All revision notes topics

PollutionIB MYP Biology: Revision notes

Section 1

Air pollution

Burning fossil fuels in power stations, factories and vehicles releases pollutants into the air.

  • Carbon dioxide (CO₂): from complete combustion. It is a greenhouse gas that contributes to global warming.
  • Carbon monoxide (CO): from incomplete combustion in a limited supply of oxygen. It is a toxic gas that combines with haemoglobin and reduces the oxygen carried by the blood.
  • Sulfur dioxide (SO₂): from burning fuels that contain sulfur. It causes acid rain and breathing problems.
  • Particulates: tiny bits of soot and unburnt carbon from diesel engines and burning. They cause breathing problems and make surfaces dirty.
Key termspollutantincomplete combustionparticulates
Common mistake

Do not mix up CO and CO₂. Carbon monoxide is the poisonous one and comes from incomplete combustion.

Section 2

Acid rain

Sulfur dioxide (and nitrogen oxides) dissolve in water droplets in clouds and make acid rain.

Effects of acid rain:

  • lowers the pH of lakes, killing fish and other water life
  • damages leaves and trees, and washes minerals out of the soil
  • corrodes limestone buildings, statues and metal structures

It can be reduced by removing sulfur from fuels, or from the waste gases of power stations, and by burning less fossil fuel.

Key termsacid rain

Section 3

Water pollution

  • Sewage: contains organic matter and disease-causing microorganisms. Bacteria feeding on it use up oxygen.
  • Fertilisers: washed off fields by rain. They cause eutrophication.
  • Plastics: do not decompose quickly. They harm marine animals that eat them or become tangled in them.

Eutrophication, step by step:

  1. Nitrates and phosphates from fertiliser or sewage enter a lake.
  2. Algae grow rapidly and form a bloom that blocks light.
  3. Plants under the surface die for lack of light.
  4. Bacteria decompose the dead plants and algae, using up the dissolved oxygen.
  5. Fish and other animals die from lack of oxygen.
Key termseutrophicationsewage
Exam tip

Many marks for eutrophication are lost by saying the algae 'use up the oxygen'. It is the bacteria decomposing the dead material that use up the oxygen.

Section 4

Land pollution

  • Landfill: household waste is buried in the ground. It takes up land, releases methane (a greenhouse gas), and can leak harmful liquids into soil and water.
  • Pesticides (insecticides, herbicides): sprayed on crops to kill pests and weeds. They can wash into rivers, kill useful organisms such as bees, and build up in food chains.

Land pollution can be reduced by recycling and reusing materials, and by using pesticides only where needed.

Key termslandfillpesticide

Section 5

Bioaccumulation

Some pollutants, such as certain pesticides and heavy metals (e.g. mercury), are not broken down by organisms and are stored in the body, often in fat.

Bioaccumulation is the build-up of a harmful substance in an organism over time. It increases along a food chain:

plankton (0.04) → small fish (0.5) → large fish (2.0) → bird (25), in mg per kg

Each consumer eats many organisms from the level below, so the concentration rises at each level. Top consumers receive the highest doses, which can poison them or stop them reproducing.

Key termsbioaccumulation

Must know

  • CO comes from incomplete combustion, SO₂ causes acid rain, particulates cause breathing problems and CO₂ is a greenhouse gas.
  • Fertilisers and sewage cause eutrophication; plastics harm wildlife.
  • Landfill and pesticides pollute land.
  • Bioaccumulation: harmful substances that are not broken down build up along food chains.

That's the notes covered.

Carry on to the next subtopic.

Exam questions on Pollution

  1. A city in northern India has heavy traffic and a coal-fired power station. Residents report smoggy air, breathing problems and damage to the stonework of old buildings. The local coal contains sulfur, and many older engines burn their fuel in a limited supply of air.
    Explain how burning the coal at the power station can cause acid rain.2 marks
  2. A lake in a farming area in the UK has become green and cloudy each summer. Farmers spread fertiliser on the surrounding fields, and heavy rain washes some of it into the lake. A leaking sewage pipe also releases waste into one of the streams feeding the lake.
    Explain how the leaking sewage pipe could reduce the oxygen in the stream.2 marks
  3. A pesticide that does not break down easily was sprayed on farmland next to a lake in Kenya. Scientists later measured its concentration in organisms from one food chain, in mg per kg of body tissue: 0.04 in microscopic plankton, 0.5 in small fish, 2.0 in large fish and 25 in fish-eating birds.
    Describe the trend in the concentration of pesticide along the food chain, and calculate how many times greater the concentration is in the birds than in the plankton.3 marks
See the full worksheet

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).