Classification of Living Things Chapter 2, section 2 pages42-49.

History of Classification Classification is the grouping of things according to similar characteristics. Classification is important because it provides a means of learning more about life on Earth and discovering relationships that exist between living things. Biological classification systems provide scientists with a method to name and organize living things in a logical and meaningful way.

Taxonomy Taxonomy is the branch of biology that is the science of classification. Scientists who work in the field are known as taxonomists. Taxonomy has a long history of developing systems of classification, changing them, and rejecting or replacing them with a better system as more information was discovered.

The First Classification Systems In the fourth century B.C., Aristotle proposed the first system, dividing living things into plants and animals. He also divided up animals by how they moved. In the seventeenth century, biologists began classifying animals according to similarities in form and structure called anatomy.

The Linnaean System In the 18th century, a Swedish scientist, Carolus Linnaeus developed the system we use today. Linnaeus did three things in his system of classification: He identified all living things as either plants or animals. He then grouped them according to similarities in structure and form. He also developed a simple system for naming living things and gave each organism a scientific name.

Naming Living Things Binomial nomenclature is the naming system developed by Carolus Linnaeus where each organism is given two names, a genus name and a species name. The genus is the family name of the animal and both words denotes the species the animal belongs to. The first (genus) name is capitalized and the species name follows, both are in italics and are normally Latin words.

Evolution and Classification Evolution is the process by which new organisms develop from previously existing organisms. Evolutionary relationships are extremely important to taxonomists. Present day taxonomists classify organisms in a way that shows evolutionary relationships.

Technology and Classification Today, scientists use the following methods to classify organisms: Examine large internal and external structures. Use the microscope to observe tiny structures within the cells of organisms. Use chemical tests to examine the building blocks of cell (DNA). All these tools help scientists to group and name organisms.

Classification Groups The system of classification used today does two jobs: It gives each organism a unique name used by scientists all over the world. It groups organisms according to their evolutionary relationships. All living things are classified into eight major levels: domain, kingdom, phylum, class, order, family, genus & species.

Domain, Kingdom, Phylum, Class, Order, Family, Genus and Species Domains are the largest and are based upon the makeup of the cell wall/membranes. Domains are divided into Kingdoms. The kingdom is the largest, most general group and contains different phylums based upon cellular characteristics and reproduction methods. . Phylums include different organisms sharing imprtnt characteristics, & evolved from a common ancestor. A species is the smallest, most specific group whose members share characteristics in appearance and behavior, and able to breed together to produce offspring.

From most specific to largest group.

Archeabacteria The first living things on earth, archeabacteria are one thousandth the size of Eukaryotic cells, and even smaller than bacteria (Prokaryotes). Archeabacteria live in oxygen free environments and can survive conditions that would kill other cells. They have rigid cell walls that do NOT contain peptiglycans (protein & sugar chains), which distinguish them from prokaryotes, who do.

Groups of Archeabacteria There are three major known groups of Archaebacteria: methanogens, halophiles (live in salty conditions), and thermophiles (can survive in extreme heat). The methanogens are anaerobic bacteria that produce methane. They are found in sewage treatment plants, bogs, and intestinal tracts. Ancient methanogens are the source of natural gas.

Prokaryotes Bacteria are placed in the kingdom Monera or Prokaryotes. Monerans are unicellular organisms that do not have a nucleus. Their cell walls are rigid & have peptiglycans. Monerans are placed into two categories: Autotrophs – make their own food Heterotrophs – cannot make their own food

Eukarya or Eukaryotes Contain all the organisms whose cells (in either unicellular or multicellular form) have a double layer membrane made of phospholipids and membrane bound organelles inside along with a nucleus. Eukarya is divided into the kingdoms of Protists, Fungi, Plants, and Animals.

Protists The kingdom Protista includes many of the unicellular organisms that have a nucleus. Some are heterotrophic, some autotrophic and some can do both Protista characteristics: Capable of animal-like movements First kinds of cells to contain a nucleus in the evolutionary line and are probably ancestors of plants, fungi, and animals.

Fungi Fungi are multicellular, heterotrophic organisms. Fungi are different from plants because they have cell walls made from a different material. Common examples of fungi include: mushrooms, mold, and yeast.

Plants Plants make up the kingdom Plantae. Most members of the plant kingdom are multicellular autotrophs. Their cells have cell walls made of cellulose. They include: flowering plants, ferns, and mosses.

Animalia Animals are multicellular organisms that comprise the kingdom Animalia. Like other multicellular organisms they have specialized tissues organized into organs. Animals are different from plants because animals are heterotrophs. Animals are different from fungi & plants because animal cells do not have cell walls.