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.

Solved Question For You

Q: On what basis can you classify plants and animals?

Sol: Plants and animals can be classified on the basis of presence or

absence of cell wall. Plants have a cell wall and animals do not have a

cell wall. Another basis is the mode of nutrition. Plants are autotrophs

(They make their own food). Animals are heterotrophs. (They depend

on others for their food)

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:

● Kingdom Monera

● Kingdom Protista

● Kingdom Fungi

● Kingdom Animalia

● Kingdom Plantae

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)

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.

Solved Questions For You

Q. Pick the correct statement from the following:

1. Fungi are unicellular.

2. Monerans are eukaryotic.

3. Protistans are eukaryotic.

4. Plants and animals are not multicellular.

Ans. Protistans are Eukaryotic is the correct option. Fungi are

microorganisms but are multicellular. Monerans are prokaryotes. And

we all know that plants and animals are multicellular.

Plant Kingdom

Everywhere you see, you see a green cover, with different types of

plants and trees. Plants and plant products are something very familiar

that you use in your everyday life. But, have you ever wondered about

the different types of plants and trees? Did you know that the Plant

Kingdom is divided into several subgroups, with each one having

special features? Delve into the depths of Kingdom Plantae and

unearth some of the fascinating facts.

Characteristic features of Plant Kingdom

These living organisms are made of eukaryotic cells and are

multicellular. The cells have a cell wall which is made of cellulose.

These are autotrophic and synthesize food by photosynthesis due to

the presence of chloroplasts.

Classification of Plant Kingdom

Based on whether plants have a well-differentiated body and the

presence or absence of specialized tissues for transport, and the ability

to bear seeds Kingdom Plantae (Plant Kingdom) is can be classified

into different divisions. The features and examples of each division

are mentioned hereunder.

Division Thallophyta

These are the lowermost plants of the plant kingdom, without a

well-differentiated body design. This means that the plant body is not

differentiated as roots, stem, and leaves. They are commonly called

algae, are permanently aquatic. Examples include Spirogyra, Chara,

and Ulothrix.

Division Bryophyta

These are small terrestrial plants. They show differentiation in the

body design, with stem, leaf-like structures, and root-like structures.

But, they do not have any specialized tissue to conduct water and

other substances. They live in damp and sandy habitats and are often

referred to as the amphibians of the plant kingdom. Examples are

Riccia, Funaria, and Marchantia

Division Pteridophyta

These are supposed to be the oldest vascular plants. The plant body is

differentiated into roots, stem, and leaves, apart from having a

specialized tissue for conduction. This tissue helps in the conduction

of water and other substances from part of the plant to the other.

These plants have naked embryos called spores. The reproductive

organs in these plants are inconspicuous. Examples: Marselia, Ferns

(Source: Wikipedia)

Division Phanerogamae

Phanerogams are seed-bearing plants. The plant body is well

differentiated with stem, leaves, and roots. There are well

differentiated reproductive tissues that produce seeds. These plants

also have a well-developed vascular system.

Depending on whether the seeds produced are naked or whether they

are enclosed, phanerogams are further classified into two subdivisions.

They are Gymnosperms and Angiosperms

Gymnosperms

Gymnosperms are plants with naked seeds. There are about 650 living

species of gymnosperm plants. The plants are usually perineal,

evergreen and woody.

They have a well-developed vascular tissue but do not have vessels.

The reproductive organs generally form cones or strobilus. There is no

fruit formation and the seeds are hence said to be naked. Examples:

Cycas, Pinus, Deodar

Pine Cone (Wikimedia Commons)

Learn about Gymnosperms in more detail here

Angiosperms

Angiosperms are seed-bearing plants. Seeds develop inside tissues that

get modified to form the fruit of the plant. Also called the flowering

plants, they are found abundantly in nature. These plants are usually

terrestrial and they may be annual, biennial or perennial. The vascular

system is very well developed with xylem and phloem. Angiosperms

also show the feature of double fertilization. Examples: Mustard plant,

Pea plant.

On the basis of the cotyledons (seed leaves) Angiosperms are further

divided into Monocotyledonous plants and Dicotyledonous plants.

Monocots have seeds with single seed leaf, having vascular bundles

arranged in a complex manner. Dicots, on the other hand, have two

cotyledons. The vascular bundle is arranged in a ring.

Learn more about the Animal Kingdom here.

