KINGDOM CLASSIFICATION
FIVE
KINGDOM CLASSIFICATION
R.H. Whittaker proposed the five-kingdom
classification in 1969. This classification was based upon certain characters
like mode of nutrition, thallus organization, cell structure, phylogenetic
relationships and reproduction. This form
of kingdom classification includes five kingdoms Monera, Protista, Fungi,
Plantae and Animalia.
Five
Kingdom Classification
The five-kingdom
classification that we see today was not the initial result of the
classification of living organisms. Carolus Linnaeus first came up with a
two-kingdom classification, which included only kingdom Plantae and kingdom
Animalia.
The two-kingdom
classification lasted for a very long time but did not last forever because it
did not take into account many major parameters while classifying. There was no
differentiation of the eukaryotes and prokaryotes; neither unicellular and
multicellular; nor photosynthetic and the non-photosynthetic.
Putting all the
organisms in either plant or animal kingdom was insufficient because there were
a lot of organisms which could not be classified as either plants or animals.
All this confusion led
to a new mode of classification which had to take into account cell structure,
the presence of cell wall, mode of reproduction and mode of nutrition. As a
result, R H Whittaker came up with the concept of the five-kingdom
classification.
The five-kingdom classification of living organisms
included the following kingdoms:
Kingdom
Monera
Bacteria are categorized underneath the Kingdom
Monera.
Features
of Monerans
- They
possess the following important features:
- Bacteria
occur everywhere and they are microscopic in nature.
- They
possess a cell wall and are prokaryotic.
- The cell
wall is formed of amino acids and polysaccharides.
- Bacteria
can be heterotrophic and autotrophic.
- The
heterotrophic bacteria can be parasitic or saprophytic. The autotrophic
bacteria can be chemosynthetic or photosynthetic.
Types
of Monerans
Bacteria can be classified into four types based on
their shape:
- Coccus
(pl.: cocci) – These bacteria are spherical in shape
- Bacillus
(pl.: bacilli) – These bacteria are rod-shaped
- Vibrium
(pl.: vibrio) – These bacteria are comma-shaped bacteria
- Spirillum
(pl.: spirilla) – These bacteria are
spiral-shaped bacteria
Monera has since been divided into Archaebacteria
and Eubacteria.
Kingdom
Protista
Features
of Protista
Protista has the following important features:
- They are
unicellular and eukaryotic organisms.
- Some of
them have cilia or flagella for mobility.
- Sexual
reproduction is by a process of cell fusion and zygote formation.
Sub-groups
of Protista
Kingdom
Protista is categorized into subsequent groups:
Chrysophytes:
The golden algae (desmids) and diatoms fall under this group. They are found in
marine and freshwater habitats.
Dinoflagellates:
They are usually photosynthetic and marine. The colour they appear is dependent
on the key pigments in their cells; they appear red, blue, brown, green or
yellow.
Euglenoids:
Most of them live in freshwater habitation in unmoving water. The cell wall is
absent in them, instead, there is a protein-rich layer called a pellicle.
Slime
Moulds: These are saprophytic. The body moves along
putrefying leaves and twigs and nourishes itself on organic material. Under
favourable surroundings, they form an accumulation and were called Plasmodial
slime moulds.
Protozoans:
They are heterotrophs and survive either as parasites or predators.
Kingdom
Fungi
The kingdom fungi include moulds, mushroom, yeast
etc. They show a variety of applications in domestic as well as commercial
purposes.
Features
of Kingdom Fungi
- The
fungi are filamentous, excluding yeast (single-celled).
- Their
figure comprises slender, long thread-like constructions called hyphae.
The web of hyphae is called mycelium.
- Some
of the hyphae are unbroken tubes which are jam-packed with multinucleated
cytoplasm. Such hyphae are labelled Coenocytic hyphae.
- The
other type of hyphae has cross-walls or septae.
- The
cell wall of fungi is composed of polysaccharides and chitin.
- Most
of the fungi are saprophytes and are heterotrophic.
- Some
of the fungi also survive as symbionts. Some are parasites. Some of the
symbiont fungi live in association with algae, like lichens. Some symbiont
fungi live in association with roots of higher plants, as mycorrhiza.
Kingdom
Plantae
Features
of Kingdom Plantae
- The
kingdom Plantae is filled with all eukaryotes which have chloroplast.
- Most
of them are autotrophic in nature, but some are heterotrophic as well.
- The
Cell wall mainly comprises cellulose.
- Plants
have two distinct phases in their lifecycle. These phases alternate with
each other. The diploid saprophytic and the haploid gametophytic phase.
