Assessing Pollution (Edexcel GCSE Biology)

Indicator Species

Higher tier only

• It is possible to use the presence or absence of particular organisms as an indicator of pollution

  • For example, some organisms are particularly sensitive to certain changes in their environment

  • This means they can be studied in order to determine the effect of human activities on a particular habitat or ecosystem

  • These organisms are known as indicator species

• Indicator species can be used to determine the level of:

  • Water pollution

  • Air pollution

Water pollution

• One form of water pollution occurs when raw sewage or fertilisers (both containing nitrates) are released into a body of water, such as a stream or pond

  • This causes microorganisms in the water to increase in number

  • As these microorganisms respire, they use up the oxygen in the water

• Some invertebrate species, such as stonefly larvae and freshwater shrimps, are highly sensitive to the concentration of dissolved oxygen in the water they are living in

  • This makes them good indicator species for water pollution

  • For example, the presence of stonefly larvae in a stream or river indicates that the water is not polluted (i.e. it is clean and has high oxygen levels)

• On the other hand, some other invertebrate species are adapted to live in polluted environments

  • This also makes them good indicator species for water pollution

  • For example, the presence of blood worms and sludgeworms in a body of water indicates a very high level of water pollution 

Air pollution

• Lichen (that grow on trees and buildings) can be used as an indicator species for air pollution

• This is due to the fact that lichens are highly sensitive to sulfur dioxide concentrations in their environment

  • Sulfur dioxide is one of the air pollutants released from car exhausts and power stations (i.e. during the combustion of fossil fuels)

• The abundance (number) and type of lichen species growing at a particular location can be monitored to determine how clean the air is

  • For example, a high abundance of lichen indicates clean air

  • In particular, a high abundance of bushy lichen indicates very clean air (as these lichens need cleaner air than crusty lichen)

• Another indicator species for air pollution is blackspot fungus, which grows on rose leaves

• Like lichen, it is also sensitive to sulphur dioxide concentrations and its presence indicates clean air

Potential disadvantages of using indicator species

• Although using indicator species is a fairly simple and cost-effective method of determining whether a habitat is polluted or not, it has some drawbacks

  • For example, it can't give accurate numerical (quantitative) figures for exactly how much pollution is present

  • In addition, the presence or absence of indicator species can also be affected by factors other than pollution (e.g. the presence of predators or disease)

• If more detailed information on pollution levels is required, non-living indicators can be used instead. For example:

  • Dissolved oxygen meters and chemical tests can be used to very accurately determine the concentration of dissolved oxygen in the water and can be used to show changes in levels of water pollution over time

  • Electronic meters and laboratory tests can be used to very accurately determine the concentration of sulfur dioxide in the air and can be used to show changes in levels of air pollution over time