Have you ever thought of the multitude oflife-forms that surround us? Each organismis different from all others to a lesser orgreater extent. For instance, consider yourselfand a friend.• Are you both of the same height?• Does your nose look exactly like your

friend’s nose?• Is your hand-span the same as your

friend’s?However, if we were to compare ourselves

and our friends with a monkey, what wouldwe say? Obviously, we and our friends havea lot in common when we compare ourselveswith a monkey. But suppose we were to adda cow to the comparison? We would thenthink that the monkey has a lot more incommon with us than with the cow.

Activity ______________ 7.1• We have heard of ‘desi’ cows and Jersey

cows.• Does a desi cow look like a Jersey cow?• Do all desi cows look alike?• Will we be able to identify a Jersey cow

in a crowd of desi cows that don’t looklike each other?

• What is the basis of our identification?

In this activity, we had to decide whichcharacteristics were more important informing the desired category. Hence, we werealso deciding which characteristics could beignored.

Now, think of all the different forms inwhich life occurs on earth. On one hand wehave microscopic bacteria of a few micrometrein size. While on the other hand we have bluewhale and red wood trees of californiaof approximate sizes of 30 metres and100 metres repectively. Some pine trees live

for thousands of years while insects likemosquitoes die within a few days. Life alsoranges from colourless or even transparentworms to brightly coloured birds and flowers.

This bewildering variety of life around ushas evolved on the earth over millions ofyears. However, we do not have more than atiny fraction of this time to try andunderstand all these living organisms, so wecannot look at them one by one. Instead, welook for similarities among the organisms,which will allow us to put them into differentclasses and then study different classes orgroups as a whole.

In order to make relevant groups to studythe variety of life forms, we need to decidewhich characteristics decide morefundamental differences among organisms.This would create the main broad groups oforganisms. Within these groups, smaller sub-groups will be decided by less importantcharacteristics.

uestions1. Why do we classify organisms?2. Give three examples of the range

of variations that you see in life-forms around you.

7.1 What is the Basis ofClassification?

Attempts at classifying living things intogroups have been made since timeimmemorial. Greek thinker Aristotle classifiedanimals according to whether they lived on

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77777DDDDDIVERSITYIVERSITYIVERSITYIVERSITYIVERSITY INININININ L L L L LIVINGIVINGIVINGIVINGIVING O O O O ORGANISMSRGANISMSRGANISMSRGANISMSRGANISMS

Chapter

land, in water or in the air. This is a verysimple way of looking at life, but misleadingtoo. For example, animals that live in the seainclude corals, whales, octopuses, starfishand sharks. We can immediately see thatthese are very different from each other innumerous ways. In fact, their habitat is theonly point they share in common. This is nogood as a way of making groups of organismsto study and think about.

We therefore need to decide whichcharacteristics to be used as the basis formaking the broadest divisions. Then we willhave to pick the next set of characteristicsfor making sub-groups within these divisions.This process of classification within eachgroup can then continue using newcharacteristics each time.

Before we go on, we need to think aboutwhat is meant by ‘characteristics’. When weare trying to classify a diverse group oforganisms, we need to find ways in whichsome of them are similar enough to bethought of together. These ‘ways’, in fact, aredetails of appearance or behaviour, in otherwords, form and function.

What we mean by a characteristic is aparticular form or a particular function. Thatmost of us have five fingers on each hand isthus a characteristic. That we can run, butthe banyan tree cannot, is also acharacteristic.

Now, to understand how somecharacteristics are decided as being morefundamental than others, let us consider howa stone wall is built. The stones used will havedifferent shapes and sizes. The stones at thetop of the wall would not influence the choiceof stones that come below them. On the otherhand, the shapes and sizes of stones in thelowermost layer will decide the shape and sizeof the next layer and so on.

The stones in the lowermost layer are likethe characteristics that decide the broadestdivisions among living organisms. They areindependent of any other characteristics intheir effects on the form and function of theorganism. The characteristics in the next levelwould be dependent on the previous one andwould decide the variety in the next level. In

this way, we can build up a whole hierarchyof mutually related characteristics to be usedfor classification.

