The following points highlight the six kingdoms of all organisms. The kingdoms are: 1. Monera 2. Protista 3. Fungi 4. Plantae 5. Animalia 6. Chromista.
Kingdom # 1. Monera:
(i) Most organisms are very simple and prokaryotic (the nucleus is incipient type in which nuclear membrane and nucleolus are absent).
(ii) Generally one-celled microscopic organism.
(iii) Mostly phototrophs and chemotrophs; some are autotrophs and heterotrophs. They can obtain food in liquid state.
(iv) Smallest among the organisms.
(v) Generally 0.1 µm -10(80) µm in length and less than 3 µm in breadth.
(vi) Absence of chlorophyll.
(vii) Absence of mitochondria and vacuole.
(viii) Locomotion by flagella in motile forms.
(ix) Flagella consist of a single fibril (microtubule).
(x) Nervous system absent.
(xi) Reproduction by only binary fission (Asexual usually).
(xii) Mostly decomposer.
(xiii) They occur in possible kinds of habitats.
Example:
Bacteria, Blue green bacteria (Cyanobacteria) and Archaeo- bacteria.
Kingdom # 2. Protista:
(i) Unicellular and eukaryotic.
(ii) Comparatively more complicated than monerans.
(iii) Nutrition holozoic, saprozoic, holophytic or parasitic.
(iv) Typical cell organelles such as nucleus, golgibodies, mitochondria, plastids and endoplasmic reticulum are present. Nucleus single, double or many.
(v) Locomotion by mainly pseudopodia, flagella or cilia.
(vi) Flagella and cilia possess 9 + 2 microtubular structures.
(vii) Conduction of stimuli in some forms.
(viii) Asexual and sexual types of reproduction.
(ix) They are found in freshwater, sea water, or in soil. Mostly are free- living, some are parasitic.
Example:
Diatoms (Bacillariophyta), Dino- flagellates (Pyrrophyta) and all protozoans such as—Euglena, Peranema, Trichonympha, Giardia, Leishmania, Trypanosoma, Chilomonas (flagellates), Amoeba, Entamoeba, Chaos, Arcella, Pelomydea, Euglypha, Actinophrys, Sphaerozoum (Sarcodines), Monocystis, Plasmodium, Gregarina, Nosema, Myxosoma (Sporozoans), and Paramoecium, Colpoda, Didinium, Ephelota, Vorticella, Stentor (Ciliates), etc.
Kingdom # 3. Fungi:
(i) Predominantly multicellular, eukaryotic and heterotrophic organisms; few unicellular (yeasts).
(ii) Body composed of coenocytic hypha except few unicellular fungi.
(iii) Absence of chlorophyll or other photosynthetic pigments.
(iv) Cell wall is composed of chitin or fungi cellulose.
(v) The stored food is the glycogen and fat.
(vi) Mostly non-motile; some lower forms are motile.
(vii) Reproduction by vegetative, asexual and sexual. No vascular system.
(viii) Asexual reproduction by different spores (e.g., motile zoospore, conidia, oidia, chlamydospores, ascorpores, etc.).
Example:
Various kinds of fungi (e.g. moulds, mushrooms, yeasts and others).
Kingdom # 4. Plantae (= Metaphyta):
(i) Green and multicellular plants.
(ii) Body consists of a simple to complex forms.
(iii) Body contains various types of cells and these cells form various organs.
(iv) Cells possess cellulose in the cell wall.
(v) Chlorophylls are single to many forms.
(vi) Starch is the store food.
(vii) They are mostly autotrophs, i.e., they can manufacture their food by the process of photosynthesis with the help of chlorophylls.
(viii) Reproduction by vegetative, asexual and sexual.
(ix) Gametes are either a flagellated or flagellated.
(x) They are found on land, in aquatic medium (freshwater, brackish water and in marine water) and some are found as epiphytes, symbionts or parasites.
Example:
Most of the multicellular algae, bryophytes, pteridophytes, gymnosperms and angiosperms.
Kingdom # 5. Animalia (= Metazoa):
(i) Multicellular, heterotrophic eukaryotes.
(ii) Multicellular bodies either with cellular grade (sponges) or tissue grade (from- Phylum Cnidaria to Phylum Chordata) of organization.
(iii) Body wall is either diploblastic or triploblastic.
(iv) Nutrition is holozoic.
(v) Mostly they have a power of motility; few groups are sessile and sedentary in habit.
(vi) Mostly they have sensory or nervous system except sponges.
(vii) Most of the groups are either aquatic or terrestrial (land). The terrestrial animals may be arboreal (live on trees) or lead to volant life (major part of the time spend in air).
About 34 phyla are placed under the kingdom Animalia.
Some phyla are:
(i) Porifera (e.g., sponges),
(ii) Placozoa (e.g., Trichoplax),
(iii) Cnidaria (e.g., Hydras, jelly fishes and sea anemones),
(iv) Ctenophora (e.g., Ctenophores),
(v) Platyhelminthes (e.g., flat worms),
(vi) Nemertea = Rhynchocoela = Nemertinea (e.g., nemerteans),
(vii) Gnathostomulida (e.g., gnathosto- mulids),
(viii) Entoprocta (e.g., entoprocts),
(ix) Cycliophora (e.g., cycliophorans),
(x) Gastrotricha (e.g., gastrotrichs),
(xi) Nematoda (e.g., round worms),
(xii) Nematomorpha (e.g., horse hair worms),
(xiii) Rotifera (e.g., rotifers),
(xiv) Acanthocephala (e.g., acantho- cephalans),
(xv) Kinorhyncha (e.g., kinorhynchs),
(xvi) Loricifera (e.g., loriciferans),
(xvii) Sipuncula (e.g., sipunculans),
(xviii) Echiura (e.g., echiurans),
(xix) Mollusca (e.g., chitons, snails, bivalves, squids, octopus, nautilus),
(xx) Annelida (e.g., polychaets, earthworms, leeches, etc.),
(xxi) Arthropoda (e.g., prawns, crabs, in-sects, spiders, scorpions),
(xxii) Tardigrada (e.g., tardigrades),
(xxiii) Onychophora (e.g., onychophorans),
(xxiv) Phoronida (e.g., phoronids),
(xxv) Brachiopoda (e.g., lampshells),
(xxvi) Bryozoa = Ectoprocta = polyzoa (e.g., moss animal),
(xxvii) Echinodermata (e.g., starfish, sea urchin, sea cucumbers),
(xxviii) Chaetognatha (e.g., chaetognaths),
(xxix) Hemichordata (e.g., hemichordates),
(xxx) Chordata (e.g., ascidians, lamprey, sharks, fish, amphibians, reptiles, birds and mammals).
Kingdom # 6. Chromista:
Cavalier-Smith (1998) has also proposed six kingdoms for the classification of organisms. He has proposed a new kingdom Chromista for some protozoans. The labyrinthomorphs and opalinids have placed under chromista for the availability of chloroplasts within the endoplasmic reticulum. So there is a trend in the increase of the number of kingdoms.
At present the five kingdoms for classification of the organisms is a best way to many biologists which have follow some distinctive features for the classification.
Brusca and Brusca (2003) have stated that there is a trend to divide the kingdom Monera into two—kingdom Eubacteria (Bacteria) and kingdom Archaea (Archaebacteria) for some distinctive features.
The kingdom Eubacteria possesses a single known polymerase, the peptidoglycan in the cell wall; photosynthesis with the help of chlorophyll in some and without the membrane bound nucleus. The kingdom Archaea contains several polymerases but without membrane bound nucleus and without chlorophyll-based photosynthesis.