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

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

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

Carolus Linnaeus developed a two-word naming system called binomial nomenclature In this system, each species is assigned a 2 part scientific name The name is always written in italics

The first word (genus) is capitalized and the second word (species) is not Ex. The llama is Lama glama Genus = 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 species In 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

Modern Evolutionary Classification 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

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

In summary, the current 6 kingdoms are Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia

The three domains are Eukarya, Bacteria, and Archaea 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)

2. Bacteria – includes eubacteria They are unicellular and prokaryotic They have thick cell walls They have a wide range from soil bacteria to deadly parasites

3. Archaea – includes archaebacteria Also unicellular and prokaryotic They live in some of the most extreme environments and usually can only survive without oxygen

Diseases caused by Bacteria Diseases caused by Viruses Lyme disease Common cold Tetanus Influenza Tuberculosis Smallpox Diphtheria AIDS Bacterial meningitis Chickenpox Strep throat Measles Tooth Decay Hepatitis (A,B, & C)