Human influences on the environment — Edexcel International GCSE Science (Double Award)
Air pollution by sulfur dioxide and carbon monoxide, greenhouse gases and global warming, water pollution by sewage, and eutrophication.
Revision notes
5 short notes, in the order of the specification. Each one in short:
Sulfur dioxide and carbon monoxide are air pollutants from burning fuels. Sulfur dioxide dissolves in rain to form acid rain, which lowers the pH of lakes so fish die and damages tree leaves. Carbon monoxide, from incomplete combustion, combines with haemoglobin more strongly than oxygen, so less oxygen is carried to the tissues for aerobic respiration.
Greenhouse gases are the gases that cause the greenhouse effect: carbon dioxide, methane, nitrous oxide, CFCs and water vapour. Human activities add to them. Burning fossil fuels and deforestation increase carbon dioxide, cattle, rice paddy fields and landfill release methane, nitrogen fertilisers release nitrous oxide, and old refrigerators and aerosols released CFCs.
The enhanced greenhouse effect is the extra warming caused when human activities increase the amount of greenhouse gases. These gases absorb infrared radiation given out by the Earth and radiate it back, so more heat is trapped and the average surface temperature rises, called global warming. Consequences include rising sea levels, extreme weather and changes in species distribution.
Untreated sewage pollutes rivers and lakes because it contains organic matter, pathogens and mineral ions. Decomposers feed on the organic matter and use up the dissolved oxygen in aerobic respiration, so fish and other aquatic animals die and biodiversity falls. Pathogens in sewage spread diseases such as cholera and typhoid, and its nitrates and phosphates can cause eutrophication.
Eutrophication is when too many mineral ions, such as nitrates and phosphates from fertilisers, are leached into lakes and rivers. Algae grow quickly, forming an algal bloom that blocks light, so plants below cannot photosynthesise and die. Decomposing bacteria feed on the dead material and use up the oxygen in aerobic respiration, so fish die.
Exam questions
6 exam-style questions (21 marks), each with its mark scheme.
Answer the questionsFlashcards
15 cards: flip them, mark what you knew, and practise the rest.
Practise the cardsMind map
The whole of ecology and the environment on one page, so you can see where this subtopic fits.
Open the mind mapPrint it
Free PDFs to print or save.
Quick check questions
What gas causes acid rain?
Show answer
Sulfur dioxide.
Why is carbon monoxide poisonous?
Show answer
It combines with haemoglobin, so the blood carries less oxygen.
Name the five greenhouse gases in the spec.
Show answer
Water vapour, carbon dioxide, nitrous oxide, methane and CFCs.
Why does sewage pollution kill fish?
Show answer
Decomposers feeding on it use up the oxygen in the water.
Frequently asked questions
What is eutrophication and what causes it?
Eutrophication happens when too many mineral ions, such as nitrates and phosphates from fertilisers, are leached into lakes and rivers. Algae grow rapidly and block light, so plants below die. Decomposing bacteria feed on the dead material and use up the oxygen in aerobic respiration, so fish and other animals die.
How does the enhanced greenhouse effect cause global warming?
The Earth gives out infrared radiation, and greenhouse gases absorb some of it and radiate it back towards the Earth. Human activities, such as burning fossil fuels, increase these gases, so more infrared radiation is trapped. The average surface temperature rises, which is global warming, causing rising sea levels and more extreme weather.
How does carbon monoxide affect the body?
Carbon monoxide combines with haemoglobin in red blood cells much more strongly than oxygen does. Haemoglobin combined with carbon monoxide cannot carry oxygen, so less oxygen reaches the tissues and cells cannot respire aerobically enough. This causes headaches, dizziness and fainting, and a high dose can cause death.
How does sulfur dioxide cause acid rain?
Sulfur dioxide is released when fossil fuels containing sulfur, such as coal and oil, are burned. It dissolves in rain water to form acidic solutions, making acid rain. Acid rain lowers the pH of lakes and rivers so fish die, damages tree leaves and washes minerals out of the soil.
Written and checked against the Edexcel IGCSE Science Double Award (4SD0) specification · Updated October 2026