Classification

Classification

 Classification is the grouping of living organisms

 Various classification schemes have been used to identify living

organisms:

 Artificial classifications group organisms based on non-predictive features

such as body parts (fins, wings, etc)

 This does not consider species relatedness and hence is not commonly used

 Natural classifications group organisms according to evolutionary

relationships

 This makes such schemes predictive and accurate, but they are also highly

mutable/changeable when new information is discovered

 Phylogenetic classifications differentiate organisms based on genetic

features

Classification

 The current classification system is universal

among biologists and has been developed at

a series of international congresses over a

period of many years

 Several revisions to the existing system have

occurred over this time

Modern classification

began with Carolus

Linnaeus. Before

Linnaeus, scientists

named organisms

with long descriptive

names, and there was

no central system for

naming organisms.

Classification

 Variation between organisms is a

defining feature of life

 There is less variation between members of

a single species, but there are still

differences between individuals

 Organisms are grouped together and

classified on the basis of shared traits:

 Morphology (structure) and genetics

 Biochemistry and embryology

 Evolutionary history Felis catus

Felis rufus

Panthera leo

Classification

 Classification is hierarchal

 Each successive taxa (level) will contain fewer species, and

those species will share a larger number of characteristics

than those in the taxa above it (more closely related)

 Binomial nomenclature is a standard way of identifying a

species with a scientific two-word name

 Latin is usually used

 Genus and species

 Capitalize the first letter of the genus

 Do NOT capitalize the species

 ALWAYS underline or use italics

 E.g. Homo sapiens

Gives the

scientific

name

Remembering the order:

Classification

Why use scientific names?

 Common names do not indicate how organisms are related or classified.

 Different organisms have the same common name

 E.g. magpies

 The same organism has several common names

 E.g. cougar/puma

Cladograms

 Cladograms are branching diagrams in which the endpoints of the

branches represent specific species

 Each branch has different defining characteristics

 They are used to show points at

which various species diverged

from common ancestral forms,

and the evolutionary

relationships between them

Cladograms

 Which two organisms on this

cladogram are most closely

related? What features do they

have in common?

 What features do wolves and

leopards have in common

 What features do horses and

leopards have in common?

Domains and Kingdoms

 After the five kingdom system was introduced, all prokaryotes were

classified together into the one group (Monera)

 However, it was discovered that some of these organisms were much

older, and different in a number of ways compared to other bacteria

 These prokaryotes were often found in extreme environments (deep sea

hydrothermal vents, volcanic hot springs, acid lakes, the Dead Sea etc),

and were referred to as extremophiles

Domains and Kingdoms

 Like eubacteria (modern bacteria), these ancient

prokaryotes are single-celled with no membrane

bound organelles

 However, they are biochemically quite different to

eubacteria – in fact they are chemically more

similar to eukaryotic cells in some ways – so they

were classified as Archaea

 Initially, this led to the addition of a sixth

kingdom.

Domains and Kingdoms

 In 1990, Dr Carl Woese proposed that above the kingdoms there should

be three domains, bacteria, archaea and eukarya

 This was based on differences and similarities seen in ribosomal RNA

(rRNA) between the three groups

Archaea

 Unicellular

 No membrane bound organelles

 Often extremophiles

 Plasma membrane made from ether-

linked lipids

 No peptidoglycan in their cell walls

Eubacteria

 Unicellular

 No membrane bound organelles

 Plasma membrane made from

phospholipid bilayer

 Peptidoglycan cell walls

 “True” bacteria and cyanobacteria

(photosynthetic)

Eukarya

 Unicellular or multicellular

 Membrane bound organelles

 Plasma membrane made from

phospholipids

 No peptidoglycan in the cell

walls of those eukaryotes that

have one

 E.g. cellulose in plant cell walls,

chitin in fungi cell walls

Comparison of the Three Domains

The Five Kingdoms

 Under the three domains,

organisms are classified

into five kingdoms:

 Monera

 Protista

 Plantae

 Fungi

 Animalia

Monera

 Prokaryotes (Eubacteria and Archaea)

 Unicellular

 No membrane bound organelles

 Autotrophs and heterotrophs

Examples:

Staphylococcus aureus (skin infections)

Cyanobacteria (blue green algae)

Proteobacteria (salmonella)

Firmicutes (Lactobacillus)

