Nomenclature: Definition and Rules of Binomial Nomenclature
Binomial Nomenclature is a two-term naming system that uses two different terms to name the species, plants, animals and living organisms. Binomial Nomenclature is also known as Binary Nomenclature. The two terms consist of a generic epithet which is genus (category) of that species, and specific epithet which indicates the species itself. This two-term naming system can also use some other different languages to create such scientific names. These scientific names are unique and help in identifying organisms anywhere in the world. Let us learn more about the system of Nomenclature.
What is Nomenclature?
A system through which organisms, including plants, animals, microorganisms and other living things are given distinct scientific names is called Nomenclature.
In biology, each group of organisms, be it plants or animals or microorganisms, is already classified under special divisions, according to the similarities and features. Therefore these living organisms should also have a common naming system that makes it easier to understand them better.
A common system of naming is essential so that it makes it widely accepted throughout the world. And therefore there evolved a system called the binomial nomenclature. This helped to a great extent in maintaining the standardization in naming living things.
Binomial Nomenclature
The Binomial Nomenclature system is a formal system of naming that was introduced by a scientist Carolus Linnaeus. He is regarded as the founder of modern taxonomy. His books are considered as the beginning of modern biological nomenclature. They outlined the rules for allocating names to plants and animals in a certain format.
System and Rules Binomial Nomenclature
In this system, there are certain rules that are followed while naming organisms. This standard set of rules is applicable to plants and animals while giving them unique names within a given system.
According to this system, each organism is known my two names – the Genus name and the species name. These names are all written in Latin. The genus name and species name of an organism written together are called its scientific name. Some rules that are followed while writing these names are mentioned hereunder.
- The name of the genus always begins with a capital letter.
- The species name begins with a small letter.
- The scientific names are always italicized.
- When handwritten, the genus name and species name have to be underlined.
A few examples of names of organisms written in this system
- Homo sapiens ( Human Beings)
- Helianthus annuus ( Sunflower Plant)
- Panthera tigris (Tiger)
- Mangifera indica (Mango Plant)
- Canis lupus familiaris (Dog)
Five Kingdom Classification
Scientists have been trying to classify living organisms in various ways for centuries. In fact, even Aristotle classified living organisms on the basis whether they lived on land, water or air. But biologists wanted a broader system of classifying living organisms. Hence came the five kingdom classification. Let us look at it in detail.
Five Kingdom Classification
Very early on, scientists began grouping the living organisms under different categories. Some biologists classified organisms into plants and animals. Ernst Haeckel, Robert Whittaker, and Carl Woese are some biologists who attempted a broader system of classification. Amongst these, the Five Kingdom Classification proposed by Robert Whittaker stood out and is widely used.
Whitaker proposed that organisms should be broadly divided into kingdoms, based on certain characters like the structure of the cell, mode of nutrition, the source of nutrition, interrelationship, body organization, and reproduction. According to this system, there are five main kingdoms. They are:
Kingdoms are divided into subgroups at various levels. The following flowchart shows the hierarchy of classification.
Kingdom → Phylum → Class → Order → Family → Genus → Species
(Source: Wikipedia)
Browse more Topics under Diversity In Living Organisms
Distinguishing Features of the Five Kingdoms
Kingdom Monera
These organisms are prokaryotic and unicellular. They do not have a well-defined nucleus and also lack cell organelles. Some organisms show the presence of cell wall while there are others without a cell wall. Consequently, some organisms are autotrophic and others are heterotrophic. Examples include Bacteria, Cyanobacteria, and Mycoplasma.
Kingdom Protista
Organisms grouped under Kingdom Protista are all unicellular, but eukaryotic organisms. These are the simplest forms of eukaryotes that exhibit either autotrophic or heterotrophic mode of nutrition. Some organisms have appendages such as cilia or flagella or pseudopodia to move around. Some examples are Diatoms, Protozoans like Amoeba, Paramoecium
(Source: Wikipedia)
Kingdom Fungi
Heterotrophic, Multicellular and Eukaryotic organisms are grouped under Kingdom Fungi. Their mode of nutrition is saprophytic as they use decaying organic matter as food. They have cell walls, which are made up of a substance called Chitin. Fungi also form a symbiotic association with some blue-green algae. Yeast, Mushroom, Aspergillus are examples of Fungi.
Kingdom Plantae
These are Eukaryotic, Multicellular organisms with a cell wall that is made up of cellulose. They are autotrophs and synthesize their own food through the process of photosynthesis. This kingdom includes all plants.