Now-a-days, we look at many inter-relatedcharacteristics starting from the nature of thecell in order to classify all living organisms.What are some concrete examples of suchcharacteristics used for a hierarchicalclassification?• A eukaryotic cell has membrane-bound

organelles, including a nucleus, whichallow cellular processes to be carried outefficiently in isolation from each other.Therefore, organisms which do not havea clearly demarcated nucleus and otherorganelles would need to have theirbiochemical pathways organised in verydifferent ways. This would have an effecton every aspect of cell design. Further,nucleated cells would have the capacityto participate in making a multicellularorganism because they can take upspecialised functions. Therefore, this isa basic characteristic of classification.

• Do the cells occur singly or are theygrouped together and do they live as anindivisible group? Cells that grouptogether to form a single organism usethe principle of division of labour. In sucha body design, all cells would not beidentical. Instead, groups of cells willcarry out specialised functions. Thismakes a very basic distinction in thebody designs of organisms. As a result,an Amoeba and a worm are very differentin their body design.

• Do organisms produce their own foodthrough the process of photosynthesis?Being able to produce one’s own foodversus having to get food from outsidewould make very different body designsnecessary.

• Of the organisms that performphotosynthesis (plants), what is the levelof organisation of their body?

• Of the animals, how does the individual’sbody develop and organise its differentparts, and what are the specialisedorgans found for different functions?

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We can see that, even in these fewquestions that we have asked, a hierarchy isdeveloping. The characteristics of body designused for classification of plants will be verydifferent from those important for classifyinganimals. This is because the basic designsare different, based on the need to make theirown food (plants), or acquire it (animals).Therefore, these design features (having askeleton, for example) are to be used to makesub-groups, rather than making broad groups.

uestions1. Which do you think is a more basic

characteristic for classifyingorganisms?(a) the place where they live.(b) the kind of cells they are

made of. Why?2. What is the primary characteristic

on which the first division oforganisms is made?

3. On what bases are plants andanimals put into differentcategories?

7.2 Classification and EvolutionAll living things are identified and categorisedon the basis of their body design in form andfunction. Some characteristics are likely tomake more wide-ranging changes in bodydesign than others. There is a role of time inthis as well. So, once a certain body designcomes into existence, it will shape the effectsof all other subsequent design changes,simply because it already exists. In otherwords, characteristics that came intoexistence earlier are likely to be more basicthan characteristics that have come intoexistence later.

This means that the classification of lifeforms will be closely related to their evolution.What is evolution? Most life forms that wesee today have arisen by an accumulation ofchanges in body design that allow theorganism possessing them to survive better.Charles Darwin first described this idea ofevolution in 1859 in his book, The Origin ofSpecies.

When we connect this idea of evolution toclassification, we will find some groups oforganisms which have ancient body designsthat have not changed very much. We willalso find other groups of organisms that haveacquired their particular body designsrelatively recently. Those in the first groupare frequently referred to as ‘primitive’ or ‘lower’organisms, while those in the second groupare called ‘advanced’ or ‘higher’ organisms. Inreality, these terms are not quite correct sincethey do not properly relate to the differences.All that we can say is that some are ‘older’organisms, while some are ‘younger’organisms. Since there is a possibility thatcomplexity in design will increase overevolutionary time, it may not be wrong to saythat older organisms are simpler, whileyounger organisms are more complex.Q

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Biodiversity means the diversity of lifeforms. It is a word commonly used torefer to the variety of life forms foundin a particular region. Diverse life formsshare the environment, and areaffected by each other too. As a result,a stable community of different speciescomes into existence. Humans haveplayed their own part in recent timesin changing the balance of suchcommunities. Of course, the diversityin such communities is affected byparticular characteristics of land,water, climate and so on. Roughestimates state that there are about tenmillion species on the planet, althoughwe actually know only one or twomillions of them. The warm and humidtropical regions of the earth, betweenthe tropic of Cancer and the tropic ofCapricorn, are rich in diversity of plantand animal life. This is called the regionof megadiversity. Of the biodiversityof the planet, more than half isconcentrated in a few countries –Brazil, Colombia, Ecuador, Peru,Mexico, Zaire, Madagascar,Australia, China, India, Indonesia andMalaysia.

DIVERSITY IN LIVING ORGANISMS 83

uestions1. Which organisms are called

primitive and how are theydifferent from the so-calledadvanced organisms?

2. Will advanced organisms be thesame as complex organisms?Why?

7.3 The Hierarchy of Classification-Groups

Biologists, such as Ernst Haeckel (1894),Robert Whittaker (1959) and Carl Woese(1977) have tried to classify all livingorganisms into broad categories, calledkingdoms. The classification Whittakerproposed has five kingdoms: Monera,Protista, Fungi, Plantae and Animalia, andis widely used. These groups are formed onthe basis of their cell structure, mode andsource of nutrition and body organisation.The modification Woese introduced bydividing the Monera into Archaebacteria (orArchaea) and Eubacteria (or Bacteria) is alsoin use.

