Biological classification 2

THE THREE KINGDOM CLASSIFICATION:

This system was proposed by Ernst Haeckel in 1866. He included Protista in this type of classification. He separated unicellular organisms, algae and fungi.  This separation was done on the basis of lack of tissue differentiation. The three kingdoms were Protista, Plantae and Animalia. This classification system was put forward in order to overcome objections and limitations of the Two Kingdom System of Classification.

Haeckel suggested that the variabilities of the two-kingdom system could be avoided by the recognition of a third kingdom, and he proposed Protista as a new kingdom to accommodate organisms exhibiting characters either common to both plants and animals, or unique to their own. Haeckel’s three kingdoms were Animalia, Plantae, and Protista.

                              Ernst Haeckel

According to this system:

·         The arrangement of kingdoms was done on the basis of:

1.   morphological complexities

2.    tissue system

3.   the division of labour, and

4.   mode of nutrition.

·         Unicellular animals, algae and fungi were separated from other organisms on the basis of lack of tissue differentiation.

·         The new group was called the kingdom Protista.

·         Organisms lacking morphological complexities, tissue system, the division

of labor, and enjoying the diversified type of modes of nutrition were segregated and put under the kingdom Protista.

·         Members of the kingdom Protista included the protozoa, fungi, bacteria, and other microorganisms.

·         Later fungi and multicellular algae were taken out from the group.

·         Organisms having diverse tissue-system with well- defined division of labour and maximum morphological complexities in their body remained segregated from protists and were divided into two categories. Those are

1. Autotrophic mode of nutrition: preparation of food by their own. It was considered to be plants and put under kingdom Plantae,

2. Heterotrophic mode of nutrition: Those that have entirely holophagic (phagotrophic) mode of nutrition were considered to be animals and put under kingdom Animalia.

·         According to this system, all known microorganisms came to be recognised as protists; neither plants nor animals.

Objections and limitations:

·         Haeckel’s system was not widely accepted, however, microorganisms continued to be classified as plants (Example: bacteria and fungi) or animals (Example: protozoa).

·         Nucleated and anucleate organisms were kept together in Kingdom Protista.

·         Heterotrophic bacteria and fungi were placed along with autotrophic algae.

Characters	Protista	Plantae	Animalia
Cell type	Eukaryotic	Eukaryotic	Eukaryotic
Cell wall	Present in some	Present	Absent
Modes of nutrition	Photosynthetic	Photosynthetic or heterotrophic	Autotrophic or heterotrophic
Multicellularity	Absent	Present	Present
Examples	Dinoflagellates, Euglenoids, Crysophytes, Protozoans.	Algae, bryophytes, pteridophytes, gymnosperms, angiosperms	Porifera to Chordata

Dinoflagellates

PROTISTA

 Euglenoids

PROTISTA

 Slime molds

PROTISTA

 Gymnosperms

PLANTAE

 Crysophytes

PROTISTA

Bryophytes

PLANTAE

THE FOUR-KINGDOM SYSTEM:

This system of classification was proposed by Stanier and Van Niel and fully developed by Herbert F Copeland in 1956. The four kingdoms in this system are Monera, Protista, Plantae and animalia. The kingdom Monera is comprised of the unicellular organisms. The protists, plants and animals are the eukaryotic organisms. This system of classification rectified certain drawbacks of the three-kingdom system, yet assemblage of fungi, algae and protozoan in one group was not acceptable. The Monerans are prokaryotic organisms. They are autotrophic (chemosynthetic and photosynthetic) and Heterotrophic (saprophytic/parasitic).They do not have cellulosic cell wall. Nuclear envelope is absent.

      Herbert F Copeland

  

Monerans