Classification

Standard 2  Life Science: Students know and understand the characteristics and structure of living things, the processes of life, and how living things interact with each other and their environment.

Vocabulary  Taxonomy  Genus  Binomial nomenclature  Phylogeny  Cladistics  Bacteria  Archaea  Eukaryote  Video: Approx. 22 minutes

The Importance of ClassificationThe Importance of Classification (2:43)  Biologists use a system called taxonomy to classify organisms and organize their knowledge of those organisms in consistent ways to categorize and name them.  Why does there need to be a system?  To avoid confusion, there needs to be a way to name organisms that’s not based on location or language. Great Britain Robin North American Robin

 Organisms are arranged in specific categories from large to small. These are called a taxon, or (plural) taxa.  Early naming systems used long, descriptive Latin phrases called polynomials, but the names were inconsistent between the systems.  A simpler more consistent system was developed by Swedish biologist, Carl Linnaeus, known as the father of taxonomy. Organization of Knowledge (2:43)

Scientific Nomenclature  Linnaeus’s system, called binomial nomenclature uses two names for each organism. This two part name is now called a scientific name.  No two species can have the same name.  A grizzly bear has the scientific name, Ursus arctos  When writing the genus and species, the genus is capitalized and the species is lower case. Both are italicized in print and when hand written, are underlined: Ursus arctos. Classification of Living Things (5:29)

Dichotomous Keys  Using a key to classify:  Show Biology Virtual Investigations

Five Kingdoms of Life (5:57)

Levels of the Modern Linnaean System  Arrange the following set of taxon from the most broad description to the most specific taxa.  Subgroup classification (4:48) Subgroup classification  Quiz # 1: 10 questions  Order  Domain  Species  Kingdom  Phylum  Class  Genus  Family

Phylogenetics  Phylogeny is the ancestral relationships between species.  Not all characters are inherited from a common ancestor.  Birds and insects have wings, but the fossil record shows insects were around long before birds.  In convergent evolution, similarities may evolve in groups not closely related due to habitat or lifestyle.  Similarities that arise through convergent evolution are called analogous characters. For example, both birds and insects have wings that perform similar functions but have different evolutionary origins.

Cladistics  Cladistics analysis is used to select the most likely phylogeny among a given set of organisms.  It focuses on finding characters shared between groups of organisms due to ancestry.  A cladogram is a phylogenic tree that groups organisms together by their shared derived characters.  A clade is a set of groups related by descent from a single ancestral group.  Quick Lab page 430: Cladogram Construction Interactive cladistics exercise

Inferring Evolutionary Relatedness  Morphological evidence refers to the physical structure or anatomy of organisms.  An important part of morphology is the pattern of development from embryo to adult. Organisms that share ancestral genes often show similarities during the process of development.

Molecular Evidence  More recently, scientists have started using genetic information to infer phylogenies.  As genes are passed on from generation to generation, mutations occur that may be passed on to all species that descend from that ancestor, enabling scientists to compare DNA, RNA and proteins for similarities.

Evidence of Order and Time  Cladistics can determine the relative order of divergence but the fossil record is used to determine time frames.  Lancelets (535 million years ago) are the closest known relative of vertebrates (450 mya), so the two must have diverged over 450 mya.  DNA mutations which occur at relatively constant rates can also be used as molecular “clocks”. Genetic differences between taxa can be used to estimate the time at which the taxa began to diverge. Lancelets

Inference using Parsimony  Modern systematists use the principle of parsimony to construct phylogenetic trees. The principle holds that the simplest explanation for something is the most reasonable unless strong evidence exists to counter that explanation.  Occam’s razor states:  Entities should not be multiplied unnecessarily.

Progression in Science  Originally, scientists only recognized two kingdoms, but as identification processes became more sophisticated, more Kingdoms were added to make 5.  Then, in the 1990’s, the Moneran Kingdom was divided into two new kingdoms: Eubacteria and Archaebacteria to make 6 kingdoms. Eubacteria Archaebacteria

Three-Domain System groups together organisms with same general characteristics  Today, scientists recognize 6 kingdoms and 3 domains.  Domain Bacteria: Equivalent to Kingdom Eubacteria, common name bacteria. These are prokaryotes with a strong exterior cell wall and unique genetic system.  Domain Archae: Equivalent to Archaebacteria Kingdom, common name archae. May have been ancient bacteria that gave rise to eukaryotes.  Domain Eukarya: Includes Kingdoms Protista, Fungi, Plantae, and Animalia.

DOMAIN: BACTERIA/EUBACTERIA  Bacteria are organisms with a strong cell wall and a unique genetic system.  All are similar in physical structure, with no internal compartments.  Bacteria are the MOST abundant organisms on Earth and found in almost any environment.

DOMAIN: ARCHAE  Domain Archae is equivalent to Kingdom Archaebacteria.  Archaea have a chemically unique cell wall and membranes and a unique genetic system.  They were first found by scientists in extreme environments like salt lakes, deep oceans and in hot springs that exceed 100 o C.  They are called extremeophiles. Thermophiles live in hot places and methanogens live in places without oxygen. Thermal vent (undersea discoveries (8:00 min)

DOMAIN: EUKARYA  Domain Eukarya is made up of eukaryotes and include the Kingdoms Protista, Fungi, Plantae and Animalia. Helpful Fungi 1:59 minutes

Characteristics of Eukaryotes  Have highly organized cells.  Have cells with a nucleus.  Sexual reproduction is an important part of the life cycle of eukaryotes.  True multicellularity and and sexual reproduction occur only in eukaryotes.  Plantae: autotrophs that produce their own food through photosynthesis. Have cell walls.  Animalia: Multicellular heterotrophs. Lack cell wall.  Fungi: Heterotrophs with cell walls made of chitin.  Protista: Any single-celled eukaryote that is not a plant, animal or fungus.