Further classification is done by namingthe sub-groups at various levels as given inthe following scheme:

KingdomPhylum (for animals) / Division (for plants)

ClassOrder

FamilyGenus

SpeciesThus, by separating organisms on the

basis of a hierarchy of characteristics intosmaller and smaller groups, we arrive at thebasic unit of classification, which is a‘species’. So what organisms can be said tobelong to the same species? Broadly, a speciesincludes all organisms that are similarenough to breed and perpetuate.

The important characteristics of the fivekingdoms of Whittaker are as follows:

7.3.1 MONERA

These organisms do not have a definednucleus or organelles, nor do any of themshow multi-cellular body designs. On theother hand, they show diversity based onmany other characteristics. Some of themhave cell walls while some do not. Of course,having or not having a cell wall has verydifferent effects on body design here fromhaving or not having a cell wall in multi-cellular organisms. The mode of nutrition oforganisms in this group can be either bysynthesising their own food (autotrophic) orgetting it from the environment(heterotrophic). This group includes bacteria,blue-green algae or cyanobacteria, andmycoplasma. Some examples are shownin Fig. 7.1.

Q

Bacteria

Restingspore

Heterocyst

Anabaena

Fig. 7.1: Monera

7.3.2 PROTISTA

This group includes many kinds of unicellulareukaryotic organisms. Some of theseorganisms use appendages, such as hair-likecilia or whip-like flagella for moving around.Their mode of nutrition can be autotrophicor heterotrophic. Examples are unicellularalgae, diatoms and protozoans (see Fig. 7.2for examples).

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to become multicellular organisms at certainstages in their lives. They have cell-walls madeof a tough complex sugar called chitin.Examples are yeast and mushrooms (see Fig.7.3 for examples).

Water vacuole

Cilia

MacronucleusMicronucleus

Oral groove

Cytosome

Food vacuole

Cytopyge

Waste

Flagellum (long)

Flagellum (short)

Eyespot

Photoreceptor

Contractilevacuole Chloroplast

Photoreceptor

Nucleolus

Nucleus

EctoplasmEndoplasm

MitochondriaNucleus

Crystals

Food vacuole

Contractile vacuole

Advancingpseudopod

Paramecium

Amoeba

Euglena

Fig. 7.2: Protozoa

7.3.3 FUNGI

These are heterotrophic eukaryoticorganisms. They use decaying organicmaterial as food and are therefore calledsaprophytes. Many of them have the capacity

Fig. 7.3: Fungi

Some fungal species live in permanentmutually dependent relationships with blue-green algae (or cyanobacteria). Suchrelationships are called symbiotic. Thesesymbiobic life forms are called lichens. Wehave all seen lichens as the slow-growinglarge coloured patches on the bark of trees.

7.3.4 PLANTAE

These are multicellular eukaryotes with cellwalls. They are autotrophs and usechlorophyll for photosynthesis. Thus, allplants are included in this group. Sinceplants and animals are most visible formsof the diversity of life around us, we will lookat the subgroups in this category later(section 7.4).

7.3.5 ANIMALIA

These include all organisms which aremulticellular eukaryotes without cell walls.They are heterotrophs. Again, we will lookat their subgroups a little later insection 7.5.

Penicillium Agaricus

Aspergillus

DIVERSITY IN LIVING ORGANISMS 85

Fig. 7.4: The Five Kingdom classification

uestions1. What is the criterion for

classification of organisms asbelonging to kingdom Monera orProtista?

2. In which kingdom will you placean organism which is single-celled, eukaryotic andphotosynthetic?

3. In the hierarchy of classification,which grouping will have thesmallest number of organismswith a maximum ofcharacteristics in common andwhich will have the largestnumber of organisms?

Q7.4 PlantaeThe first level of classification among plantsdepends on whether the plant body has well-differentiated, distinct components. The nextlevel of classification is based on whether thedifferentiated plant body has special tissuesfor the transport of water and othersubstances within it. Further classificationlooks at the ability to bear seeds and whetherthe seeds are enclosed within fruits.

