Classification

Chapter 8

Learning OutcomesBy the end of this week, you should: recognise the value of identification and scientific

naming (nomenclature). develop knowledge of the principles of

classification. recognise that biological classification contains a

hierarchy of levels. become aware that taxonomic systems are

subject to change. recognise features typically used in constructing

major taxonomic groups.

Why is identification important?Endemic animals

Deadly and harmless snakesPersonal safety

Knowing the difference between poisonous and harmless plants.

Early settlers and stockQuarantineMedicineConservationForensics

PalynologyAgriculture and horticulture

Pests and control measures

What do scientists use to classify organisms?Whole specimens

Actual, image or verbal descriptionBits and pieces

Microscopic – plant cell walls, leaf vein patterns, pollen grains, seed shape

Macroscopic – feathers, hair, teeth, shells, fruitsMolecular – genetic material

Indirect evidenceTrack, burrows, nests, scratchings, scats,

calls/songsReference collections – herbaria, museumsKeys

KeysDichotomous key – choosing between two

alternatives

Complete the key activities.

Scientific namingBased on Latin or Greek words – pages 227, 228

Two part names (binomial) – internationalLinnaeus’ binomial naming system

1758SystematicFirst part = generic (which genus it belongs

to), always begins with a capital letterSecond part = specific name (which species

it belongs to), lower caseInformative about how closely related

organisms are

Why is scientific naming important?Universal, no matter what languageCommon names can be reused for different

speciesAn indication of relatednessCommon names may be misleading –

suggesting relationships that are not valid

Complete the quick-check questions on pages 224 and 229

What is classification?Naming and describing.Organising closely related species into

groups.Combining these groups to form larger,

more inclusive groups.

What is a species? Pages 230-231

Use of structural similarities?The ability to interbreed?The use of chromosomes and DNA?

Principles of classificationSeparating into groupsBased on the presence of absence of

various featuresUses a series of decisions in a dichotomous

key

Features of classificationClassification schemes can vary depending n their

function.Usefulness of the scheme depends on the criteria

selected:Objective (not subjective) – the same meaning for

different people = reproducible and predictable results

Meaningful (not arbitrary) – conveys useful information

Schemes are not fixed, but can change when new information becomes available.

Schemes can be single or multi-level (hierarchical).

Benefits of classificationEasier to deal with smaller numbers of

groups than very large number of separate items.

Provides information about relationships between organisms.

New items can be added in a predictable way.

Information can be easily retrieved.Predictions can be made about an item

based on its classification.

Hierarchical SystemLevels of classification are called taxa (sing. taxon)The closer the evolutionary relationship between two

organisms, the more similar their classification.The hierarchical system of classification:

KingdomPhylumClassOrderFamilyGenusSpecies

Come up with a pneumonic to help you remember!

Look at pages 240-242. Complete the

quick-check questions on page

242.

DomainsBacteria - prokaryotesArchaea – extremophiles Eukarya - eukaryotes

Watch the Clickview video and answer the

questions on classification.

CladisticsIdentifying the relationships between

various organisms and deciding which organisms should be included in particular groups.

“How many derived features do they share?”

Primitive characters – features that were present in a common ancestor, and so appear in all members of the group.

Derived characters – advanced or modified features that evolved later and appear in some members of the group.

CladogramsShows the evolutionary relationship

between particular organisms based on the derived characters they share.

A fork/branching point appears whenever a derived feature appears in some members of the group.

Classifications can changeBased on further study.DNA and protein sequencing can show

differences.