Cambridge IGCSE Biology 0610: Human influences on ecosystems – Revision Notes

These notes condense topic 20, Human influences on ecosystems, of the Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028 (sections 20.1 to 20.4) for your final weeks of revision. Supplement content is marked Extended only; Core candidates (Papers 1 and 3) can skip it, while Extended candidates (Papers 2 and 4) need all of it. For full explanations and worked examples, use the Human influences on ecosystems study guide.

Also useful: the IGCSE Biology hub, the 0610 checklist, the practice questions for this topic, the Organisms and their environment revision notes for food webs and nutrient cycles, and the free Core and Extended diagnostics.

20.1 Food supply (Core)

Five ways food production has increased

Method	Benefit
Agricultural machinery	Larger areas of land farmed; improved efficiency
Chemical fertilisers	Improved yields
Insecticides	Improved quality and yield (fewer insect pests)
Herbicides	Less competition with weeds
Selective breeding	Improved production by crop plants and livestock

Monocultures and intensive livestock

	Advantages	Disadvantages
Large-scale monoculture	Efficient use of machinery; high yield; lower cost per unit	Low biodiversity; pests and diseases spread easily; heavy use of pesticides and fertiliser; habitats such as hedgerows removed
Intensive livestock	Less energy lost in movement and heat, so faster growth; high output at lower cost; less land per animal	Disease spreads quickly; waste can pollute water; welfare concerns; needs large amounts of crop feed

20.2 Habitat destruction (Core)

• Biodiversity: the number of different species that live in an area.
• Reasons for habitat destruction: more land for housing, crop plants and livestock; extraction of natural resources; freshwater and marine pollution.
• Humans can harm habitats by altering food chains and food webs (removing or introducing species).

Deforestation – five undesirable effects

Effect	Because
Reduced biodiversity	Forest species lose food and shelter
Extinction	Species found only there die out
Loss of soil	No roots to hold soil; rain washes it away
Flooding	Less water taken up and transpired; more run-off
More CO₂ in the atmosphere	Less photosynthesis; burning and decay of wood release CO₂

20.3 Pollution

Core

• Untreated sewage: bacteria decompose the organic matter and use up dissolved oxygen; aquatic animals die. Also adds mineral ions.
• Excess fertiliser: run-off adds nitrate and other ions; producers grow rapidly; when they die, decomposition lowers oxygen; animals die.
• Non-biodegradable plastics: not broken down by decomposers. Aquatic: entanglement, swallowed and block guts, small fragments enter food chains. Terrestrial: fill landfill, trap or are eaten by animals.
• Carbon dioxide sources: combustion of fossil fuels; burning forests. Methane sources: livestock such as cattle; rice fields; landfill.
• Effects: enhanced greenhouse effect → more thermal energy kept in the atmosphere → climate change.

Eutrophication in six steps (Extended only)

1. More nitrate and other ions in the water.
2. More growth of producers (algae).
3. Producers die; more decomposition.
4. More aerobic respiration by decomposers.
5. Dissolved oxygen falls.
6. Organisms needing dissolved oxygen die (fish, many invertebrates).

Method: percentage change

1. Subtract to find the change.
2. Divide by the original value.
3. Multiply by 100 and state “increase” or “decrease”.

20.4 Conservation

Core

• Sustainable resource: one which is produced as rapidly as it is removed from the environment so that it does not run out.
• Resources that can be conserved and managed sustainably: forests and fish stocks.
• Why species become endangered or extinct: climate change, habitat destruction, hunting, overharvesting, pollution, introduced species.
• How endangered species are conserved: monitoring and protecting species and habitats; education; captive breeding programmes; seed banks.

Extended only

Resource	Conservation methods
Forests	Education; protected areas; quotas; replanting
Fish stocks	Education; closed seasons; protected areas; controlled net types and mesh size; quotas; monitoring

Reasons for conservation programmes: maintain or increase biodiversity; reduce extinction; protect vulnerable ecosystems; maintain ecosystem functions (nutrient cycling; resource provision – food, drugs, fuel, genes).

AI: sperm collected from a male, stored or transported, placed in a female. No need to move animals. IVF: eggs fertilised outside the body; embryos placed in a female.

Small population risk: reduced genetic variation → fewer individuals able to survive environmental change or new disease → higher risk of extinction.