7.4.1 THALLOPHYTA

Plants that do not have well-differentiatedbody design fall in this group. The plants inthis group are commonly called algae. These

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plants are predominantly aquatic. Examplesare Spirogyra, Ulothrix, Cladophora and Chara(see Fig. 7.5).

7.4.2 BRYOPHYTA

These are called the amphibians of the plantkingdom. The plant body is commonlydifferentiated to form stem and leaf-likestructures. However, there is no specialisedtissue for the conduction of water and othersubstances from one part of the plant bodyto another. Examples are moss (Funaria) andMarchantia (see Fig. 7.6).

Fig. 7.5: Thallophyta – Algae

Cell-wall

Chloroplast

Pyrenoids

Nucleus

Cytoplasm

Ulothrix

Cladophora

Ulva

Spirogyra

Chara

Fig. 7.6: Some common bryophytes

7.4.3 PTERIDOPHYTA

In this group, the plant body is differentiatedinto roots, stem and leaves and hasspecialised tissue for the conduction of waterand other substances from one part of theplant body to another. Some examples areMarsilea, ferns and horse-tails (see Fig. 7.7).

The thallophytes, the bryophytes and thepteridophytes have naked embryos that arecalled spores. The reproductive organs ofplants in all these three groups are veryinconspicuous, and they are therefore called‘cryptogamae’, or ‘those with hiddenreproductive organs’.

Riccia

Marchantia Funaria

DIVERSITY IN LIVING ORGANISMS 87

On the other hand, plants with well-differentiated reproductive tissues thatultimately make seeds are calledphanerogams. Seeds are the result of thereproductive process. They consist of theembryo along with stored food, which servesfor the initial growth of the embryo duringgermination. This group is further classified,based on whether the seeds are naked orenclosed in fruits, giving us two groups:gymnosperms and angiosperms.

7.4.4 GYMNOSPERMS

This term is made from two Greek words:gymno– means naked and sperma– meansseed. The plants of this group bear nakedseeds and are usually perennial, evergreenand woody. Examples are pines, such asdeodar (see Fig. 7.8 for examples).

7.4.5 ANGIOSPERMS

This word is made from two Greek words:angio means covered and sperma– meansseed. The seeds develop inside an organ whichis modified to become a fruit. These are alsocalled flowering plants. Plant embryos inseeds have structures called cotyledons.Cotyledons are called ‘seed leaves’ becausein many instances they emerge and becomegreen when the seed germinates. Thus,cotyledons represent a bit of pre-designedplant in the seed. The angiosperms aredivided into two groups on the basis of thenumber of cotyledons present in the seed.Plants with seeds having a single cotyledonare called monocotyledonous or monocots.Plants with seeds having two cotyledons arecalled dicots (see Figs. 7.9 and 7.10).

Marsilea Fern

Leaf

Sporocarp

Stem

Root

Fig. 7.7: Pteridophyta

Pinus

Fig. 7.8: Gymnosperms

Cycas

Fig. 7.9: Monocots – Paphiopedilum

Fig. 7.10: Dicots – Ipomoea

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Activity ______________ 7.2• Soak seeds of green gram, wheat,

maize, peas and tamarind. Once theybecome tender, try to split the seed. Doall the seeds break into two nearlyequal halves?

• The seeds that do are the dicot seedsand the seeds that don’t are themonocot seeds.

• Now take a look at the roots, leaves andflowers of these plants.

• Are the roots tap-roots or fibrous?• Do the leaves have parallel or reticulate

venation?

Fig. 7.11: Classification of plants

• How many petals are found in theflower of these plants?

• Can you write down furthercharacteristics of monocots and dicotson the basis of these observations?

uestions1. Which division among plants has

the simplest organisms?2. How are pteridophytes different

from the phanerogams?3. How do gymnosperms and

angiosperms differ from eachother?

Q

DIVERSITY IN LIVING ORGANISMS 89

7.5 AnimaliaThese are organisms which are eukaryotic,multicellular and heterotrophic. Their cellsdo not have cell-walls. Most animals aremobile.

They are further classified based on theextent and type of the body designdifferentiation found.

7.5.1 PORIFERA

The word means organisms with holes. Theseare non-motile animals attached to some solidsupport. There are holes or ‘pores’, all overthe body. These lead to a canal system thathelps in circulating water throughout thebody to bring in food and oxygen. Theseanimals are covered with a hard outside layeror skeleton. The body design involves veryminimal differentiation and division intotissues. They are commonly called sponges,and are mainly found in marine habitats.Some examples are shown in Fig. 7.12.

layers of cells: one makes up cells on theoutside of the body, and the other makes theinner lining of the body. Some of these specieslive in colonies (corals), while others have asolitary like–span (Hydra). Jellyfish and seaanemones are common examples (seeFig. 7.13).

