Question 1
Paper 4 short-answer style1 markName one gas that causes the enhanced greenhouse effect. (1 mark)
Model answer
Carbon dioxide (or methane).
Why this scores
One mark for 'carbon dioxide' or 'methane'.
Launching your learning experience…
Detailed notes on Human Influences on Ecosystems for Cambridge IGCSE Biology, covering key concepts, explanations, examples, and exam-focused revision points.
Air, water, land — pollution everywhere. Cambridge wants the greenhouse effect, acid rain, and the real-world consequences.
Mapped to the Cambridge IGCSE 0610 syllabus (2026-2028).
Greenhouse gases trap heat. Natural amount is fine; human-added amounts are warming the planet.
The natural greenhouse effect.
Human enhancement.
Net effect: more greenhouse gas in atmosphere → more heat trapped → temperatures rising.
Evidence of warming:
Consequences (in detail):
1. Sea level rise.
2. Extreme weather.
3. Habitat changes.
4. Agriculture.
5. Biodiversity loss.
Worked qualitative. Why does CUTTING TREES make global warming WORSE in TWO ways?
Cambridge tip. Memorise the chain: SUN → EARTH → INFRARED → GAS TRAPS → WARMING. Specifically state INFRARED.
SO₂ and NOₓ from fossils + water → sulfuric and nitric acid → acidic rain → kills life.
Formation:
Effects:
1. Forests damaged.
2. Lakes acidified.
3. Buildings + statues eroded.
4. Soil acidification.
Reducing acid rain:
Reduced significantly in Europe + N America since 1980s due to clean air laws. Still major problem in some developing countries.
Worked qualitative. Why does acid rain kill fish even when the lake's chemistry seems otherwise fine?
Cambridge tip. Always state SO₂ + NOₓ → acidic rain → effects. Cambridge marks each link.
Plastic, oil, sewage, heavy metals, noise — all problematic.
Plastic pollution.
Oil spills.
Sewage pollution.
Heavy metals.
Pesticides.
Noise pollution.
Worked qualitative. Why is MERCURY in TUNA an example of BIOACCUMULATION?
Cambridge tip. Memorise BIOACCUMULATION as the technical term. Cambridge marks it.
Verbatim phrases and definitions Cambridge mark schemes credit.
Pollution appears every Paper 4 (8-12 marks: greenhouse effect, acid rain, eutrophication, types). Examiner reports flag students missing infrared in greenhouse explanation.
Sources: Cambridge IGCSE Biology 0610 syllabus 2026-2028 (20.3); 0610/42 May/Jun 2024 — Q25 (pollution); 0610 Examiner Reports 2022-2024. Last reviewed 2026-05-07.
Step-by-step solutions to past-paper-style questions on pollution, written exactly the way a tutor would explain them at the board.
Question
Name a pollutant of (a) the air, (b) freshwater and (c) the land, and state one harmful effect of each.
Step-by-step solution
Step 1
(a) Air: carbon dioxide (or methane) — a greenhouse gas that causes global warming.
Step 2
(b) Freshwater: untreated sewage or excess fertiliser — causes eutrophication, killing aquatic life.
Step 3
(c) Land: non-biodegradable plastic — does not decay, harming wildlife and spoiling habitats.
Answer
Air: CO₂/methane (greenhouse warming). Water: sewage/fertiliser (eutrophication). Land: plastic (harms wildlife, does not decay).
Question
State two ways in which non-biodegradable plastics harm ecosystems.
Step-by-step solution
Step 1
Because they are non-biodegradable, plastics are not broken down by decomposers, so they build up in the environment for a very long time.
Step 2
Animals can become entangled in plastic, or eat it (mistaking it for food), which can injure or kill them.
Step 3
Plastics also break into tiny pieces (microplastics) that enter food chains in water and on land.
Answer
Plastics do not decay, so they build up; animals become entangled in them or eat them and are harmed; they break into microplastics that enter food chains.
Question
Explain how the enhanced greenhouse effect causes global warming.
