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The Diversity of Life Biologists have identified about 1.5 million organisms. Thousands more remain to be found. Great variation in organisms exists. Diversity continued Some organisms are clearly plant or animal. Other organisms are more difficult to classify. Thus we need a classification system! Plant and Animal Characteristics As previously discussed, it is relatively simple to distinguish plants from animals. See handout. Classification Categories The categories used by biologists to classify an organism are: Kingdom, Phylum,Class, Order, Family, Genus, and Species. See Table 6.1 on page 95. Nomenclature Nomenclature is a system for naming organisms. Linnaeus developed the binomial system of nomenclature. Nomenclature continued Binomial means two names. The names must be in Latin. The first name is the Genus and the second name is the Species. For example for a human it is Homo sapiens and for the frog Rana pipiens. Modern Taxonomy In the mid 1800’s the common belief was that species did not change. Biologists collected single specimens that were used to represent all species of that one organism. They called these type specimens. Variations were ignored. Later in 1859 it was noted that over long periods of time a species will change in response to the environment. Species The term species refers to a similar population of organisms that can interbreed in nature. Over time, species may interbreed, evolve and form new species. This phenomenon further supports the need for a classification system. Classification of Living Organisms Handout This handout, shows us that we have two broad categories of living things: Prokaryotes and Eukaryotes The Prokaryotes Cells are called prokaryotic. Lack a nucleus. Lack membrane bound organelles. Ribosomes are smaller than those in eukaryotic cells. DNA lacks histones (Special protein) Flagella are twisted strands of protein. Ex. Bacteria Eukaryotes Cells are called eukaryotic Cells have a well defined nucleus, with DNA containing histones. Membrane bound organelles are present(mitochondria, etc.) Flagella have microtubules in the 9+2 pattern. Three Domain System Latest system to classify living things. Developed in the last 20 years by microbiologists who believe that microbes dominate the diversity of life on Earth. This system is based on gene studies and in particular on rRNA, which is found in all living things. Three Domain System continued The three domains include 2 groups for bacteria and 1 for the rest of the living things. 1. Archaea Bacteria: includes ancient bacteria that can be found in very harsh environments. Ex. Methane producers, salt lovers,and heat lovers. Three Domain System continued 2. Eubacteria: This domain includes the true bacteria that are found in various environments such as E.coli that is found in the intestines of warm blooded animals. Blue - green algae are also included in this group. 3. Eucharya: All remaining organisms. Cells have distinct nuclei and organelles.