Five - Kingdom System Of Classification

Robert H. Whittaker , in 1996 , proposed a five Kingdom system of classification of organism. In this system, the following three criteria were used for classification.

1) Complexity of cell structure.

2) Complexity of the organism body.

3) Mode of nutrition

Whittaker recognised the following five kingdom:

1) Kingdom Monera

This kingdom comprises prokeryotic single celled organisms. These includes all bacteria possessing ribosomes and a naked, circular strand of DNA that serves as a chromosome, but generally lacking membrane bound organelles such as mitochondria, lysosomes, peroxisomes, and endoplasmic reticulum and a true nucleus. They divided by binery fission rather than mitosis but may undergo genetic recombination. There fossils have been found in rock strata that are 3.5 billion year old. 
Monera is divided into two sub kingdoms:
1) Archaebacteria
2) Eubacteria

2) Kingdom Protista

The kingdom Protista includes all eukaryotic unicellular organisms. Some of these organisms are animal, like protozoans, others resemble plants.
Protists evolved about 1.6 billion year ago. They are extremely complex; their cells show even more diversity than is found among the cells in multicellular kingdoms. Their phylogeny is equally complex and is not yet completely understood.

3) Kingdom Fungi

This kingdom includes multicellular,heterotrophic organisms. Many of these are parasitic on other multicellular forms. Yeasts are a group of exceptional fungai which have a single-celled body. Although they resemble protists in being unicellular, their mode of sexual reproduction indicates their relationship with fungai.
Fungi are at least 400 million years old. Most Fungi posses cell wall made of chitin, an amino- containing polysaccharide.

4) Kingdom Plantae

kingdom plantae includes multicellular, autotrophic organisms. More than 400 million year ago the ancestral forms of today's land plants began to spread through the terrestrial environment.
Plants are characterized by possessing a rigid cellulosic cell wall, and are devoid of locomotion.

5) Kingdom Animalia

Kingdom Animalia includes multicellular, heterotrophic organisms. Most animals prey on other animals and are known as carnivores, whereas some ingest plants and are said to be herbivores. 

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