Based on the body differentiation and presence or absence of specialized vascular tissue, Kingdom Plantae is divided into different divisions, namely Thallophyta, Bryophyta, Pteridophyta, Gymnosperms, and Angiosperms. Examples are Spirogyra, Ferns, Pines, and Mango Plant etc.
Kingdom Animalia
This Kingdom includes organisms that are Multicellular, Eukaryotic, without the presence of cell wall. They have a heterotrophic mode of nutrition. They also exhibit great diversity. Some organisms are simple while others have a complex body with specialized tissue differentiation and body organs.
The Animal Kingdom is divided into many phyla and classes. Some of the phyla are Porifera, Coelenterata, Arthropoda, Echinodermata, Chordata etc. Examples – Hydra, Starfish, Earthworms, Monkeys, Birds etc.
Classification and its Types
With the millions of different species and organisms on earth, in various ecosystems, would it be easy to study each one in detail? Of course not! And therefore, there evolved a system of categorizing the organisms into different groups. Let us study this types of classification.
What is Classification?
One look at your surroundings will show you what glaring differences and striking similarities are present in all things around you. There is a multitude of life forms that surround you. Not all plants are same and not all animals, same. There is a great deal of variability amongst the living organisms. This is nothing but biological diversity, a term that shows the variety of life on earth.
Classification of organisms is a systematic method of arranging organisms into different groups and subgroups, based on their similarities and their differences.
Advantages of classification
The foremost advantage of classifying organisms is that it makes the study of a wide variety of organisms very easy and convenient. It also shows the interrelationship between various groups. In biology, there is a basic need to identify organisms correctly and place them in the right category. This helps in learning about the large numbers of organisms in an accurate manner. Classifying organisms also helps in increasing the scope of biological sciences.
Types of Classification
Organisms can be classified on the basis of several different factors. According to this, the different factors include the nature of the cell; the mode of nutrition seen in organisms and also based on the body organization. Broadly, the following are the different types of classification.
1] Cell nature –Are cells Prokaryotic or Eukaryotic?
Depending on whether cells of the organisms are prokaryotic or eukaryotic, organisms can be classified into two categories. Prokaryotic organisms have prokaryotic cells, in which nuclei and cell organelles are not demarcated clearly. Eukaryotic organisms, on the other hand, have eukaryotic cells, which have a clear nucleus and membrane-bound cell organelles.
2] Cells – Do they occur Singly or in Clusters?
Organisms can be divided into unicellular and multicellular organisms. If there is only one cell, then it is a unicellular organism. Amoeba is an example of a unicellular organism. Multicellular organisms have many cells which group together forming specialized tissues. These form a single organism. Every group of specialized cells has a specialized function. Example: worms, insects etc.
3] Mode of Nutrition
Depending on the mode of nutrition, organisms can be classified into autotrophs and heterotrophs. Autotrophs can make their own food, by the photosynthesis process. Heterotrophs cannot make their own food and depend on others for their food.
4] Level of Body Organization
Every organism has specialized body parts and body organization. In plants, the different parts include roots, stems, leaves, branches. And in animals, there are specialized organs that perform various functions of breathing, circulation etc.
Many mnemonic devices can be used to remember the order of the taxonomic hierarchy, such as “Dear King Philip Came Over For Good Spaghetti”.
Taxonomy Definition
Taxonomy is the branch of biology that classifies all living things. It was developed by the Swedish botanist Carolus Linnaeus, who lived during the 18th Century, and his system of classification is still used today. Linnaeus invented binomial nomenclature, the system of giving each type of organism a genus and species name. He also developed a classification system called the taxonomic hierarchy, which today has eight ranks from general to specific: domain, kingdom, phylum, class, order, family, genus, and species.
The Taxonomic Hierarchy
A taxon (plural: taxa) is a group of organisms that are classified as a unit. This can be specific or general. For example, we could say that all humans are a taxon at the species level since they are all the same species, but we could also say that humans along with all other primates are a taxon at the order level, since they all belong to the order Primates. Species and orders are both examples of taxonomic ranks, which are relative levels of grouping organisms in a taxonomic hierarchy. The following is a brief description of the taxonomic ranks that make up the taxonomic hierarchy.
Domain
A domain is the highest (most general) rank of organisms. Linnaeus did invent some of the taxonomic ranks, but he did not invent the domain rank, which is relatively new. The term domain wasn’t used until 1990, over 250 years after Linnaeus developed his classification system in 1735. The three domains of life are Bacteria, Archaea, and Eukaryota. Archaea are single-celled organisms similar to bacteria; some archaea live in extreme environments, but others live in mild ones. Eukaryota, or every living thing on earth that is not a bacterium or archaeon, is more closely related to the domain Archaea than to Bacteria.
