Transcript Classification

Classification
Chapter 14
Thousands of new species are
discovered every year. In order for
biologists to study all of the
organisms possible, it is necessary
to classify them into groups.
Taxonomy is the branch of biology
that groups organisms according to
their characteristics and
evolutionary history.
Taxonomy started over two thousand years ago with the
Greek thinker Aristotle. Aristotle classed organisms as
either plant or animal. He grouped animals into land,
water, or air dwellers. He groups plants as herbacious,
grass, or woody stems. Aristotle’s main criteria was
external morphology.
As more organisms were
discovered, biologists found that
Aristotles groups were not
adequate. They didn’t show
relationships. And common
names could be confusing.
In the eighteenth century, Carolus Linnaeus
devised a hierarchical system of categories to
classify organisms. For the most part, Linnaeus
used an organism’s morphology to classify it.
Linnaeus’s categories follow:
Domain
Kingdom
Phylum-- Division
Class
Order
Family
Genus
Species
In Linnaeus’s system, the species
name or scientific name has two parts.
The first part is the genus and the
second part is the species or species
identifier. Because of these two part
names, the system is called the
Binomial System of Nomenclature.
The scientific names are latinized so
that they are the same in every
language. We placed in text, they are
underlined or printed in italics.
Botanists sometimes split plant species into varieties and
zoologists sometimes separate animal species into
subspecies.
The Biological Species
Concept states that a species
is a group of individuals that can
produce fertile offspring and are
reproductively isolated from
other species.
Taxonomists now consider a field
of evidence in classification:
Morphology
 Phylogeny
 DNA and Embryology
 Cladistics

Systematics or Phylogeny is a
family tree that shows
evolutionary or phylogenetic
relationships thought to exist
among organisms. This places
organisms into distinct, related
groups.
Evidence used in systematics
includes the fossil record. The
fossil record provides some
distinct framework but careful
systematic investigation is
necessary to fill in the gaps.
Homologous and analogous
characteristics are important
morphology structures to study.
This connects to embryology.
Homologous structures have
the same embryonic origin even
though they may perform
different functions.
Analogous structures have
different embryonic origins even
though they may perform the
same function.
Embryological patterns of development also show
relationships on the phylogenetic tree. Shortly
after the zygote forms in development, mitosis
forms a hollow ball of cells called the blastula.
Shortly, an indentation forms in the blastula called
the blastopore. In most animals, this forms the
anterior part of the digestive system. However, in
echinoderms and vertebrates, the blastopore
forms the posterior part of the digestive system.
This would put these two groups closer to each
other on the phylogenetic tree.
A relatively new field of systematic
classification is called cladistics. Cladistics
uses certain features of organisms called
shared derived characters to establish
relationships. A derived character is a trait
that exists only in the group of organisms
being considered and not in other groups.
This method of classification can be used to
make cladograms to show ancestry.
Kingdoms
(Chapter 19)
The kingdom system of
classification has been changed
by some modern biologists. By
studying ribosomal RNA, they
have divided the organisms of
the world up into three large
domains.
The domains include:
• Archaea
• Bacteria
• Eukarya
Modern biologists use six kingdoms
to classify organisms:






Archaebacteria
Eubacteria
Protista
Fungi
Plants
Animals
The Domain Bacteria contains
one kingdom, the Eubacteria.
This kingdom includes the
bacterial decomposers, soil
components, science
specimens, and pathogens that
we know today.
Bacterial cell walls are
composed of peptidoglycan.
Archaebacteria
These are unicellular prokaryotes with distinctive
cell membrane and other biochemical properties
different from all other forms of life. Some are
autotrophic. These bacteria live in extreme
environments such as hot springs and salt lakes.
They may produce high levels of methane and live
in anaerobic environments such as the intestines
of animals. These organisms probably flourished
before the earth had an oxygen rich atmosphere.
Archaebacteria may be
classified as extreme
thermophiles, extreme
halophiles, or methanogens.
Protista—The kingdom Protista is
made up of a wide variety of
eukaryotic, single celled organisms.
Some may be colonial. The
members of this group are not
exactly plants, animals, or fungi.
The exact reproductive cycle of
many is not known. Some, such as
Euglena, may live as an autotroph
or a heterotroph.
The most ecologically important
protists are probably algae.
They form plankton in the ocean
and make up the base for many
food chains.
Fungi—Fungi are both unicellular
and multicellular heterotrophs that
absorb their nutrients rather than
eating. The exact reproductive
cycle of many of them is unknown
but most are able to involve genetic
recombination. Members include
mushrooms, morels, rusts,
smuts, molds, and yeast.
Many forms of fungus clump
together with strands called
hyphae.
Plantae—These are a wide
variety of modern, multicellular
organisms that use
photosynthesis to organize their
own nutrients. Most plants live
on land and have a sexual life
cycle based on meiosis. They
include mosses, ferns, conifers,
and flowering plants.
One of the most important
developments of plants was the
development of vascular tissue.
Animalia-- Animals are modern
multicellular heterotrophs that
have symmetrical body
organization and move about
their environment. Most all
animals have a sexual
reproductive cycle showing
recombination of genes.
Ninety-nine percent of all
animals are invertebrates.