SyconEuplectelia

Spongilla

Fig. 7.12: Porifera

Tentacles

Sea anemone

Tentacles

Stinging cell

Mouth

EpidermisMesoglea

Gastrodermis

Gastrovascularcavity

Foot

Fig. 7.13: Coelenterata

7.5.3 PLATYHELMINTHES

The body of animals in this group is far morecomplexly designed than in the two othergroups we have considered so far. The bodyis bilaterally symmetrical, meaning that theleft and the right halves of the body have thesame design. There are three layers of cellsfrom which differentiated tissues can bemade, which is why such animals are calledtriploblastic. This allows outside and insidebody linings as well as some organs to bemade. There is thus some degree of tissueformation. However, there is no true internalbody cavity or coelom, in which well-developed organs can be accommodated. Thebody is flattened dorsiventrally, meaning fromtop to bottom, which is why these animalsare called flatworms. They are either free-living or parasitic. Some examples are free-living animals like planarians, or parasiticanimals like liverflukes (see Fig. 7.14 forexamples).

Hydra

7.5.2 COELENTERATA

These are animals living in water. They showmore body design differentiation. There is acavity in the body. The body is made of two

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7.5.5 ANNELIDA

Annelid animals are also bilaterallysymmetrical and triploblastic, but in additionthey have a true body cavity. This allows trueorgans to be packaged in the body structure.There is, thus, extensive organ differentiation.This differentiation occurs in a segmentalfashion, with the segments lined up one afterthe other from head to tail. These animalsare found in a variety of habitats– fresh water,marine water as well as land. Earthwormsand leeches are familiar examples (seeFig. 7.16).

Acetabulum

Scolex SuckerNeck

Tape wormLiverfluke

EyesBranchedgastrovascularcavity

PharynxMouth

and anus

Planareia

Fig. 7.14: Platyhelminthes

7.5.4 NEMATODA

The nematode body is also bilaterallysymmetrical and triploblastic. However, thebody is cylindrical rather than flattened.There are tissues, but no real organs,although a sort of body cavity or a pseudo-coelom, is present. These are very familiaras parasitic worms causing diseases, suchas the worms causing elephantiasis (filarialworms) or the worms in the intestines(roundworm or pinworms). Some examplesare shown in Fig. 7.15.

Female

Male

Ascaris Wuchereria

Fig. 7.15: Nematodes (Aschelminthes)

Tentacle

Palp

Parapodia

Parapodia

Nereis Earthworm Leech

Fig. 7.16: Annelida

7.5.6 ARTHROPODA

This is probably the largest group of animals.These animals are bilaterally symmetrical andsegmented. There is an open circulatorysystem, and so the blood does not flow in well-defined blood vessels. The coelomic cavity isblood-filled. They have jointed legs (the word‘arthropod’ means ‘jointed legs’). Somefamiliar examples are prawns, butterflies,houseflies, spiders, scorpions and crabs (seeFig. 7.17).

Genitalpapillae

Anus

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Palamnaeus(Scorpion)

7.5.7 MOLLUSCA

In the animals of this group, there is bilateralsymmetry. The coelomic cavity is reduced.There is little segmentation. They have anopen circulatory system and kidney-likeorgans for excretion. There is a foot that isused for moving around. Examples are snailsand mussels (see Fig. 7.18).

7.5.8 ECHINODERMATA

In Greek, echinos means hedgehog, andderma means skin. Thus, these are spinyskinned organisms. These are exclusivelyfree-living marine animals. They aretriploblastic and have a coelomic cavity. Theyalso have a peculiar water-driven tube systemthat they use for moving around. They havehard calcium carbonate structures that theyuse as a skeleton. Examples are starfish andsea urchins (see Fig. 7.19).

