20.3

Pollution

Cambridge IGCSE Biology (0610)  · Unit 20: Human influences on ecosystems  · 12 flashcards

Pollution is topic 20.3 in the Cambridge IGCSE Biology (0610) syllabus , positioned in Unit 20 — Human influences on ecosystems , alongside Food supply, Habitat destruction and Conservation.  In one line: Eutrophication is the enrichment of an ecosystem with chemical nutrients, typically compounds containing nitrogen or phosphorus. It often results from runoff of fertilizers from agricultural land. This enrichment then leads to a cascade of ecological effects.

This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical). Past papers from 2022 to 2025 show this topic across 7 questions worth 75 marks (around 1.1% of all Biology marks in those years).

The deck below contains 12 flashcards — 1 definition, 4 key concepts, 5 process cards and 2 identification cards — covering the precise wording mark schemes reward.  Use the definition card to lock down command-word answers (define, state), then move on to the concept and application cards to handle explain, describe and compare questions.

Key definition

Eutrophication

Eutrophication is the enrichment of an ecosystem with chemical nutrients, typically compounds containing nitrogen or phosphorus. It often results from runoff of fertilizers from agricultural land. This enrichment then leads to a cascade of ecological effects.

What the Cambridge 0610 syllabus says

Official 2026-2028 spec

These are the exact learning objectives Cambridge sets for this topic. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks.

  1. Describe Describe the effects of untreated sewage and excess fertiliser on aquatic ecosystems
  2. Describe Describe the effects of non-biodegradable plastics, in both aquatic and terrestrial ecosystems
  3. Describe Describe the sources and effects of pollution of the air by methane and carbon dioxide, limited to: the enhanced greenhouse effect and climate change
  4. Explain Explain the process of eutrophication of water, limited to: increased availability of nitrate and other ions; increased growth of producers; increased decomposition after death of producers; increased aerobic respiration by decomposers; reduction in dissolved oxygen; death of organisms requiring dissolved oxygen in water Supplement
Key Concept Flip

How do untreated sewage and excess fertiliser impact aquatic ecosystems?

Answer Flip

Untreated sewage introduces pathogens and organic matter, increasing decomposers and decreasing oxygen. Excess fertilizer leads to algal blooms, which die and decompose, similarly depleting oxygen levels and harming aquatic life such as fish and invertebrates.

Key Concept Flip

What are the negative effects of non-biodegradable plastics in aquatic ecosystems?

Answer Flip

Non-biodegradable plastics persist for long periods, entangling marine life like turtles and seabirds, causing injury or death. They also break down into microplastics, ingested by organisms and potentially disrupting food chains, affecting species like zooplankton and fish.

Key Concept Flip

What are the negative effects of non-biodegradable plastics in terrestrial ecosystems?

Answer Flip

In terrestrial environments, plastics can contaminate soil, hindering plant growth by preventing water and nutrient absorption. Animals may ingest plastic, leading to blockages or toxicity within their digestive systems. An example would be earthworms and badgers.

Key Concept Flip

What are the main sources of methane as an air pollutant?

Answer Flip

Methane is released from sources like livestock farming (

Example: cattle digestion), decomposition in landfills, and natural gas leaks. These sources contribute significantly to atmospheric methane concentrations. Rice paddy fields also contribute to methane emmisions.
Key Concept Flip

What are the main sources of carbon dioxide as an air pollutant?

Answer Flip

Carbon dioxide primarily originates from the burning of fossil fuels (coal, oil, and natural gas) in power plants, vehicles, and industrial processes. Deforestation, through burning of trees, is also a major contributor.

Key Concept Flip

How do methane and carbon dioxide contribute to the enhanced greenhouse effect?

Answer Flip

Methane and carbon dioxide are greenhouse gases that trap heat in the Earth's atmosphere. Increased concentrations prevent heat from escaping into space, leading to a rise in global temperatures. This effect is particularly important for plants which require specific conditions.

Key Concept Flip

What is the link between the enhanced greenhouse effect and climate change?

Answer Flip

The enhanced greenhouse effect, caused by increased levels of greenhouse gases like carbon dioxide and methane, leads to climate change. This results in rising sea levels, altered weather patterns (

Example: more frequent extreme weather events), and disruptions to ecosystems.
Definition Flip

What is eutrophication?

Answer Flip

Eutrophication is the enrichment of an ecosystem with chemical nutrients, typically compounds containing nitrogen or phosphorus. It often results from runoff of fertilizers from agricultural land. This enrichment then leads to a cascade of ecological effects.

Key Concept Flip

Explain the first step of eutrophication: increased availability of nitrate and other ions.

Answer Flip

The process begins with increased levels of nutrients, such as nitrates and phosphates, entering a water body. These nutrients come from sources like agricultural runoff (fertilizers) or sewage.

Example: rainwater can wash excess nitrate into lakes.
Key Concept Flip

Explain the second step of eutrophication: increased growth of producers.

Answer Flip

The increased availability of nutrients fuels rapid growth of aquatic producers like algae and phytoplankton. This rapid growth is termed an algal bloom and can cause the water to become murky.

Example: *Chlamydomonas* reproduces rapidly.
Key Concept Flip

Explain the third step of eutrophication: increased decomposition after death of producers.

Answer Flip

Following the algal bloom, the algae die and sink to the bottom of the water body. Decomposers, such as bacteria and fungi, break down the dead organic matter.

Example: *Aspergillus* bacteria perform aerobic respiration.
Key Concept Flip

Explain the final step of eutrophication: reduction in dissolved oxygen and death of organisms.

Answer Flip

Decomposers consume large amounts of dissolved oxygen during aerobic respiration. This reduces the oxygen available for other aquatic organisms, leading to their death. Fish (

Example: trout), invertebrates, and other oxygen-dependent species will die.

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20.2 Habitat destruction 20.4 Conservation

Key Questions: Pollution

What is eutrophication?

Eutrophication is the enrichment of an ecosystem with chemical nutrients, typically compounds containing nitrogen or phosphorus. It often results from runoff of fertilizers from agricultural land. This enrichment then leads to a cascade of ecological effects.

Tips to avoid common mistakes in Pollution

More topics in Unit 20 — Human influences on ecosystems

Pollution sits alongside these Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.

20.1 Food supply

11 flashcards
20.2 Habitat destruction

11 flashcards
20.4 Conservation

12 flashcards

Cambridge syllabus keywords to use in your answers

These are the official Cambridge 0610 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.

pollution air pollution water pollution land pollution eutrophication acid rain sulfur dioxide nitrogen oxide greenhouse gas carbon dioxide methane global warming climate change greenhouse effect ozone depletion CFC nuclear fallout

Key terms covered in this Pollution deck

Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.

Eutrophication

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How to study this Pollution deck

Start in Study Mode, attempt each card before flipping, then rate Hard, Okay or Easy. Cards you rate Hard come back within a day; cards you rate Easy push out to weeks. Your progress is saved in your browser, so come back daily for 5–10 minute reviews until every card reads Mastered.