Pollution — Cambridge IGCSE Biology
The effects of sewage, fertiliser, eutrophication, plastics, methane and carbon dioxide on ecosystems and climate.
Revision notes
3 short notes, in the order of the specification. Each one in short:
Eutrophication is the chain of events when extra nitrate and other ions from excess fertiliser or untreated sewage enter water. Algae and water plants grow fast and block light, so producers deeper down die. Decomposers increase and their aerobic respiration uses up dissolved oxygen, so fish and other organisms that need dissolved oxygen die.
Non-biodegradable plastics are plastics that microorganisms cannot break down, so they stay in the environment for a very long time. In aquatic ecosystems, animals such as turtles and seabirds swallow plastic, which can block their digestive system, or become tangled and drown. Tiny pieces enter food chains. On land, plastic builds up in landfill and soil.
The enhanced greenhouse effect is the extra heating caused when human activities increase the concentrations of carbon dioxide and methane, so more infrared radiation is trapped in the atmosphere. Carbon dioxide comes from burning fossil fuels and forests; methane comes from cattle, rice paddy fields and landfill. This causes global warming and climate change, such as rising sea level.
Exam questions
6 exam-style questions (19 marks), each with its mark scheme.
Answer the questionsFlashcards
8 cards: flip them, mark what you knew, and practise the rest.
Practise the cardsMind map
The whole of human influences on ecosystems on one page, so you can see where this subtopic fits.
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Free PDFs to print or save.
Quick check questions
Why does excess fertiliser harm rivers and lakes?
Show answer
Nitrates cause rapid growth of algae and water plants, which can lead to eutrophication and the death of other organisms.
Why do non-biodegradable plastics last so long?
Show answer
Microorganisms cannot break them down.
Name two sources of methane.
Show answer
Cattle (livestock); rice paddy fields; landfill sites.
What is the enhanced greenhouse effect?
Show answer
Extra heat trapped in the atmosphere because human activity has raised carbon dioxide and methane levels.
Frequently asked questions
What is eutrophication and what causes it?
Supplement Eutrophication is caused by extra nitrate and other ions entering water from excess fertiliser or untreated sewage. Algae and water plants grow faster, forming an algal bloom that blocks light. Producers deeper in the water die, and decomposers increase. Their aerobic respiration uses up dissolved oxygen, so fish and other organisms that need oxygen die.
How does plastic pollution affect marine life?
Plastic pollution harms marine life because plastics are non-biodegradable, so they last a very long time. Turtles, seabirds and fish swallow plastic, which can block their digestive system so they starve. Animals become tangled in plastic and drown or cannot move. Plastic also breaks into tiny pieces that enter food chains.
What causes the enhanced greenhouse effect?
The enhanced greenhouse effect is caused by human activities increasing the concentrations of carbon dioxide and methane in the atmosphere. Burning fossil fuels and forests releases carbon dioxide, while cattle, rice paddy fields and landfill sites release methane. These gases trap more infrared radiation, so the Earth's average temperature rises, causing climate change.
What are the sources of methane?
The main sources of methane are cattle and other livestock, which release it from their digestion, rice paddy fields, and the decomposition of waste in landfill sites. Methane is a greenhouse gas: like carbon dioxide, it traps infrared radiation in the atmosphere, so increasing its concentration adds to the enhanced greenhouse effect.
Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026