Five Kingdom Classification of Organisms

Five Kingdom Classification

In 1969, Robert H. Whittaker proposed that organisms should be broadly divided into kingdoms, based on certain characters like the structure of the cell, mode of nutrition, the source of nutrition, interrelationship, body organisation, and reproduction.

The kingdoms include –

• • Bacteria are in the Kingdom Monera
  • Protozoa are in the Kingdom Protista
  • Fungi are in the Kingdom Fungi
  • Plants are in the Kingdom Plantae
  • Animals are in the Kingdom Animalia

Basis of Classification

The Whittaker used following basis of classification for organisms to be classified into Kingdom are –

• • Cell Structure
  • Thallus Organisation
  • Mode of Nutrition
  • Mode of Reproduction
  • Phylogenetic Relationships

 

Kingdom Monera

• The Kingdom Monera consists of prokaryotic organisms which includes the most primitive forms of life.

General Characteristics

• Monerans are unicellular and diverse in habitat. Many of them form the decomposer biomass of the ecosystem.
• The nuclear material remains freely suspended in the cellular cytosol. It is called nucleoid or incipient nucleus.
• They lack membrane bound cell organelles like mitochondria, nucleus, chloroplasts, etc.
• The plasma membrane invaginates (folds inside) to form respiratory structure called Mesosome and photosynthetic structure called They contain respiratory and photosynthetic pigments, respectively. Chlorosome are present in some autotrophic bacteria e.g., green sulphur bacteria.
• The cell wall is mainly made up of peptidoglycan (a macromolecule which is a combination of amino acids and sugars), teichoic acid, and lipoprotein.
• Monerans have 70S type of
• They multiply or reproduce They lack true sexual reproduction. They are incapable of gametogenesis, but genetic recombination may occur by the help of conjugation, transformation or transduction.
• The cellular division involves amitosis or Binary Fission, which does not involve the complex mitotic machinery of spindle apparatus formation.
• The principle hereditary material is a circular DNA called There may be other accessory circular DNA molecules present in a Monerans cell, such as plasmids and episomes. Plasmids carry the additional information of the bacteria such as toxin production, antibiotic resistance etc.

Major Monera groups

• Two major groups of Monera include : –
  • Archaebacteria (ancient bacteria) They are extremophiles (found in extreme conditions) and are mostly anaerobic
  • Eubacteria is of further two types; bacteria and cyanobacteria.
• Some other groups of monerans are mycoplasma, rickettsiae and actinomycetes.
• Archaebacteria are of three major types –
  • Methanogens are obligate anaerobes. In bio­gas fermenters, these bacteria produce methane. Eg. – Methanobacterium, Methanococcus.
  • Halophiles are “salt-loving bacteria” as they are found to live in environments with a very high salt concentration.
  • Thermoacidophiles live in extremely acidic environments (pH less than 2) that have extremely high temperatures (upto 110°C). They are found in hot sulphur springs. – Thermoplasm

Mycoplasma

• Mycoplasma, the smallest monerans, are pleomorphic (flexible in shape as they lack cell wall) and are called PPLOs (Pleuro­pneumonia like organisms).
• These are insensitive to antibiotics that affect cell wall synthesis like penicillin because cell wall is absent.
• Mycoplasma can survive without oxygen.
• They can live as saprophytic or are parasitic on humans, plants and animals.

 

Kingdom Protista

• Kingdom Protista includes all the unicellular eukaryotic organisms. Kingdom Protista acts as a connecting link between the prokaryotic Kingdom Monera on one hand and the complex multicellular Kingdoms – Fungi, Plantae and Animalia on the other hand.

General Characteristics

• These are microscopic, unicellular, eukaryotic organisms, with diverse
• Organisms have one or more, well developed nucleus with well-developed membrane bound organelles.
• Mode of nutrition may be parasitic, ingestive, photosynthetic, saprophytic, mixotrophic
• This group includes photosynthetic phytoplankton, non-photosynthetic zooplanktons, and disease causing parasites.
• Some of the individuals have cell wall like peripheral coverings called cellular exoskeleton (present in Marine form generally), sometimes covered by a soft pellicle, but most of them are with plasmalemma only.
• Pseudopodia, flagella (with 9+2 fibril arrangement) and cilia are the principal locomotory organs.
• Contractile vacuoles, present in the cytosol, help in osmoregulation.
• Reproduction occurs generally by asexual methods like – binary or multiple fissions (under favorable conditions), budding, spore Formation (during unfavorable conditions). Sexual reproduction is executed through conjugation or by the fusion of nuclei called syngamy.
• Two types of life cycles are found in protists – Life cycle showing zygotic meiosis (in some dinoflagellates and cellular slime moulds), and life cycle showing gametic meiosis (in majority of protozoan protists, diatoms and acellular slime moulds).

Major Protista groups

• 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 motionless water. The cell wall is absent in them, instead, there is a protein-rich layer called 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

• Fungi is a eukaryotic organism that includes microorganisms such as yeasts, moulds, and mushrooms. These are non-photosynthetic, heterotrophic organisms with diverse forms, sizes and modes of reproduction.

