Cambridge IGCSE Biology 0610: Human influences on ecosystems – Study Guide

This study guide teaches topic 20, Human influences on ecosystems, of the Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028. It covers syllabus sections 20.1 to 20.4: food supply, habitat destruction, pollution and conservation. Everything is Core unless it is labelled Extended only (Supplement content). Core candidates are examined on Papers 1 and 3; Extended candidates sit Papers 2 and 4, which test Core and Supplement content together.

Useful links: the Cambridge IGCSE Biology hub, the printable 0610 checklist, the revision notes for this topic and the practice set with worked answers. Food chains, food webs and the carbon and nitrogen cycles are taught in the Organisms and their environment study guide. To find your weak spots, try the Core diagnostic or the Extended diagnostic.

What this topic covers

Section	What you must be able to do	Tier
20.1 Food supply	Describe five ways humans have increased food production; advantages and disadvantages of monocultures and intensive livestock production	Core
20.2 Habitat destruction	Define biodiversity; reasons for habitat destruction; human impact through food webs; undesirable effects of deforestation	Core
20.3 Pollution	Effects of untreated sewage and excess fertiliser; non-biodegradable plastics; methane and carbon dioxide	Core
20.3 (continued)	Explain eutrophication step by step	Extended only
20.4 Conservation	Define a sustainable resource; forests and fish stocks; why species become endangered; how endangered species are conserved	Core
20.4 (continued)	Conserving forests and fish stocks; reasons for conservation programmes; AI and IVF in captive breeding; risks of reduced genetic variation	Extended only

20.1 Food supply

How humans have increased food production

The syllabus limits this to five methods:

Method	How it increases food production
Agricultural machinery	Allows larger areas of land to be farmed and improves efficiency
Chemical fertilisers	Supply mineral ions such as nitrate, improving yields
Insecticides	Kill insect pests, improving quality and yield
Herbicides	Kill weeds, reducing competition with the crop for light, water and mineral ions
Selective breeding	Improves production by crop plants and livestock, for example higher-yielding varieties

Large-scale monocultures of crop plants

A monoculture is a large area growing a single crop.

Advantages: machinery can plant, spray and harvest efficiently; conditions can be tailored to one crop; large yields at lower cost per unit.

Disadvantages: reduces biodiversity, because one species replaces many; pests and diseases of that crop spread easily, so more pesticide is used; the same mineral ions are removed from the soil each year, so more fertiliser is needed; hedgerows and natural habitats are often removed to create large fields.

Intensive livestock production

Animals are kept indoors or in small spaces, with controlled food and conditions.

Advantages: less energy is lost in movement and keeping warm, so more of the food eaten goes into growth; large amounts of meat, eggs or milk at lower cost; less land needed per animal.

Disadvantages: disease spreads quickly in crowded conditions, so antibiotics are often used; concentrated animal waste can pollute water; animal welfare concerns; large amounts of crop feed are needed, and growing it uses land.

20.2 Habitat destruction

Biodiversity is the number of different species that live in an area.

Reasons for habitat destruction

• Increased area for housing, crop plant production and livestock production.
• Extraction of natural resources, such as mining, quarrying and logging.
• Freshwater and marine pollution, which makes habitats unsuitable for the species living there.

Through altering food webs and food chains, humans can also have a negative impact on habitats. Removing one species, or adding a new one, affects the organisms that feed on it or compete with it.

Undesirable effects of deforestation

Deforestation is the syllabus example of habitat destruction. You must explain five effects:

Effect	Explanation
Reducing biodiversity	Many species live only in forest; removing trees removes their food and shelter
Extinction	Species found in only one forest may have nowhere else to live and die out
Loss of soil	Tree roots no longer hold soil, and there is no canopy to shield it from heavy rain, so soil is washed or blown away
Flooding	Fewer trees take up water and transpire, and less rain is intercepted, so more water runs off into rivers
Increase of carbon dioxide in the atmosphere	Fewer trees remove carbon dioxide by photosynthesis; burning or decomposing wood releases carbon dioxide

Worked example. Satellite images show that a forest covered 6.0 million hectares and ten years later covered 5.1 million hectares. Calculate the percentage decrease.

percentage decrease = (original − new) ÷ original × 100
                    = (6.0 − 5.1) ÷ 6.0 × 100
                    = 0.9 ÷ 6.0 × 100
                    = 15 %

Always divide by the original value.

20.3 Pollution

Untreated sewage and excess fertiliser in water (Core)

• Untreated sewage contains organic matter. Bacteria decompose it and use up dissolved oxygen as they respire, so fish and other animals may die. Sewage also adds mineral ions that cause rapid growth of algae.
• Excess fertiliser washed off fields adds nitrate and other ions to rivers and lakes, causing rapid growth of algae and other producers. When these die, decomposition uses up dissolved oxygen, and organisms that need oxygen die.

