Classification Notes

What does it mean to classify? Would you say that a grocery store has classified its products?

Classify – to group things together based on similarities

Why Classify ?

To make organisms/items easier to identify

To make organisms/items easier to compare

How do we classify ?

Compare Traits – features or characteristics of an organism/item

When dealing with living things, the science of classification is called Taxonomy

Challenges in Classification1. There are many different kinds of living

things –lots of diversity

o Today we have identified and named 1.5 million species

o Millions more are believed to be unclassified

o Organisms scattered all over the world, some in harsh, difficult to reach environments

2. Classifications are made by people

o Opinions may differ from scientist to scientist

Classification Timeline

384 – 322 B.C. Aristotleo 2 Kingdom Broad Classification

1735 - Carl Linnaeus o 2 Kingdom Multi-divisional

Classification 1860’s - Evolutionary Classification

o After Darwin; Grouped by lines of Evolutionary Descent

1950s - 5 Kingdom System Early 1990s - 6 Kingdom System Late 1990s - 3 Domain System

Plants are green and do not moveAnimals are NOT green and DO move

1. Do you see a problem with this classification system?

2. How would you classify this organism?

Carl Linnaeus - 1735 Swedish Botanist Called his classification Systema

Naturae Linnaeus added Taxons to Aristotle’s

system where each group is classified based on a specific trait (backbone, diet, behaviors, etc.)

This system is still used today

Linnaeus introduced scientific naming

Binomial Nomenclature is the 2 word scientific name of an organism; uses Genus and Species

Genus is capitalized, species is lower case, both are italicized

When writing the name, since you can’t italicize, underline it

All scientific names are written in Latin Latin can be understood by all

scientists, regardless of native language

There is only one proper scientific name per organism but one organism could have several common names

Ex: Cougars, Pumas, and Panthers are all the same organism

The common name depends upon where you live, but the Scientific name is the same WORLDWIDE

The scientific name is Felis concolor

Here is a mnemonic for remembering the levels (or

make your own):

All animals

All vertebrates

All mammals (mammary glands)

All meat eaters

All cats

All roaring cats

Leopard

What is the scientific name of the gray wolf?

Category Taxon

Dichotomous Key – aka taxonomic key or classification key – Used to identify organisms

Based on Comparison of Morphological Traits

Use physical features to compare / contrast

Determines if unknown organism is in a group or not, based on the key’s criteria

At each level there are only a couple of contrasting characteristics to choose from (It does have or doesn’t have certain characteristics)

Tennis shoe or non-Tennis shoe Has less than 3 legs or Has more than 3 legs

Tools Used to Classify Organisms

To classify organisms according to how they are related, scientists must look at more than just morphological traits. Modern classification is based on figuring out evolutionary relationships using evidence from living species (behaviors), the fossil record, and molecular data (DNA, RNA, proteins).

The evolutionary history for a group of species is called a phylogeny. Phylogenies can be shown as branching tree diagrams which show how species are related.

Identifying Unknown Organisms

Dichotomous Key“2 branching” - uses PAIRED STATEMENTS to

classify

Use this dichotomous key to name these organisms.

Breeding BehaviorDiffers between species

o Ex. Mating calls of frogs

Differences in breeding behavior can result in isolation and allows for SPECIATION to occur

Molecular Clocks use mutations to estimate evolutionary time

New mutations are added over evolutionary time; the more recent the organism, the more mutations are seen

Which organisms are most closely related?

1. Dog Amino acid sequence: Met-pro-iso-asp-val-phe

2. Whale Amino acid sequence: Met-pro-iso-asp-leu-phe

3. Shark Amino acid sequence: Met-val-iso-his-leu-arg

Molecular Evidence Reveals Species’ Relatedness

Nuclear DNAo Mutation rates can be compared across

species to determine relatedness Mitochondrial DNA

o Only passes maternally; The mutations rate of mtDNA is about 10 times faster than nuclear DNA, which makes it a good molecular clock for closely related species

RNAo rRNA has a very low mutation rate

compared to DNA so it is useful to comparing distantly related species

o Carl Woese first used rRNA to establish that archaea diverged from the common ancestor they share with bacteria almost 4 billion years ago.

Proteinso Amino acid sequences can be compared

across species to determine relatedness

Cladistics Uses an “order of appearance”

approach Cladogram - shows groups of

organisms evolving from a common ancestor and utilizes “derived characters”, but not specific times

In cladistics, similar characteristics that come from a common ancestor are used to divide organisms into groups.

o Derived characteristics - novel characters which define their grouping

A cladogram will begin by grouping organisms based on a derived characteristic displayed by all the members of the group.

