THE BASICS OF CLASSIFICATIONThe Last PPT of the Year

What is taxonomy? Why is it necessary to classify living things?

How does classification benefit us? Who was the father of taxonomy? What kinds of major taxonomic categories

are used today? Can you list the six kingdoms that are in use

today?

I. WHY CLASSIFY Biologists estimate that there are about 4-

100 million species of living organisms today.

Classifying them makes it easier to study them.

Why study them: To understand their anatomy and physiology To understand their origin To know how they fit into their environment and

interact with it To use some of their characteristics or molecules

in medicine, materials science, technology, food science etc.

II. THE BASICS OF PHYLOGENY Phylogeny – a field of biology that studies

evolutionary relationships between various species

Taxonomy – organizing living things into categories based on a set of characteristics

Carl Linneaus – the father of taxonomy, also invented binomial nomenclature

When we classify organisms, we use the following categories (largest to smallest): domain, kingdom, phylum, class, order, family, genus, and species

Species – a group of organisms that are similar in appearance and are actually or potentially capable of interbreeding and producing living and fertile offspring

We frequently use branching diagrams called phylogenetic trees to represent evolutionary relationships between various organisms.

Note: You must be able to explain and analyze these diagrams.

Some special phylogenetic trees (ultrametric trees) can also show when the common ancestors of the organisms separated from each other.

II. HOW ARE PHYLOGENIC RELATIONSHIPS DETERMINED Homologous structures – similar

anatomical structures due to shared ancestry

Analogous structures – these structures do not show common ancestry but became similar because of similar environmental pressures

Molecular systematics – molecular evidence is used to determine evolutionary relationships (DNA or proteins)

Molecular clocks – methods used to measure the time of evolutionary change based on the number of mutations

III. CONSTRUCTING PHYLOGENETIC TREES BY USING CLADOGRAMS We will construct a cladogram together. You

need to be able to do this on your own in the future.

Steps of constructing a cladogram: Select the taxa (species, genus) that you want to

include in your cladogram. Describe their characteristics Select an outgroup (taxa that shares only

primitive characteristics with all the others) Design a character table (assign 1 if the organism

has this characteristic and 0 if it does not) Start to draw your cladogram from a common

ancestor Branch each taxa off depending on their number

of shared characteristics

Cladograms – diagrams that show ancestral relationships of organisms. These diagrams are the first steps of constructing phylogenetic trees.

IV. DOMAINS OF LIFE Now biologists use a three –domain system –

Bacteria, Archaea, Eukarya Characteristics of Bacteria: nuclear envelope and

membrane-bound organelles are missing; introns and histones are also missing from the chromosomes; they have one circular chromosome; the cell wall is a unique substance called peptidoglican. They are always single-celled

http://www.ted.com/talks/lang/eng/bonnie_bassler_on_how_bacteria_communicate.html

Archaea: they are also single-celled organisms with circular chromosomes; they don’t have nuclear envelopes or membrane-bound organelles; however, their chromosomes are wrapped by histones and they also have introns. They have cell walls but these are not made up of peptidoglycan. They usually live under extreme conditions (high salinity, temperature, acidic environment etc.)

Eukarya – organisms with a nucleus and membrane-bound organelles. They can be single-celled or multicellular. They may or may not have cell walls. They have histones and introns. Their chromosomes are X-shaped and there is usually multiple of these in each nucleus.

V. KINGDOMS OF LIFE Eubacteria – very likely the first life forms

on Earth with peptidoglycan cell wall, circular chromosomes, no histones, introns, nuclei or membrane-bound organelles. They are always single-celled, with rod, sphere or spiral-shaped cells. They respond to and killed by antibiotics (unless they are resistent)

Archaebacteria – single-celled organisms without a nucleus or membrane-bound organelles. They have a cell wall that is not made up of peptidoglycan. They do not respond to antibiotics. They are able to live under extreme conditions such as high temperature, high or low pH, high salt concentration etc.

Protists – the first eukaryotic kingdom with very diverse organisms. Most of them are unicellular with a real nucleus. They can be autotroph or heterotroph. Even the multicellular species do not have real specialized tissues. Many live in water but some can survive on land in moist environments.

Single celled, aquatic protists (phytoplankton) are the most important sources of oxygen on the Earth

Important examples: Paramecium --

http://www.youtube.com/watch?v=l9ymaSzcsdY Euglena --

http://www.youtube.com/watch?v=0rNI8Bos_BQ Amoeba --

http://www.youtube.com/watch?v=7pR7TNzJ_pA Algae

Fugni – usually multicellular organisms with chitin cell walls. They are made up of fibers (hyphae) that are formed from fused cells. Can cover very large areas. Heterotroph organisms that inject their enzymes into their food and absorb the already digested material.

http://blog.ted.com/2008/05/06/paul_stamets/

Plants – autotrophic organisms that supply large quantities of oxygen and most organic material by photosynthesis for all other living organisms. They are always multicellular with cellulose cell wall. They have a wide range of ways to adapt to dry land.

http://www.ted.com/talks/lang/eng/jonathan_drori_why_we_re_storing_billions_of_seeds.html

Animals – we discuss them in the next unit

End of Unit