(1) All organisms on the earth are different. They differ in height, colour, food, habitat etc.
Eg:- The range of variations that we see in life – forms around us are given below –
(i) Some pine trees live for thousands of years while insects like mosquitoes die within a few days.
(ii) Life also ranges from colourless or even transparent worms to brightly coloured birds and flowers.
(iii) Microscopic bacteria have size of few micrometer while blue whale is the largest fish.
(2) Greek thinker Aristotle classified animals on the basis of their habitat, ie, water, land or air.
But, it is not always correct because animals which live in same habitat are different in many ways.
Eg:- Sea animals fish, corals octopus, crocodiles etc. live in the sea but have different characteristics.
Therefore, we need sub division on the basis of characteristics.
Hierarchical classification on the basis of characteristics –
(i) Nucleus can be a basis of the classification of the cell.
Some cells have nucleus which allow cellular processes to be carried out efficiently in isolation from each other. But some cells do not have nucleus and they have their biochemical pathways organised in very different ways.
(ii) Cells have different designs in unicellular organism and multicellular organisms.
Eg:- Amoeba is a single cell organism and worm etc. are multicellular cell organisms. Both have different body design of cells.
(iii) Design will be different for cells which are able to produce own food and which take food from outside.
(iv)Cells are different in animals which are used for specialised functions.
Classification of organism makes study of organisms essay because organisms are classified according to their different characteristics.
(3) Classification and Evolution
The characteristics that came into existence earlier are more basic than characteristics that have come into existence later for classification. It means that classification of life forms will be closely related to their evolution.
Charles Darwin first described idea of evolution in 1859 in his book “The Origin of Species”.
The change in characteristics of spices over many generations with natural selection to survive better is known as evolution.
How to do classification with evolution –
(i) Some organisms have ancient body design and considered as primitive group.
(ii) Some organisms have relatively recent body design and considered as advanced group.
But, this classification is not proper because they do not relate to the proper difference.
(4) The Hierarchy of Classification of groups –
Biologists Ernst Haeckel (1894), Robert Whittaker (1969) and Carl Woese (1977) classified all living organisms into broad group called kingdoms.
Whittaker proposed five kingdoms on the basis of cell structure, mode and source of nutrition and body organisation. Woese modified this classification by dividing the Monera into Archaebacteria (or Archaea) and Eubacteria (or Bacteria) is also in use.
These kingdoms are –
This kingdom is further divided in to sub groups as given below –
Species is a basic unit of classification. A species includes all organisms that are similar enough to breed and perpetuate.
(a) These organisms do not have a defined nucleus or organelles.
(b) These organisms do not show multi – cellular body designs. These are unicellular prokaryotes.
(c) Some of them have cell wall and some of them do not have cell – wall.
(d) These organisms get nutrition either by synthesising their own food (autotrophic) or from the environment (heterotrophic).
(e) Eg;- Bacteria, blue – green algae or cyanobacteria, and mycoplasma.
(a) This group includes many kinds of unicellular eukaryotic organisms.
(b) Some of these organisms use appendages (hair like cilia or whip like flagella for moving around).
(c) The mode of nutrition of these organisms can be autotrophic or heterotrophic.
(d) Eg:- Algae, diatoms and protozoans
(a)These are eukaryotic organisms.
(b) The mode of nutrition of these organisms is heterotrophic. Some of them use decaying organic material as food and are therefore called saprotrophs.
(c) Some organisms are parasites. They require living protoplasm of a host organism for food.
(d) Many of them can become multicellular organisms at certain stages in their lives.
(e) They have cell walls made of a tough complex sugar called chitin.
(f) Eg:- Yeasts, molds and mushrooms
(g) Some fungal species live in permanent mutually dependent relationships with blue green algae which is called symbiotic relationship. These symbiotic life forms are called lichens.
(a)All plants are included in this group.
(b) These are multicellular eukaryotes with cell walls.
(c) The mode of nutrition of these organisms is autotrophs and they use chlorophyll for photosynthesis.
Classification of Plantae
(a) Thallophyta is the division of plantae.
(b)Plants that do not have well – differentiated body design fall in this group.
(c) The plants in this group are commonly called algae.
(d) These plants are predominantly aquatic.
(e) Eg:- Spirogyra, Ulothrix, Cladophora, Ulva and Chara.
(a) These are called the amphibians of the plants kingdom.
(b) The plant body is differentiated to form stem and leaf like structures.
