154 ❯ STEP 4. Review the Knowledge You Need to Score HighTaxonomyis the field of biology that classifies organisms according to the presence or
absence of shared characteristics in an effort to discover evolutionary relationships among
species. A taxonis a category that organisms are placed into and can be any of the levels of
the hierarchy. There are seven common categories of classification; listed from broadest to
most specific, they are kingdom, phylum, class, order, family, genus, species. A way to
remember this sequence is through the use of a silly sentence such as this:
“Karaokeplayerscanorderfreegrapesoda” or
“KingPhillipcameoverforgoodspaghetti.”
Kingdom–phylum–class–order–family–genus–species.
Akingdomconsists of organisms that share characteristics such as cell structure, level of
cell specialization, and mechanisms to obtain nutrients. Kingdoms are split into phyla,which
are split into classes, which are further divided into orders.Orders are split into families,
which are made up of the different genera.The final and most specific division is the species.
This is the only naturally occurring taxon. These seven categories apply to many but not all
organisms. The plant kingdom has divisionsinstead of phyla. Bacterial species tend to be
placed into groups called strains.Five or Six Kingdoms?
The current system of classification is a five-kingdom system that divides all the organisms
of the planet into one of five kingdoms: Monera, Protista, Plantae, Fungi, and Animalia.
Do not be confused or alarmed if you hear mention of a six-kingdom system.
The difference in the six-kingdom system is that the kingdom Monera is split into
Eubacteria and Archaebacteria. Other than that, the kingdom delineations are similar. Let’s
begin the tour of the various kingdoms with the kingdom Monera.Kingdom Monera
The members of this kingdom are prokaryotes: single-celled organisms that have no
nucleus or membrane-bound organelles. Since this chapter is an exercise in painful amounts
of classification, subclassification, and further classification based on the previous classifica-
tion of classifications, and so on, we thought we would point out a few of the many differ-
ent ways that the kingdom Monera can be subdivided. The Monera kingdom can be
further classified by nutritional class, reactivity with oxygen, and whether they are eubacte-
ria or archaebacteria.Nutritional Class
Moneran organisms can be classified as either autotrophs or heterotrophs. Autotrophsare
the producers of the world:- Photoautotrophs:photosynthetic autotrophs (used to be called blue-green algae) that
produce energy from light. - Chemoautotrophs:produce energy from inorganic substances (e.g., S bacteria).
Heterotrophsare the consumers of the world. Examples of prokaryotic heterotrophs,
including parasitic bacteria that feed off hosts, and saprobes,such as bacteria of decay,
which feed off dead organisms.
KEY IDEABIG IDEA 1.B.2
Phylogenetic trees
are visual represen-
tations of ancestry.