Chapter 18:Classification

Section 18-1 Learning Targets

• Explain how living things are organized for study

• Describe binomial nomenclature

• Explain Linnaeus’s system of classification

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To help us work with the diversity of life we need a system

of biological classification that names and orders

living organisms in a logical manner.

Why do we classify things?

* All accepted biological classification systems have two

important characteristics.1. They assign a single universally accepted name to each organism 2. Place organisms into groups that have real biological meaning.

Grouping with meaning….

• The groups to which an organism belongs is called a taxa and science of naming organisms and assigning them to groups is called Taxonomy.•In the eighteenth century scientists

decided to use Latin to name all species because it was a universally understood language.

• The first scientific names were based on the physical characteristics of biological organisms; however, there were two main problems:

• Names for the organisms could be very long!

• It was difficult to standardize the names of organisms because different scientists described different characteristics.

Carolus Linnaeus• Carolus Linnaeus, a Swedish

botanist, was the scientist who decided to use bionomial nomenclature…

– FYI: Linnaeus’ real name was actually Carl von Linnaeus but changed his name once he created his naming system of biological organisms

Binomial Nomenclature• Binomial nomenclature is a

classification system in which each species is assigned a two-part scientific name.

Canis lupus

Binomial Nomenclature, cont.• Binomial nomenclature is

written as follows:– If typing the scientific name

is written in italics or if handwritten the word is underlined.

– The first word is ALWAYS capitalized and the second word is ALWAYS lowercased.

Canis lupus

Linnaeus’ System of Classification

• There are 7 taxonomic categories used in Linnaeus’s classification system.

Kingdom Phylum

Class Order Family

Genus Species

Let’s talk about Taxons!

•Each level in the system of classification is called a taxon

•The smallest taxon is the species which a group of organisms so closely related that they can reproduce fertile offspring

Taxons continued• If two species share similar

features but are different biological organisms then they are said to be in the same genus.

Both the beagle and the wolf are both members of the genus Canis

Taxons Cont

• Species in a genus share many common characteristics– Groups of genera that share

many common characteristics are placed in families

– For example, all genera of bear-line animals belong to the family Ursidae.

Taxons Cont

•Several families of similar organisms make up the next taxon which is the Order.–For example: dogs, cats, and bears that eat meat all belong to the order of Carnivora.

Taxons Cont

•Orders are grouped into Classes.–For example all carnivores belong to the class Mammalia.

Taxons Cont• In turn, all mammals are

placed into the 2nd largest taxon, the phylum.– Mammals are placed into

phylum Chordata because they share common characteristics of body plan (a backbone) and internal functions.

Taxons Cont

•FINALLY, all phyla belong to either the Animal Kingdom or the Plantae Kingdom, which are the largest taxons in our classification system.

Section 18-2 Learning Targets

•Explain how evolutionary relationships are important in classification

•Explain how we can compare very dissimilar organisms

Evolutionary Classification•Linnaeus’s system of basing

classification on characteristics was limited

•Ex) How would you classify Dolphins?

•As fish because they have fin like appendages and live in the water or mammals because they breath air and feed their young with milk?

•Biologists now group organisms into categories that represent lines of evolutionary descent, not just physical similarities.

Modern Evolutionary Classification• Sometimes due to

convergent evolution organisms that are quite different from each other evolve similar body structures.

– These apparent similarities made it difficult for taxonomists to decide how many organisms should be classified.

Classification Using Cladograms

• To refine the process of evolutionary classification, scientists now prefer to use a method called cladistic analysis.

• Cladistic analysis identifies and considers only those new characteristics that arise as lineages evolve over time.

• Characteristics that appear in recent parts of a lineage but not in the older members are called derived characteristics.

Cladograms cont• Scientists use characteristics such as

homolgous stuctures in adults and embryos and biochemical similarities.

• A cladogram is a diagram that shows the evolutionary relationships among a group of organisms.Branch

points are those characteristics that first arrived among the organisms

Cladograms cont• Cladograms are useful tools that help

biologists understand evolutionary relationships among organisms.

• Species thought to be closely related are classified together.

• Other species may look like but possess analogous structures only are classified in different groups.

• However deciding which structures are important is not always easy.

Similarities in DNA and RNA

• All organisms use DNA and RNA to pass on information to their offspring and to control growth and development.

RNA

DNA

DNA/RNA cont• For example: virtually every

organism has its own from of cytochrome C, which is a complicated protein that is used in the electron transport chain this information can be used to tell how closely related organisms are to one another.

Molecular Clocks

• Molecular clocks use DNA comparison to estimate the length of time that two species have been evolving independently by monitoring mutations in their genetic code.

•Simple mutations occur all the time!

•Some mutations have big effects which can be both positive and negative on organisms

•These mutations or changes build up in the DNA over time

•The degree of dissimilarity is an indication of how long ago the two species shared a common ancestor.

Molecular Clocks cont• However, the use of molecular clocks

is not simple because there is not just one molecular clock within the genome.

–This is because genes acquire different mutations at different rates.

–However, these different clocks allow scientists to time different kinds of evolutionary events

Section 18-3 Learning Targets

•Name the six Kingdoms of life as they are now identified

•Describe the three-domain system of classification.

Kingdoms and Domains

• As biologists learned more about the natural world, they realized that Linnaeus’ two kingdoms, Animalia and Plantae, did not adequately represent the full diversity of life.

• Eventually because a deeper understanding of biological organisms, biologists created a 6 kingdom system.

Kingdoms and Domains• The 6 kingdoms

–Archaebacteria–Eubacteria–Protista –Fungi–Plantae–Animalia

Animal Kingdom

• These eukaryotic, multicellular organisms have no cell walls or chloroplasts and are heterotrophs.

–Examples: sponges, worms, insects, fishes and mammals

sponge insect Koala

Segmented worm

Pomacanthus

Archabacteria Kingdom• The prokaryotic unicelluar

organisms have cell walls without peptidoglycan.

–Examples: Methanognes & halophiles

methanogens

Halophiles

Eubacteria Kingdom

• These prokaryotic, unicellular organisms have cell walls with peptidoglycan.

Escherichia ColiA general bacterium

Fungi Kingdom

• These eukaryotic, multicellular (mostly) organisms have cells walls made of chitin and are heterotrophs.

• These organisms do not carry on photosynthesis

• Although fungi have many nuclei they do not always have separate cells divided by complete cell walls

–Examples: mushrooms & yeast

yeast

mushroom

Plantae Kingdom

• These eukaryotic, multicelluar organisms have cells walls composed of cellulose and have chloroplasts and are autotrophs

• These organisms carry on photosynthesis

–Examples: Mosses, ferns, flowering plants

Calla lillies

FernsMoss on a tree

Protista Kingdom

• All eukaryotes possess membrane-enclosed organelles, a nucleus, and mitochrondria or chloroplasts

• The Protista kingdom is further subdivided into three categories

– Animal-like– Plant-like– Fungi-like

• Examples: Amoeba, Paramecium, slime molds and giant kelp

Amoeba

Paramecium

Slime mold

Giant Kelp

The Three-Domain System

• Molecular analyses have created a new taxonomic category bigger than a Kingdom called a Domain.

• Classification is a growing and ever changing field of Biology. It’s hope is to further classify and specify each of the organisms on earth.

Domains• A domain is a more inclusive and is

larger than a kingdom• The three domains are:

–Domain Bacteria•Kingdom Eubacteria

–Domain Archaea•Kingdom Archaebacteria

–Domain Eukarya•Kingdom Protista, Fungi, Plantae and Animalia

Be sure to check out page 459 in your textbook for Figure 18-12!!!!

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