Biodiversity, Classification & Natural Selection



  • Biodiversity is the variety of organisms in an area. It can be considered on different levels including habitat, species and genetic diversity of an area
  • Habitat diversity refers to the range of habitats present in a region
  • Species diversity is the number of species and the number of individuals wihtin each species in a specified area. It takes into account species richness and eveness
  • Species richness is a measure of the number of different species in a community
  • Species eveness is a measure of the relative abundances of different species in an area
  • Genetic diversity is the variety of all the genes (number of different alleles of genes) possessed by the individuals in a population or whole species
  • Alleles are different forms of the same genes
  • The greater the genetic diversity, the greater the ability of the species to adapt to a changing environment
  • Genetic diversity can be estimated by comparing physical characteristics or by analysing genomes
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Biodiversity continued...

  • Species with a greater number of polymorphic genes tend to have greater genetic diversity

Genetic diversity = no. of loci with more than one allele/ total no. of loci X 100

  • Simposon's diversity index (D) measure biodiversity taking into account species richness and eveness
  • Factors affecting biodiversity include
    • Human population growth increases the demand for resources from the environment
    • Agriculture reduces biodiversity by monoculture, use of herbicide & pesticides, hedgerow removal and woodland clearance
    • Climate change is causing animals to migrate or die
  • Reasons for maintaining biodiversity can be
    • Ecological
    • Economical
    • Aesthetic
    • Ethical
  • Cpnservationists protect biodiversity with methods such as: giving endangered species legal protection, protected areas & the environmental stewardship scheme
  • A balance between conservation and agriculture is needed 
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  • The Biological Species Concept- a species contains all organsims that are capable of breeding together to produce living, fertile offspring
  • Classification is the process of sorting living things into groups
  • Classification hierarachy comprises the taxa: Domain, Kingdom, Phylum, Class, Order, Family, Genus and Species
  • Classification are constantly updated as new methods are discovered to infer relationships eg.physical characteristics to DNA sequencing, amino acids sequencing or cytochrome C comparison

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Classification continued...

  • Animalia
    • Animals are eukaryotic, multicellular, heterotrophic and usually able to move around
  • Plantae
    • Eukaryotic autotrophic, autotrophic, multicellular, have a cellulose cell wall, and contain chlorophyll
  • Fungi
    • Eukaryotic, single-celled or multicellular, saprophytic, have a chitin cell wall and a multinucleate cytoplasm
  • Protoctista
    • Eukaryotic, mostly free living, single-celled or multicellular, autotrophic or heterotrophic
  • Prokaryotae
    • Smaller ribosomes, a naked loop of DNA, free living or parasitic, no nucleus or no other membrane bound organelles
  • The binomial naming system names a species by their genus and speices name
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  • Phylogeny is the study of evolutionary relationships between organisms
  • In Phylogenetic diagrams, branch tips represent species at the end of their specific lineage, branching points represent common ancestors & the closer the branches, the closer the evolutionary relationship

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Natural Selection

  • Predation, diease and competition means that not all individuals within a population survive to get a chance to reproduce. This differential survival and reproduction is the process by which natural selection acts
  • Genetic variation within a population creates intraspecific competition. The organisms with the phenotype that provides the selective advantage are more likely to survive and reproduce thus pass on their favourable alleles to the next generation.
    • This means that the proportion of individuals with the favourable allele will increase in the next generation within the population. 
      • This is evolution by natural selection
  • Evolution is the change in allele frequencies in a population over time
  • An adaptation is a trait that enchances survival in a habitat
    • Anatomical adaptations are structural features
    • Behaviourable adaptations
    • Physiological adaptations are changes to cellular processes
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Natural Selection continued...

  • Convergent evolution occurs when organisms that live in similar conditions are subject to the same selection pressures, resulting in similar adaptations
  • Evidence for the theory of natural selection comes form the fossil record and biological molecules, including mRNA
  • Evolution by natural selection has resulted in antibiotic resistance bacteria and pesticide resistance in insects
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  • Interspecific variation is the differences between any two species 
  • Intraspecific variation is the differences between the members of the same species
  • Characteristics that show continuous variation are normally polygenic (determined by many gene loci that have additive effects on each other)
  • Characteristics that show discontinuous variation are usually monogenic (determined by a single gene loci)
  • Variation is due to genetic and environmental factors
  • The main source of genetic variation is mutations, which can produce different alleles of genes
  • Futher sources of genetic variation include meiosis (independent assortment and crossing over) and the random fertilisation of gametes during sexual reproduction to create new allele combinations
  • The environment can influence the way an organism's genes are expressed. This can be because of biological factors such as predators or non-biological factors such as sunlight
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