Abiotic & Biotic Factors (OCR Gateway GCSE Biology: Combined Science)

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Abiotic & Biotic Factors

  • The environment in which communities of plants and animals live changes all the time
  • These changes are caused by abiotic (non-living) and biotic (living) factors
  • These factors affect communities in different ways, for example
    • For some species, certain factors may cause their population size to increase, whereas for other species, that same change may cause their population size to decrease
    • For some species, certain factors may cause the distribution of their populations (i.e. where they live) to change

Abiotic factors

  • In Biology, ‘abiotic’ means non-living
  • An abiotic factor is a non-living factor within an environment such as temperature, light intensity and water availability
  • An example of an abiotic factor is a high soil pH which is unsuitable for wild azaleas to grow
    • Wild azaleas prefer a soil pH of 4.5 to 6.5
    • Azaleas would need to find another habitat
  • The table below explains how these abiotic factors may affect a community of organisms
    • One abiotic factor not included in this table is the presence and levels of pollutants, which can change the size and distribution of populations of certain species
    • For example, some lichen species are very sensitive to air pollution and are not able to grow if the concentration of sulfur dioxide (an air pollutant) rises above a certain level

Abiotic Factors that Affect Communities Table

Abiotic factors that affect a community table, IGCSE & GCSE Biology revision notes

Biotic factors

  • In Biology, ‘biotic’ means living
  • A biotic factor is a living factor in the environment such as competition, predation, camouflage and disease
  • An example of a biotic factor is the chameleon, whose camouflaged skin makes it a very effective predator of insects, thus reducing the insect species' populations
  • More examples of biotic factors are shown in the table below

Biotic Factors that Affect Communities Table

Biotic factors that affect a community table, IGCSE & GCSE Biology revision notes

Exam Tip

Be aware that most populations are in fact determined by the combination of abiotic and biotic factors. For example, the arrival of a family of beavers in a river will benefit the dragonfly population; this can be regarded as biotic, but there is also an abiotic element. The beavers' dams slow the flow of water, which attracts insects such as mosquitos and pond skaters. These insects are the dragonflies' prey. The abiotic factor is the flow rate of the river, despite the fact that a living organism caused the flow rate to drop.

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Author: Phil

Phil has a BSc in Biochemistry from the University of Birmingham, followed by an MBA from Manchester Business School. He has 15 years of teaching and tutoring experience, teaching Biology in schools before becoming director of a growing tuition agency. He has also examined Biology for one of the leading UK exam boards. Phil has a particular passion for empowering students to overcome their fear of numbers in a scientific context.