Biodiversity, pollution, land use and global warming – GCSE Biology exam questions with mark scheme

1Grade 4–54 marks

Biodiversity is being reduced by human activities.

(a) Peat bogs are being destroyed to produce compost for gardens. Explain how this contributes to global warming. [2]

(b) Give two programmes that could be used to reduce the negative effects of humans on biodiversity. [2]

(a) peat decays / is broken down by microorganisms or is burned(1)
(a) releasing (stored) carbon dioxide, a greenhouse gas
allow carbon stored in the peat is released as carbon dioxide(1)
(b) any two from: breeding programmes for endangered species; protection and regeneration of rare habitats; reintroduction of field margins and hedgerows; reduction of deforestation; reduction of carbon dioxide emissions; recycling resources rather than dumping waste in landfill(1)
(b) a second programme(1)
Answer: (a) Decay/burning of peat releases stored CO₂ (b) e.g. breeding programmes; replanting hedgerows.
Examiner tip: 'Pollution' is not an explanation – name carbon dioxide and how it is released.

2Grade 1–3Foundation5 marks

A nature reserve contains woodland, a lake and an area of grassland. Many different species live there.

(a) What is meant by biodiversity? [1]

(b) The nature reserve has a high biodiversity.

Explain why an ecosystem with a high biodiversity is more stable than an ecosystem with a low biodiversity. [2]

Give two human activities that reduce the amount of land available for other animals and plants. [2]

(a) the variety of all the different species (of organisms) on Earth / in an ecosystem
allow 'the range of different species / types of organism (in an area)'
do not accept 'the number of organisms' (must refer to species / types)(1)
(b) (more species, so) each species is less dependent on any one other species for food / shelter / maintaining the physical environment
ignore 'species depend on each other' with no idea of reduced dependence(1)
(b) so if one species is lost / decreases, other species have alternatives (e.g. other food sources) / are less affected, so populations do not crash
ignore 'there are more animals' unqualified(1)
(c) any one from: building (houses / roads / factories) · quarrying · farming / agriculture · dumping waste / landfill(1)
(c) a second, different activity from the list above
ignore 'pollution' unqualified · ignore 'deforestation' alone (it removes forest, but the question asks about land use) — allow 'clearing land for farming'(1)
Answer: (a) The variety of all the different species in an ecosystem (or on Earth). (b) With more species, each species depends less on any one other species for food and shelter, so if one species is lost the others have alternatives and the ecosystem is less affected. (c) Any two of: building, quarrying, farming, dumping waste.
Examiner tip: In (a) 'lots of animals' gets no mark — biodiversity is about the number of different species, not the number of organisms.

3Grade 1–3Foundation6 marks

Humans produce waste that can pollute the environment.

(a) The table shows four pollutants.

Complete the table by writing air, land or water to show what each pollutant mainly pollutes. [2]

Pollutant	Mainly pollutes
Untreated sewage from a pipe
Smoke from burning fuels
Household rubbish in a landfill site
Fertiliser washed off fields by rain

(b) The amount of waste produced by humans is increasing.

Give two reasons why. [2]

Explain how. [2]

(a) two or three rows correct = 1 mark
answers: sewage – water; smoke – air; landfill – land; fertiliser – water(1)
(a) all four rows correct = 2 marks(1)
(b) human population is increasing / growing (rapidly)
allow 'more people'(1)
(b) standard of living is increasing / people use more resources / buy more products
allow 'more packaging / more things are thrown away'(1)
(c) recycling paper means fewer trees are cut down / less deforestation or less waste goes to landfill(1)
(c) so (forest) habitats / food sources for other species are not destroyed or less land is used for dumping waste, so more land / habitat is left for other organisms
consequence must be linked to the action given for the first mark; allow 'trees are saved, so animals keep their homes / food'; allow 'less waste burned, so less air pollution' for 1 mark only(1)
Answer: (a) water, air, land, water (b) Human population is increasing; standard of living is rising so more resources are used. (c) Fewer trees are cut down so habitats are kept; less waste goes to landfill so less land is lost.
Examiner tip: In (c) link the action to biodiversity: 'saves trees' needs '…so habitats / food for other species are not destroyed' to score fully.

4Grade 4–56 marks

Large areas of tropical forest are being cut down.

The bar chart shows the area of forest cleared in one country in one year, and what the cleared land was used for.