Pariplaneta(Cockroach)

Palaemon(Prawn)

Aranea(Spider)

Fig. 7.17: Arthropoda

ChitonOctopus

Pila

Unio

Fig. 7.18: Mollusca

Antedon(feather star)

Holothuria(sea cucumber)

Echinus (sea urchin) Asterias (star fish)

7.5.9 PROTOCHORDATA

These animals are bilaterally symmetrical,triploblastic and have a coelom. In addition,they show a new feature of body design,namely a notochord, at least at some stagesduring their lives. The notochord is a longrod-like support structure (chord=string) thatruns along the back of the animal separatingthe nervous tissue from the gut. It provides aplace for muscles to attach for ease ofmovement. Protochordates may not have aproper notochord present at all stages in their

Fig. 7.19: Echinodermata

Musca(House fly)

Butterfly

Scolopendra(Centipede)

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lives or for the entire length of the animal.Protochordates are marine animals.Examples are Balanoglossus, Herdemaniaand Amphioxus (see Fig. 7.20).

7.5.10 (i) PISCES

These are fish. They are exclusively water-living animals. Their skin is covered withscales/plates. They obtain oxygen dissolvedin water by using gills. The body isstreamlined, and a muscular tail is used formovement. They are cold-blooded and theirhearts have only two chambers, unlike thefour that humans have. They lay eggs. Wecan think of many kinds of fish, some withskeletons made entirely of cartilage, such assharks, and some with a skeleton made ofboth bone and cartilage, such as tuna or rohu[see examples in Figs. 7.21 (a) and 7.21 (b)].

Proboscis

Collarette

Collar

Branchial region

Gill pores

Dorsallycurvedgenital wings

Middosrsalridge

Hepatic caeca

Hepatic region

Posthepaticregion

Anus

Fig. 7.20: A Protochordata: Balanoglossus

7.5.10 VERTEBRATA

These animals have a true vertebral columnand internal skeleton, allowing a completelydifferent distribution of muscle attachmentpoints to be used for movement.

Vertebrates are bilaterally symmetrical,triploblastic, coelomic and segmented, withcomplex differentiation of body tissues andorgans. All chordates possess the followingfeatures:

(i) have a notochord(ii) have a dorsal nerve cord(iii) are triploblastic(iv) have paired gill pouches(v) are coelomate.

Vertebrates are grouped into five classes.

Caulophyryne jordani(Angler fish)

Synchiropus splendidus(Mandarin fish)

Pterois volitans(Lion fish)

SpiracleEye

Pelvic finDorsal fin

Caudal fin

Tail

Electric ray (Torpedo)

Sting ray

Mouth

Dorsal finTailEye

Gills Pectoralfin

Pelvicfin

Fig. 7.21 (a): Pisces

Scoliodon (Dog fish)

DIVERSITY IN LIVING ORGANISMS 93

7.5.10 (ii) AMPHIBIA

These animals differ from the fish in the lackof scales, in having mucus glands in the skin,and a three-chambered heart. Respiration isthrough either gills or lungs. They lay eggs.These animals are found both in water andon land. Frogs, toads and salamanders aresome examples (see Fig. 7.22).

7.5.10 (iii) REPTILIA

These animals are cold-blooded, have scalesand breathe through lungs. While most ofthem have a three-chambered heart,crocodiles have four heart chambers. Theylay eggs with tough coverings and do not needto lay their eggs in water, unlike amphibians.Snakes, turtles, lizards and crocodiles fall inthis category (see Fig. 7.23).

Eye Head

Nostril

MouthPectoralfinPelvic

fin

Caudalfin

Labeo rohita (Rohu)

PectoralfinMouth

Broodpouch

Dorsalfin

TailMale Hippocampus

(Sea horse)

Wing like pectoral

TailPelvic fin

Scales

Exocoetus (Flying fish)

Anabas (Climbing perch)

Fig. 7.21 (b): Pisces

Fig. 7.22: Amphibia

Rana tigrina(Common frog)

Toad

Hyla (Tree frog)

Salamander

Turtle

Chameleon

King Cobra

House wall lizard(Hemidactylus)

Flying lizard (Draco)

7.5.10 (iv) AVES

These are warm-blooded animals and have afour-chambered heart. They lay eggs. Thereis an outside covering of feathers, and twoforelimbs are modified for flight. They breathethrough lungs. All birds fall in this category(see Fig. 7.24 for examples).

Fig. 7.23: Reptilia

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7.5.10 (V) MAMMALIA

Mammals are warm-blooded animals withfour-chambered hearts. They have mammaryglands for the production of milk to nourishtheir young. Their skin has hairs as well assweat and oil glands. Most mammals familiarto us produce live young ones. However, afew of them, like the platypus and the echidnalay eggs, and some, like kangaroos give birthto very poorly developed young ones. Someexamples are shown in Fig. 7.25.

