Different Systems of Classification

Early Taxonomists

2000 years ago, Aristotle was the first taxonomist Aristotle divided organisms into plants & animals

He subdivided them by their habitat —land, sea, or air dwellers.

Biological classification is a scientific procedure that includes arranging organisms into a hierarchical series of groups and sub-groups based on their similarities and non-similarities.

Need of Classification

It is necessary to classify organisms for several reasons. Aristotle was the first scientist to make an effort for scientific basis of classification. There are millions of species of plants. Plants are divided based on simple morphological features to classify plants such as trees, shrubs, or herbs. When we  study the character of a particular class, we get information about all the plants coming under it.

Organic evolution is the main evidence.

To give knowledge of new plant discoveries.

To give knowledge of plant arrangement.

A plant found in a particular environment is feudal in size or organs. like – Algae, Fungi

What is Classification?

Arrangement of organisms into orderly groups based on their similarities. Classification is also known as taxonomy. Taxonomists are scientists that identify & name organisms

Carolus Linnaeus (1707 – 1778)

18th century taxonomist Classified organisms by their structure.

Developed naming system still used today

Called the “Father of Taxonomy”

Developed the modern system of naming known as binomial nomenclature

Two-word name (Genus & species)

Standardized Naming

Binomial nomenclature used

Genus species

Latin or Greek

Italicized in print

Capitalize genus, but NOT species

Underline when writing

Rules for Naming Organisms

The International Code for Binomial Nomenclature contains the rules for naming organisms

All names must be approved by International Naming Congresses (International Zoological Congress)

This prevents duplicated names

Classification Groups

Taxon ( taxa-plural) is a category into which related organisms are placed. There is a hierarchy of groups (taxa) from broadest to most specific Domain, Kingdom, Phylum, Class, Order, Family, Genus, species

Classification Systems  

There are three main types of classification systems.

1.Artificial System- The artificial system consists of knowledge of the colour, form, shape, size, location, and use of animals for humans. one or more examples of artificial systems are: Aquatic Animals, Terrestrial Animals, Domestic Animals, Useful Animals, and Parasitic animals.

2.Natural System- Linnaeus produced the book Systema Naturae in 1758, in which he described a special term for scientific names of organisms, which we call binomial nomenclature. Linnaeus is the father of Modern Taxonomy.

3.  Phylogenetic System- Based on phylogeny in this system  organisms are divided into Animalia, Plantae, Protista, Monera and Fungi.

Types of Classification System

Linnaeus classification system divides all living organisms into two kingdoms. These are Plantae and Animalia. 

Kingdom Plantae

These are multicellular organisms. Cellulose is present around the cells or vacuoles are found in cells.  They make their food by photosynthesis that is these group organisms are autotrophs. They stored food in the form of starch. These cells are Eukaryotes. The cell wall is present. Such as –  Algae, Fern.

Kingdom Animalia 

These are multicellular animals. Animalia group of organisms are not making their food by Photosynthesis. There has no cell wall. There are no inorganic crystals available in their cells. The central vacuole is absent. Growth is limited and well-defined growing points are not present. Only a heterotrophic mode of nutrition is available. Excretory organs are present such as-nervous system and sense organs. glycogen is used as reserve food. 

Three Kingdom Classifications

J. Hogg and Ernst Haeckel, 1860. The idea of ​​Kingdom Protista for all unicellular organisms and Kingdom Plantae or Metaphytes for multicellular plants and Kingdom Animalia or Metazoa for multicellular animals in the three kingdom system, in 1860.

Four Kingdom Classifications

After the three Kingdom classifications, the suggestion of four Kingdom classifications was observed. In this classification, the kingdom of Monera or Protista was recognized in place of Protoctista by Herbert F. Copeland in 1938. Later, Fungi was also placed in the kingdom Fungi before Plantae which gave Five Kingdom Classifications.

1. Kingdom Monera

These are unicellular prokaryotes cell incipient Nucleus is present. for example- Bacteria, Cyanobacteria

 2. Kingdom Protista

These are unicellular and colonial. They are Eukaryotes Nucleus Is present in the kingdom Plantae. Many protist organisms live in water, and many protists live in moist soil or even in the body of humans and plants. Motion is often by flagella or cilia. For example-Amoeba, Euglena

3. Kingdom Fungi

These are multicellular and Heterotrophic organisms. Mycelium is present. The Cell Wall is made up of Chitin. Photosynthesis is absent. Such as-Rhizopus.

Five Kingdom Classifications

This classification was established in 1969 by American scientist R.H. Whittaker. There were the main criteria for classification: 

Cell Structure-Cells are of two types. One is eukaryotes and the second is prokaryotes.

In eukaryotes nuclei are present while missing in prokaryotic cell.