The lengths of the diploid and haploid phases vary among dissimilar groups
of plants. Alternation of Generation is what this phenomenon is called.
Kingdom
Animalia
Features
of Kingdom Animalia
- All
multicellular eukaryotes which are heterotrophs and lack cell wall are set
aside under this kingdom.
- The
animals are directly or indirectly dependent on plants for food. Their
mode of nutrition is holozoic. Holozoic nutrition encompasses ingestion of
food and then the use of an internal cavity for digestion of food.
- Many
of the animals are adept for locomotion.
- They
reproduce by sexual mode of reproduction.
Ø The
five-kingdom classification of living organisms took a lot into consideration
and is till now the most efficient system.
Ø The
older system of classification was based only on one single characteristic
according to which two highly varied organisms were grouped together. For
example, the fungi and plants were placed in the same group based on the
presence of the cell wall. In the same way, unicellular and multicellular
organisms were also grouped together.
Ø Therefore,
all the organisms were classified again into the five kingdoms known as the
five-kingdom classification, starting with Monera, where all the prokaryotic
unicellular organisms were placed together.
Ø Following
that, all the eukaryotic unicellular organisms were placed under the kingdom
Protista.
Ø The
organisms were then classified based on the presence and absence of a cell
wall. The ones without the cell wall
were classified under kingdom Animalia and the ones with cell wall were
classified under kingdom Plantae.
Ø The
organisms under kingdom Plantae were further classified into photosynthetic and
non-photosynthetic, which included Plantae and fungi respectively.
Ø This
system of classification of living organisms is better than following the older
classification of plants and animals because it eradicated the confusion of
putting one species in two different kingdoms.
Six Kingdom classification
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Archaebacteria
Archaebacteria are
single-celled prokaryotes originally thought to be bacteria. They are
in the Archaea domain and have a unique ribosomal RNA type.
The cell
wall composition of these extreme organisms allows them to live
in some very inhospitable places, such as hot springs and hydrothermal
vents. Archaea of the methanogen species can also be found in the guts of
animals and humans.
- Domain: Archaea
- Organisms: Methanogens,
halophiles, thermophiles, and psychrophiles
- Cell Type: Prokaryotic
- Metabolism: Depending
on species, oxygen, hydrogen, carbon dioxide, sulfur, or sulfide may be
needed for metabolism
- Nutrition Acquisition: Depending
on species, nutrition intake may occur through absorption,
non-photosynthetic photophosphorylation, or chemosynthesis
- Reproduction: Asexual
reproduction by binary fission, budding, or fragmentation
EIGHT KINGDOM
The 8 kingdom
classification, by Cavalier-Smith includes the following kingdoms:
Eubacteria
Eubacteria are
prokaryotic microorganisms that have a single cell that lacks a nucleus and one
circular chromosome that contains DNA.
Archaebacteria
- The oldest known living things on
earth are archaebacteria.
- They are categorised as bacteria
because, when viewed under a microscope, they resemble bacteria and are
members of the Monera kingdom.
Archezoa
One of the
kingdom-level taxa postulated by Cavallier-Smith, which is thought to be an
intermediate form between prokaryotes and eukaryotes because it contains the
oldest unicellular eukaryotes with a nucleus and rod-shaped chromosomes but no
mitochondria or plastid.
Protozoa
- A category of single-celled eukaryotes
that feed on organic substances, such as other microbes or organic tissues
and waste, are known collectively as protozoa.
- They can be parasitic or
free-living.
Chromista
Chromista is a kingdom
of eukaryotic organisms that includes single-celled and multicellular species
that have comparable characteristics in their photosynthetic organelles
(plastids).
Plantae
- All plants are included in Kingdom
Plantae.
- These organisms are eukaryotic,
multicellular, and autotrophic.
- A stiff cell wall can be found in
plant cells.
- The pigment chlorophyll and
chloroplast found in plants are necessary for photosynthesis.
Fungi
Fungi are eukaryotic
organisms that include microorganisms such as yeasts, moulds and mushrooms.
Animalia
- Kingdom Animalia constitutes all
animals. Amongst the five kingdoms, the largest kingdom is the animal
kingdom.
- Animals are multicellular
eukaryotes.
- However, like plants, they do not
possess chlorophyll or a cell wall.
- Therefore, members of the animal
kingdom exhibit a heterotrophic mode of nutrition.
Reference
Kingdom Classification According to Whittaker
- Biology LibreTexts
An Overview On
The Five Kingdom Classification (byjus.com)
4.3.1:
Kingdom Classification According to Whittaker - Biology LibreTexts
What are the
8 kingdoms? (byjus.com)