(a) Calculate the percentage of the cleared forest that was used for biofuel crops. [2]

(b) Explain how clearing tropical forest for cattle ranching reduces biodiversity. [3]

(c) Using the cleared land for cattle ranching and rice fields increases the concentration of a greenhouse gas other than carbon dioxide.

Name this gas. [1]

(a) total area = 2600 + 800 + 1200 + 400 = 5000 (km²) or 1200 ÷ 5000 seen(1)
(a) 24 (%)
allow 1 mark only for 1200 ÷ (incorrect total) × 100 correctly evaluated(1)
(b) the trees / many plant species are removed and replaced by grass (only one or a few plant species)
allow 'habitats are destroyed'(1)
(b) animals lose their food sources / shelter / nesting sites
allow 'animals lose their habitat' if not already credited for the first (b) mark(1)
(b) so animal species die out / move away / become extinct (tropical forests contain very many species)
allow 'species that depend on the lost plants / animals are also lost (interdependence)'
ignore 'it causes global warming' unless linked to loss of species(1)
(c) methane
allow CH₄
do not accept 'carbon monoxide'(1)
Answer: (a) 24% (b) Trees and many plant species are removed and replaced by grass; animals lose their food and shelter; so many species die out or move away (some may become extinct). (c) Methane.
Examiner tip: In (b) don't stop at 'animals lose their homes' — say what is lost (food, shelter) and that species then die out or leave the area.

5Grade 6–76 marks

Scientists have measured the concentration of carbon dioxide in the air at a monitoring station since 1960.

The mean concentration was 317 parts per million (ppm) in 1960 and 414 ppm in 2020.

(a) Calculate the percentage increase in the mean carbon dioxide concentration between 1960 and 2020.

Give your answer to 3 significant figures. [2]

(b) Within each year, the carbon dioxide concentration at the station is lower in summer than in winter.

Suggest an explanation for this. [2]

(c) Most scientists agree that the increase in carbon dioxide is causing global warming. Their evidence is published in peer-reviewed journals.

Explain why evidence that has been peer-reviewed is more likely to be accepted. [2]

(a) (414 − 317) ÷ 317 × 100 or 97 ÷ 317 × 100(1)
(a) 30.6 (%)
allow 1 mark for 30.599… or 31 (not to 3 s.f.)
do not accept 23.4 (dividing by 414)(1)
(b) (in summer) plants / trees carry out more photosynthesis
allow 'more leaves on trees' / 'more light / warmer, so faster photosynthesis'(1)
(b) so more carbon dioxide is removed / taken in from the air
allow 'rate of photosynthesis is greater than rate of respiration'
allow, as an alternative for 1 mark: more (fossil) fuels are burned for heating in winter, releasing more carbon dioxide
ignore 'plants respire less in summer'(1)
(c) it has been checked / evaluated by other scientists who are experts in the same field (before publication)(1)
(c) so errors / bias / invalid methods are more likely to have been found / corrected
allow 'so the conclusions are more likely to be valid / supported by the data'
ignore 'it is reliable' unqualified(1)
Answer: (a) 30.6% (b) In summer plants photosynthesise more, so more CO₂ is removed from the air. (c) It has been checked by other experts in the same field, so mistakes or bias are more likely to have been found.
Examiner tip: In (a) divide the increase by the original value (317), not the final value — 23.4% scores no marks.

6Grade 6–76 marks

Some farmers leave a strip of wild flowers around the edge of each field. This strip is called a field margin.

Scientists compared two wheat farms of the same size.

	Farm A (no field margins)	Farm B (6 m field margins)
Number of bumblebee species recorded	3	9
Number of bird species recorded	12	21
Wheat yield in tonnes per hectare of the whole farm	8.0	7.6

(a) Calculate the percentage decrease in wheat yield on Farm B compared with Farm A. [2]

(b) Explain why Farm B has more species of birds than Farm A. [2]

(d) A student said: “The data prove that field margins increase biodiversity on all farms.”

