Classification is a means of grouping organisms into catagories such as kingdom or order. Each organism is classified into each of these groups. The scale; Kingdom, Phylum, Class, Order, Family, Genus, Species, helps scientists map an organisms ancestery back billions of years. These groups are known as taxa because classification is part of scientific taxonomy. Example 1 The root of of biological classification is the work of Carolus Linnaeus. He grouped organisms according to shared physical characteristics, this was the basis for the Darwinian principal of Common Descent. the first big step to understanding classification is understanding binomial nomenclature. Linnaeus developed binomial nomenclature, in which each species is assigned a two part scientific name in Latin or Greek. A polar bear for example, is called Ursus maritimus. Ursus is the genus in which the organism belongs, this contains many other bears such as the Brown or Grizzly bear. Maritimus is specific to the polar bear, a brow bear would be called Ursus arctos, genus Ursus (bear) is the same but the species are different to show that they are different animals. When writting scientific names the genus always comes first and is always Capitalized. The species comes last and is always lowercased. And when writting scienfic names the genus and the species must be either underlined or italiczied. VIDEO Dichotomous keys are used as a visual way of identifying organisms. Keys start with the most common ancestor and separate
s the related organism by physical traits. Dichotomous key

The science of naming and grouping organisms is called systematics
The study of evolutionary relationships among organisms is called phylogeny

Linnaean System Of Classification:
Linnaeas's classification system consists of seven different levels, called taxa. They are:
Kingdom-Group of similiar phyla
Phylum-Group of similar coasses
Class-Group of similar orders
Order-Group of similar familes
Family-Group of similar genera
Genus- group of closely related species

Evolutionary Classification-
Evolutionary classification puts organisms into higher taxa whose members are more closely related. Evolutionary classification is more specific and detailed than the Linnaeus Classification System. It is better for organisms like dolphins, for example, because there are so many differet types. Biologists can now group organisms into categories that represent lines of evolutionary descent, not just physical similarities.

A cladogram is a diagram that shows how organisms in higher taxa are related. It shows how evolutionary lines break off from common ancestors.
--> The place where the evolutionary olineage splits is called a node. They represent the point where new lines shared a common ancestor.
-->The bottom of the diagram represents the ancestor shared by all of the organisms.
--> A derived character is a trait that rose in the most recent common ancestor and was passed to all of its descendants.

-The genes of many organisms reveal similarities at the molecular level. They can be used as criteria to help determine classification. Scientists can read the information coded in DNA, and they can compare DNA of different organisms to trace the history of genes over millions of years.

Molecular Clocks- Molecular clocks use DNA comparisons to estimate the length of time that two species have been evolving independently. It is similar to a swinging pendelum, which is used to mark time.

Organisms are also classified into Kingdoms and Domains. There are six-kingdom systems of classification that include the kingdoms Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia.
There are three domains that are: the domain Bacteria, which corresponds to the kingdom Eubacteria; the domain Archae, which corresponds with the kingdom Archaebacteria; and the domain Eukarya which is composed of protists, fungi, plants, and animals.
The members of the domain Bacteria are unicellular and prokaryotic and correspond with the kingdom Eubacteria. These bacteria are ecologically diverse, ranging from free-living soil organisms to deadly parasites. Some photosynthesize, while others do not. Some need oxygen to survive while others are killed by it. Bacteria have thick, rigid cell walls that are made up of a substance known as peptidoglycan that surround the cell membrane.
Members of the domain Archaea live in some of the most extreme environments you can imagine- volcanic hot springs, brine pools, and black organic mud totally devoid of oxygen. Many of these bacteria can survive only in the absence of oxygen. Their cell walls lack peptidoglycan, and their cell membranes contain unusual lipids that are not found in any other organism. The domain Archaea corresponds to the kingdom Archaebacteria.
The domain Eukarya consists of all organisms that have a nucleus. It is organized into the four remaining kingdoms of the six-kingdom system: Protista, Fungi, Plantae, and Animalia.
The Protista kingdom is composed of eukaryotic organisms that cannot be classified as animals, plants or fungi. Most Protista are single-celled organisms, but some, such as the multicellularalgae, are not. Some Protista are photosynthetic and others are heterotrophic
The members of the Fungi kingdom are heterotrophs. Most feed on dead or decaying organic matter. Most fungi are multicellular, most reconizable fungi are mushrooms. Some fungi, such as yeast are unicellular.
Members of the kingdom Plantae are multicellular organisms that are photosynthetic autotrophs.

Scientists have found and described approximately 1.75 million species on Earth. Plus, new species are being discovered every day. From tiny bacteria to yeasts to starfish to blue whales, life's diversity is truly impressive! With such a diversity of life on Earth, how does one go about making sense of it all?
One way to make sense of it is by classification. Scientists put similar species into groups so that those millions of species do not seem so overwhelming. People rely on their knowledge of classification to understand what different species are like. You may have done this without even thinking about it! For instance, let’s say that a friend of yours tells you that he saw an egret last weekend. You have never heard of an egret before, but if he tells you that an egret is a type of bird, you should have some idea of what it is like.

These three groups are called domains. The figure at the left shows the three domains of life. The distance between groups indicates how closely related they are. Groups that are close together, like plants and animals, are much more closely related than groups that are far apart, like plants and bacteria. Do you see how the two types of microbes, Archaea and Eubacteria, are about as similar to one another as they are to animals? Recent studies have found that microbes are far more diverse than anyone had suspected.
The Eukaryota domain is divided into several groups called kingdoms.