Small worked reminders

Monoculture and pests (Core). A farmer grows one variety of maize over 500 hectares. An insect pest that feeds on maize can move from plant to plant without meeting any other crop, so its population grows quickly. The farmer sprays more insecticide, which may also kill insects that are not pests. This is why “pests spread easily” and “more pesticide used” are linked disadvantages.

Intensive livestock and energy (Core). Chickens kept indoors move less and are kept warm. Less of the energy in their food is released in respiration for movement and keeping warm, so more is available for growth. Link the advantage to energy, not just to “more meat”.

Plastic in a food chain (Core). Small fragments of plastic are eaten by small animals in the sea, which are eaten by fish, which are eaten by birds. The plastic passes along the chain because it is not broken down.

Captive breeding (Extended only). A zoo has one male of an endangered cat; a zoo in another country has two females. Using AI, sperm from the male can be frozen and sent abroad, so the animals do not have to travel. Breeders choose unrelated parents so genetic variation in the captive population is kept as high as possible.

Method: answering an “explain” question on this topic

1. Name the human activity (for example, felling trees).
2. State the immediate change (fewer roots holding the soil).
3. State the consequence for the ecosystem (soil washed away by rain; fewer producers).
4. Where marks allow, add the effect on organisms or on people (loss of habitat; flooding downstream).

Must-know distinctions

• Insecticide kills insects; herbicide kills weeds.
• Greenhouse effect is natural; the enhanced greenhouse effect is caused by extra CO₂ and methane.
• In eutrophication, decomposers use up oxygen, not the algae.
• Biodiversity counts species, not individual organisms.
• Quota limits how much is taken; closed season limits when; protected area limits where; mesh size limits which (size) fish are caught.
• AI puts sperm into a female; IVF fertilises eggs outside the body.

Quick self-test

1. Describe biodiversity.
2. State how herbicides increase food production.
3. Give one advantage and one disadvantage of a large-scale monoculture.
4. Explain why deforestation can lead to flooding.
5. Name two sources of methane.
6. Dissolved oxygen falls from 8.4 mg/dm³ to 2.1 mg/dm³ downstream of a sewage outlet. Calculate the percentage decrease.
7. Extended: in eutrophication, which organisms’ respiration reduces dissolved oxygen?
8. Describe a sustainable resource.
9. A forest of 40 000 ha has 1 200 ha felled and 800 ha replanted each year. Is it managed sustainably? How many years until it has lost 10% of its area?
10. Extended: explain how a larger mesh size helps conserve fish stocks.
11. Extended: explain why a small population is at greater risk of extinction.
12. State two ways endangered species can be conserved.

Answers

1. The number of different species that live in an area.
2. They kill weeds, reducing competition with the crop.
3. Advantage: efficient harvesting with machinery (or high yield). Disadvantage: lower biodiversity (or pests spread easily).
4. Fewer trees take up water and transpire, and soil is lost, so more rain runs off into rivers.
5. Any two: cattle (livestock); rice fields; landfill sites.
6. (8.4 − 2.1) ÷ 8.4 × 100 = 75 % decrease.
7. The decomposers (bacteria).
8. One which is produced as rapidly as it is removed from the environment so that it does not run out.
9. No: net loss is 1 200 − 800 = 400 ha per year. 10% of 40 000 = 4 000 ha; 4 000 ÷ 400 = 10 years.
10. Young fish escape through the net, so they survive to reproduce.
11. Genetic variation is reduced, so fewer individuals may have alleles that let them survive environmental change or disease.
12. Any two: monitoring and protecting species and habitats; education; captive breeding; seed banks.

Where marks are usually lost

• Leaving out step 4 of eutrophication (aerobic respiration by decomposers) or giving the steps out of order.
• Writing “the greenhouse effect” instead of the enhanced greenhouse effect.
• Listing deforestation effects without the explanation the command word “explain” requires.
• Giving “pesticides” when the question asks specifically about insecticides or herbicides.
• Stating that a sustainable resource “never runs out” without the rate comparison.
• Describing fish conservation methods without saying how each lets the population recover (for example, closed seasons protect breeding).
• Confusing AI with IVF, or saying IVF happens inside the female.
• Dividing by the new value, not the original, in percentage-change calculations.
• Answering a plastics question with aquatic effects only when the question asks about terrestrial ecosystems too; give points for each ecosystem named.
• Saying intensive livestock production is an advantage because it gives “more meat” without linking it to less energy lost in movement and keeping warm.

Official syllabus

Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028 (Version 3), Cambridge University Press & Assessment (Cambridge International Education). Topic 20, sections 20.1 to 20.4.