Classification

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Classification

• Candidates should be able to
• (a) define the terms classification, phylogeny
  and taxonomy
• (b) explain the relationship between
  classification and phylogeny
• (c) describe the classification of species into
  the taxonomic hierarchy of domain, kingdom,
  phylum, class, order, family, genus and species
• (d) outline the characteristic features of the
  following five kingdoms Prokaryotae (Monera),
  Protoctista, Fungi, Plantae, Animalia
• (e) outline the binomial system of nomenclature
  and the use of scientific (Latin) names for
  species
• (f) use a dichotomous key to identify a group of
  at least six plants, animals or microorganisms
• (g) discuss the fact that classification systems
  were based originally on observable features but
  more recent approaches draw on a wider range of
  evidence to clarify relationships between
  organisms, including molecular evidence (HSW1,
  7a)
• (h) compare and contrast the five kingdom and
  three domain classification systems (HSW4, 7a,
  7b).

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Key Terms

• Classification The process of placing living
  things into groups- the detailed study of the
  individuals in a species
• Phylogeny the study of how closely different
  species are related
• Taxonomy the study of the principles behind
  classification (the differences between species).
  These differences can be used to classify
  species.

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Phylogeny

• The more closely two species are related, the
  closer they appear on the evolutionary tree and
  the more recently they shared a common ancestor

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The Current System of Classification

• The current system uses eight taxa
• Domain
• Kingdom
• Phylum
• Class
• Order
• Family
• Genus
• Species

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Five Kingdoms

• Traditionally, all living things have been
  grouped into a number of kingdoms- this used to
  be two- plants and animals, but not all living
  things can fit into these two categories, so it
  is now 5
• Prokaryotes, protoctists, fungi, plants, animals

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Prokaryotes

• No nucleus
• Loop of DNA that is not arranged in linear
  proteins (not associated with histone proteins-
  Histones are the major structural proteins of
  chromosomes)
• No membrane bound organelles
• Small ribosomes
• Carry out respiration in special membrane systems
  called mesosomes
• Have smaller cells than eukaryotes
• May be free living, parasitic, or cause disease

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Protoctists

• All are eukaryotes
• Mostly single celled
• Have a variety of forms
• Show plant or animal like features
• Mostly free living
• Have autotrophic (photosynthesis) or
  heterotrophic (ingesting prey or extracellular
  enzymes) nutrition
• It is sometimes referred to as the dustbin group
  as they have features that do not belong in any
  other kingdom

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Fungi

• Are eukaryotes
• Have a mycelium (a network of strands called
  hyphae)
• Have walls made of chitin (not cellulose)
• Have a multinucleate cytoplasm (more than one
  nucleus)
• Are mostly free living and saprophytic (cause
  decay of organic matter)

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Plants

• Eukaryotes
• Multicellular
• Have a cellulose cell wall
• Produce multicellular embryos from fertilised
  eggs
• Have autotrophic nutrition (carry out
  photosynthesis)

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Animals

• Are eukaryotes
• Are multicellular
• Have heterotrophic nutrition (eat other
  organisms, digest and absorb them)
• Have fertilised eggs that develop into a ball of
  cells called a blastula
• Can usually move around

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Classifying a Species

• A species means a group of organisms that can
  breed together to produce fertile offspring
• Carl Linnaeus devised a system of naming living
  organisms that uses two names- called the
  binomial system
• Before this, scientists used to use long,
  detailed descriptions or a common name, however
  this did not work well because
• The same organisms had different names in
  different parts of the country
• Translation of languages may give different names
• The same common name may be used for different
  species in other parts of the world

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The Binomial System

• Latin is a universal language so species are
  given a universal name
• All scientists around the world will use the same
  name
• Binomial means two names, the first name is for
  the genus, the second is for the species e.g.
  Homo sapiens- Homo is the genus, sapiens is the
  species
• The genus name always starts with a capital
  letter
• It is always used in a way that makes it stand
  out- if typed, it is in italics, and if written
  it is underlined.

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Identifying Organisms

• Before you collect a species sample, you must
  check it will not harm the environment
• You would first have to carry out an EIA-
  Environmental impact assessment
• Scientists need to know what species are present,
  if they are rare, and if habitat destruction
  would have a large impact
• For example a pond that contains great crested
  newts must not be harmed, as it is protected
  under the wildlife and countryside act 1981- it
  is illegal to catch, possess handle, cause death,
  harm or disturb them

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Using a Key

• A dichotomous key is a way of identifying
  organisms you have found
• It is based on questions and answers- usually yes
  or no
• The answer to each question leads to a different
  question and finally the name of the specimen
• A good dichotomous key has one question fewer
  than the number of species it can identify

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You must make sure you know how to use a
dichotomous key to identify a group of at least
six plants, animals or microorganisms
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Ancient Classification

• Early classification was based on observable
  features, so was limited to what you could see
• In the 17th century (1600s), they had microscopes
  to help so they could see cells
• Aristotle (384BC) based his observation on
  appearance and anatomy he said organisms were
  either plant or animal, then he further
  classified them into three groups, those that
  live and move in water, live and move on land and
  move through the air
• Unfortunately, this meant that he grouped fish
  with turtles, birds with insects and mammals with
  frogs.
• Classification is now more accurate as more
  research has been carried out.

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Modern Classification

• Originally, one celled organisms that were plant
  like were classified with plants and animal like
  ones classified with animals, but some
  unicellular organisms have features of both
  animal and plant, also there was the problem with
  fungi having hyphae and not carrying out
  photosynthesis.
• This is why we now have the 5 kingdom
  classification, however there are now even more
  ways of classifying organisms

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Biochemistry

• Certain large biochemical molecules are found in
  all living things, but they may not be identical
  in all living things
• This can be used to show evolutionary
  relationships and how closely related species are
  to one another

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Cytochrome C

• Cytochrome C is a protein used in respiration
• All living organisms except chemosynthetic
  prokaryotes must respire, so must have Cytochrome
  C
• Cytochrome C is not identical in all species- it
  is a protein made from amino acids, and some of
  the amino acid sequences differ between species.
• If the amino acid sequence is the same, the two
  species must be closely related, the more
  differences there are, the less the species is
  related

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DNA

• All organisms use DNA or RNA
• Comparisons of DNA sequences provides a way to
  classify species
• The more similar the sequence, the more closely
  related the species
• We can use this to clarify or correct
  evolutionary relationships that we are unsure
  about

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Three Domains

• In 1990, Carl Woese suggested a new
  classification system based on RNA
• He divided the kingdom Prokaryote into two the
  bacteria (Eubacteria) and the Archaeae
  (Archaebacteria)
• He said that Bacteria have a different cell
  membrane structure, different flagella, different
  enzymes for building RNA, no proteins bound to
  their genetic material and different DNA
  replication mechanisms
• He also said Archaea share features with
  eukaryotes e.g. similar enzymes for building RNA,
  similar DNA replication mechanisms and production
  of the same proteins that bind to DNA
• Woese suggested that the differences between
  Archaeae and Eubacteria are greater than the
  differences between Eukaryotes and bacteria- this
  is now widely accepted by biologists

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Questions
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Total 4 marks
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Task

• Now complete the end of chapter test as an open
  book activity