Give one reason why the student is wrong. [1]

(a) (8.0 − 7.6) ÷ 8.0 × 100 or 0.4 ÷ 8.0 × 100(1)
(a) 5 (%)
allow 5.0
do not accept 5.3 (dividing by 7.6)(1)
(b) field margins / wild flowers provide food (e.g. nectar, seeds) or habitat / shelter / nesting sites for more species (of insects / birds)(1)
(b) more insects / bumblebee species, which are food for (more species of) birds
allow 'there are more food sources for birds'
max 1 if no link between the field margin and birds(1)
(c) less land for growing crops, so lower yield / less income / less profit
allow 'yield falls by 5%' / 'margins may contain weeds or pests that spread to the crop'(1)
(d) any one from: only two farms compared / only one farm of each type · the farms may differ in other ways (e.g. pesticide use, location, surrounding habitat) · the data are from only one study / one time
ignore 'need to repeat' unqualified(1)
Answer: (a) 5% (b) Field margins provide food and habitats for more insect species, which are food for more bird species. (c) Less land for crops so lower yield/profit. (d) Only two farms compared — they could differ in other ways.
Examiner tip: In (b) make the link in the food chain: margins → more insects / seeds → more food for birds.

7Grade 4–56 marks

Untreated sewage leaked from a pipe into a river.

Students counted the number of different species of invertebrate animals in samples taken from the river.

A sample taken 200 m upstream of the pipe contained 20 species.
The graph shows the results for samples taken downstream of the pipe.

(a) How many species were found 100 m downstream of the pipe? [1]

(b) Calculate the percentage decrease in the number of species between the upstream sample and the sample 100 m downstream. [2]

(d) Suggest one reason for the change you described in part (c). [1]

(e) Sewage is one pollutant of water. Give one other pollutant of water. [1]

(a) 5(1)
(b) (20 − 5) ÷ 20 × 100 or 15 ÷ 20 × 100
allow their (a) value used correctly(1)
(b) 75 (%)(1)
(c) the number of species increases (from 5 to 19)
allow 'it increases, then levels off / almost returns to the upstream number'(1)
(d) the sewage is diluted (by river water) / broken down / decomposed (by microorganisms) further downstream
allow 'less pollution further away from the pipe' / 'more oxygen in the water further downstream'(1)
(e) fertiliser · toxic chemicals (e.g. pesticides, herbicides, industrial waste)
allow named toxic chemical, e.g. heavy metals / oil
ignore 'rubbish' / 'plastic' unqualified(1)
Answer: (a) 5 (b) 75% (c) It increases (to 19). (d) The sewage is diluted / broken down further downstream. (e) e.g. fertiliser.
Examiner tip: In (b) divide the decrease by the upstream (original) number, 20 — not by 5.

8Grade 8–9Higher6 marks

A company wants to clear 5000 hectares of tropical rainforest to grow oil palms. The palm oil will be used to make biofuel to replace diesel made from crude oil.

The table gives some information about the plan.

Information	Value
Mean number of tree species per hectare in the rainforest	150
Number of tree species per hectare in an oil palm plantation	1
Carbon dioxide released when 1 hectare of rainforest is cleared and burned	650 tonnes
Carbon dioxide emissions saved each year by using biofuel from 1 hectare of oil palms instead of diesel	6.5 tonnes
Number of jobs created for local people	2000

Evaluate the plan to clear the rainforest to grow oil palms for biofuel.

Use information from the table and your own knowledge. [6]

For: 2000 jobs / income for local people / economic development of the country(1)
For: biofuel is a renewable fuel / replaces a fossil fuel, saving 6.5 tonnes of CO₂ per hectare each year (32 500 tonnes per year for 5000 ha)(1)
For: less dependence on crude oil (a finite resource) / oil palms absorb some CO₂ by photosynthesis as they grow(1)
Against: biodiversity falls from about 150 tree species per hectare to 1 (a monoculture) – loss of habitats / food sources, so many animal species are lost too / possible extinction(1)
Against: clearing releases 650 × 5000 = 3 250 000 tonnes of CO₂, from burning and from decay of the remaining wood by microorganisms(1)
Against: it would take 650 ÷ 6.5 = 100 years of using the biofuel to make up for the CO₂ released by clearing – so in the short term the plan increases CO₂ / global warming(1)
Against: fewer trees means less CO₂ removed by photosynthesis; lower stability of the ecosystem (fewer interdependent species)(1)
Against: the land could be needed for growing food / the jobs may be low-paid or temporary; data give no information on other costs (e.g. fertiliser, pesticides polluting rivers)(1)
Judgement supported by the data, e.g. 'the plan should not go ahead: the 100-year CO₂ payback and loss of almost all tree species outweigh the jobs and fuel benefits — the biofuel would be better grown on land that is already cleared'(1)

Level	Marks	What it looks like
Level 3	5–6	Weighs advantages against disadvantages, using processed data from the table (e.g. total CO₂ released or the years needed to repay it) together with relevant biological knowledge, and gives a conclusion that follows from the points made.
Level 2	3–4	Gives at least one advantage and one disadvantage with some explanation or some use of the data; any conclusion is only partly justified.
Level 1	1–2	Makes simple relevant statements, which may be one-sided or just repeat values from the table without comment.
No relevant content	0	Nothing worthy of credit.