The scheme of classification of animals isshown in Fig. 7.26.

White Stork(Ciconia ciconia)

Ostrich(Struthio camelus)

Male Tufted Duck(Aythya fuligula)

Pigeon

Sparrow

Crow

Fig. 7.24: Aves (birds)

Fig. 7.25: Mammalia

uestions1. How do poriferan animals differ

from coelenterate animals?2. How do annelid animals differ

from arthropods?3. What are the differences between

amphibians and reptiles?4. What are the differences between

animals belonging to the Avesgroup and those in the mammaliagroup?

QCarolus Linnaeus (Karlvon Linne) was born inSweden and was a doctorby professsion. He wasinterested in the study ofplants. At the age of 22,he published his firstpaper on plants. Whileserving as a personalphysician of a wealthygovernment official, he studied thediversity of plants in his employer’sgarden. Later, he published 14 papers andalso brought out the famous bookSystema Naturae from which allfundamental taxonomical researches havetaken off. His system of classification wasa simple scheme for arranging plants soas to be able to identify them again.

Carolus Linnaeus(1707-1778)

Whale

Human

Cat

Rat

Bat

DIVERSITY IN LIVING ORGANISMS 95

Fig. 7.26: Classification of animals

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7.6 NomenclatureWhy is there a need for systematic naming ofliving organisms?

Activity ______________ 7.3• Find out the names of the following

animals and plants in as manylanguages as you can:1. Tiger 2. Peacock 3. Ant4. Neem 5. Lotus 6. Potato

As you might be able to appreciate, itwould be difficult for people speaking orwriting in different languages to know whenthey are talking about the same organism.This problem was resolved by agreeing upona ‘scientific’ name for organisms in the samemanner that chemical symbols and formulaefor various substances are used the worldover. The scientific name for an organism isthus unique and can be used to identify itanywhere in the world.

The system of scientific naming ornomenclature we use today was introducedby Carolus Linnaeus in the eighteenthcentury. The scientific name of an organismis the result of the process of classification

which puts it along with the organisms it ismost related to. But when we actually namethe species, we do not list out the wholehierarchy of groups it belongs to. Instead, welimit ourselves to writing the name of thegenus and species of that particularorganism. The world over, it has been agreedthat both these names will be used in Latinforms.

Certain conventions are followed whilewriting the scientific names:

1. The name of the genus begins with acapital letter.

2. The name of the species begins with asmall letter.

3. When printed, the scientific name isgiven in italics.

4. When written by hand, the genusname and the species name have tobe underlined separately.

Activity ______________ 7.4• Find out the scientific names of any

five common animals and plants. Dothese names have anything in commonwith the names you normally use toidentify them?

Whatyou havelearnt• Classification helps us in exploring the diversity of life forms.

• The major characteristics considered for classifying allorganisms into five major kingdoms are:

(a) whether they are made of prokaryotic or eukaryotic cells

(b) whether the cells are living singly or organised into multi-cellular and thus complex organisms

(c) whether the cells have a cell-wall and whether they preparetheir own food.

• All living organisms are divided on the above bases into fivekingdoms, namely Monera, Protista, Fungi, Plantae andAnimalia.

• The classification of life forms is related to their evolution.

DIVERSITY IN LIVING ORGANISMS 97

• Plantae and Animalia are further divided into subdivisions onthe basis of increasing complexity of body organisation.

• Plants are divided into five groups: Thallophytes, Bryophytes,Pteridophytes, Gymnosperms and Angiosperms.

• Animals are divided into ten groups: Porifera, Coelenterata,Platyhelminthes, Nematoda, Annelida, Arthropoda, Mollusca,Echinodermata, Protochordata and Vertebrata.

• The binomial nomenclature makes for a uniform way ofidentification of the vast diversity of life around us.

• The binomial nomenclature is made up of two words – a genericname and a specific name.

Exercises1. What are the advantages of classifying organisms?

2. How would you choose between two characteristics to be usedfor developing a hierarchy in classification?

3. Explain the basis for grouping organisms into five kingdoms.

4. What are the major divisions in the Plantae? What is the basisfor these divisions?

5. How are the criteria for deciding divisions in plants differentfrom the criteria for deciding the subgroups among animals?

6. Explain how animals in Vertebrata are classified into furthersubgroups.