WJEC AS Biology Unit 2.1 - Classification and Biodiversity

Classification

• Putting/placing organisms into groups based on their evolutionary relationships

• Places organisms into discrete and hierarchical groups with other closely related species

Taxonomic levels

• Domain

• Kingdom

• Phylum

• Class

• Order

• Family

• Genus

• Species

• More closely related down the levels

Binomial system of naming organisms

• Genus + species used to generate unique binomial name

• Avoids confusion between organisms in scientific communications

• Universal - same in all languages

Taxa

• Groups within a system of classification

• Taxa are discrete

  • At any level of classification, an organism belongs in one taxon and in no othe

The need for classification

• A phylogenetic classification system allows us to infer evolutionary relationships

• Can predict other characteristics of a new or organism based on knowledge of its species

• Ease of communication

• More useful to count families when describing health of an ecosystem or rate of extinction

Tentative nature of classification

• Classification may change as additional information becomes available

• system for classification depends on our current knowledge

• Systems may be altered as knowledge advances

• Classification can change to incorporate new nucleotide base sequencing

The 3 domain system

• biochemical evidence shows the kingdom prokaryotes can be split into 2 separate groups based on fundamental biochemical differences. All other organisms have eukaryotic cells

• Eubacteria

• Archaea

• Eukaryota

• The organisms of each domain share a distinctive, unique pattern of rRNA, which established their close evolutionary relationship

Eubacteria

• the true bacteria

• Prokaryotic cells structure

Archaea

• Bacteria

• Prokaryotic cell structure

• Includes the extremophile prokaryotes

Extremophiles

Organisms able to exist, survive and grow in extreme environmental conditions, e.g. extremes of temperature, pH, salinity and pressure

Eukaryota

• Includes all eukaryotic organisms

  • Plantae

  • Animalia

  • Fungi

  • Protoctista

The 5 Kingdom system

• Prokaryotae

• Protoctista

• Fungi

• Plantae

• Animalia

• Prokaryota = eubacteria and archaea

• Protoctista, Fungi, Plantae and Animalia = Eukaryota

Prokaryota

• composed of prokaryotic cells, which lack a nuclear envelope and membrane-bound organelles (the cell wall does not contain cellulose or chitin)

• Microscopic

• Includes all bacteria, Archaea and Cyanobacteria

Protoctista

• mainly single cell eukaryotes

• No tissue differentiation

• Some have only one cell, some have many similar cells

Fungi

• Heterotrophic eukaryotes

• Cell walls of chitin

• Most have filaments called hyphae

• Reproduce by spores

Plantae

• multicellular eukaryotes

• Photosynthetic

• Cellulose cell walls

• Some reproduce with spores, others with seeds

Animalia

• Nervous coordination

• Multicellular eukaryotes

• No cell wall

• Heterotrophic

• Great range of body plans, most are motile at some stage in their life cycle

Summary of 5 kingdoms

The use of physical features to assess relatedness

• look for type of features → discover the type of evolution which has taken place

Divergent evolution

• The development of difference structures over long periods of time, from the equivalent structures is related organisms

• Similar development/evolutionary origin

• Share a recent common ancestor

• Gives rise of homologous structures

Adaptive radiation

Divergent evolution

Homologous structures

Structures in different species with a similar anatomical positions and developmental origin but different functions, derived from a recent common ancestor. Have evolved from the same original structure for different functions

Convergent evolution

• The development of similar features in unrelated organisms over long periods of time, related to natural selection of similar features in a common environment

• Difference developmental/evolutionary origin

• Do not share a recent common ancestor

• Gives rise to analogous structures

Analogous structures

• structures evolved from different species with a similar/corresponding/same functions and different structure but a different developmental origin

Using structures to assess relatedness

• look for and use homologous structures to asses relatedness and classify the organisms

• Analogous structures are not a suitable criteria for classifying living organisms

Assessing relatedness with genetic evidence via biochemical methods

• measure the proportion of DNA of proteins shared between the species to estimate relatedness

• Usually displayed as bands

• Can reduce the mistakes made in classification due to convergent evolution

• More similar → more closely related

Genetic profiling

DNA hybridisation

• comparing the DNA base sequences of 2 species

• DNA from both is extracted, separated into single strands and cut into fragments

• Fragments from the 2 species are mixed and there they have complementary base sequences, they hybridise together

