Whitaker’s Five Kingdom system and Carl Woese’s three Domain system
Kingdom (Latin: regs, pl. regia) is the second-highest taxonomic rank in biology, after the domain. Kingdoms are further subdivided into smaller groups known as phyla.
When Carl Linnaeus introduced the rank-based system of nomenclature into biology, the highest rank was named “kingdom,” followed by four other main or principal ranks: class, order, genus, and species. Later, two additional major ranks were added, resulting in the sequence kingdom, phylum or division, class, order, family, genus, and species. In the 1960s, a new rank, domain (or empire), was introduced above kingdom, so the kingdom is no longer the highest rank.
Whitaker’s Five Kingdom system
R.H. Whittaker proposed a Five Kingdom Classification in 1969. He named the kingdoms as Monera, Protista, Fungi, Plantae, and Animalia. He uses cell structure, thallus organization, mode of nutrition, reproduction, and phylogenetic relationships as his primary classification criteria. The table compares and contrasts the various characteristics of the five kingdoms.
1) Kingdom Monera – Characteristics
- Unicellular or filamentous prokaryotes
- Omnipresent (air, soil, hot springs, deserts, deepsea, snow and as parasites),
- The cell wall is composed of polysaccharides and amino acids (peptidoglycans or murein)
- Autotrophic (photo and chemosynthetic) and heterotrophic (saprophytic and parasitic). Reproduce by vegetative, asexual and sexual methods
Major groups of Monera
a) Archaebacteria: Methanogens, Halophiles, thermoacidophiles
b) Eubacteria: Vibrio, Mycobacteria
c) Cyanobacteria: Nostoc, Anabaena
2) Kingdom Protista – Characteristics
- Unicellular eukaryotes
- Freshwater, marine, or parasitic forms.
- The cell wall is usually absent if present it is impregnated with silica (diatoms).
- Photosynthetic or nonphotosynthetic.
- The locomotory structure may be cilia, flagella, pseudopodia, or absent.
- Reproduce by sexual and asexual methods.
Major groups of kingdom Protista:
Chrysophyta: Diatom, Pinnularia
Euglenoids : Euglena, Peranema
Slime Moulds: Physaram, Stemonitis
3) Kingdom fungi – Characteristics
- Unicellular or multicellular eukaryotes
- Heterotrophs – Parasites (Puccinia), saprophytes (Agaricus), Symbionts (Parmelia in lichens) and some are associated with the roots of higher plants (mycorrhizal)
- The thalloid plant body is called mycelium
- Mycelium is made up of tubular thread-like hyphae
- The cell wall is made up of chitin.
- Reproduce by
a) Vegetative (fragmentation. fission, budding)
b) Asexual (sporangiospores, conidia )
c) Sexual (Plasmogamy, Karyogamy, and meiosis resulting in the formation of haploid spores like oospore, ascospore, and basidiospore)
Major Group of Kingdom Fungi
a) Phycomycetes: Mucor Rhizopus
b) Ascomycetes (Sac Fungi): Penicillium
c) Basidiomycetes (Club Fungi): Agaricus, Puccinia
d) Deuteromycetes (Imperfect Fungi): Cercospora, Alternaria
4) Kingdom Plantae – Characteristics
- Plants cells have cellulose walls that uphold their size
- They contain chlorophyll A and B and carotenoid pigment. to utilize the sun’s energy.
- Plants store their food in the form of starch
- Plants are a multicellular organism with cells that are specialized to form tissues and organs
- They possess reproductive organs that are shielded by non-reproductive cells to avoid gametes or sex cells from drying up.
- The female reproductive structure of plants supplies nutrients and water to the developing embryo.
- They have a life cycle that displays an alternation of two-generation:
(a) A diploid sporophyte that makes spores by meiosis
(b) A haploid gametophyte that creates gametes and eventually produces a sporophyte by fertilization.
Major groups of tracheophytes
a) Filicinophyta — ferns (Pterophyta)
b) Cycadophyta — cycads
c) Coniferophyta — pines
d) Angiospermophyta — flowering plants (Anthophyta)
5) Kingdom Animalia – Characteristics
- Multicellular – This means that they are made up of more than one cell. Some members of other kingdoms are just made up of one cell, like bacteria or amoeba.
- They are heterotrophic, which means they must obtain their own food. Autotrophic plants produce their own food through photosynthesis. Members of the Animalia Kingdom must ingest, or eat, other organisms because they cannot produce their own food.
- Eukaryote – This is the type of cells animals have. Eukaryote cells are more complex than the simpler prokaryote cells found in bacteria.
- No cell wall – plants, fungi, and prokaryote cells have a cell wall, which is a rigid outer layer that gives cells structure. Animal cells do not have this structure.
Three-Domain System of Carl Woese
1) Domain Archaea
2) Domain Bacteria
3) Domain Eukarya
- Kingdom Fungi or fungi
- Kingdom Plantae or plants
- Kingdom Animalia or animals
- Kingdom Chromalveolate — a group of eukaryotes that represent a descent from an organism that had an endosymbiosis between a line related to a bikont and a red alga. However, the monophyly of this group is challenged.