Unit 4: Classification of Organisms
Essential Terminology
1. Archaea - one of the 3 domains, microorganisms that are prokaryotic and have cell
walls, more simple than bacteria; not sensitive to antibiotics that affect Bacteria; most
live in extreme environments, may be the oldest organisms on Earth; includes
methanogens, extreme halophiles, thermophiles; contains the kingdom Archaebacteria
2. Bacteria - one of the 3 domains, prokaryotic microorganisms that have a cell wall,
sensitive to antibiotics, contains the kingdom Eubacteria, which includes cyanobacteria
and E. coli
3. Classification - the arrangement of organisms into orderly groups based on their
similarities and presumed evolutional relationships
4. Class - the level of classification after phylum; the organisms in all phyla are sorted
into classes
5. Dichotomous Key - an aid to identifying an unknown organism that consists of several
pairs of descriptive statements; of each pair of statements, only one will apply to the
unknown organism, and the statement will lead to another set of standards, and so on,
until the unknown organism can be identified
6. Domain - highest level of classification including Eukarya, Bacteria and Archaea
7. Eukarya - eukaryotic organisms: contains the 4 kingdoms of Protist, Fungus, Plant and
Animal
8. Family - the level of classification after order; the organisms in all orders are sorted
into families
9. Genus - the level of classification after family; the organisms in all families are sorted
into genera
10. Kingdom - level of classification under domain; contains 6 kingdoms
(Archaebacteria, Eubacteria, Protista, Fungi, Plantae, Animalia)
11. Order - the level of classification after class; the organisms in all the classes are
sorted into orders
12. Phylum - the level of classification after kingdom; the organisms from all the
kingdoms are sorted into several phyla
13. Species - the most specific of the seven levels of classification; characterized by a
group of organisms that can mate with one another to produce fertile offspring
14. Taxonomy - the science of identifying, classifying and naming living things