Revision Notes

21.4 More Sources & Effects of Pollution

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Plastic Pollution

  • Plastics have a large negative impact on both land and water habitats due to their non-biodegradability
  • In marine habitats:
    • Animals often try to eat plastic or become caught in it, leading to injuries and death
    • As the plastic breaks down it can release toxins that affect marine organisms
    • Once it has broken down into very small particles, it is commonly ingested by animals and enters the food chain
  • On land:
    • Plastic is generally disposed of by burying in landfills
    • As it breaks down, it releases toxins into the surrounding soil and as such the land is no good for growing crops or grazing animals and can only be used for building on several decades after burial
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Female Hormones

  • Female contraceptive hormones are excreted from the body in urine and then make their way into the water supply, as they are not filtered out by sewage treatment plants
  • If they reach male aquatic organisms, such as fish and frogs, which are very sensitive to the hormones, it causes feminisation
  • This is where male organisms begin to produce eggs and lose the ability to reproduce
  • Consequently, a smaller amount of offspring is produced which can harm the species survival and also disrupts food chains for animals that usually feed off these organisms
  • In addition, these hormones can reduce the sperm count in human males, which causes fertility problems
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  • Runoff of fertiliser from farmland enters the water and causes increased growth of algae and water plants
  • The resulting ‘algal bloom’ blocks sunlight so water plants on the bottom start to die, as does the algae when competition for nutrients becomes too intense
  • As water plants and algae die in greater numbers, decomposing bacteria increase in number and use up the dissolved oxygen whilst respiring aerobically
  • As a result there is less oxygen dissolved in water, so aquatic organisms such as fish and insects may be unable to survive

Eurtrophication, IGCSE & GCSE Biology revision notesSequence of events causing eutrophication in lakes and rivers

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Acid Rain

  • Combustion of fossil fuels that contain sulfur impurities creates sulfur dioxide
  • This is released into the atmosphere where it combines with oxygen to form sulfur trioxide
  • Sulfur trioxide dissolves in water droplets in clouds and forms acid rain

More Sources & Effects of Pollution table, IGCSE & GCSE Biology revision notes

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Climate Change

  • A greenhouse gas is a gas that absorbs infrared radiation from the Sun so it remains trapped in the Earth’s atmosphere
  • This is important to ensure Earth is warm enough for life, however if levels of these gases in the atmosphere increase it leads to an increase in the greenhouse effect which causes the Earth’s average temperature to rise
  • There are many greenhouse gases, the most important are:
    • Water vapour
    • Carbon dioxide
    • Methane
    • Nitrous oxides
    • CFCs
  • The greenhouse effect works in the following way:
    • The Sun emits rays that enters the Earth’s atmosphere
    • The heat bounces back from the Earth’s surface
    • Some heat is reflected back out into space
    • Some heat is absorbed by greenhouse gases and is trapped within the Earth’s atmosphere – this is normal
    • However, as the levels of greenhouse gases in the atmosphere rise due to human activities the Earth’s average temperature rises beyond normal (an enhanced greenhouse effect), causing global warming or climate change


The Greenhouse effect, IGCSE & GCSE Biology revision notesHow the greenhouse effect works


Consequences of global warming due to an enhanced greenhouse effect

  • Ocean temperatures increase which causes melting of polar ice caps / rising sea levels / flooding / coral bleaching
  • Increasing temperatures can cause extreme weather like super storms, flooding, droughts
  • These extreme weather events can lead to changes in or loss of habitats
  • This means that there will be a decrease in biodiversity as food chains are disrupted and extinction rates increase
  • There could also be increases in migration of species to new places, increased spread of pests and disease

Exam Tip

Water pollution from sewage and water pollution from fertiliser runoff have the same end result (increase in decomposing bacteria leading to a decrease in dissolved oxygen and death of aquatic organisms) but they do not arrive at this point in the same way.

You need to learn both and be aware of the differences between them. A common misconception is that sewage pollution also causes growth of water plants and algal blooms – this is very rarely the case, only runoff of fertiliser does this.

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

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