Step-by-step solution
Step 1
Greenhouse gases such as carbon dioxide and methane are present in the atmosphere.
Step 2
Energy from the Sun reaches the Earth and warms it; the Earth radiates this energy back as heat (infrared radiation).
Step 3
The greenhouse gases absorb this heat and re-emit some of it back towards the Earth, so heat is trapped in the atmosphere.
Step 4
Human activities (burning fossil fuels, deforestation, livestock farming) have increased the amount of these gases, trapping more heat — the enhanced greenhouse effect — so the Earth's average temperature rises (global warming).
Answer
Greenhouse gases (CO₂ and methane) absorb the heat the Earth radiates and send some back, trapping heat. Human activity has increased these gases, trapping more heat and raising the temperature (global warming).
Examiner tip
Cambridge limits the air-pollution greenhouse gases to methane and carbon dioxide. The mechanism is trapping the heat (infrared) radiated by the Earth.
Question
Describe the harmful effects of untreated sewage and excess fertiliser on a river or lake.
Step-by-step solution
Step 1
Untreated sewage and fertiliser run-off add extra nutrients (nitrate and other ions) to the water.
Step 2
These extra nutrients cause water plants and algae to grow rapidly (an algal bloom).
Step 3
When the plants and algae die, decomposers (bacteria) break them down and use up the oxygen dissolved in the water as they respire.
Step 4
With little oxygen left, fish and other organisms that need dissolved oxygen die — this is eutrophication. (Sewage can also spread disease.)
Answer
Sewage and fertiliser add nutrients that make algae bloom; when they die, decomposers use up the oxygen, so fish and other organisms die (eutrophication).
Question
Explain the process of eutrophication, in order, from the entry of nutrients to the death of organisms.
Step-by-step solution
Step 1
There is an increased availability of nitrate and other ions in the water (from fertiliser run-off or sewage).
Step 2
This causes an increased growth of producers (algae and water plants).
Step 3
When the producers die, there is increased decomposition of the dead material, and so increased aerobic respiration by the decomposers.
Step 4
This respiration causes a reduction in the dissolved oxygen in the water, leading to the death of organisms that need dissolved oxygen, such as fish.
Answer
More nitrate/ions → more growth of producers → they die → more decomposition → more aerobic respiration by decomposers → less dissolved oxygen → death of organisms needing oxygen.
Examiner tip
Follow the syllabus chain exactly: nitrate ↑ → producer growth ↑ → decomposition ↑ → decomposer respiration ↑ → dissolved oxygen ↓ → organisms die.
Question
Describe some effects of the global warming caused by the enhanced greenhouse effect.
Step-by-step solution
Step 1
Melting of ice (glaciers and polar ice) and the expansion of warming water cause sea levels to rise, leading to coastal flooding.
Step 2
There are more extreme weather events, such as storms, heatwaves, droughts and floods.
Step 3
Habitats and the distribution of species change, and species that cannot move or adapt may become extinct.
Step 4
Changing temperature and rainfall can also reduce crop yields, threatening food supplies for humans.
Answer
Rising sea levels (melting ice) and flooding; more extreme weather; shifts in habitats and possible extinctions; reduced crop yields and threats to food supply.
Examiner tip
Climate change is the broader consequence of global warming — link warming to physical and biological effects.
High-scoring sample answers for pollution on the Cambridge IGCSE 0610 paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.
Name one gas that causes the enhanced greenhouse effect. (1 mark)
Model answer
Carbon dioxide (or methane).
Why this scores
One mark for 'carbon dioxide' or 'methane'.
State two harmful effects of non-biodegradable plastics on ecosystems. (2 marks)
Model answer
Plastics are not broken down by decomposers, so they build up in the environment; and animals can become entangled in them or eat them, which injures or kills them.
Why this scores
Two distinct effects: they do not decay/build up; harm animals (entanglement/eating); enter food chains as microplastics.
Explain how the enhanced greenhouse effect leads to global warming. (3 marks)
Model answer
Greenhouse gases such as carbon dioxide and methane absorb the heat (infrared radiation) that the Earth radiates back into space, and re-emit some of it towards the Earth, trapping heat in the atmosphere. Human activities have increased the amounts of these gases, so more heat is trapped and the Earth's average temperature rises.