Taxonomic ranks are always capitalized, except for species. This allows people to differentiate between bacteria (the organisms; could refer to all bacteria or just two specific bacteria) and Bacteria (the domain, which includes all bacteria).
Kingdom
Before domains were introduced, kingdom was the highest taxonomic rank. In the past, the different kingdoms were Animalia, Plantae, Fungi, Protista, Archaea, and Bacteria (Archaea and Bacteria were sometimes grouped into one kingdom, Monera). However, some of these groupings, such as Protista, are not very accurate. Protista includes all eukaryotic organisms that are not animals, plants, or fungi, but some of these organisms are not very closely related to one another. There is no set agreement on the kingdom classification, and some researchers have abandoned it altogether. Currently, it continues to be revised; in 2015 researchers suggested splitting Protista into two new kingdoms, Protozoa and Chromista.
Phylum
Phylum (plural: phyla) is the next rank after kingdom; it is more specific than kingdom, but less specific than class. There are 35 phyla in the kingdom Animalia, including Chordata (all organisms with a dorsal nerve cord), Porifera (sponges), and Arthropoda (arthropods).
Class
Class was the most general rank proposed by Linnaeus; phyla were not introduced until the 19th Century. There are 108 different classes in the kingdom Animalia, including Mammalia (mammals), Aves (birds), and Reptilia (reptiles), among many others. The classes of Animalia that Linnaeus proposed are similar to the ones used today, but Linnaeus’ classes of plants were based on attributes like the arrangement of flowers rather than relatedness. Today’s classes of plants are different than the ones Linnaeus used, and classes are not frequently used in botany.
Order
Order is more specific than class. Some of Linnaeus’ orders are still used today, such as Lepidoptera (the order of butterflies and moths). There are between 19-26 orders of Mammalia, depending on how organisms are classified—sources differ. Some orders of Mammalia are Primates, Cetaceans (whales, dolphins, and porpoises), Carnivora (large carnivores/omnivores), and Chiroptera (bats).
Family
Family is, in turn, more specific. Some families in the order Carnivora, for example, are Canidae (dogs, wolves, foxes), Felidae (cats), Mephitidae (skunks), and Ursidae (bears). There are 12 total families in the order Carnivora.
Genus
Genus (plural: genera) is even more specific than family. It is the first part of an organism’s scientific name using binomial nomenclature; the second part is the species name. An organism’s scientific name is always italicized, and the genus name is capitalized while the species name is not. Genus and species are the only taxonomic ranks that are italicized. The scientific name for humans is Homo sapiens. Homo is the genus name, while sapiens is the species name. All other species in the genus Homo are extinct. Some were ancestral to humans, such as Homo erectus. Others lived at the same time, were closely related, and interbred with Homo sapiens, such as Homo neanderthalensis, the Neanderthals.
Species
Species is the most specific major taxonomic rank; species are sometimes divided into subspecies, but not all species have multiple forms that are different enough to be called subspecies. There are an estimated 8.7 million different species of organisms on Earth, but the vast majority have yet to be discovered and categorized. While each genus name is unique, the same species names can be used for different organisms. For example, Ursus americanus is the American black bear, while Bufo americanus is the American toad. The species name is always italicized, but never capitalized. It is the only taxonomic rank that is not capitalized. In scientific articles where the species name is used many times, it is abbreviated after the first full use by using just the first letter of the genus name along with the full species name. Homo sapiens is abbreviated to H. sapiens.
Examples of Taxonomy
The scientific classification of humans is as follows:
- Domain: Eukaryota
- Kingdom: Animalia
- Phylum: Chordata
- Class: Mammalia
- Order: Primates
- Family: Hominidae
- Genus: Homo
- Species: sapiens
Another example of taxonomy is the diagram below, which shows the classification of the red fox, Vulpes vulpes (sometimes the genus and species names are the same, even though these are two different ranks).
Many mnemonic devices can be used to remember the order of the taxonomic hierarchy, such as “Dear King Philip Came Over For Good Spaghetti”.
Related Biology Terms
- Taxon – A population of organisms that has been grouped together by taxonomists.
- Binomial nomenclature – A two-part system of naming species; species are referred to by their genus name followed by their species name.
- Taxonomic hierarchy – An ordered group of taxonomic ranks used to classify organisms from general to specific.
- Taxonomic rank – A level of a group of organisms in a taxonomic hierarchy.