Classification Week 14-A

What is Classification? To study the diversity of life, biologists use a classification system to name organisms and group them in a logical manner. In taxonomy, scientists classify organisms and assign each organism a universally accepted name. Early efforts at naming organisms were just extremely detailed descriptions. The problems were that the names could be very long, and not everyone looked at the same characteristics.

Carolus Linnaeus Carolus Linnaeus developed a two-word naming system called binomial nomenclature. In binomial nomenclature, each species is assigned a two-part scientific name. Always in italics First word capitalized Second word lowercased

Linnaeus’s System Linnaeus’s hierarchical system of classification includes seven levels, or taxons. Kingdom Phylum Class Order Family Genus Species

Characteristics Phylogeny is the study of evolutionary relationships among organisms. Biologists now group organisms into categories that represent lines of evolutionary descent, or phylogeny, not just physical similarities. This is called evolutionary classification. Derived characters are characteristics that appear in recent parts of a lineage but not in its older members.

Characteristics The genes of many organisms show important similarities at the molecular level. Similarities in DNA can be used to help determine classification and evolutionary relationships. A molecular clock is a model that uses DNA comparisons to estimate the length of time that two species have been evolving independently.

Current System The current six-kingdom system of classification includes the kingdoms Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia. With the recent additions, scientists have added the “domain” category, which is larger and more inclusive than a kingdom. The three domains are the domain Eukarya (composed of protests, fungi, plants, and animals), Bacteria (Eubacteria), and Archaea (Archaebacteria).

Domains Bacteria are unicellular and prokaryotic. Eubacteria are ecologically diverse, ranging from soil organisms to deadly parasites, some need oxygen, others are killed by oxygen, some use photosynthesis, others do not. Archaea are also unicellular and prokaryotic, but they live in the most extreme environments; volcanic hot springs, brine pools, black organic mud totally devoid of oxygen. Eukarya consists of all organisms that have a nucleus.

Eukarya Protista are all organisms that cannot be classified as animals, plants or fungi. Fungi are heterotrophs. Most feed on dead or decaying organic matter, and secrete digestive enzymes into their food source, then absorb smaller food molecules. Plantae are multicellular organisms that are photosynthetic autotrophs. They are non-mobile, and have cell walls that contain cellulose. Animalia are multicellular and heterotrophic. Animals do not have cell walls, and most can move.