Solved Questions For You

Q: Specialized tissue for conduction of water and other substances is

present in which of the following?

a. Gymnosperms

b. Pteridophyta

c. Both of these

d. None of these

Ans: The correct option is “C”. Gymnosperms and Pteridophytes both

have a specialized vascular tissue. Learn more about Pteridophytes in

detail here.

Q: Thallophyta, Bryophyta, and Pteridophyta are together called as?

Ans: They are called as Cryptogams as they are non-seed bearing

plants.

Animal Kingdom

Scientists predict that only 15% of species are known to man from the

estimated 8.7 million species. That leaves almost 85% species yet to

be discovered. Only about 953,434 species of animals have been

catalogued in the Animal Kingdom. Let us study this classification of

animals.

Classification of Animals and Plants

There are millions of living organisms in this world. There are some

which are even yet to be discovered. These living organisms that are

known to man, very broadly include animals, plants, microorganisms

etc. All of them show great diversity. Yet, there are some

characteristics that are similar between groups of organisms and this is

what binds them together.

Classification of animals helps us to understand their characteristics,

as well as their differences with other organisms. The best-known

organisms are the animals. In scientific terminology, they are grouped

under the Kingdom Animalia, better known as the Animal Kingdom.

Let us learn more about this famous Kingdom!

Animal Kingdom

Kingdom Animalia consists of organisms that range from the simplest

of the animal forms to the most complex. At one end of this

classification of animals, you have the microscopic organisms. And at

the other end, you see animals that you probably come across in your

daily life. You and your friends, for example, are members of the

Animal Kingdom. Your pet dog, bird, cat or even those pesky insects

that you find in the gardens are all part of this gigantic kingdom.

Scientifically speaking, all organisms that belong to this Kingdom are

Eukaryotic organisms. They are all multicellular, with many cells

present. The cells do not have cell walls in them. Another important

feature is that they have a heterotrophic mode of nutrition, which

means that they cannot make their own food.

The Different Phyla

Classification of animals is termed as Kingdom Animalia. It is further

divided into different phyla. These are nothing but divisions in which

animals/organisms with the same characteristics are included under

them. Apart from the primary distinguishing features of the Animal

Kingdom (Eukaryotic, Multicellular, without a cell wall and

heterotrophic); each phylum has organisms that have common

characteristics. In the classification of animals chart, they move from

the simplest to the most complex.

The different phyla in the classification of animals are as follows:

● Phylum Porifera

● Phylum Coelenterata

● Phylum Platyhelminthes

● Phylum Nematoda

● Phylum Annelida

● Phylum Arthropoda

● Phylum Mollusca

● Phylum Echinodermata

● Phylum Protochordata

● Phylum Vertebrata

Let us now look at some important features of each Phylum.

Phylum Porifera

These are the simplest multicellular animals, found mainly in marine

habitats. These organisms have pores all over the body. They have a

canal system that helps in circulating water and food particles and

oxygen. The body design shows minimal differentiation and division

of tissues. Commonly called as Sponges, some of the examples are

Spongilla, Sycon etc.

Phylum Coelenterata

These organisms show more body differentiation. They live in water.

The body has a sac-like cavity, with a single opening for ingestion an

egestion. These animals have two germ layers and hence are called

diploblastic. You can see these animals living solitarily or n colonies.

Examples include Jellyfish, Sea Anemone, and Hydra.

(Source: Wikipedia)

Phylum Platyhelminthes

These are commonly called flatworms. Their bodies are flattened

dorsoventrally. They are the first triploblastic animals, with three germ

layers. The body is also bilaterally symmetrical, with both the left and

right halves of the body having the same design. Flatworms can be

either parasitic or free living. A few examples are Planaria, Liver

Fluke, and Tapeworm.

Phylum Nematoda

The bilateral symmetry and triploblastic nature continue in these

animals. The body, however, is more cylindrical and not flattened.

The body cavity is not a true coelom. And hence it is called a pseudo

coelom. Tissues are present, but organs are absent. These organisms

show a complete alimentary canal which is straight. Most of these

organisms belonging to this phylum are parasitic worms, which cause

diseases. Examples are Ascaris, Wucheria.

Phylum Annelida

Annelids are found in different habitats, such as land, fresh water, and

even marine mater. They have a bilaterally symmetrical body with

three germ layers (Triploblastic). A distinguishing feature here is that

they have a true body cavity. The body is also segmented with some

organ differentiation seen. Examples are Earthworms, Leeches.

Phylum Arthropoda

They make up the largest group in the animal kingdom. Most of the

insects are included in this phylum. “Arthropoda” means jointed legs.

