Chapter 18 Classification

Why Classify?? Human nature- we love to put things in their place! Organization Identification Less Confusion Show Relationships

Taxonomy The branch of biology that names and groups organisms according to their characteristics and evolutionary history. Classify the thousands of new species discovered each year million so far ?? millions yet to be discovered.

Biologists use the characteristics of newly discovered species to classify it with organisms having similar characteristics. The way we group organisms today continues to change and reflect the evolutionary history of organisms.

Early Systems of Classification Aristotle Linnaeus

Aristotle Greek Philosopher BC First classified organisms more than 2000yrs ago as either plants or animals. –Animals: land dwellers, water dwellers, or air dwellers. –Plants: three categories based on differences in their stems.

Aristotle

Carolus Linnaeus Father of Taxonomy Swedish naturalist years before Darwin!

1735 – published Systema Naturae. Devised a system of grouping organisms into hierarchical categories. Used an organism’s morphology (form and structure) – it’s appearance

Levels of Classification Kingdom Phylum or Division Class Order Family Genus Species

Under the modern Linnaean system, the classification of an organism places the organism within a nested hierarchy of taxa. (taxon – singular)

Binomial Nomenclature Scientific Name has two parts. –1st part is the genus –2nd part is the species which is the identifier or descriptive word. Genus name is capitalized and both names are underlined or written in italics.

Latin used by all scientists as a standard. Linnaeus classified 1000’s of organisms. Versions of his system are still used today.

Scientific Names May describe the organism, suggest geographic range, or honor a person Homo sapiens (homo = man sapiens = wise) Chaos chaos (amoeba never appear the same shape)

Linnaea borealis (Linnaeus’ favorite, borealis = northern)

Lupinus texensis Texas bluebonnet

Phylogeny Phylogeny is evolutionary history Much of Linnaeus’ work in classification is relevant even in the context of phylogeny because morphological features are largely influenced by genes and are clues of common ancestry.

Biologists now group organisms into categories that represent lines of evolutionary descent, or phylogeny, not just physical similarities Phylogeny – the study of evolutionary relationships Evolutionary Classification

Modern taxonomic placement involves: Morphology Chromosomal characteristics Nucleotide and amino acid sequences (chromosomes) Embryological development Information from the fossil record.

Phylogenetic tree Family tree that shows the evolutionary relationships thought to exist among groups of organisms. Represents a hypothesis and is based on several lines of evidence. Subject to change as new information arises.

Phylogenetic Tree

Interpreting a Phylogenetic Tree Organism at base of tree is common ancestor to all the others in the tree. Branch points indicate the evolution of some characteristic that splits a group into two groups. Groups shown at tips of branches include organisms that have evolved most recently.

Molecular Clocks This model uses comparisons of DNA, RNA and proteins to estimate the length of time that two species have been evolving independently. The degree of dissimilarity is, in turn and indication of how long ago the two species shared a common ancestor.

DNA comparisons (Artic bluegrass)Artic bluegrass

DNA banding patterns

Cladistics Relatively new system of phylogenetic classification. Uses certain features of organisms called shared derived characteristics to establish evolutionary relationships.

Derived character: feature that apparently evolved only within the group under consideration. Example: feathers in birds are inherited from a common ancestor.

To interpret a cladogram: Begin at the bottom and move up the axis that shows branch points. Groups and derived characteristics appeared in the order shown. Example: all groups branching above “lungs” have lungs. Those below do not.

Cladogram

Two Modern Systems of Classification Six Kingdom System Three Domain System

Six Kingdom System Kingdom Archaebacteria Kingdom Eubacteria Kingdom Protists Kingdom Fungi Kingdom Plantae Kingdom Animalia

Six Kingdoms

Kingdom Archaebacteria

Kingdom Archeabacteria Prokaryotic Unicellular Cell walls (without peptidoglycan) Autotroph or heterotroph

Kingdom Archaebacteria Some autotrophic – produce food by chemosynthesis and methane waste. “archae” = ancient May be directly descended from and very similar to first organisms on Earth

Can withstand extreme conditions –Thermophiles (heat) –Halophiles(salt) –Methanogens (methane gas) Many live in harsh environments – sulfurous hot springs, salty lakes, anaerobic environments, intestines of animals.

Kingdom Eubacteria

“eu” = true Prokaryotic Unicellular Cell walls (with peptidoglycan) Autotroph or heterotroph

Bacteria that affect your life: tooth decay, turn milk to yogurt, food poisoning, illness Most use oxygen, but a few cannot live in O 2 Both Eubacteria and archaebacteria make up the greatest number of living things on Earth.

Eubacteria and archaebacteria reproduce by binary fission but do have methods of genetic recombination to allow evolution to occur. Short generation times (30 minutes) allow rapid evolutionary response to environmental change. Example: antibiotic resistant bacterial infection.

Kingdom Protista

Eukaryotic Cell walls of cellulose Mostly single-celled organisms, but some multicellular but lack specialized tissues Autotrophic and heterotrophic Include Protozoa and Algae

Many species distantly related. Broad kingdom contains all eukaryotes that are not plants, animals, or fungi. 50,000 species. Sexual cycles of many are unknown but thought to have some process of genetic recombination.

Kingdom Fungi

Unicellular and multicellular Eukaryotic Cell walls of chitin Heterotrophic Absorb nutrients rather than ingesting 100,000 species – mushrooms, yeast, mildews, and molds.

Sexual cycles not known for many fungi. It is likely that all species have some way of promoting genetic recombination.

Kingdom Plantae

Multicellular plants All except for a few parasitic forms are autotrophic and use photosynthesis as a source of energy Eukaryotic Most live on land Sessile – don’t move around

Most have a sexual cycle based on meiosis 350,000 species identified including mosses, ferns, conifers, flowering plants.

Kingdom Animalia

Eukaryotic Heterotrophs Multicellular No cell walls Most have symmetrical body organization Move about their environment Have a sexual cycle based on meiosis About 1,000,000 species

Three Domain System Molecular biology has led to an alternative to the 6 kingdom system Comparing sequences of ribosomal RNA in many organisms. Estimated how long ago pairs of organisms shared a common ancestor.

Phylogenetic tree drawn from this data shows that living things seem to fall naturally into 3 broad groups or domains.

The Three Domains (and the kingdoms they include) Bacteria (Eubacteria) Archaea (Archaebacteria) Eukarya (Eukaryotes): includes Protista, Fungi, Plantae, Animalia

Three Domains

Conclusions from the Three Domain System All eukaryotes have true nuclei with linear chromosomes and membrane-bound organelles. The most variation in Eukarya is among protists.

When considered from the perspective of the complete diversity of life on Earth, the fungi, plants, and animals are quite similar to each other.