Chapter 18 Classification of Organisms
I.
Biodiversity
A. Classifying Organisms
1. Biodiversity is the variety of organisms considered at all levels
from populations to ecosystems
B. Taxonomy
1. The science of describing, naming, and classifying organisms
2. Aristotle was the first two classify organisms
a. Used two taxa – plants and animals
b. Animals on the basis of whether they lived on land, in water, or
in the air
c. Plants by differences in their stems
3. Common names of organisms (robin, great white shark, jellyfish)
are not useful to identify organisms because common names vary
from place to place and many don’t accurately define a species
C. Levels of Classification
1. Carolus Linnaeus devised a hierarchical categorical system for
grouping organisms (started with 7 levels)
2. The system has eight levels
3. Starting from the largest to the smallest (most specific)
a. Domain
b. Kingdom
c. Phylum (animals), Division (plants)
d. Class
e. Order
f. Family (end in idae or aceae)
g. Genus
h. Species
4. Binomial nomenclature is the two-part name or scientific name of
an organism (genus and species)
5. Rules for writing a scientific name
a. Name is in Latin
b. The name is written in italics or underlined
c. The genus is always capitalized
d. The species is always lower case
6. Other categories can be added (superorders, subclasses)
7. A human is classified as:
a. Domain – Eukarya
b. Kingdom – Animalia
c. Phylum – Chordata
d. Class – Mammalia
e. Order – Primates
f. Family – Hominidae
g. Genus – Homo
h. Species – sapiens
8. An easy way to remember the levels of classification is the
following sentence. King Philip Came Over From Germany
Smiling.
II.
Systematics
A. Classifying organisms in terms of their natural relationships
B. Phylogenetics
1. The analysis of the evolutionary or ancestral relationships among
taxa
2. Evidence includes:
a. Similarities between living and fossilized organisms
b. Patterns of embryonic development (include gene expression)
c. Compare DNA, RNA, and proteins from different
3. Phylogenetic diagram (phylogenetic tree): looks like a family tree,
with a branching pattern that indicates how closely related a subset
of taxa are thought to be
4. Evidence of shared ancestry
a. Fossils are key, but what about soft bodied organisms that
don’t fossilize well?
b. Homologous features (items that share a common ancestry), the
greater the number of homologous features shared by two
organisms, the more closely related they are
c. Embryological evidence: Amniotes example pg. 342
C. Cladistics
1. (Hennig) system of phylogenetic analysis that uses shared and
derived characters as the criteria for grouping taxa
2. Shared character – is a feature that all members of a group have in
common
3. Derived character – is a feature that evolved only within the group
under consideration
4. It’s assumed that organisms that share one or more derived
characters probably inherited those characters from a common
ancestor
5. Clade – the group of organisms that includes an ancestor plus all
of its descendants
6. The phylogenetic diagram used is called a cladogram (Figure 17-3
pg. 342)
7. Difference between cladistics and traditional systematic (pg. 342343)
8. Constructing a Cladogram (pg. 343, Figure 17-4 and Table 17-2)
9. Out-group organism is an organism that is only distantly related to
the other organisms
D. Molecular Cladistics (Figure 17-5, pg. 344)
1. Counting shared, derived amino acids at each position in a protein
and can construct a tree that hypothesizes relationships between
various species
2. Molecular clock – a tool for estimating the sequence of past
evolutionary events
a. Use evolutionary changes in the sequence of DNA, RNA, and
proteins
b. The greater the differences between a pair of sequences, the
longer ago those two sequences diverged from a common
ancestor
3. Chromosomes (Figure 17-6, pg. 344)
a. Analyzing karyotypes
b. Chromosomes can be used by looking at their banding pattern
c. If two species have the same banding pattern in regions of
similar chromosomes, the regions are likely to have been
inherited from a single chromosome in the last common
ancestor of the two species
E. Putting It All Together (example Figure 17-7, pg. 345)
III.
Modern Classification
A. The Tree of Life
1. Two groups: prokaryotes and eukaryotes
2. Revising the tree
a. Carl Woese : Revise Earth’s diversity into 6 kingdoms
b. He used rRNA (ribosomal RNA), the genes that encode rRNA
seem to have changed little throughout most of evolutionary
history
c. rRNA genes are useful for studying the most basic evolutionary
relationships between Earth’s diverse organisms
B. Three Domains of Life
1. rRNA gene analysis provided insights about relationships among
organisms and suggested a new “tree of life” (pg. 347)
a. The data are consistent with the hypothesis that all living
organisms inherited their rRNA genes from an ancient
organism or form of life. This unknown ancestor is called (the
last universal common ancestor)
b. At broadest level, all living things seem to be related by
ancestry to one of three major lineages (Domains)
c. Domain Archaea differ greatly from bacteria. Modern Archaea
descended from a unique kind of prokaryotes that existed early
in Earth’s history
2. The three Domains are:
a. Domain Bacteria (Prokaryotes)
b. Domain Archaea (Prokaryotes)
c. Domain Eukarya (Eukaryotic organisms)
C. For the quiz, know some features of each domain
D. Six Kingdoms (Table 17-3, pg. 349)
1. Kingdom Eubacteria (domain Bacteria)
a. True bacteria
2. Kingdom Archaebacteria (domain Archaea)
a. Ancient bacteria
b. Use hydrogen to produce methane (chemosynthesis)
3. Kingdom Protista (domain Eukarya)
a. The kingdom has organisms that are not plants, fungi, or
animals
b. Examples: amoebas, paramecium, and seaweed
4. Kingdom Fungi (domain Eukarya)
a. Fungi absorb rather than ingest nutrients
b. Examples: Mushrooms, mildews, and molds
5. Kingdom Plantae (domain Eukarya)
a. Autotrophic, use photosynthesis
b. Examples: Mosses, ferns, conifers, and flowering plants
6. Kingdom Animalia (domain Eukarya)
a. Heterotrophic organisms that develop from embryos
b. Examples: Sponges, corals, worms, snails, insects, fish, frogs,
snakes, tigers, and humans