Eutrophication (Extended only)

The syllabus limits the explanation to six linked steps. Learn them in order:

1. Increased availability of nitrate and other ions (from fertiliser or sewage).
2. Increased growth of producers, such as algae.
3. Producers die, so there is increased decomposition after their death.
4. Increased aerobic respiration by decomposers (bacteria).
5. Reduction in dissolved oxygen in the water.
6. Death of organisms requiring dissolved oxygen, such as fish.

The key link that is often missed is step 4. It is the decomposers’ aerobic respiration that uses up the oxygen, not the algae.

Worked example. Dissolved oxygen is 9.0 mg/dm³ above a farm drain and 2.7 mg/dm³ 400 m downstream. Calculate the percentage decrease.

(9.0 − 2.7) ÷ 9.0 × 100 = 6.3 ÷ 9.0 × 100 = 70 %

Non-biodegradable plastics

Non-biodegradable plastics are not broken down by decomposers, so they persist for a very long time.

• Aquatic ecosystems: animals become entangled and drown or cannot feed; animals swallow plastic, mistaking it for food, and their guts become blocked; plastic breaks into small pieces that enter food chains.
• Terrestrial ecosystems: plastic fills landfill sites; animals eat or become trapped in plastic waste; litter makes habitats less suitable for organisms.

Methane and carbon dioxide in the air

Gas	Main sources
Carbon dioxide	Combustion of fossil fuels; burning of forests (deforestation)
Methane	Cattle and other livestock (from digestion); rice fields; decomposition of waste in landfill sites

Effects (limited to): both gases absorb thermal energy that would otherwise be lost from the Earth. Higher concentrations cause an enhanced greenhouse effect, increasing the mean global temperature and causing climate change, such as changing rainfall patterns, more extreme weather and rising sea levels.

20.4 Conservation

Sustainable resources

A sustainable resource is one which is produced as rapidly as it is removed from the environment so that it does not run out. Some resources can be conserved and managed sustainably; the syllabus limits these to forests and fish stocks.

Why organisms become endangered or extinct

Climate change, habitat destruction, hunting, overharvesting, pollution and introduced species. In an answer, link the cause to the population: “hunting removes breeding adults faster than they are replaced”.

Conserving endangered species (Core)

• Monitoring and protecting species and habitats (counting populations; protected reserves; laws against hunting).
• Education, so people understand why species matter and how to avoid harming them.
• Captive breeding programmes, breeding animals in zoos and releasing offspring into the wild.
• Seed banks, storing seeds of plant species so they can be grown again if wild populations are lost.

Conserving forests (Extended only)

• Education: people learn the value of forests and sustainable use.
• Protected areas: logging is banned or limited in parts of the forest.
• Quotas: a limit on the number of trees that can be felled.
• Replanting: new trees are planted to replace those felled.

Conserving fish stocks (Extended only)

• Education: people learn why fish stocks must be managed, and choose sustainably caught fish.
• Closed seasons: no fishing during the breeding season, so fish can reproduce.
• Protected areas: no fishing in certain zones, such as breeding grounds.
• Controlled net types and mesh size: a larger mesh lets young fish escape, so they survive to breed.
• Quotas: a limit on the mass or number of fish that can be caught.
• Monitoring: counting fish populations so quotas can be adjusted.

Reasons for conservation programmes (Extended only)

Limited to: maintaining or increasing biodiversity; reducing extinction; protecting vulnerable ecosystems; maintaining ecosystem functions, limited to nutrient cycling and resource provision, including food, drugs, fuel and genes.

AI and IVF in captive breeding (Extended only)

• Artificial insemination (AI): sperm is collected from a male and placed into a female. Sperm can be stored frozen and transported between zoos, so animals do not need to be moved, and males from different populations can be used.
• In vitro fertilisation (IVF): eggs are collected from a female and fertilised by sperm outside the body. The embryos are then placed into a female to develop.

Both help animals that do not breed readily in captivity, and both let breeders choose unrelated parents.

Risks of a small population (Extended only)

When a population becomes very small, genetic variation is reduced. The species is then less likely to have individuals with alleles that help them survive a change in the environment or a new disease, so the whole population is at greater risk of extinction.

Common errors

• Saying herbicides kill insects or insecticides kill weeds.
• Writing that algae use up the oxygen in eutrophication. The decomposers’ aerobic respiration does.
• Stating “the greenhouse effect” when the syllabus term is the enhanced greenhouse effect.
• Describing a sustainable resource as one that “will not run out” without saying it is produced as rapidly as it is removed.
• Listing deforestation effects without explaining them.
• Calling biodiversity “the number of organisms” instead of the number of different species.
• Describing a larger mesh size as catching “fewer fish” without saying young fish escape to breed.

Where to go next

Condense this into the revision notes, then try the practice questions.

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.