Kingdom

Kingdom is a taxonomic rank in the biological classification system, or taxonomy, of organisms. It is second only to domain, which is the broadest level of classification. Kingdoms are divided into smaller groups called phyla (or divisions, in plants).

Historically, kingdoms were divided into two main groups: the Animalia (animals) and the Plantae (plants). However, in the modern system of classification, there are five kingdoms: Animalia, Plantae, Fungi, Protista, and Monera. Some scientists also include a sixth kingdom, Archaea, but this is not universally accepted.

Classification

The classification of organisms into kingdoms is based on several factors, including cell type, cell structure, and mode of nutrition.

• Animalia: This kingdom includes all animals. They are multicellular, eukaryotic organisms, which means their cells have a nucleus and other complex structures. Animals are heterotrophic, meaning they obtain their nutrition by eating other organisms.

• Plantae: This kingdom includes all plants. They are also multicellular, eukaryotic organisms, but they are autotrophic, meaning they produce their own food through photosynthesis.

• Fungi: This kingdom includes organisms such as mushrooms, molds, and yeasts. They are eukaryotic and can be either multicellular or unicellular. Fungi are heterotrophic, but unlike animals, they obtain their nutrition by absorbing nutrients from their environment.

• Protista: This kingdom includes a wide variety of organisms, most of which are unicellular and eukaryotic. Protists can be either autotrophic or heterotrophic.

• Monera: This kingdom includes all prokaryotic organisms, which are unicellular organisms that lack a nucleus and other complex cell structures. Monera is divided into two groups: the bacteria and the cyanobacteria (or blue-green algae).

History

The concept of a kingdom in biology was first introduced by Carl Linnaeus in the 18th century. He classified all known organisms into two kingdoms, Animalia and Plantae.

In the 19th century, the German biologist Ernst Haeckel proposed a third kingdom, Protista, for organisms that did not fit into either the animal or plant kingdom.

The five-kingdom system was developed by Robert Whittaker in 1969. He added the kingdoms Fungi and Monera to the existing three kingdoms.

The possible sixth kingdom, Archaea, was proposed in the late 20th century based on genetic evidence that these organisms are fundamentally different from bacteria.

See also

• Taxonomy (biology)
• Biological classification
• Domain (biology)

Kingdom Resources
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