ClassificationChapter 17, Sections 1 and 4

Why classify?Provides a way to

organize living things

Ensures scientists are using a common language when talking about living things

How are Things Classified?Old way – by physical similaritiesNew way – by molecular (DNA,

RNA, amino acid) similarities Increased understanding about

DNA has caused some revisions

Who & When: Development of Today’s Classification

SystemCarolus

Linnaeus - a Swedish botanist

During mid-1700s

Only 2 kingdoms – plants and animals

Levels of ClassificationFrom broadest

(biggest) group to most specific (smallest): Kingdom Phylum Class Order Family Genus Species

There are many mnemonic devices to help you remember these levels; write down your favorite or make up a new one:

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Rules for Scientific NamingEach species’ name is unique and

usually descriptiveScientific names:

Latin or Latinized wordsGenus and species name

This is called binomial nomenclature (two-name naming)

Genus name is capitalizedSpecies name is all lowercaseBoth words are italicized or

underlined

Two KingdomsUp until the 1950s – 1960s, most

textbooks still only referred to two kingdoms:Plants, which included all bacteria

and fungiAnimals, which included all protozoa

(single-celled, eukaryotic organisms)

Five Kingdoms In 1959, Whittaker developed the

5-Kingdom system

Monera included all of the prokaryotes (cells without nuclei); all others were eukaryotic.

Six KingdomsMore recently,

scientists split the kingdom Monera into two distinct groups (Eubacteria & Archaebacteria), creating 6 Kingdoms

Kingdoms of Life, cont’dThese six

kingdoms have now been grouped under a higher category: domain

There are 3 domains:BacteriaArchaeaEukarya

Characteristic Archae-bacteria Bacteria Protista Fungi Plantae Animalia

Cell Type (prokaryotic or

eukaryotic)Prokaryotic Prokaryotic Eukaryotic Eukaryotic Eukaryotic Eukaryotic

# of cells (uni or multicellular) Unicellular Unicellular Unicellular &

MulticellularUnicellular & Multicellular Multicellular Multicellular

Presence or absence of

nucleus in cellAbsent Absent Present Present Present Present

Presence or absence of cell

wallPresent Present Present in

some Present Present Absent

Cell wall composition

No peptidoglycan Peptidoglycan Varies Chitin cellulose n/a

Mode of nutrition (hetero /

autotrophic)

Autotrophic & heterotrophic

Autotrophic & heterotrophic

Autotrophic & heterotrophic Heterotrophic Autotrophic Heterotrophic

Presence or absence of locomotion

Present in some

Present in some

Present in some Absent Absent Present

Characteristics of Each Kingdom

Dichotomous KeysDichotomous keys are used to

distinguish between organisms that are closely related.

At each step on the key, the user is given two choices. Each alternative leads to another question, until the organism is identified.

Sample Dichotomous Key

Sample Dichotomous Key

This simple example of a dichotomous key shows

how each “question” must be a yes / no

question that divides the organisms into two

groups.