The bodies of these animals are divided into head, thorax, and

abdomen. Apart from the jointed legs, they also have a pair of

compound eyes. Another distinguishing feature of these animals is the

presence of an open circulatory system. Examples are butterfly

housefly, spiders, mosquitoes, crabs etc.

Phylum Mollusca

The bilateral symmetry and the triploblastic nature of the body layers

are seen here too. Molluscans form a very diverse group and form an

important part of the ecosystem. These animals can be seen aquatic

habitats. They can be either marine or freshwater species. The body

does not show much segmentation and the coelomic cavity is also

reduced. The body is typically divided into anterior head, ventral

muscular foot, and a dorsal visceral mass. The foot helps in the

locomotion of the animals. Examples are Snails, Mussels, and

Octopus.

Phylum Echinodermata

Moving on with the classification of animals we come to Phylum

Echinodermata. Echinoderms are animals with spiny skin. They live

exclusively in a marine habitat. They are free-living animals. The

larvae show bilateral symmetry whereas the adults show radial

symmetry. These animals are triploblastic and have a coelomic cavity.

They have a peculiar water driven tube system that helps them in

moving around. They also have a hard exoskeleton that is made up of

calcium carbonate. Examples are Starfish, Sea cucumber, Sea Urchin.

Phylum Protochordata

The protochordate animals are bilaterally symmetrical and

triploblastic. They have a coelom. A new body feature that is seen in

these animals is the presence of notochord at some stage in their life

cycle. Due to this very presence of a notochord, they are called as

chordates. However, it is sometimes rudimentary. They are

exclusively marine animals. Examples include Herdmania,

Balanoglossus.

Phylum Vertebrata

These are the advanced group of animals, showing some really

advanced features of a proper digestive system, circulatory system etc.

There is a complex differentiation of body tissues and organs. These

animals have a true vertebral column with an internal skeleton. All

chordates have the following features:

● Notochord

● Dorsal Nerve Cord

● Post-anal tail

● Pharyngeal slits

Phylum Vertebrata is classified into five classes. They are:

1. Pisces

2. Amphibia

3. Reptilia

4. Aves

5. Mammalia

Class Pisces

These are exclusively aquatic animals, commonly called as Fish. Their

skin is covered by scaly plates. The body is streamlined. A muscular

tail helps in the movement. Respiration occurs through gills. The heart

is present with two chambers. Examples are Tuna, Rohu, Anglerfish,

and Electric ray.

Class Amphibia

Amphibians can live both on land and in water. They have mucus

glands in the skin. The heart is three chambered, with respiration

occurring through gills or lungs. They are egg-laying animals, with a

distinctive head and trunk. Examples are Frogs, Toads, and

Salamander.

Class Reptilia

Reptilians are cold-blooded animals, which have scales on their body.

They breathe through lungs. In most of these animals, the heart is

three chambered, with the exception of crocodiles, which have a

four-chambered heart. Examples are Snakes, turtles, Crocodiles etc.

Class Aves

They are warm-blooded animals with the body being covered by

feathers. The forelimbs are modified into wings. They have a

four-chambered heart. They breathe through lungs. And they lay eggs.

All birds are classified under this class. Examples are Parrot, Crow,

and Ostrich.

Class Mammalia

Mammals are warm-blooded with a four-chambered heart. They have

mammary glands. Their skin has sweat and oil glands. They give birth

to young ones. Respiration occurs through lungs. Examples are human

beings, gorilla, and cow.

Solved Questions For You

Q: What are the smallest birds and the largest birds?

Ans. Smallest Bird – Humming Bird; Largest Bird – Ostrich

Q: Centipedes and prawns belong to phylum Annelida. Is it true?

Ans. False. Centipedes and Prawns belong to the Phylum Arthropoda,

as they show the characteristic features of jointed legs; bodies of these

animals are divided into head, thorax, and abdomen.

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.

Carl Linnaeus ( Wikipedia)

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)

Solved Questions For You

Q: What is the scientific name of the tiger? Are there any advantages

of using scientific names?

Ans: The scientific name of the tiger is Panthera tigris.

There are advantages in using a standard and scientific way of naming

organisms. These names are unique and widely accepted throughout

the world. The nomenclature system is also guided by the rules laid

down in the International Code of Biological Nomenclature.

Q: Define Binomial Nomenclature.

Ans: A standard and widely accepted system of naming plants and

animals is the binomial nomenclature. It involves the naming an

organism with the help of two names, the genus name, and the specific

name. Example – Mangifera indica is the scientific name of the

mango plant.