BIOLOGY 19.1

Introduction to Kingdoms and Domains

THE SIX KINGDOMS OF LIFE

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 AND CELL WALLS

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

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.

Eukaryotic cell

Prokaryotic cell

BODY TYPE

Body Type:

•Organism are either unicellular (one celled) or multicellular (many celled).

•Two kingdoms consist of only unicellular organisms.

•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.

Multicellular bacteria

Unicellular organism

NUTRITIONNutrition:

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.

NUTRITION

Today, biologists group organisms into six kingdoms based upon their similarities:

•Eubacteria•Archaebacteria•Protista•Fungi•Plantae•Animalia

THREE DOMAINS OF LIFE

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 super-kingdom Eukarya holding all other remaining living organisms.

We call these super-kingdoms the three domains of life: Bacteria, Archaebacteria and Eukarya

THREE DOMAINS OF LIFE

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)

DOMAIN BACTERIA

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 BACTERIACharacteristics 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 BACTERIAKinds 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 ARCHAEAThe 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

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.

KINDS OF ARCHAEBACTERIA

There are three basic kinds of Archaebacteria:

• Methanogens• Extremophiles• Nonextremophiles

methanogens

extremophiles

KINDS OF ARCHAEBACTERIA

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 whereExtremophiles arefound

THE DOMAIN EUKARYYAThe third domain of life, Eukarya, is made up of four kingdoms

•Protista•Fungi•Animalia•Plantae

CHARACTERISTICS OF EUKARYA

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.

KINDS OF EUKARYOTES

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.

KINDS OF EUKARYOTES: FUNGI

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.

EUKARYOTES: PLANTAE AND ANIMALIA

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.

TABLE KINGDOM AND DOMAIN CHARACTERISTICS