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Detailed notes on Human Influences on Ecosystems for Cambridge IGCSE Biology, covering key concepts, explanations, examples, and exam-focused revision points.
Modern farming feeds billions but has costs. Cambridge wants the methods, the trade-offs, and EUTROPHICATION in detail.
Mapped to the Cambridge IGCSE 0610 syllabus (2026-2028).
Five big tools: fertilisers, pesticides, monoculture, intensive farming, breeding.
1. Fertilisers.
2. Pesticides + herbicides.
3. Monoculture.
4. Intensive (factory) farming.
5. Selective breeding.
Other:
Worked qualitative. Why does WHEAT grown today yield 4-5× more per hectare than wheat from 1900?
Cambridge tip. When asked how to increase food supply, give 4-5 methods with their effect. Cambridge marks both.
The chain of events that turns rivers into dead zones.
The chain (memorise):
Excess FERTILISER washes off fields → into LAKES, RIVERS, COASTAL WATERS.
Extra NITRATES + PHOSPHATES in water → ALGAE BLOOM (and other water plants).
Algae cover the surface → BLOCK SUNLIGHT → underwater plants can't photosynthesise → die.
Algae also die naturally (short-lived).
BACTERIA decompose dead algae + plants → use up DISSOLVED OXYGEN in water (aerobic respiration).
Low O₂ in water → fish, insects, other aquatic animals SUFFOCATE → die.
Lake becomes a 'dead zone' — almost lifeless except for anaerobic bacteria.
Where it happens:
Reducing eutrophication:
Worked qualitative. Why does sewage discharge ALSO cause eutrophication?
Cambridge tip. Memorise the chain. Cambridge often asks for it word-for-word. Keywords: ALGAE BLOOM, BLOCK LIGHT, BACTERIA DECOMPOSE, OXYGEN DEPLETED, FISH DIE.
Modern agriculture feeds billions but isn't sustainable as-is. Alternatives exist.
The core dilemma.
Sustainable alternatives:
1. Crop rotation.
2. Biological pest control.
3. Integrated pest management (IPM).
4. Organic farming.
5. Genetic modification.
Worked qualitative. Why might INSECT POPULATIONS be CRASHING globally?
Cambridge tip. When asked sustainable alternatives, give 3-4. Cambridge marks each.
Verbatim phrases and definitions Cambridge mark schemes credit.
Food supply appears Paper 4 (5-7 marks: methods, eutrophication chain). Examiner reports flag students missing eutrophication steps (algae bloom → block light → bacteria → O₂ depletion).
Sources: Cambridge IGCSE Biology 0610 syllabus 2026-2028 (20.1); 0610/22 May/Jun 2024 — Q13 (food supply); 0610 Examiner Reports 2022-2024. Last reviewed 2026-05-07.
Step-by-step solutions to past-paper-style questions on food supply, written exactly the way a tutor would explain them at the board.
Question
Describe five ways in which humans have increased food production.
Step-by-step solution
Step 1
Agricultural machinery — allows larger areas of land to be farmed efficiently.
Step 2
Chemical fertilisers — add minerals (e.g. nitrate) to the soil to improve crop yields.
Step 3
Insecticides — kill insect pests, improving the quality and yield of crops.
Step 4
Herbicides — kill weeds, reducing competition with the crop. Selective breeding — produces higher-yielding crops and livestock.
Answer
Machinery (larger areas), fertilisers (higher yields), insecticides (kill pests), herbicides (kill weeds), and selective breeding (better crops and animals).
Question
State the purpose of using: (a) a fertiliser; (b) an insecticide; (c) a herbicide.
Step-by-step solution
Step 1
(a) A fertiliser adds minerals to the soil to improve crop growth and yield.
Step 2
(b) An insecticide kills insect pests that would damage or eat the crop.
Step 3
(c) A herbicide kills weeds, reducing competition with the crop for light, water and minerals.
Answer
(a) Fertiliser adds minerals for growth; (b) insecticide kills insect pests; (c) herbicide kills weeds.
Question
Give two advantages and two disadvantages of growing a large-scale monoculture (a single crop over a large area).