Why this scores
Three marks: gases (CO₂/methane) absorb the heat radiated by the Earth; re-emit/trap it; more gas traps more heat → temperature rises.
Describe the effects of adding untreated sewage and excess fertiliser to a river. (4 marks)
Model answer
The sewage and fertiliser add extra nutrients (such as nitrate) to the water, which cause the algae and water plants to grow rapidly. When these plants and algae die, decomposers break them down and use up the oxygen dissolved in the water during their respiration. With little dissolved oxygen left, fish and other aquatic organisms die. (Sewage may also contain pathogens that spread disease.)
Why this scores
Four marks: extra nutrients added; rapid growth of algae/plants; decomposers use up oxygen on their death; fish/organisms die.
Explain the process of eutrophication of water caused by excess fertiliser. (5 marks)
Model answer
Excess fertiliser washed into the water causes an increased availability of nitrate and other ions. This leads to an increased growth of producers, such as algae and water plants. When these producers die, there is increased decomposition of the dead material, which causes increased aerobic respiration by the decomposers. This respiration causes a reduction in the dissolved oxygen in the water. As a result, organisms that require dissolved oxygen, such as fish, die.
Why this scores
Five marks, following the syllabus chain: more nitrate/ions; more producer growth; more decomposition on death; more respiration by decomposers; less dissolved oxygen → organisms die.
Describe the sources of methane and carbon dioxide in the atmosphere, and explain how they cause global warming and climate change. (6 marks)
Model answer
Carbon dioxide is released mainly by the burning of fossil fuels (in vehicles, power stations and industry) and by deforestation (burning trees and reducing the number that remove CO₂). Methane is released from livestock such as cattle, from rice fields (paddy fields) and from the decay of waste in landfill sites. Both gases are greenhouse gases: they absorb the heat (infrared radiation) that the Earth radiates and re-emit some of it back towards the Earth, trapping heat in the atmosphere. As human activities have increased the amounts of these gases, more heat is trapped, so the Earth's average temperature rises — this is global warming. The warming causes climate change, including the melting of ice and rising sea levels, more extreme weather, changes to habitats and the distribution of species (with some becoming extinct), and reduced crop yields.
Why this scores
Up to 6 marks: sources of CO₂ (fossil fuels/deforestation); sources of methane (cattle/rice fields/landfill); both absorb the heat radiated by the Earth and trap it; more gas → more heat trapped → temperature rises; consequences (sea-level rise/extreme weather/habitat change/crop yields).
Definitions to memorise and the exact keywords mark schemes credit for pollution answers — sharpened from recent examiner reports for the 2026 0610 sitting.
The extra trapping of heat in the atmosphere by increased greenhouse gases (carbon dioxide and methane) from human activity, causing global warming.
The increase in the Earth's average temperature, caused mainly by the enhanced greenhouse effect.
The process in which extra nutrients (nitrate and other ions) cause producers to grow rapidly; when they die, decomposers use up the dissolved oxygen, killing organisms that need it.
A material (such as many plastics) that cannot be broken down by decomposers, so it builds up in the environment.
The traps other students keep falling into on pollution questions — taken from recent Cambridge IGCSE 0610 examiner reports and mark schemes — and how to avoid them.
Why it happens
It sounds like they warm the air.
How to avoid it
Greenhouse gases do not produce heat — they TRAP the heat that the Earth radiates back towards space, re-emitting some of it towards the Earth.
Why it happens
It causes warming.
How to avoid it
Some greenhouse effect is natural and keeps the Earth warm enough for life. The PROBLEM is the ENHANCED effect from human emissions.
Why it happens
Both involve chemicals in water.
How to avoid it
Fertiliser causes EUTROPHICATION: it makes algae grow, which die and are decomposed, using up the oxygen — the fish die from lack of oxygen, not poisoning.
The things students keep getting wrong in this sub-topic, answered.