Subsequently, the larger group, or clade, will contain increasingly smaller groups (clades) that share the traits of the clades before them, but also exhibit distinct changes as the organism evolves.

Systematics Uses a fan-like approach that

communicates a timeline Instead of a few derived characters,

systematics uses as many characteristics of organisms as possible and makes groupings based on overall degree of similarity

Cladistics vs.

Systematics

More closely related species share more derived characters

The oldest relatives are at the bottom of the cladogram

Nodes represent the most recent common ancestor of a clade

Here, the colors represent different clades

Classification is always a work in progressAs new discoveries are made and new technologies are created, scientists will continue to refine and reorganize the tree of life.

How many more kingdoms will be added in the future?

Our current classification system consists of 3 Domains and 6 Kingdoms:

Scientists constructed this tree by comparing rRNA sequences from species in each of the 6 kingdoms.

The distances between branches are proportional to the number of differences in rRNA sequences among the species.

DOMAIN BACTERIA Includes Kingdom Eubacteria

Unicellular Prokaryotes

o Single cells with No Nucleus

o Ecologically Diverse – live everywhere, including inside you!

Cell Walls contain substance called Peptidoglycan – special protein and sugar

o Peptidoglycan is used to distinguish themselves from Archaebacteria

o The peptidoglycan cell wall is the target of many antibiotics

DOMAIN ARCHAEA – Ancient Bacteria

Includes Kingdom Archaebacteria

Unicellular Prokaryotes

o Single cells with No nucleus

o Live in Extreme environments like those of early Earth

Hyperthemophiles (very high heat), thermophiles (high heat), psychrophiles (very cold), halophiles (high salt content), etc.

Cell walls without Peptidoglycan

DOMAIN EUKARYA Includes Kingdoms:

o Protista, Fungi, Plantae, Animalia

Eukaryotic, unicellular OR multicellular organisms

o Nucleus

o Includes most visible life

Archaebacteria Kingdom archae = Greek for "ANCIENT“ (Ancient bacteria)

o Modern archaebacteria MAY BE directly descended from (and are very similar to) the first organisms on Earth

o Biochemical & genetic properties differ from ALL other kinds of life

UNICELLULAR PROKARYOTESo No distinct nucleus with membrane around it

Cell wall = made of pseudopeptidoglycan Most are heterotrophic, a few are autotrophic, and

some are chemotrophic Live in harsh environments

o Sulfurous hot springs, very salty lakes, and in ANAEROBIC environments, such as the intestines of mammals

Examples: Thermococcus, Pyrococcus, Halobacterium, Methanobacterium

Eubacteria Kingdom EU = "TRUE“ (True bacteria) UNICELLULAR PROKARYOTES

o No distinct nucleus with membrane around it

Cell wall = made from peptidoglycan Most are mesophiles (live in middle

temperatures, like the human body) Some are heterotrophic, some are

autotrophic, some are chemotrophico Most of the Bacteria (Germs) that

affect your lifeo Includes the disease-causing bacteria

such as tooth decay or food poisoning

Examples: E. coli, Salmonella, Streptococcus, Clostridium

Protista Kingdom Eukaryotes Lacks complex organ systems Live in moist environments Cell wall = variety: some are polysaccharide, some

silica, some DON’T have one Mostly unicellular (some colonial = multicellular) Heterotrophic or Autotrophic, some parasitic 3 types: plant-like, animal-like, fungus-like

Examples: AMOEBA, PARAMECIUM, EUGLENA, ALGAE

Fungi Kingdom Eukaryotes Heterotrophs/decomposers; some parasitic Do not move (sessile) Cell wall = made from chitin (same

carbohydrate as the exoskeleton of insects) Mostly multicellular

o A few are unicellular Examples: MUSHROOMS, MOLDS &

MILDEWS, and YEAST (unicellular)

Plantae Kingdom Eukaryotes Multicellular Autotrophs Sessile (do not move) Cell walls made of cellulose Have complex organ systems Examples: MOSS, FERNS, FLOWERING PLANTS,

BUSHES, TREES

Animalia Kingdom Eukaryotes Multicellular Heterotrophs NO CELL WALL MOSTLY Motile Have complex organ systems Examples: INSECTS, JELLYFISH, HYDRA,

CRABS, FISH, BIRDS, LIONS, TIGERS, and BEARS (oh my!)

The 6 Kingdoms of Life

Overview