Step-by-step solution
Step 1
Advantage 1: it is efficient — the same machinery, fertiliser and methods can be used over the whole area, and harvesting is easier.
Step 2
Advantage 2: it produces a large amount of one crop, which is profitable.
Step 3
Disadvantage 1: it reduces biodiversity — only one type of plant grows, so fewer species of animals and plants can live there.
Step 4
Disadvantage 2: a pest or disease can spread easily through the whole crop, because all the plants are the same and close together.
Answer
Advantages: efficient (one set of methods/machinery), large yield of one crop. Disadvantages: reduces biodiversity; pests and disease spread easily.
Question
Give two advantages and two disadvantages of intensive livestock production (keeping animals in large numbers in a small space).
Step-by-step solution
Step 1
Advantage 1: it produces more meat, eggs or milk from a small area of land, more cheaply.
Step 2
Advantage 2: keeping animals warm and limiting their movement means less energy is wasted, so more goes into growth.
Step 3
Disadvantage 1: the crowded conditions can cause animal welfare problems and allow disease to spread easily.
Step 4
Disadvantage 2: antibiotics are often used to prevent disease, which can lead to antibiotic-resistant bacteria.
Answer
Advantages: more food per area, cheaper, less energy wasted (so faster growth). Disadvantages: poor animal welfare/disease spreads; overuse of antibiotics → resistance.
Question
Explain the benefit of using nitrate fertiliser and a problem it can cause for nearby rivers and lakes.
Step-by-step solution
Step 1
Benefit: nitrate provides the nitrogen plants need to make amino acids and proteins, so the crop grows faster and gives a higher yield.
Step 2
Problem: if it rains, excess fertiliser can be washed (leached) into rivers and lakes.
Step 3
The extra nitrate causes water plants and algae to grow rapidly; when they die, decomposers use up the oxygen in the water.
Step 4
This eutrophication lowers the dissolved oxygen, so fish and other aquatic organisms die.
Answer
Nitrate fertiliser boosts crop growth and yield (more protein), but excess washed into water causes eutrophication — algal growth, decomposition, oxygen depletion and death of fish.
Examiner tip
Link the fertiliser benefit (nitrate → proteins → yield) to the problem (run-off → eutrophication → low oxygen → death of fish).
Question
Modern farming greatly increases food production but can harm the environment. Discuss this statement, giving examples.
Step-by-step solution
Step 1
Benefits: machinery, fertilisers, pesticides and selective breeding all increase yields, so more people can be fed.
Step 2
Harm 1: clearing land and growing monocultures reduces biodiversity and destroys habitats.
Step 3
Harm 2: pesticides can kill useful insects (such as pollinators), and fertiliser run-off causes eutrophication.
Step 4
Balance: the methods feed a large human population, but need careful management (e.g. controlled use of chemicals) to limit the environmental damage.
Answer
Modern methods raise yields and feed more people, but reduce biodiversity, harm useful insects and pollute water (eutrophication). They must be managed carefully to limit the damage.
Examiner tip
A balanced answer gives both the gains (more food) and the environmental costs (biodiversity loss, pollution), then a reasoned conclusion.
High-scoring sample answers for food supply on the Cambridge IGCSE 0610 paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.
State one way in which agricultural machinery has helped to increase food production. (1 mark)
Model answer
It allows larger areas of land to be farmed (more efficiently).
Why this scores
One mark for 'farm larger areas / work more efficiently'.
State two methods, other than machinery, used to increase crop yields. (2 marks)
Model answer
Using chemical fertilisers to improve yields, and insecticides to kill pests (or herbicides to kill weeds, or selective breeding for higher-yielding crops).
Why this scores
Any two of: fertilisers; insecticides; herbicides; selective breeding.
Describe one advantage and one disadvantage of growing a large-scale monoculture. (3 marks)
Model answer
Advantage: it is efficient and produces a large amount of one crop, because the same machinery and methods can be used over the whole field, making harvesting easier (1–2 marks). Disadvantage: it reduces biodiversity, and a pest or disease can spread quickly through the whole crop because all the plants are the same and close together (1–2 marks).