(c)The organism of this group do not have specialised vascular tissue for the transportation of water and other substances from one part of the plant body to another.
(d) Eg:- Moss (Funaria) and Marchantia.
(a) The plant body is differentiated to form stem and leaf like structures.
(b) The organism of this group have specialised vascular tissue for the transportation of water and other substances from one part of the plant body to another.
(c) Types or examples of petridophyta are Marsilea, ferns and horse – tails.
(d) The reproductive organs are not visible and are called ‘cryptogams’.
(a)The plants with well – differentiated reproductive parts that ultimately make seed are called phanerogams.
(b) Seeds consist of the embryo along with stored food, which assists for the initial growth of the embryo during germination.
Classification of the phanerogams-
(a) The term is derived from two Greek words: gymno means naked and sperma means seed.
(b) The plants of this group bear naked seeds.
(c) The plants are perennial, evergreen and woody.
(d) Eg:- Pines and deodar
(a) The term is derived from two Greek words: angio means covered and sperma means seed.
(b) These are also called flowering plants.
(c) The seeds develop inside an ovary which becomes fruit.
(d) The structures in plant embryos in seeds are called cotyledons which are also called “seed leaves” because in many instances they emerge and become green when the seed germinates.
Classification of angiosperms
Monocotyledonous or monocots – These plants with seeds having a single cotyledon.
Eg:- Sugar cane, banana, bamboo, onion etc.
Dicots – Plants with seeds having two cotyledons.
Eg:- Rose, oak etc.
(a) These are eukaryotic organisms.
(b) These are multicellular.
(c) The mode of nutrition is heterotrophic.
(d) They do not have cell – walls.
(e) Most of them can move.
Classification of animalia
(a) These are non – motile animal attach to some solid support.
(b) The word Porifera means organisms with holes. The organisms of this group have holes or pores and canals or channels all over body.
(c) These holes or pores and a canal system helps in circulating water throughout the body.
(d)These organisms take food and oxygen with water with the help of canal system and pores.
(e) Skeleton or hard outside layer covered these organisms.
(f) The body of these organisms shows very minimal differentiation and division into tissues.
(g) They are found in marine habitat.
(h)Eg :- Sponges
(B) Coelenterate (Cnidaria)
(a) These animals live in water.
(b) They show more body design differentiation.
(c) These organisms have cavity in their bodies.
(d) The body is made of two layers of cells.
(e) The one layer makes up cells on the outside of the body and the other makes the inner lining of the body.
(f) Some lives in colonies like corals and others live alone like hydra.
(g) Eg:- Jellyfish and sea anemones.
(a) The body of organisms of this group is very complexly designed.
(b) The body is bilaterally symmetrical, ie, left and right halves of the body has the same design.
(c) These animals are called triploblastic because they have three layers of cells from which differentiated tissues can be made.
(d) There is no internal body cavity or coelom.
(e) These animals are called flat worms because they have flat bodies from top to bottom.
(f)These animals are free – living or parasitic.
(g) Eg:- Free living animals like planarians or parasitic animals like liverflukes.
(a) These are bilaterally symmetrical.
(b) These animals are triploblastic.
(c)They have cylindrical body.
(d) There are tissues but no real organs.
(e)These animals have a body cavity or a pseudocoelom.
(f) These are parasitic worms causing diseases.
Eg:- Worms causing elephantiasis (filarial worms) or worms in the intestines (roundworm or pinworms).
(g) Eg:- Ascaris and Wuchereria
(a) These animals are also bilaterally symmetrical.
(b) These animals are also called triploblastic.
(c) They have a true body cavity that allows true organs to be packaged in the body structure.
(d) The differentiation occurs in segments lines up one after other from head to tail.
(e) These animals are found in fresh water, sea water and on land.
(f) Eg:- Earthworms and leeches.
(a) This is the largest group of the animals.
(b)These animals are bilaterally symmetrical and segmented.
(c) They have open circulatory system and so the blood does not flow in the well defined blood vessels.
(d) The coelomic cavity is blood filled.
(e) The word ‘arthropod’ means ‘jointed legs’. Therefore, these animals have jointed legs.
(f) These animals are found in marine, fresh water and air.
(g) Eg:- Prawns, butterflies, houseflies, spiders, scorpions and crabs.
(a) These animals are bilateral symmetry.
(b) These animals has reduced coelomic cavity.
(c) There is little segmentation.
(d)These animals have an open circulatory system.
(e)They have kidney like organs for excretion.
