CLASSIFICATION OF LIFE(27.5)

HOW DO WE TELL LIVING THINGS APART?

SYSTEMATICS Definition: the study of grouping living

things based on their shared characteristics.

Each organism is placed into larger and larger categories called taxa (plural form of taxon).

Carl Linnaeus was a HUGE contributor to this.

All my work… summed up in a cheap MS Paint

picture. Thou art cruel, Mr. Paschak

SYSTEMATICS In modern biology, we use the following

taxa/categories (from LEAST specific to MOST specific): Domain Kingdom Phylum Class Order Family Genus Species

There are only 3 domains, but around 2 million species (discovered so far).

Some estimates place the number of species on Earth at 8.7 million.

**As you go lower down the ranking, the number of taxa increases.**

TAXONOMY Definition: the assignment of a specific

scientific name to an organism. An organism’s name is usually binomial

(contains two words) – its Genus and its species are listed. Linnaeus created this approach. Eg: Homo sapiens, Escherichia coli

These can be abbreviated Eg: H. sapiens, E. coli

PHYLOGENY Definition: the evolutionary relationship

among organisms. The goal of systematics is to put

closely-related species into similar groups.

Classification should reflect phylogeny. Members of the same family should be

more related than members of a different family.

THE FIVE-KINGDOM SYSTEM Living things are divided into five

kingdoms based on: Whether or not their cells have nuclei. How many cells they’re made up of. How they obtain their food/nutrition.

THE FIVE KINGDOM SYSTEM

THE FIVE KINGDOM SYSTEM Suggests that monerans (bacteria,

archaea) evolved first and don’t have nuclei.

Protists evolved from monerans. Plants, animals, and fungi share some

common, protist ancestor. This system is now considered to be

inaccurate, though.

THE SIX KINGDOM SYSTEM Carl Woese’s analysis of bacteria

suggested that they should be divided into two kingdoms: Eubacteria (also called “true” bacteria)

and Archaebacteria

This caused the creationof a sixth kingdom.

THREE-DOMAIN SYSTEM Evidence in DNA and RNA (ribonucleic

acid) helps to sort living things into larger domains.

Domains are based on RNA, molecular evidence, and cell structures.

The three domains are: Eukarya, Bacteria, and Archaea.

THREE-DOMAIN SYSTEM

BACTERIA All bacteria are prokaryotes (they

have no nuclei) and unicellular (a whole bacterium is made up of just one cell).

Found in nearly every environment you can think of.

ARCHAEA Also unicellular prokaryotes. Have a different cell wall and membrane

compared to bacteria. Tend to inhabit extreme conditions

Highly salty waters Hot springs Extremely cold waters

More closely-related to Eukarya than to bacteria.

EUKARYA All of these organisms are eukaryotes

(have cells that contain a nucleus). Can be either unicellular (protists,

yeasts) or multicellular (plants, animals, many fungi).

This domain is made up of 4 of the original five kingdoms (Plantae, Animalia, Fungi,

and Protista).

How to figure out which category is the right one…

CATEGORICAL LOGIC

LOGIC IN CLASSIFICATION If something is true about a category,

then it MUST be true for ALL members of that category.

This is called categorical reasoning. It is the basis for classification. It looks like this:

Premise: All wizards wear glasses.Given: Mr. Paschak wears glasses.Conclusion: Mr. Paschak is a wizard.

LOGIC IN CLASSIFICATION Example: Premise: All birds are vertebrates. Given: A robin is a bird. Conclusion: A robin is a vertebrate.

Using this example, construct an argument to show that Mr. Paschak is a mammal.

QUICK ASSIGNMENT1) Construct a categorical argument to

show that a spruce tree is a plant.2) Consider this argument:Premise: All horses are herbivores.Given: Organism X is a herbivore.Conclusion: Organism X is a horse.Is this argument correct? Why or why not?

FOR NEXT TIME Consult section 1.2 of your textbook

and/or an online resource in order to find the following: Two defining characteristics of Archaea Two defining characteristics of Bacteria

(or Eubacteria) Two defining characteristics of Eukarya.

Arrange these into a table in your notes.

CLADISTICS Also called “phylogenetics”. This is

the new direction in classification. Organisms are put into groups called

clades. Each clade contains an ancestor and ALL species that have descended from it.

Continued… (incoming t-chart!)

PHYLOGENETICS VS TAXONOMY

PHYLOGENETICS TRADITIONAL VIEW

Organisms arranged by ancestry (shared genes, common ancestors).

Grouped into different clades.

Physical characteristics within a clade can be VERY different.

Organisms arranged by physical characteristics.

Grouped into phyla, classes, orders, etc.

Physical characteristics in groups tend to be similar.

CLADOGRAMS

Note that in this diagram, 7 distinct animals all belong to a single clade!

CLADOGRAMS CAREFUL! Even though the cladogram

used one trait at a time to arrange the organisms, real phylogeneticists will use much more data.

Data for creating clades includes: Physical characteritics DNA sequences and genes RNA sequences