Body Structure- one or more organisms are unicellular and multicellular,

Life cycle of organisms, phylogenetic relationship, reproduction.

Property	Monera	Protista	Fungi	Plantae	Animalia
Cell Type	Prokaryotes	Eukaryotic	Eukaryotic	Eukaryotic	Eukaryotic
Cell wall	Polysaccride+ amino acid is the main component of the monera cell wall	Present	Made up of Chitin	Made up of Cellulose	Absent
Structure Complexity	Unicellular components	Unicellular	Multicellular	Multicellular	Multicellular
Mode of Nutrition	Chemosynthetic Autotropic/heterotropic	Autotrophic/heterotropic	Heterotropic	Autotropic	Heterotropic

Six Kingdom Classifications

Carl Woese gave the Six Kingdoms classification system in the year 1990. He was a professor in the Department of Microbiology at the University of Illinois. It was also called the three-domain system because it classified organisms into three domains, that is, Archaea, Bacteria, and Eukarya.

It mainly used the basic principles of the Five Kingdom system but split Monera into two domains Archaebacteria (Archae), Eubacteria (Bacteria), and other Eukaryotes in the Third domain.

1. Archaea: Archaebacteria include prokaryotic organisms and they are unicellular. These consist of a monolayer core of lipids in the cell membrane and their 16S RNA containing different nucleotides. These are methanogens, halophiles, or thermoacidophiles. 

2. Bacteria: The bacterial domain contains typical prokaryotes that lack membrane-covered cell organelles. They do not contain microchambers to separate the different metabolic activities. It has a single kingdom-Eubacteria.

Kingdom-Eubacteria: The members of this kingdom have peptidoglycan cell walls all, naked DNA in coiled form, and glycogen food reserves. There is no sap vacuole and 70S ribosomes are present. The members of this kingdom are bacteria, mycoplasma, actinomycetes, rickettsiae, spirochaetes, cyanobacteria, and firmicutes.

3. Eukarya: The domain eukarya contain all the eukaryotes. The four kingdoms of this domain are:

•Protista

•Animalia

•Plantae

•Fungi

Hence, organisms have been divided among three domains: Bacteria (the true bacteria or eubacteria), Archaea, and Eucarya (all eukaryotic organisms).

1. Bacteria are prokaryotes that are usually single-celled organisms. Most have cell walls that contain the structural molecule peptidoglycan.

They are abundant in soil, water, and air, and are major inhabitants of our skin, mouth, and intestines. Some bacteria live in environments that have extreme temperatures, pH, or salinity.

Although some bacteria cause disease, many more play beneficial roles such as cycling elements in the biosphere, breaking down dead plant and animal material, and producing vitamins.

Cyanobacteria (once called blue-green algae) produce significant amounts of oxygen through the process of photosynthesis.

2. Archaea are procaryotes that are distinguished from Bacteria by many features, most notably their unique ribosomal RNA sequences.

They lack peptidoglycan in their cell walls and have unique membrane lipids.

Some have unusual metabolic characteristics, such as the methanogens, which generate methane gas.

Many archaea are found in extreme environments, including those with high temperatures (thermophiles) and high concentrations of salt (extreme halophiles).

Pathogenic archaea have not yet been identified.

3. Eucarya includes microorganisms classified as protists or fungi. Animals and plants are also placed in this domain.

Protists are generally unicellular but larger than procaryotes. Photosynthetic protists, together with the cyanobacteria, produce about 75% of the planet’s oxygen. These phytoplankton are the foundation of aquatic food chains.

Protozoa are unicellular, animal-like protists that are usually motile. Many free-living protozoa function as the principal hunters and grazers of the microbial world. They obtain nutrients by ingesting organic matter and other microbes. They can be found in many different environments, and some are normal inhabitants of the intestinal tracts of animals, where they aid in digestion of complex materials such as cellulose. A few cause disease in humans and other animals.

Slime molds are protists that are like protozoa in one stage of their life cycle but like fungi in another. In the protozoan phase, they hunt for and engulf food particles, consuming decaying vegetation and other microbes.

Fungi are a diverse group of microorganisms that range from unicellular forms (yeasts) to molds and mushrooms.

Molds and mushrooms are multicellular fungi that form thin, threadlike structures called hyphae. They absorb nutrients from their environment, including the organic molecules that they use as a source of carbon and energy.

Because of their metabolic capabilities, many fungi play beneficial roles, including making bread rise, producing antibiotics, and decomposing dead organisms. Some fungi associate with plant roots to form mycorrhizae.

Mycorrhizal fungi transfer nutrients to the roots, improving the growth of the plants, especially in poor soils.

Other fungi cause plant diseases (e.g., rusts, powdery mildews, and smuts) and diseases in humans and other animals.