General Characteristics

• These are unicellular or multicellular, organisms, with broad Many of them form the decomposer biomass of the ecosystem.
• They have Cell wall which is composed of chitin and polysaccharides. The nucleus is dense, clear, with chromatin threads. The nucleus is surrounded by a nuclear membrane.
• Fungi consists of long thread-like structures known as hyphae. These hyphae together form a mesh-like structure called mycelium. Hyphae may be septate or aseptate. Multinucleated coenocytic hyphae are commonly present.
• Fungi are They absorb soluble matter from dead organisms and hence they exhibit saprotrophic mode of nutrition. Food material is stored in the form of glycogen.
• Some of them depend on living plants or animals for nutrition and are called Some of them can live as symbionts in association with roots of higher plants as mycorrhiza.
• Fungi produce a chemical called pheromone which leads to sexual reproduction in fungi.
• Reproduction in fungi may be sexual or asexual.
  • Vegetative reproduction – By budding, fission, and fragmentation
  • Asexual reproduction– This takes place with the help of spores called conidia or zoospores or sporangiospores
  • Sexual reproduction– ascospores, basidiospores, and oospores

Major Fungi groups

• The morphology of mycelium, mode of sporogenesis, structure of fruiting body or vegetative body forms the basis for the division of Kingdom Fungi into various groups.
• Fungi include –
  • Zygomycetes (e.g. Mucor, Rhizopus, Albugo etc.),
  • Ascomycetes (e.g. Sacbaromyces, Penicillium, Aspergillus, Claviceps, Neurospora etc.),
  • Basidiomycetes (e.g. Agaricus, Mushrooms; Ustilago, Smuts; and Puccinia, rust fungi),
  • Deuteromycetes are called fungi imperfecti as their perfect stages (sexual stages) are either absent or not discovered so far, g., Trichoderma, Alternaria, etc.

 

Kingdom Plantae

It includes all the plants on the earth. They are eukaryotic, multicellular, photoautotrophic organisms, and have a rigid structure that surrounds the cell membrane called the cell wall.

General Characteristics

• Eukaryotic cells bound by cell wall are present. They are multicellular organisms and contains vacuoles.
• These contain photosynthetic pigment in plastids. They are called as chromoplasts, chloroplasts, or leucoplasts (non-pigmented storage plastids) are present.
• Plant pigments include chlorophyll, carotenes, xanthophylls, phycobillins,
• The principle mode of nutrition is photosynthesis due to the presence of chlorophyll. Due to photosynthetic activity, plants are called producers.
• They are primarily non-motile and live anchored to a base.
• Reproduction is both by sexual (by fertilisation of gametes and formation of seeds) and asexual means (by the formation of spores or by vegetative propagation).
• Growth is indefinite, number and structure of organs are not definite.

Classification

• Different plant groups have been assumed to be originated from ancestral algal cell.
• The plant kingdom has been classified into five subgroups. They are as follows:
  1. 1. Thallophyta
     2. Bryophyta
     3. Pteridophyta
     4. Gymnosperms
     5. Angiosperms
• On the basis of seeds, This Kingdom has been further divided into –
  1. 1. Cryptogamae (plants without seeds) and
     2. Phanerogamae (seed bearing plants).

 

Kingdom Animalia

Kingdom Animalia is composed of all animals. It includes organisms which are multicellular, eukaryotes and do not possess chlorophyll. This group includes great diversity of organisms like mammals, birds, reptiles, fish, worms, insects, etc. which are found in almost all types of ecological habitat.

General Characteristics

• Eukaryotic cells are present and cell wall and central vacuole is absent.
• Heterotrophic holozoic mode of nutrition is found. They are consumers in the ecological trophic level.
• Animals are heterotrophs; they must consume living or dead organisms since they cannot synthesize their own food and can be carnivores, herbivores, omnivores, or parasites.
• Members possess capability of contraction and relaxation of body parts due to the presence of muscle cells, and most of them show locomotion.
• Nerve cells are present which help to transmit impulses in response to external stimuli.
• Body has definite shape and organs are present internally. They follow a definite growth pattern and grow into adults with a definite shape and size.
• Sexual reproduction is predominant, but the lower invertebrate forms also exhibit asexual reproduction through parthenogenesis, budding, or fragmentation.
• A multicellular embryo is formed during development of the zygote.
• Inspite of differences in the structure and form of different animals, there are fundamental features common to various groups in relation to arrangement of cells, body symmetry, nature of body cavity or coelom, patterns of internal systems (circulatory, digestive, reproductive etc.). These features are used as the basis of animal classification.

Classification

• Kingdom Animalia has been classified into ten different subphyla based on their body design or differentiation. The different phylum of the animal kingdom are as follows –

1. 1. Porifera
   2. Coelenterata (Cnidaria)
   3. Platyhelminthes
   4. Nematoda
   5. Annelida
   6. Arthropoda
   7. Mollusca
   8. Echinodermata
   9. Hemichordata
   10. Chordata

Merits and Demerits of Five Kingdom Classification

Merits

• The five kingdom classification gives a clear indication of cellular organization and modes of nutrition, the characters which appeared very early in the evolution of life.
• Autotrophs and heterotrophs are placed in separate groups.
• Prokaryotes have got a separate place as kingdom Monera in five kingdom classification as they differ from other organisms in their cell structure, physiology reproduction mode etc.
• Fungi are placed in a separate kingdom as their mode of nutrition differs from all other plants.
• Separation of intermediate or transitional forms of unicellular eukaryotes into kingdom Protista, so that, the plant and animal kingdoms become more systematic.
• In five kingdom classification, animal and plant kingdoms are more homogeneous than they are in precedence of two-kingdom classification.
• It describes phylogenetic relationships in the living world.

Demerits

• The Monera and Protista kingdoms are still heterogeneous because both include autotrophic and heterotrophic forms and some with or without cell wall.
• Viruses have not been included in this system of classification.
• Unicellular algae are kept in kingdom Protista, whereas multicellular algae are kept in kingdom Plantae. But similar organisms must be put together.
• Archaebacteria differ from other bacteria in structure, composition and physiology.
• Similarly, Mycoplasma are quite different form bacteria where they have been placed along with prokaryotes.
• Phylogeny in lower organisms is not fully reflected.

So, this was all about the Five Kingdom Classification of Organisms. In the Next Post, (Click here) we will learn about Kingdom Monera in Detail. If you want to read more notes of Biology – Click Here.

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