA expects you to know 3+ strategies: reserves, regeneration, hedgerows, recycling, etc. too.
Mistake
In evaluation questions, listing pros/cons but giving no conclusion.
Why it happens
Running out of time.
How to avoid it
Always finish with a JUDGEMENT — 'on balance' or 'in the long term'.