Two, Three and Five Kingdoms Systems of Classification - Home of Knowledge

Two, Three and Five Kingdoms Systems of Classification

Two, Three and Five Kingdoms Systems of Classification

TWO-KINGDOM CLASSIFICATION SYSTEM OF CLASSIFICATION: It is the oldest system of classification put forwarded by Aristotle, the father of biology.

  • kingdom plantae:All organisms that can prepare food from simple inorganic materials and thus can store energy, are autotrophs and are included in kingdom plantae. According to this system, bacteria, fungi and algae were included in kingdom plantae.
  • Kingdom Animalia:Organisms that cannot synthesize their food and depend on autotrophs or others are heterotrophs and are included in kingdom animalia.

Drawbacks of two kingdom system of classification: Some taxonomists found this system unworkable because; many unicellular organisms like Euglena have both plant-like (presence of chlorophyll) and animal-like (heterotrophic mode of nutrition in darkness and lack of cell wall) characters. So there should be a separate kingdom for such organisms. This system also ignores the difference between organisms having prokaryotic and those having eukaryotic cells.

 

Question#10) Who propose the three kingdoms system of classification? Why this system was rejected?

Answer: THREE-KINGDOM CLASSIFICATION SYSTEM: 

In 1866, Ernst Hackel solved the first objection and proposed a third kingdom i.e. protista to accommodate euglena-like organisms. He also included bacteria in kingdom protista. In this system, fungi were still included in the kingdom plantae.

Drawbacks of three kingdom system of classification: This system did not clear the difference between prokaryotes and eukaryotes. Some biologists disagreed about the position of fungi in kingdom plantae. Fungi resemble plants in many ways but are not autotrophs. They are special form of heterotrophs that get their food by absorption. They do not have cellulose in their cell walls rather possess chitin.

 Question#11) Explain the base for establishing five kingdoms of living organisms? Write down the detail of each kingdom?

 

Answer: FIVE-KINGDOM CLASSIFICATION SYSTEM

In 1937, E-Chatton suggested the terms of, “Procariotique” (prokaryotic) to describe bacteria and “Eucariotique”(eukaryotic) to describe animal and plant cells. In 1967, Robert Whittaker introduced the five-kingdom classification system. This system is based on;

Basis for establishing five kingdoms of classification:

  • The levels of cellular organization i.e. prokaryotic, unicellular eukaryotic and multicellular eukaryotic.
  • The principal modes of nutrition i.e. photosynthesis, absorption, and ingestion.

On this basis, organisms are classified into five Kingdoms: monera, protista, fungi, plantae and animalia.

In 1988Margulis and Schwartz modified the five-kingdom classification of Whittaker. They considered genetics along with cellular organization and mode of nutrition in classification. They classified the organisms into the same five kingdoms as proposed by Whittaker.

 

THE FIVE KINGDOMS

The general characteristics of the five kingdoms are as follows ;

  1. Kingdom monera:It includes prokaryotic organisms i.e. they are made of prokaryotic cells. Monerans are unicellular, although some types form chains, clusters, or colonies of cells. Prokaryotic cells are radically different from eukaryotic cells. Most are heterotrophic but some perform photosynthesis because they have chlorophyll in their cytoplasm. Within this kingdom, there are two different kinds of organisms i.e. bacteria and cyanobacteria.
  2. Kingdom protista:It includes eukaryotic unicellular and simple multicellular organisms. There are three main types of protists.
  • Algae are unicellular, colonial or simple multicellular. They resemble plant cells with cell walls and chlorophyll in chloroplasts. Simple multicellular means that they do not have multicellular sex organs and do not form embryos during their life cycles.
  • embryos during their life cycles.
  • Protozoans resemble animals whose cells lack chlorophyll and cell walls.
  • Some protists are fungi-like.
  1. Kingdom fungi:It includes eukaryotic multicellular heterotrophs which are absorptive in their nutritional mode e.g. mushrooms. Most fungi are decomposers. They live on organic material, secrete digestive enzymes and absorb small organic molecules formed by the digestion by enzymes.
  2. Kingdom plantae:It includes eukaryotic multicellular autotrophs. Plants are autotrophic in nutritional mode, making their own food by photosynthesis. They have multicellular sex organs and form embryos during their life cycles. Mosses, ferns and flowering plants are included in this kingdom.
  3. Kingdom Animalia:It includes eukaryotic multicellular consumers. Animals live mostly by ingesting food and digesting it within specialized cavities. They lackcell wall and show movements.

Distinguishing characters of the five kingdoms of life.

Kingdom

Cell Type

Nuclear Envelope

Cell Wall

Mode of Nutrition

Multi-Cellularity

Monera

Prokaryotic

Absent

Non-cellulose

(polysaccharide

plus amino acids)

Autotroph

or heterotroph

Absent

Protista

Eukayrotic

Present

Present in some forms, various types

Photosynthetic or heterotroph, or combination

Absent in most forms

Fungi

Eukaryotic

Present

Chitin

Absorptive

heterotroph

Present in most forms

Plantae

Eukaryotic

Present

Cellulose and other

polysaccharides

Photosynthetic

Present in all forms

Animalia

Eukaryotic

Present

Absent

Ingestive

heterotroph

Present

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