(f)These animals have a foot used for moving around.
(g) Eg:- Snails and mussels.
(a) In Greek, echinos means hedgehog (spiny mammal) and derma means skin. Thus, these animals are spiny skinned organisms.
(b) These are free – living marine animals.
(c) These animals are triploblastic.
(d) These animals have a coelomic cavity.
(e) These animals have a peculiar water driven tube system that is used for moving around.
(f) These animals have skeleton that is hard calcium carbonate structures.
(g) Eg:- Sea – stars and sea urchins.
(a) These animals are triploblastic.
(b) These animals are triploblastic.
(c)These animals have a coelomic cavity.
(d) At some stages of life of protochordata animals show a new feature of body design named as notochord that provides a place for muscles to attach for ease of movement.
Notochord is a long rod – like support structure that runs along the back of the animal separating the nervous tissue from the gut.
(e) These animals may not have a proper notochord present at all stages in their lives or for the entire length of the animal.
(f) These animals are marine animals.
(g) Eg:- Balanoglossus, Herdmania and Amphioxus.
(a) These animals have a true vertebral column and internal skeleton.
(b) These animals have a completely different distribution of muscle attachment points to be used for movement because of vertebral column and internal skeleton
(c) These animals are bilateral symmetry.
(d) These animals have segmentation.
(e) These animals are triploblastic.
(f) These animals have a coelomic cavity.
(g) These animals have complex differentiation of body tissues and organs.
(h) These animals have a notochord.
(i) These animals have a dorsal nerve cord.
(j) These animals have paired gill pouches.
Classification of the vertebrata
These are grouped in six classes. These are discussed below –
(a) These are jawless vertebrates.
(b) They have an elongated eel – like body.
(c) They have circular mouth.
(d) They have slimy and scaleless skin.
(e) They are ectoparasites or borers of other vertebrates.
(f) Eg:- Petromyzon (Lamprey) and Myxine (Hagfish)
(a) These are fish.
(b) They are aquatic animals.
(c) Their skin is covered with scales or plates.
(d) They have gills to take oxygen dissolved in water.
(e) Their body is streamlined.
(f) They have a muscular tail for movement.
(g) They are cold – blooded.
(h) Their heart has two chambers.
(i)They lay eggs.
(j)Some fishes with skeletons made entirely of cartilage.
(k) Some fishes with a skeleton made of both bone and cartilage.
Eg:- Tuna or rohu.
(l) Other examples of this group are Mandarin fish, Lion fish, Electric ray , Flying fish etc.
(a) These animals respirate through either gills or lungs.
(b) They lay eggs.
(c) These animals are found both in water and on land.
(d) Amphibians lack of scales.
(e) They have mucus glands in the skin.
(f) They have a three chambered heart.
(g) Eg:- Frogs, toads and salamanders etc.
(a)These animals have scales.
(b) They breathe through lungs.
(c) These animals are cold – blooded.
(d) Most of these animals have three chambered heart. But crocodiles have four heart chambers.
(e) They lay eggs with tough covering.
(f) They do not lay their eggs in water.
(g) Eg:- Snakes, turtles, lizards and crocodiles etc.
(a) These are warm – blooded animals.
(b) They have four chambered heart.
(c) They lay eggs.
(e) These animals have outside covering of feathers and two forelimbs are modified for flight.
(f) They breathe through lungs.
(g) All birds fall in this category.
(h) Eg:- Ostrich, Pigeon, crow and sparrow etc.
(a) Mammals are warm – blood animals.
(b) They have four – chambered heart.
(c) They have mammary glands for the production of milk to nourish their young.
(d) Their skin has hairs.
(e)These animals have sweat and oil glands.
(f) These animals produced live young ones. But few of them like platypus and the echidna lay eggs.
(g) Eg:- Human, kangaroos, cat , elephant etc.
The scientific system of nomenclature for animals is introduced by Carolus Linnaeus in the 18th Century.
Use of the nomenclature –
People know animals in different languages with different names. This makes difficult to recognise the animals for people many times. This problem was resolved by scientists by giving animals a scientific name.
The scientific name of an organism is the result of the process of classification. When we actually name the species, we write the name of the genus and species of the organisms. Genus and species should be in Latin language.
Following conventions should be followed while writing the scientific names –
(a) The name of the genus begins with a capital letter.
(b) The name of the species begins with a small letter.
(c) When printed, the scientific name is given in italics.
(d) When written by hand, the genus name and the species name have to be underlined separately.