Edexcel A SNAB Topic 4

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  • Topic 4
    • Definitions
      • Species - A group of organisms with similar physiology and behaviour, who can interbreed and produce fertile offspring. They are reproductively isolated.
      • Habitat - where organisms live. Each habitat has a set of conditions which supports distinctive organisms.
      • Population - a group of interbreeding individuals of the same species found in an area.
      • Community - the various populations within one area.
      • Niche - the way an organism exploits its environment.
    • Adaptations
      • Behavioural - actions by organisms that help them to survive or reproduce.
      • Physiological - features of the internal makeup of an organism which help them to survive or reproduce.
      • Anatomical - structures that can be seen when an organism is dissected.
    • Natural Selection
      • 1. A few organisms within a population have naturally-occuring genetic variation with new alleles created through mutations.
        • 2. A change in the environment causes a change in the selection pressures acting on the population.
          • 3. An allele that had no previous advantage is now favourable.
            • 4. Organisms with that allele are more likely to survive and reproduce.
              • 5. Their offspring are more likely to have the allele, so it becomes more common in the population.
                • This changes: - the size of the gene pool
    • Biodiversity
      • Refers to the diversity within a species.
      • Species Richness - the number of species present in a given habitat.
      • A highly diverse community will have high species richness and high species evenness.
      • A hotspot is an area with particularly high diversity.
    • Taxonomy
      • Kingdom Phylum   Class     Order   Family Genus Species
    • Endemic Species
      • A species which is geographical isolated and can only be found in one area.
      • These species are often endangered.


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