Photobacterium (bioluminescence)

Protista

 Eukaryotes

 Unicellular or multicellular

 Generally aquatic

 Autotrophs and heterotrophs

 Protozoans – animal like

 Algae – plant like

 Molds – fungi like

Examples:

Paramecium – motile protozoan

Chlorella – single cell photoautotroph

Plasmodium – malaria parasite

Fungi

 Eukaryotes

 Unicellular or multicellular

 Chitin cell wall

 Heterotrophs (external digestion, many are

saprotrophs/decomposers)

 Yeasts, molds and mushrooms

Examples:

Bakers yeast – unicellular

Bracket fungi – multicellular

Penicillium – produces antibiotic

Plantae

 Eukaryotes

 Always multicellular

 Cellulose cell walls

 Autotrophs

 Photosynthetic

Examples:

Bryophytes (moss)

Ferns

Grasses

Trees

Plantae Classification

Traditionally, plants are classified into

their larger groups based on features

such as:

 Vascular tissue

 Presence or absence of xylem and

phloem tissue, roots etc

 Seeds

 Do they reproduce using seeds or

spores?

 Flowers

 Do they develop their seed in a

cone, or do they utilise flowers for

reproduction?

 Flowering plants are by far the

largest and most successful group

due to more successful fertilisations

occurring

Animalia

 Eukaryotes

 Multicellular

 No cell walls

 Heterotrophs

 Vertebrates and invertebrates

Examples:

Invertebrates (jellyfish, worms, snails, insects etc)

Vertebrates (fish, amphibians, reptiles, birds, mammals etc)

Animalia Classification

Traditionally, animals were classified

into their larger groups based on

features such as:

 Tissue development

 Do their cells develop into specific

tissue groups?

 Body symmetry

 Radial - repetition around a central

axis, can be divided into identical

pieces

 Bilateral – can be divided in to

mirror images (left and right halves)

 Gut development

 Protostome and deuterostome –

refers to the order in which the

openings to the gut develop

Modern Classification

 In recent years, the addition of genetic

analysis to traditional classification has

complicated the Five Kingdom system

 It has become apparent that neither

Monera or Protista are monophyletic

groups (a single group of related

organisms that evolved from a common

ancestor)

 This has led to numerous (and ongoing)

studies and discussions on the way that

organism groups should be classified

Crash Course

Classification Questions

1. Why is a worldwide system of scientific names necessary?

2. What genus does each of these examples belong to?

a) Macropus rufus (red kangaroo)

b) Homo sapiens

c) Escherichia coli

Domestic cat

Kingdom Animalia

Phylum Chordata

Class Mammalia

Order Carnivora

Family Felidae

Genus Felis

Species catus

3. The classification of an organism can

tell you a lot about its characteristics.

What does the classification of a

domestic cat to the right tell you about

the features or characteristics of the

organisms?

Classification Questions

4. Can you match the scientific names with the common names?

5. What features of the name did you use to match the names?

6. What is the scientific definition of a species?

7. Give an example of an issue with the species definition.

Equus caballus Lion

Thylacinus cynocephalus Horse

Panthera leo Dolphin

Delphinus delphis Tasmanian tiger

Red Panda Example

 The Red panda (Ailurus fulgens) - what is it?

 Red pandas were previously placed in the

bear family, Ursidae. They eat primarily

bamboo, but also small mammals or birds,

fruits, mushrooms and insects

 However the teeth and shape of the skull

resemble that of the giant panda, and it has

forepaws adapted for handling bamboo, also

like the giant panda

Red Panda Example

 Question:

 What characteristics does the red panda share with the giant panda? How

does it differ?

 However, scientists observed that

in many ways the red panda

resembled raccoons, Procyonidae

 Both have dextrous forepaws,

pointed ears, are omnivorous,

and have similar body sizes

Red Panda Example

 Question:

What similarities can you see

between the red panda and

the raccoon?

 How are they different in

appearance?

What could this mean in terms

of classification?

Red Panda Example

 DNA evidence has provided another twist in the classification of the red

panda

 It is now classified in Family Ailuridae, the only extant (still existing) member

of this family

 Characteristics of Ailuridae:

 Thick fur

 Long tail

 Round face

 Tear tracks around eyes

 In fact, DNA research shows a close relationship amongst the red panda,

raccoons and weasel family (Mustelidae)