Chapter 18 – Classification

Section 18-1: Finding Order in Diversity

To study the great diversity found on Earth, biologists give organisms names Biologists use a

classification system to name organisms and group them in a logical manner this is known as taxonomy

Larger, more general categories are needed as well as smaller specific categories

Organisms in the same group are more similar to one another than organisms in a nearby group

Using scientific names makes sure that everyone is talking about the same organism

Scientists began giving organisms scientific names in the 18th century because common names were just too confusing

Latin and Greek were well known languages and were used for scientific naming

The first attempts at scientific naming usually described physical characteristics and could end up being very long names

This also gave naming some subjectivity because a different scientist could describe the organisms in a different way

In this system, each species is assigned a 2 part scientific name

The name is always written in italics

Carolus Linnaeus developed a two-word naming system called binomial nomenclature

The first word (genus) is capitalized and the second word (species) is not

Ex. The llama is Lama glamaGenus = a group of closely related species

The species is usually a Latin description of the organism

A dichotomous key can be used to help identify unfamiliar organisms - it is a series of paired statements that describe physical characteristics of different organisms

Linnaeus’s classification system is hierarchical – it consists of levels

The system includes 7 levels; (largest to smallest) kingdom, phylum, class, order, family, genus, and speciesIn taxonomic

nomenclature, each level is a taxon

Kingdom is the largest and most inclusive of the categories – there are 6 kingdoms

Phyla are made up of several different classes that share at least several important characteristics

The phylum chordate is made up of the classes of Mammalia, Aves (birds), Reptilia, Amphibia, and all classes of fish because they share important body plan features and internal functions

Classes are composed of similar orders

The class of Mammalia includes animals that are warm-blooded, have body hair, and produce milk

Orders are broad categories made up of similar families

Llamas belong to the order Artiodactyla, which are even toed hoofed animals – this order also includes pigs, hippos, giraffes, antelopes, and sheep as well as others

Families are composed of similar genera

Llamas are part of the Camelidae family with other similar organisms like alpacas and camels

Section 18-2: Modern Evolutionary Classification

Scientists have tried to group organisms according to biologically important characteristics – however there are some limitations to this

Classification was mainly based on visible similarities and differences, but which ones are important?

Darwin’s ideas about decent with modification has given rise to the study of phylogeny = the evolutionary relationships among organisms

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

This method of classification is evolutionary classification

In evolutionary classification, species in a genus share a recent common ancestor

Similarly, all genera in a family share a common ancestor

The higher the level of taxon, the further back in time the ancestor is

Just because two organisms look similar doesn’t necessarily mean they share a common ancestor – natural selection may just have been working on each organism in similar environments this is convergent evolution

Cladistic analysis identifies and considers only those characteristics of organisms that are evolutionary innovations – new characteristics that have evolved

Derived characteristics = characteristics that appear in recent parts of a lineage but not older parts

Cladograms are diagrams that show relationships among a group of organisms

They help scientists understand how one lineage branched from another (it is like a family tree for organisms)

Characteristics can appear along the branches of the cladograms

The genes of organisms show important similarities at the molecular level

Similarities in DNA can help determine classification and evolutionary relationships

Genes in very dissimilar organisms can code for proteins with somewhat similar functions

DNA sequences can show relationships the closer the DNA, the closer the evolutionary relationship

DNA can also be used as a “molecular clock” to estimate the amount of time two species have been evolving independently

Section 18-3: Kingdoms and Domains

When Linnaeus first came up with his classification system, he named only two kingdoms – Animalia and Plantae

The view of life was simpler and visible differences were considered

As biologists learned more about the natural world, they realized that the two kingdoms didn’t fit for every living organism

Microorganisms like bacteria and protists were quite different and given their own kingdom, Protista

Only recently did scientists realize that Monera was made of two distinct groups and they were now named Eubacteria and Archaebacteria

Mushrooms, yeasts and molds were still different and given their own kingdom, Fungi Later, scientists realized

that bacteria were still different from protists and were given a new kingdom, Monera

In summary, the current 6 kingdoms are Eubacteria, Archaebacteria,

Protista, Fungi, Plantae, and Animalia

Recent work with RNA lead scientists to create a new taxonomic category – the domain – which is larger and more inclusive that kingdoms

The three domains are Eukarya, Bacteria, and

Archaea

1. Eukarya – includes protists, fungi, plants and animals

All eukarya have a nucleus

Protists are any organisms that can’t be classified as animals plants or fungi – they have a very wide range

Fungi are heterotrophs that usually feed on dead or decaying matter

Plants are photosynthetic autotrophs and also nonmotile (can’t move from place to place)

They are unicellular and prokaryotic

They have thick cell walls

They have a wide range from soil bacteria to deadly parasites

2. Bacteria – includes eubacteria

Also unicellular and prokaryotic

They live in some of the most extreme environments and usually can only survive without oxygen

3. Archaea – includes archaebacteria

Diseases caused by Bacteria

Diseases caused by Viruses

Lyme disease Common coldTetanus Influenza

Tuberculosis SmallpoxDiphtheria AIDS

Bacterial meningitis ChickenpoxStrep throat MeaslesTooth Decay Hepatitis (A,B, & C)