ICSE Class 6 Biology Chapter 2 Classification of Living Organisms

Unit 2: Classification Of Living Organisms

Learning Objectives

Systems of classification

Nomenclature

Classification of plants

Classification of animals

There are millions of living organisms around us. It is essential to classify them in various groups to make their study easy and systematic. Classification is the process of grouping together organisms on the basis of similarities and differences. Grouping of organisms helps to obtain maximum information about them. The branch of biology that deals with the systemic classification of living things is called taxonomy.

Aristotle, a Greek philosopher who is regarded as the father of biology, was the first person who proposed the method of classification of living organisms. Aristotle divided all living organisms known in his time into two categories - Plants and Animals. He also classified animals on the basis of their habitats - air, land, or water.

Know Your Scientist

Aristotle was a Greek philosopher, a student of Plato and teacher of Alexander the Great. He wrote on diverse subjects, including physics, metaphysics, poetry (including theater), biology and zoology, logic, rhetoric, politics, government, and ethics. Along with Socrates and Plato, Aristotle was one of the most influential of the ancient Greek philosophers. Some consider Plato and Aristotle to have founded two of the most important schools of Ancient philosophy. Aristotle's theory of classification is still considered a milestone in the field of biology.

Aristotle (384 BC - 322 BC)

Systems Of Classification

As more and more plants and animals continued to be discovered, it became increasingly difficult to put them into simple groups on the basis of where they lived or how they appeared from outside. So, taxonomists started to include other similarities such as internal appearances, anatomy, cell composition, etc. to classify living organisms.

There are two basic systems of classification.

The Artificial System

This system tries to classify organisms on the basis of their simple features like habits and habitats, internal similarities, or the way they reproduce, etc. This system is based on mere observation.

The Natural System

In the natural system, more detailed features like developmental history, external and internal structures and their modifications, etc. are also taken into account. This system is considered as the modern system of classification.

It is a hierarchical system of biological classification in which a particular kind of plants or animals are grouped together bearing close resemblance to each other. Many such groups are again put into a bigger group of organisms based on some general similarities, and so on. Like this the world of living organisms is arranged into a concentric system, in which different groups of organisms belonging to the same level form a bigger group of a higher rank, and so on. The similarities become more generalized as the rankings move from a lower level to a higher level. In other words, as we go down the ranking order, the similarities become more and more pronounced.

The major ranks from the highest to the lowest order in biological classifications are:

Kingdom

It is the largest division of living beings. In the early days of classification, the living world was divided into two broad kingdoms of plants and animals. But the systematic growth of scientific studies showed it to be a very simplistic way of categorisation. The modern system of classification divides living organisms into five kingdoms - monera, protista, fungi, plantae (plants) and animalia (animals).

Phylum/Division

Based on some basic similarities, the animal kingdom is divided into many groups called phyla, (singular: phylum). For example, all the animals bearing jointed legs such as ants, butterflies, lobsters and spiders are put into one phylum, Arthropoda. Similarly, the plant kingdom is divided into two divisions, i.e. flowering plants and non-flowering plants.

Class

Organisms belonging to a phylum are again separated into different classes based on the principle of similarities and dissimilarities. For example, all animals which give birth to young ones are put under a class mammalia and all birds that lay eggs or fly are put under a class called aves. Similarly, there are different classes of plants in the plant kingdom.

Order

Each class is divided into different groups called orders. Organisms of one order have much more common features than the organisms of one class.

Family

Under one order of organisms, there are many families. Organisms of one family have more common characteristics than the similarities they share with members of other families. For example, onion and garlic are from one family.

Genus (plural 'genera')

Each family is divided into many genera. Organisms of one genus are much more similar than the other organisms of the same family. For example, cats and tigers are from the same family but they belong to different genera.

Species

The basic unit of classification is the species. It includes a group of animals or plants that bear the closest resemblances and can breed among themselves. For example, the domestic cats we see in our houses belong to one species.

Classification Of Lion

Kingdom: Animalia

Phylum: Chordata (Since it has a neural tube, it is called notochord.)

Class: Mammalia (It has mammary gland and has hair on the skin.)

Order: Carnivora (flesh eating)

Family: Felidae (It has retractive claws.)

Genus: Panthera

Species: Leo

(Biological name: Panthera leo)

Nomenclature

Identification and naming of an organism is an important step in taxonomy. The system of naming an organism is called nomenclature.

In day-to-day life, we refer to animals by their common names in our native languages. But the common names of animals and plants vary widely from region to region and language to language. In India alone, we have hundreds of languages and dialects. The same thing is called by different names in different languages. For example, the onion is known as ponoru in Assamese, piyaz in Hindi, dungari in Gujarati, neerulli and ullagaddi in Kannada, ulli in Malayalm, piaja in Oriya, and vengayam in Tamil.

It is natural that onion is known by different names all over the world. It may be convenient to use the local name for our day-to-day use, but it will become nearly impossible for any scientific study if a plant or animal does not have a uniform name of reference for scientists all over the world.

Keeping in view the problems in common names of organisms, biologists world over worked to devise a uniform system of classification throughout the world. A number of systems were proposed. Finally, Carolus Linnaeus, a Swedish botanist, developed a system of binomial nomenclature. The system has been adopted throughout the world now and an organism is known by a particular scientific name. In binomial system of nomenclature, each organism has two parts in its name. The first part is known as generic name and the second part is known as its specific name. For example, Allium cepa is the name of the onion plant. Here Allium is the name of the genus and cepa is the specific name. As per rule, the generic name always begins with a capital letter and the specific name begins with a small letter.

Know Your Scientist

Linnaeus was a Swedish botanist, physician and zoologist who laid the foundations for the modern scheme of nomenclature. He is now known as the father of modern taxonomy.

Carolus Linnaeus (1707 - 1778)

Linnaeus was born in southern Sweden, on May 23, 1707. He was groomed as a youth to be a churchman, walking in his father's path, but showed little enthusiasm for it. Instead his interest in botany made him the most renowned botanist of his time. Linnaeus's last years were troubled by weak health, and he suffered from gout and tooth aches. A stroke in 1774 greatly weakened him, and two years later he suffered another, losing the use of his right side. He died on January 1778 in Uppsala, during a ceremony in the Uppsala Cathedral. He was buried in the cathedral.

Teacher's Note

Scientific naming helps us identify plants and animals precisely, just like how every person has a unique full name that distinguishes them from others worldwide.

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