Ch. 20: The Classification of Organisms

1
Ch. 20 The Classification of Organisms

• Tiffany Liu
• Period 1

2
Species

• More than 5 million different species have been
  grouped and named by biologists
• Species the most basic unit of biological
  classification ( means kind in Latin)
• Practical purposes species is a category that
  has certain guidelines as to an organisms
  structure and appearance.

3
More species

• 1940 Ernest Mayr of Harvard University said that
  species are groups of actually or potentially
  interbreeding natural populations which are
  reproductively isolated from other such groups.
• If members of one species exchanged genes with
  another species, they would no longer have
  special characteristics that identify them as
  different organisms.

4
Speciation

• A group (species) of organisms are reproductively
  united but can change as time passes, and as they
  move over the Earth,
• Over 3.5 million years, speciation has led to
  the diversity of organisms.

5
Genera

• Groups of closely related species are genera
  (singular, genus).
• The genus is the 1st part of an organisms
  scientific name genus epithet (adj.). This is
  known as a binomial.
• Genus and species names are given by whoever
  discovers it. Some name them after themselves or
  friends, but some name them for fun (ex. Ytu
  brutus, a beetle)

6
Taxonomy

• The classification of organisms
• -consists of groups within groups
• taxon a particular group
• Category the level at which the taxon is ranked.
• http//www.differentphotos.com/IMAGES/E_rubecula1.
  jpg

7
Carolus Linnaeus

• Three categories were in use in his time genus,
  species, and kingdom.
• Kingdom the highest level.
• He and other scientists added many levels
  families, orders, classes, and phyla/ divisions.
• Division used for prokaryotes, algae, fungi, and
  plants
• Phylum used for protozoa and animals

8
Taxonomy continued

• Kingdom Plantae
• Division Anthophyta
• Class Dicotyledones
• Order Sapindales
• Family Aceraceae
• Genus Acer
• Species Acer rubrum
• English name Red maple
• 
  
• 
  http//www.ridgecrestnursery
  .com/Trees/Maple_Trees/Red_Maple_Montgomery.jpg

9
Evolutionary Systematics

• Phylogeny an organisms evolutionary history
• Systematics the study of the historical
  relationships among organisms
• 
  
  
  http//www.gov.bw/tourism/multimedia/im
  g/leopard.jpg

10

• Monophyletic the idea that the members of a
  taxon should all be descended from the nearest
  common ancestral species.
• Polyphyletic the idea that some taxa containing
  organisms descended from more than one ancestral
  line.

11
Homology and Analogy

• Structures that have a common origin but not a
  common function are called homologues.
• Ex Arm of a human to that of a crocodile
• http//users.rcn.com/jkimball.ma.ultranet/BiologyP
  ages/T/Taxonomy.html
• Structures that have a common function and
  appearance but not a common origin and called
  analogues.
• Ex wing of a bird to that of an insect

12
Evolutionary Taxonomy

• The organism is assigned, tentatively, to a taxon
  based on its outward appearance.
• The similarities are tested for homologies.
• Fossils are taken into account when possible, as
  well as patterns of embryonic development.

http//users.rcn.com/jkimball.ma.ultranet/BiologyP
ages/T/Taxonomy.htmlEmbryonicDevelopment
13
Alternative Methods

• Numerical Phenetics
• This is based only on the characteristics that
  can be observed, thus homology is not taken into
  account.
• The characteristics are divided into characters
  that cant be divided even more, then they are
  assigned numbers.
• The data is then processed and scores
• Ex Both lizards and humans have 5 fingers, while
  a snake has none, so lizards and humans are more
  closely related.

14
Another Alternative Method

• Cladistics
• Ignores overall similarity and is based solely on
  genealogy.
• More recent branches are assigned lower ranks.
• Holophyletic a taxon that includes all of the
  descendants from an ancestor, as well as the
  ancestor.
• Paraphyletic A taxon that consists of a
  holophyletic group from which very different
  members, and perhaps the ancestor even, have been
  removed.

15
Biochemical techniques

• They offer two advantages
• The results can be counted
• Diverse organisms can be compared
• They can compare enzymes, reaction pathways,
  hormones, and structural molecules
• It is now possible to compare organisms on the
  level of the gene.

16
Amino Acid Sequences Cytochrome c

• One of the 1st proteins that was analyzed was
  cytochrome c. The molecule, from many organisms,
  was analyzed, and showed the number of amino
  acids that the organisms differed by. The greater
  the number, the more distant their evolutionary
  relationship. The results were similar to the
  phylogenies made by other methods.

17
Amino Acid Sequences contd

• Some biologists believe that the differences in
  protein structure represent functional
  differences
• Others think that they occur at random because of
  random mutations and represent the passage of
  time. The random- tick hypothesis states that
  they can be used to determine when a particular
  group branched off (molecular clocks).

18
Nucleotide sequences

• Far easier since there are only 4 nucleotides vs.
  20 amino acids
• More sensitive since changes in nucleotides do
  not necessarily reflect in amino acids
• Analyses between rRNA and tRNA of prokaryotes can
  begin determining relationships among them.
• However there are many molecular clocks, ticking
  at different speeds (ex. mutations and introns).

19
DNA-DNA Hybridization

• One of the earliest techniques used to study
  nucleic acids
• Charles G. Sibley and Jon E. Ahlquist
• Produced hybrid radioactive DNA, then reheated it
  to determine similarity the higher the
  temperature at which it broke apart, the more
  similar the DNA.
• 50 dissociation temp. is a base line a 1 degree
  C change equals a 1 difference in the nucleotide
  sequences which equals a 4.5 million year
  evolutionary separation.

20
DNA-DNA Hybridization contd

• Mitochondrial DNA evolved faster than nuclear DNA
• Answers questions about relationships of
  organisms
• Helped prove the giant panda is a bear, not a
  raccoon.
• Helps ask more questions
• about evolutionary
• relationships.
• http//leisure.mytrip.net/shirahama/img/map/panda.
  jpg

21
Kingdoms Before

• The placement of taxa within kingdoms remains an
  unsolved problem
• In Linnaeuss time there were only three
  kingdoms animals, plants, and minerals
• Fungi, algae, and bacteria were grouped with
  plants
• Protozoa were grouped with animals

22
Kingdoms are Modified

• 20th century bacteria are placed in separated
  kingdom due to new evidence
• Resulted from improvements in microscopes and
  biochemical techniques.
• More evidence on evolutionary systems
• Eukaryotes arose from prokaryotes
• Multicellular organisms from unicellular
  organisms.

23
Kingdoms After

• Monera
• Based on cellular organization and biochemistry
• Protista
• Eukaryotes
• autotrophic and heterotrophic
• Unicellular and multicellular

• Fungi
• Absorb nutrients from their environment
• Plantae
• Photosynthesize their organic molecules
• Animalia
• Eat other organisms