chapter 18 – classification section 18-1: finding order in diversity
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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)
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