Biodiversity Notes for Biology

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Biodiversity, Evolution & Natural Selection Notes


  • Variety of different organisms within a habitat. Two aspects to consider are:
  • Species richness: the number of different species within an area of known size at a particular time. A species is a group of organisms with so many features in common that they can mate and produce fertile offspring.
  • Genetic diversity: the genetic variation within a species


  • Where a species is found in only one particular area
  • The ring tailed lemur is restricted to the island of Madagascar, so is endemic to Madagascar
  • Happens because the organism evolved within the region hasn’t migrated out to other areas

Molecular phylogeny :

  • Compares the structure of a particular molecule from different organisms to discover their degree of evolutionary relatedness
  • The more similar the structure of the molecule, the more closely related the organisms are because changes in molecule structure generally occur slowly as they are caused by mutations
  • The three domains are archaea, bacteria and eukaryota


  • The niche of a species is the way that the species exploits its environment
  • If two different species are present in the same niche at the same time, there will be competition and one will out compete the other so that the better adapted will survive

Types of adaptation:

  • Anatomical: a physical/structural adaptation, it may be external or internal e.g. kidneys of some desert mammals are modified to reduce water loss by producing very concentrated urine
  • Behavioural: a change in the behaviour of an organism to increase its survival chances e.g. lizards orientate themselves to face the Sun
  • Physiological: tend to be changes in the internal biochemical functioning of the organism in response to an altered environmental stimulus e.g. formation of hard skin on hands due to repeated pressure
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Natural selection and evolution:

  • Natural selection is the survival of individuals in a population because they have alleles that improve their chances of survival and reproduction
  • Evolution is the change in the frequency of certain alleles in a gene pool over time due to natural selection

Evolutionary sequence:

  • A population of organisms shows genetic diversity due to having a variety of alleles (caused by mutations)
  • Environmental conditions change
  • Natural selection removes some individuals with alleles that are not as advantageous
  • The remaining individuals grow and reproduce, passing on the advantageous alleles
  • Over many generations the frequency of ...

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