Answer: Balanced evaluation: jobs and renewable fuel (6.5 t CO₂ saved per ha per year) vs. loss of biodiversity (150 → 1 tree species per ha), 3 250 000 t CO₂ released, 100-year payback; conclusion justified.
Examiner tip: Top-level answers process the data — e.g. 650 ÷ 6.5 = 100 years to repay the carbon released — and then reach a justified conclusion.

9Grade 8–9Higher6 marks

A species of frog is endangered because the ponds where it breeds have been drained or polluted.

A zoo runs a breeding programme. All of the frogs in the programme are descended from 10 frogs caught in the wild.

Young frogs from the zoo were released in two ways:

400 frogs were released into an existing polluted pond.
400 frogs were released into a pond that had been cleaned and replanted (a regenerated habitat).

After one year, 64 frogs were still alive in the polluted pond and 184 were still alive in the regenerated pond.

(a) Calculate the difference between the percentage survival in the regenerated pond and the percentage survival in the polluted pond. [2]

(b) Use the results to explain why breeding programmes alone may not be enough to maintain biodiversity. [2]

(a) 64 ÷ 400 × 100 = 16 (%) and 184 ÷ 400 × 100 = 46 (%)
or (184 − 64) ÷ 400 × 100
allow 0.16 and 0.46(1)
(a) 30 (percentage points)
allow 30%
correct answer with no working = 2 marks
do not accept 120 (difference in numbers) or 2.9 (ratio) for this mark(1)
(b) survival is much lower in the polluted pond (16% vs 46%) / almost three times as many frogs survive in the regenerated pond(1)
(b) so the habitat must also be protected / regenerated (and pollution reduced) for released animals to survive and breed
allow 'if the habitat is not restored the released frogs die, so the population does not recover'(1)
(c) all the frogs come from 10 frogs, so there is little genetic variation / the frogs have similar alleles
allow 'small gene pool' / 'inbreeding'(1)
(c) so it is unlikely that any frogs have alleles for resistance to the disease, so none survive (to reproduce)
allow 'if one frog is killed by the disease they are all likely to be' / 'natural selection cannot occur because no frogs are resistant'(1)
Answer: (a) 46% − 16% = 30 percentage points (b) Survival is far lower in the polluted pond, so the habitat must also be protected/regenerated. (c) Descended from only 10 frogs, so little genetic variation; unlikely any have alleles for resistance, so all could die.
Examiner tip: In (a) compare percentages, not numbers of frogs — 184 − 64 = 120 earns nothing on its own.

10Grade 4–56 marks

Scientists recorded the position of the most northerly population of a species of butterfly in Britain every five years.

The graph shows how far north of a fixed line this population was found.

(a) Describe the trend shown by the graph. [1]

(b) Calculate the mean rate at which the butterfly moved north between 1985 and 2020.

Give your answer in km per year. [2]

(d) Changes in distribution are one biological consequence of global warming.

Give one other biological consequence of global warming. [1]

(a) the butterfly is found further north over time / distance north increases (every five years)
allow 'the butterfly's range is moving north'
ignore 'it increases' without saying what increases(1)
(b) (160 − 20) ÷ (2020 − 1985) or 140 ÷ 35(1)
(b) 4 (km per year)
allow 4.0(1)
(c) (global warming means) the mean temperature has increased(1)
(c) so areas further north are now warm enough for the butterfly (or its food plants) to survive / reproduce
allow 'the butterfly can live / breed in places that used to be too cold'
ignore 'butterflies like warmth'(1)
(d) any one from: changes in migration patterns · loss of biodiversity / extinction of species · changes in timing of breeding / flowering
ignore changes in distribution / range of any species (given in the question)
do not accept a non-biological consequence, e.g. 'sea levels rise' or 'more flooding' on its own(1)
Answer: (a) The butterfly is found further north over time. (b) 140 ÷ 35 = 4 km per year. (c) Global warming has raised temperatures, so areas further north are now warm enough for the butterfly to survive. (d) e.g. changes in migration patterns / loss of biodiversity.
Examiner tip: In (b) read both values from the graph and divide by the number of years (35), not the number of points plotted.

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