Biology unit 5 definitions

Definitions of common biological terms used in topic 5 of SNAB A2 Biology.

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  • Created by: Lottie
  • Created on: 17-12-10 14:22

Abiotic factors

Chemical and physical factors of an ecosystem.


  • Soil type
  • Climate
  • Topography (altitude, slope, aspect and drainage)
  • Pollution
  • Solar input
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Biotic factors

Factors which are determined by arganisms.


  • Competition
  • Grazing, preditation, parasitism
  • Mutualism
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Anthropogenic factors

Biotic and abiotic factors which arise from human activity.


  • Deforestation
  • Introducing new species
  • Buildings
  • Use of fossil fules
  • creating artificial ecosystems (such as a fish tank
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Ecosystems, Habitats and niches and the communitie

Ecosystem- a place with distinct biotic and abiotic factors in which numerous organisms live.

Habitat- An area within an ecosystem with a distinc set of conditions where organisms live

Niche- An area of a habitat, the food source, time of feeding, shelter site which is specific to a species.

Population- A group of individuals of the same species found in a habitat.

Community- The various populations sharing a habitat or ecosystem. Each occupies a different niche, avoiding competition.

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Primary succession

Occurs on bare rock, sand or in open water where there has never been a community before.

  • Pioneer species (such as lichens and algae) begin to grow. These brake up the rock allowing some organic material to accumulate. This alters conditions allowing secondary species (such as wind-blown moss spores) to grow.
  • These new species build up more organic material forming soil which is capable of holding water. Seeds of shallow-rooted plants establish growth
  • As conditions improve, seeds of taller, lager plants establish which out-compete the existing community.
  • Eventually, the climax community forms. This is usually dominated by trees and will remain stable.
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Secondary and deflected succession

Secondary succession:

This occurs on bare soil where a previous community has been cleared. This usually occurs faster than primary succession as some seeds may already be in the soil and conditions are already stable enough for these to grow.

Deflected succession:

This is when a community only stays stable because human activity prevents succession from running it's course. For example, sheep grazing on grassland prevents succession. This is caused by human activity because humans put the sheep there.

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Liking this, it's simple but straight to the point!

Taslima Baksh


This is unit 4 of SNAB!



Very good notes, but it has a few grammatical errors. But that's a minor niggle.



Thanks! Taslima, it is for sure Unit 5. -only the ecology section though- 

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