Biology Today - May 2018

Numerical Taxonomy : It evaluates resemblances and differences through statistical methods based on a large number of characters

obtained from all disciplines of biology.

Cytotaxonomy : It is based on cytological information like chromosome number, structure and meiotic behaviour.

Chemotaxonomy : It uses the chemical constituents of the plants as these are generally specific and stable.

Two Kingdom Classification

• Two kingdom classification system was suggested by Carolus Linnaeus (the father of taxonomy) in 1758.


• The organisms were divided into two kingdoms - Kingdom Plantae and Kingdom Animalia.
  Two kingdom system of classification did not distinguish between the eukaryotes and prokaryotes, unicellular and multicellular and
  photosynthetic (green algae) and non-photosynthetic (fungi) organisms. Hence, two kingdom classification was found inadequate.

Three Kingdom Classification

• Haeckel (1866) separated unicellular animals, algae and fungi from other organisms on the basis of lack of tissue differentiation.
  The new group was called Kingdom Protista.


• Later on fungi and multicellular algae were taken out from the group so that Kingdom Protista came to have only unicellular
  organisms. The organisms were divided into three Kingdoms : Plantae, Protista and Animalia.

Four Kingdom Classification

• With the discovery of electron microscope, it became clear that bacteria and related organisms have a different nuclear
  structure as compared to others.


• They are prokaryotes in contrast to others which have a true nucleus and are called eukaryotes.


• Copeland (1956) created a separate Kingdom Monera for them.


• This divided the living world into four Kingdoms : Monera, Protista, Plantae and Animalia.


• In this system fungi continued to remain with the plantae.

Five Kingdom Classification

• Five kingdom classification was proposed by an American taxonomist, R.H. Whittaker (1969).


• The kingdoms were named Monera, Protista, Fungi, Plantae and Animalia.


• The main criteria for classification used by him include cell structure, thallus organisation, mode of nutrition, reproduction
  and phylogenetic relationships.
  Table: Characteristics of the five kingdoms
  Characters Five Kingdoms
  Monera Protista Fungi Plantae Animalia
  Cell type Prokaryotic Eukaryotic Eukaryotic Eukaryotic Eukaryotic

Cell wall Non-cellulosic

(Polysaccharide + amino acid)

Present in

some

Present (without

cellulose)

Present

(cellulose)

Absent

Nuclear membrane Absent Present Present Present Present

Body organisation Cellular Cellular Multicellular/

loose tissue

Tissue/organ Tissue/organ/

organ system

Mode of

nutrition

Autotrophic (chemosynthetic

and photosynthetic) and

heterotrophic (saprophyte/

parasite)

Autotrophic

(photosynthetic)

and heterotrophic

Heterotrophic

(saprophytic/

parasitic)

Autotrophic

(Photosynthetic)

Heterotrophic

(Holozoic/

Saprophytic

etc.)

Shortcomings of five kingdom classification

• The Kingdoms Monera and Protista are still heterogenous groups. Both include photosynthetic (autotrophic) and non-
  photosynthetic (heterotrophic), walled and wall-less organisms.