Why this scores
Three marks across: an advantage (efficiency/high yield of one crop); a disadvantage (reduced biodiversity / disease and pests spread easily).
Describe the advantages and disadvantages of intensive livestock production. (4 marks)
Model answer
Advantages: it produces more meat, milk or eggs from a small area of land and more cheaply, and because the animals are kept warm and cannot move about much, less energy is wasted, so more is used for growth. Disadvantages: the crowded conditions raise animal welfare concerns and allow diseases to spread quickly, and the heavy use of antibiotics to prevent disease can lead to antibiotic-resistant bacteria.
Why this scores
Four marks: two advantages (more food per area/cheaper; less energy wasted → faster growth) and two disadvantages (crowding/welfare/disease; antibiotic use/resistance).
Explain how chemical fertilisers and insecticides increase food production, and state one problem caused by each. (5 marks)
Model answer
Fertilisers add minerals such as nitrate to the soil; nitrate is used by plants to make amino acids and proteins, so the crop grows faster and gives a higher yield. A problem is that excess fertiliser washed into rivers and lakes causes eutrophication, lowering the oxygen and killing fish. Insecticides kill the insect pests that would eat or damage the crop, so more of the crop survives and the yield is higher. A problem is that insecticides can also kill useful insects, such as bees and the natural predators of pests, and may build up in food chains.
Why this scores
Five marks: fertiliser adds minerals/nitrate → proteins → higher yield; problem = eutrophication; insecticide kills pests → higher yield; problem = kills useful insects / bioaccumulation.
Discuss the advantages and disadvantages of using modern intensive farming methods to increase food supply. (6 marks)
Model answer
Modern intensive farming methods bring important advantages. Using machinery, fertilisers, pesticides and selective breeding greatly increases the yield of crops and livestock, so a large and growing human population can be fed more cheaply, and growing monocultures and keeping animals intensively makes efficient use of land and labour. However, there are serious disadvantages. Monocultures and the clearing of land reduce biodiversity and destroy habitats, and a pest or disease can spread rapidly through a single crop or a crowded herd. Pesticides can kill useful insects such as pollinators, and excess fertiliser washed into water causes eutrophication, which kills aquatic organisms. Intensive livestock farming raises animal welfare concerns and the heavy use of antibiotics can lead to antibiotic-resistant bacteria. Overall, intensive methods produce much more food, but at an environmental and ethical cost, so they need to be managed carefully — for example by using chemicals responsibly and protecting some natural habitats — to make food production more sustainable.
Why this scores
Up to 6 marks: advantages (higher yields/feeds more people; efficient use of land); disadvantages (reduced biodiversity/habitat loss; disease/pest spread; pesticides harm useful insects; fertiliser → eutrophication; welfare/antibiotic resistance) and a reasoned conclusion.
Definitions to memorise and the exact keywords mark schemes credit for food supply answers — sharpened from recent examiner reports for the 2026 0610 sitting.
Growing a single crop over a large area. Efficient, but reduces biodiversity and lets pests and disease spread easily.
A substance added to the soil to increase plant growth. Usually supplies nitrate, phosphate and potassium.
An insecticide kills insect pests; a herbicide kills weeds. Both increase crop yields but can harm other species.
Keeping large numbers of animals in a small space with high inputs, to produce more meat/milk/eggs per area.
The traps other students keep falling into on food supply questions — taken from recent Cambridge IGCSE 0610 examiner reports and mark schemes — and how to avoid them.
Why it happens
Their purpose is to protect crops.
How to avoid it
Pesticides also kill BENEFICIAL insects (e.g. pollinators and natural predators) and can build up in food chains. There is a trade-off.
Why it happens
More plants are grown.
How to avoid it
A monoculture is ONE type of plant, so it REDUCES biodiversity — fewer species of plants and animals can live there.
Why it happens
Both involve water and chemicals.
How to avoid it
Fertiliser causes EUTROPHICATION: algae grow then die, decomposers use up the oxygen, and the fish die from lack of oxygen — an indirect chain of events.
The things students keep getting wrong in this sub-topic, answered.