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The Nature of Ecosystems

Edexcel A-level BiologyTopic 14 of 1639 lessons

Revision notes for The Nature of Ecosystems in Edexcel Biology B (9BI0). Every lesson in BrainCake comes with R.E.C.I.P.E. recall steps, a quick check and spaced reviews.

  1. EcosystemAn ecosystem is a community of organisms interacting with each other and with the non-living (abiotic) environment in which they live.
  2. HabitatA habitat is the place where an organism lives.
  3. CommunityA population is a group of organisms of the same species living in the same area at the same time, which can interbreed.
  4. Abiotic FactorsAbiotic factors are the non-living, physical and chemical features of an ecosystem that affect the organisms living there.
  5. Biotic FactorsBiotic factors are the effects of living organisms on other organisms in an ecosystem.
  6. BiosphereThe biosphere is the part of the Earth and its atmosphere in which living organisms are found.
  7. Primary SuccessionSuccession is the gradual change in the community of an area over time.
  8. Climax CommunitySuccession ends when a stable community is reached that does not change further as long as conditions stay the same.
  9. Secondary SuccessionSecondary succession happens on land where soil is already present but the existing community has been removed or destroyed.
  10. Case Study: Sand Dune SuccessionSand dune succession is a well-studied example of primary succession, found on coasts such as Studland in Dorset.
  11. LightLight is the main source of energy for almost all ecosystems, because producers use it for photosynthesis.
  12. TemperatureTemperature affects organisms mainly through its effect on enzymes.
  13. Wind and Water CurrentsWind affects organisms on land in several ways: • Water loss.
  14. Water AvailabilityAll organisms need water.
  15. Oxygen AvailabilityMost organisms need oxygen for aerobic respiration, which releases far more ATP than anaerobic respiration.
  16. Edaphic FactorsEdaphic factors are the properties of the soil that affect the organisms living in or on it.
  17. PredationPredation is when one animal (the predator) kills and eats another (the prey).
  18. Finding a MateFor a population to survive, individuals must find a mate and reproduce.
  19. TerritoryA territory is an area that an animal, a pair or a group defends against other members of the same species.
  20. Parasitism and DiseaseA parasite is an organism that lives in or on another organism, the host, and obtains nutrients from it, harming the host.
  21. Case Study: Snowshoe Hare and LynxA classic case study of how two populations interact comes from the snowshoe hare and its predator, the Canada lynx, in the forests of northern…
  22. Case Study: Red Grouse and ParasitesRed grouse living on heather moorland in northern England and Scotland show population cycles, with numbers crashing every 4 to 8 years or so.
  23. Density Dependent FactorsA density-dependent factor is one whose effect on a population depends on population density: the larger and more crowded the population, the…
  24. Density Independent FactorsA density-independent factor affects the same proportion of a population whatever its density.
  25. CompetitionCompetition occurs when two or more organisms need the same resource and that resource is in short supply.
  26. Intraspecific CompetitionIntraspecific competition is competition between individuals of the same species.
  27. Interspecific CompetitionInterspecific competition is competition between individuals of different species for the same limiting resource, for example red and grey squirrels…
  28. Species AbundanceAbundance is the number of individuals of a species in a given area.
  29. Species DistributionDistribution describes where a species is found within a habitat and how its individuals are spread out.
  30. Ecological TechniquesEcologists cannot count every organism in a habitat, so they take samples and use them to estimate the whole population.
  31. QuadratsA quadrat is a square frame, often 0.5 m × 0.5 m (0.25 m2) or 1 m × 1 m, placed on the ground to mark out a standard area for sampling.
  32. ACFOR ScaleCounting individuals or estimating percentage cover precisely can be slow, so ecologists sometimes use a quick subjective abundance scale.
  33. Point QuadratsA point quadrat (point frame) is a frame holding a row of long pins, usually 10, which are lowered one at a time to the ground.
  34. Permanent QuadratsA permanent quadrat is a sampling area that is marked out and left in place, often with pegs or posts at its corners, so that exactly the same area…
  35. TransectsA transect is a line across a habitat along which samples are taken systematically.
  36. More Ecological TechniquesQuadrats work for plants and slow-moving animals, but mobile animals need other methods.
  37. Hypothesis TestingEcological data vary naturally, so a difference or trend in results could be due to chance.
  38. Spearman's Rank Correlation CoefficientSpearman's rank correlation coefficient (rs) tests whether there is a significant correlation between two variables, for example light intensity and…
  39. Student's t-TestThe Student's t-test tests whether there is a significant difference between the means of two sets of data, for example the mean shell height of…

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