Why do we classify things? Finding Order in Diversity Classification provides scientists and students a way to sort and group organisms for easier study. Taxonomy – branch of biology that deals with the classification and naming of living things There are millions of organisms on the earth! (approximately 1.5 million have been already named)

Classifying and Naming Organisms 1.Grouping organisms based on comparing characteristics makes it easer to study the diversity of live. 2.Binomial Nomenclature – 2 word system of identifying each kind of organism; avoids confusion A. Carolus Linnaeus – founder of modern taxonomy; used structural similarities as a basis for his classification system

Carolus Linnaeus Why do biologists consider Linnaeus’s system an improvement over earlier systems?

Classifying and Naming Organisms 1.Binomial Nomenclature (cont.) B. Scientific Name – both names together i. 1 st name – genus (always capitalized) ii. 2 nd name – identifies species within the genus (lower case) ii. 2 nd name – identifies species within the genus (lower case) iii. Name is written in italics or underlined iii. Name is written in italics or underlined

Linnaeus’s Classification System – hierarchical system from most inclusive to least inclusive are:

This illustration shows how a grizzly bear, Ursus arctos, is grouped within each taxonomic category.

Go to Fig What do the scientific names of the polar and grizzly bears tell you about their similarity to each other?

Linnaeus’s system was limited because similarities and differences were mainly visible What was invented that helped to change the way scientists classify organisms?

Evolutionary classification based on Darwin’s Theory of Evolution – Decent with Modification Species gradually change, or evolve, over time from pre-existing species

Classifying species based on easily observed adult traits can pose problems. Which of these organisms seem most alike?

Cladograms – a diagram that shows evolutionary relationships among organisms based on shared derived characters (Fig. 18-7)

Structural – ex. Skeletal structure, leaf anatomy

Behavioral – similar behaviors may indicate a close relationship – Fig American and African vultures look very much alike and were once classified together. American vultures have a peculiar behavior: When they get overheated, they urinate on their legs to cool down. The stork is the only other bird known to behave this way.

Biochemical – information about DNA, RNA & proteins can be used to help determine relationships and can be used to estimate how long different species have been separated African Vulture American VultureWood Stork

Cytological – cellular structure – ex. Prokaryotic vs. eukaryotic, plant cell vs. animal cell

Embryological – early stages of development may show shared characteristics that are absent at the adult stages (Fig pg. 385)

Fossil Formation – establish relationships between modern-day species & those that lived years ago