DNA base sequences

• during evolution, species undergo changes in DNA base sequences, which accumulate until the organisms are considered different species

• Analysis can confirm evolutionary relationship and correct mistakes made in classification based on physical features

Amino acid sequences

Degree of similarity in the amino acid sequence of the same protein the 2 species will reflect how closely related they are

Species

Organisms which can interbreed to produce fertile offspring

Biodiversity

The number of species and the number of individuals of each species in a given environment

Differences in biodiversity

• affected by genetic, environmental and human factors

• Low water availability → decrease

• Low population → increase as less habitat loss

• Higher between tropics as greater li and higher water availability → more plant species and more food sources

• Highest = tropical rainforests and coral reefs → high energy input and plentiful water supply supporting a greater number of plant species

• High latitude → decrease

Importance of biodiversity

• plants → source of medicine and food + varieties of crop for agriculture for food production

• Increase in diversity of plants → more food sources and supports more complex food webs → more biodiversity

• Preserve heritage breeds and varieties of plants for selective breeding

• Provides the genes for developing genetically modified crops and gene products

• Indirect support to human existence (pollination of crops/natural pest control)

• Cultural heritage of the earth

• Unique ecosystems

Assessment of biodiversity in a habitat

• count the number of species present (species richness) and the number of individual within each species population (species evenness)

• Can calculate the diversity of a habitat by using an index diversity (SDI)

• Any value 0 → 1

• Greater the value, greater the sample diversity

Assessment of biodiversity within a species at a genetic level

• look at the variety of alleles in the gene pool of a population/proportion of polymorphic loci across the genome

• The genes for which theee is 2 or more alleles at frequencies greater than those procured br mutation

• Three alleles; I^O, I^A, I^B

• Genetic fingerprinting can slide be used

• Reflects variation in non-coding parts of the genes

Genetic polymorphism

• the existences of a number of phenotypes that cannot be explained by mutation alone

• A number of alleles for the same gene/locus

How generic biodiversity can be assessed

• Number of alleles at a locus

• Proportion of the population that have a particular allele

Abundance

number of individuals of a species

Richness

Number of different species

Assessment of biodiversity at a molecular level

• DNA fingerprinting and sequencing

• Collect samples of DNA due to difficulties in counting every single allele in a population

• Analyse the base sequence to look for variations between individuals

• The greater the variation in the base sequence, the greater the genetic diversity of the species

Generation of biodiversity

• generated through natural selection

Natural selection

Individuals with advantageous phenotypes/alleles are more likely to survive and reproduce. Over many generations, this increases the frequency of advantageous alleles

Evolution

A change to the average phenotype of an organism and this can lead to be formation of new species (speciation)

Process of evolution by natural selection

• ADAPTIVE RADIATION

• Variation;

  • Individuals of the same species show variation in phenotype

  • Variation increased by meiosis in sexual reproduction

  • Mutations can result in new alleles and changes to characteristics/phenotypes

• Competition and natural selection

  • Many offspring born, with many dying

  • There is competition in the enviro for limited resources

  • Results in selection pressure where those individuals with a competitive advantage are more likely to survive

  • Example of selective pressure include;

    • Availability of food

    • Predation

    • Disease

    • Availability of shelter and nesting sites

• Reproduction and changes to allele frequency

  • Individuals with a competitive advantage are more likely to reproduce successfully

  • Able to pass on advantageous alleles to the next generation

  • The allele frequency increases

• Speciation

  • Breeding groups (demes) become reproductively isolated

  • Once they are no longer able to interbreed with the original population l, 2 species are formed

Types of adaptations

• Anatomical

• Physiological

• Behavioural

Anatomical adaptations

• Adaptations in the anatomy of an organism

Physiological adaptations

• Adaptations in the function or physiology of the organism

Behavioural adaptations

• Adaptations in the behaviour of an organism for survival

Phylogenetic trees

• The simplest and most likely tree is always correct

• Move forward in time from root to tip

• Tips represent descendants alive today

• Nodes represent speciation/evolutionary events/disappearance of common ancestor

• The line leading up to the node represent is an ancestor to the descendants that branch off from the node

• A clade is a group that share a common ancestor

• The higher up the tree the more closely related a clade is

• Clades can be nested. The ones that have branches off more recently are more closely related

Succession

Change in composition of a community overtime