Classification of Organisms

Taxonomy The process of describing the ways in which organisms are grouped or classified according to similarities and differences. Assigns organisms a universally accepted name. Why is this important? To understand the relationships among living organisms. To more efficiently identify an unknown organism. To improve communication among scientists.

Taxonomy and Classification What characteristics do these organisms have that might lead scientists to group them together? What differences do they have that distinguish one from the other?

Categories of Classification Each category of classification is based on characteristics that are shared by all the organisms in the category. The more levels an organism shares with another, the more closely related they are considered to be. Scientists use an 8-level system to classify organisms.

8 levels of classification Domain Kingdom Phylum Class Order Family Genus Species Dumb Kangaroos Playing Catch On Freeway Get Squashed 8 levels of classification Domain Species Most diverse Least diverse Most general Least general (most specific) Most Inclusive Least inclusive Most differences Least differences

Order Carnivora But, the number of groups within each level will increase as you move from the domain level to the species levels 16 Families 128 Genera 281 Species The number of different TYPES of organisms will decrease as you move from the domain level to the species level.

Examples Organism Cat Wolf Fly Domain Eukarya Kingdom Animalia Phylum Chordata Arthropoda Class Mammalia Insecta Order Carnivora Diptera Family Felidae Canidae Muscidae Genus Felis Canis Musca Species domesticus lupus domestica What type of animal is Musca domestica? From the table, which 2 animals are most closely related? 3. At what classification level does the evolutionary relationship between cats and wolves diverge (become different)? If two organisms share a level of classification, they belong to the same levels above it, but not necessarily the levels below it. Example: If two organisms are in the same family, then they are in the same domain, kingdom, phylum, class and order.

Scientific names Scientific names give biologists a common way of communicating regardless of the language they speak. Using common names is confusing because many organisms may have several different common names. Example: The cougar is also known as a mountain lion, puma, or catamount…thus the need for a scientific name. Swedish biologist Carl Linnaeus developed binomial nomenclature, the two word system for naming all of the organisms in the world. Carl Linnaeus, 1707-1778

Assigning scientific names The first part of the scientific name is the genus. This word is always written first and the first letter is capitalized. The second part of the scientific name is the species name. This word is always written second and the first letter is not capitalized. Both the genus and species names are in italics or are underlined. Homo sapien Ursus arctos

How related? What do the scientific names of the polar, grizzly, and panda bears tell you about their similarity to each other? Ursus maritimus Ursus arctos Ailuropoda melanoleuca

EVOLUTIONARY CLASSIFICATION Biologists group organisms into categories that represent lines of evolutionary descent, or phylogeny, not just physical similarities. Phylogeny: The study of evolutionary relationships among organisms.

CLADOGRAMS When the traits appears above an organism, the organism lacks that trait. When the traits appears below the organism, the organism possesses that derived character. Which organisms are most closely related? Which organisms are least closely related?

According to this phylogenetic tree, which organism is most closely related to Organism V? A Q B U C W D X

What happens when you don’t know what an organism is? One way to identify an unknown organism is to use a dichotomous key. A dichotomous key is an identification tool that uses pairs of contrasting descriptions. Each description will either send you to another pair of descriptions or will identify an object.

Dichotomous Keys Before you use a key: Look over all the traits of your organisms Identify key features and terms Try to narrow down what you are looking at (for example---if you are using a field guide for birds---don’t use it to classify flowers) Always start your “search” for the correct scientific name at the beginning of the key

Dichotomous Key Example Ursus maritimus Ursus arctos A. melanoleuca 1a The bear is a solid color…go to 2 1b The bear is not a solid color…Ailuropoda melanoleuca 2a The bear is brown…Ursus arctos 2b The bear is white…Ursus maritimus

Your turn… Create a dichotomous key for the animals shown here