Introduction
to Kingdoms
and Domains
Biologists have long organized living
things into large groups called
kingdoms. For example;
hummingbirds, earthworms,
elephants and butterflies are all
members of the animal kingdom.
Given the diversity of life it is easy
to forget that all living things have
many aspects in common.
The following are the key
characteristics that can make it
easier for us to see how these living
organisms relate to each other
within their kingdom classifications;
cell type, cell walls, body type and
nutrition.
Cell Type:
Organisms are either prokaryotes (having
simple prokaryotic cells) or they are
eukaryotes (having more complex eukaryotic
cells).
Scientists generally recognize two kingdoms
of prokaryotes and four kingdoms of
eukaryotes
Eukaryotic cell
Cell Walls:
•In four of the six kingdoms organisms
have cell walls.
•In one of the six kingdoms, organisms
lack cell walls.
•In the remaining kingdoms, some have
cell walls and some do not.
Prokaryotic cell
Body Type:
•Organism are either unicellular (one
celled) or multicellular (many celled).
•Two
kingdoms consist of only unicellular
organisms.
Multicellular bacteria
•Two
other kingdoms have both single
celled and multicellular organisms.
•The
two remaining kingdoms consist
entirely of multicellular organisms, many
of which have tissue and organs.
Unicellular organism
Nutrition:
Many organisms are autotrophs;
organisms that make their nutrients
from inorganic materials. All plants
are autotrophs.
Many other organisms are
heterotrophs; organisms that must
consume other organisms to get
their food. All animals are
heterotrophs.
Three kingdoms consist of both
autotrophic and heterotrophic
organisms. One kingdom consists of
autotrophs. The other two kingdoms
have only heterotrophic organisms.
Today, biologists group
organisms into six kingdoms
based upon their similarities:
•Eubacteria
•Archaebacteria
•Protista
•Fungi
•Plantae
•Animalia
For many decades scientists broke basic
life forms into only two categories;
prokaryotes and eukaryotes, based on
their types of cells.
Than in the late 1970s, scientists realized
that some prokaryotes were so different
from each other that the group needed to
be divided into two separate divisions of
prokaryotes; bacteria and archaebacteria.
Eukaryotes (having complex eukaryotic
cells) than made up the remaining superkingdom Eukarya holding all other
remaining living organisms.
We call these super-kingdoms the three
domains of life: Bacteria, Archaebacteria
and Eukarya
The domain thought to be the oldest is
Bacteria which is composed of the
organisms in the kingdom Eubacteria.
Archaea is the second prokaryotic
domain and is made up of the single
kingdom of Archaebacteria.
The third domain, Eukarya is made up
of all four Eukaryotic kingdoms
•Animalia (animals)
•Fungi (fungi-mushrooms)
•Protista (protists)
•Plantae (plants)
The Domain Bacteria:
The domain bacteria consists of a single
kingdom, the kingdom Eubacteria. The
common name for all it’s members is
bacteria.
Bacteria are prokaryotes that have the same
kind of lipid in their cell membranes as do
eukaryotes.
Bacteria are found in almost every
environment on Earth and affect us every
day in many forms; both good and bad.
Bacteria are similar in structure, with no
internal compartments, and they obtain their
nutrients in several different ways.
Bacteria cell Structure
Characteristics of Bacteria:
Cell wall: bacteria have strong exterior cell
walls made up of peptidoglycan; a web-like
molecule made up of carbohydrate strands
cross-linked by short peptide bridges.
Gene Translation Apparatus:
Scientists can infer (guess) at
evolutionary relationships between
organisms based in part on similarities of
amino acid sequences found in their
proteins (ribosome proteins and RNA
polymerases).
The amino acid sequences found in
bacteria differ widely from those found
in eukaryotes and archaebacteria,
distinguishing them as a separate
domain.
Kinds of Bacteria:
•Bacteria are the most abundant life forms
on Earth. There are more bacteria in your
mouth than mammals on the Earth’s
surface.
•Some bacteria cause diseases while other
bacteria can be used to process our foods;
such as to make yogurt or cheeses.
•Traditionally bacteria have been classified
according to their shape, the nature of
their cell wall, and their type of
metabolism.
•Traditional groupings of bacteria may
change as scientists get more information
from analyzing their RNA and DNA
sequence patterns.
The domain Archaea also contains a single
kingdom, the kingdom of Archaebacteria.
Archaebacteria are prokaryotes that seem to
have diverged very early on from bacteria. They
are more closely related to more complex
eukaryotes than bacteria.
Characteristics of Archaebacteria:
•Cell wall and membrane: The cell walls of
Archaebacteria do not have peptidoglycan, as
the cell walls of bacteria do. Archaebacteria
contain lipids very different than those of
bacteria or eukaryotes.
•Gene Structure: As with the genes of
eukaryotes, the genes of archaebacteria are
interrupted by introns. The ribosomal
proteins (RNA and DNA similarities) of
archaebacteria are very similar to those of
eukaryotes and very different than the
structure of bacteria.
Archaebacteria
The first archaebacteria found by
scientists were discovered in extreme
environments, such as hot springs and salty
lakes.
In recent years scientists have found that
archaebacteria are not only found in
extreme environments, but also in more
common environments.
Several “signature sequences of DNA” have
been found to be in common among all
archaebacteria.
Once identified, these sequences of DNA
have led scientists to find many new
varieties of archaebacteria in even the soil
around us.
There are three basic kinds of
Archaebacteria:
•
•
•
Methanogens
Extremophiles
Nonextremophiles
methanogens
extremophiles
Methanogens are archaebacteria that obtain
energy by combining hydrogen gas and
carbon dioxide to form methane gas.
Methanogens live deep in the mud of swamps
and are poisoned by even traces of oxygen.
Extremophiles live in extreme environments. A
group of extremophiles called thermophiles
live in very hot environments- hot waters up
to 106 degrees Celsius. Halophiles live in
salty lakes that can three times as saltier
than sea waters.
Nonextremophiles are archaebacteria that will
grow in all the environments that bacteria
grow in.
methanogens
Hot spring lake where
Extremophiles are
found
The third domain of life, Eukarya, is made
up of four kingdoms
•Protista
•Fungi
•Animalia
•Plantae
All Eukaryotes have cells with a nucleus and other
internal compartments or organelles. This allows
specialization of functions within a cell.
True multicellularity, in which activities of
individual cells are coordinated with activities of
other cells, occurs only in Eukaryotes.
Sexual reproduction: Although an exchange of
genes occurs in bacteria, the exchange of genes in
eukaryotes is a more regular process. Eukaryotes
have a life cycle that involves sexual reproduction.
Because genes are donated by two parents in sexual
reproduction, the offspring tend to be more
genetically diverse- providing the raw fuel for
evolution to occur.
A wide variety of eukaryotes
are unicellular. Most unicellular
eukaryotes are grouped in the
kingdom of Protista.
Protista contains both
unicellular and multicellular
organisms, many of which are
aquatic.
Protista are grouped together
primarily because they do not
fit any other kingdom of
Eukaryotes.
Fungi are a group of heterotrophs
that are mostly multicellular.
Fungi are composed of cells with
cell walls made of chitin.
One group of fungi, the yeasts, is
unicellular.
Many fungi live on, and decompose,
dead organisms while many other
fungi are parasitic.
Plants and animals (Plantae and
Animalia) are all multicellular
organisms.
Almost all plants are autotrophs,
making their food themselves, and
have cells with cell walls composed
of cellulose.
All animals are heterotrophs,
getting their nourishment from
consuming other organisms, and
their cells do not have cell walls.
Most plants and animals have
tissue and organs.