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9   diversity in living organisms
 

9 diversity in living organisms

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    9   diversity in living organisms 9 diversity in living organisms Document Transcript

    • C hapter 7 DIVERSITY IN LIVING ORGANISMSHave you ever thought of the multitude of for thousands of years while insects likelife-forms that surround us? Each organism mosquitoes die within a few days. Life alsois different from all others to a lesser or ranges from colourless or even transparentgreater extent. For instance, consider yourself worms to brightly coloured birds and flowers.and a friend. This bewildering variety of life around us• Are you both of the same height? has evolved on the earth over millions of• Does your nose look exactly like your years. However, we do not have more than a friend’s nose? tiny fraction of this time to try and• Is your hand-span the same as your understand all these living organisms, so we friend’s? cannot look at them one by one. Instead, we However, if we were to compare ourselves look for similarities among the organisms,and our friends with a monkey, what would which will allow us to put them into differentwe say? Obviously, we and our friends have classes and then study different classes ora lot in common when we compare ourselves groups as a whole.with a monkey. But suppose we were to add In order to make relevant groups to studya cow to the comparison? We would then the variety of life forms, we need to decidethink that the monkey has a lot more in which characteristics decide morecommon with us than with the cow. fundamental differences among organisms. This would create the main broad groups of Activity ______________ 7.1 organisms. Within these groups, smaller sub- • We have heard of ‘desi’ cows and Jersey groups will be decided by less important cows. characteristics. Q • Does a desi cow look like a Jersey cow? • • Do all desi cows look alike? Will we be able to identify a Jersey cow uestions in a crowd of desi cows that don’t look 1. Why do we classify organisms? like each other? 2. Give three examples of the range • What is the basis of our identification? of variations that you see in life- In this activity, we had to decide which forms around you.characteristics were more important informing the desired category. Hence, we werealso deciding which characteristics could beignored. Now, think of all the different forms in 7.1 What is the Basis ofwhich life occurs on earth. On one hand we Classification?have microscopic bacteria of a few micrometrein size. While on the other hand we have blue Attempts at classifying living things intowhale and red wood trees of california groups have been made since timeof approximate sizes of 30 metres and immemorial. Greek thinker Aristotle classified100 metres repectively. Some pine trees live animals according to whether they lived on
    • land, in water or in the air. This is a very this way, we can build up a whole hierarchysimple way of looking at life, but misleading of mutually related characteristics to be usedtoo. For example, animals that live in the sea for classification.include corals, whales, octopuses, starfish Now-a-days, we look at many inter-relatedand sharks. We can immediately see that characteristics starting from the nature of thethese are very different from each other in cell in order to classify all living organisms.numerous ways. In fact, their habitat is the What are some concrete examples of suchonly point they share in common. This is no characteristics used for a hierarchicalgood as a way of making groups of organisms classification?to study and think about. • A eukaryotic cell has membrane-bound We therefore need to decide which organelles, including a nucleus, whichcharacteristics to be used as the basis for allow cellular processes to be carried outmaking the broadest divisions. Then we will efficiently in isolation from each other.have to pick the next set of characteristics Therefore, organisms which do not havefor making sub-groups within these divisions. a clearly demarcated nucleus and otherThis process of classification within each organelles would need to have theirgroup can then continue using new biochemical pathways organised in verycharacteristics each time. different ways. This would have an effect Before we go on, we need to think about on every aspect of cell design. Further,what is meant by ‘characteristics’. When we nucleated cells would have the capacityare trying to classify a diverse group of to participate in making a multicellularorganisms, we need to find ways in which organism because they can take upsome of them are similar enough to be specialised functions. Therefore, this isthought of together. These ‘ways’, in fact, are a basic characteristic of classification.details of appearance or behaviour, in otherwords, form and function. • Do the cells occur singly or are they What we mean by a characteristic is a grouped together and do they live as anparticular form or a particular function. That indivisible group? Cells that groupmost of us have five fingers on each hand is together to form a single organism usethus a characteristic. That we can run, but the principle of division of labour. In suchthe banyan tree cannot, is also a a body design, all cells would not becharacteristic. identical. Instead, groups of cells will Now, to understand how some carry out specialised functions. Thischaracteristics are decided as being more makes a very basic distinction in thefundamental than others, let us consider how body designs of organisms. As a result,a stone wall is built. The stones used will have an Amoeba and a worm are very differentdifferent shapes and sizes. The stones at the in their body design.top of the wall would not influence the choice • Do organisms produce their own foodof stones that come below them. On the other through the process of photosynthesis?hand, the shapes and sizes of stones in the Being able to produce one’s own foodlowermost layer will decide the shape and size versus having to get food from outsideof the next layer and so on. would make very different body designs The stones in the lowermost layer are like necessary.the characteristics that decide the broadest • Of the organisms that per for mdivisions among living organisms. They are photosynthesis (plants), what is the levelindependent of any other characteristics in of organisation of their body?their effects on the form and function of the • Of the animals, how does the individual’sorganism. The characteristics in the next level body develop and organise its differentwould be dependent on the previous one and parts, and what are the specialisedwould decide the variety in the next level. In organs found for different functions?D IVERSITY IN L IVING O RGANISMS 81
    • We can see that, even in these few When we connect this idea of evolution toquestions that we have asked, a hierarchy is classification, we will find some groups ofdeveloping. The characteristics of body design organisms which have ancient body designsused for classification of plants will be very that have not changed very much. We willdifferent from those important for classifying also find other groups of organisms that haveanimals. This is because the basic designs acquired their particular body designsare different, based on the need to make their relatively recently. Those in the first groupown food (plants), or acquire it (animals). are frequently referred to as ‘primitive’ or ‘lower’Therefore, these design features (having a organisms, while those in the second groupskeleton, for example) are to be used to make are called ‘advanced’ or ‘higher’ organisms. InQsub-groups, rather than making broad groups. reality, these terms are not quite correct since they do not properly relate to the differences. uestions All that we can say is that some are ‘older’ organisms, while some are ‘younger’ 1. Which do you think is a more basic organisms. Since there is a possibility that characteristic for classifying complexity in design will increase over organisms? evolutionary time, it may not be wrong to say (a) the place where they live. that older organisms are simpler, while (b) the kind of cells they are younger organisms are more complex. made of. Why? 2. What is the primary characteristic on which the first division of Biodiversity means the diversity of life organisms is made? forms. It is a word commonly used to 3. On what bases are plants and refer to the variety of life forms found animals put into different in a particular region. Diverse life forms categories? share the environment, and are affected by each other too. As a result,7.2 Classification and Evolution a stable community of different species comes into existence. Humans haveAll living things are identified and categorised played their own part in recent timeson the basis of their body design in form and in changing the balance of suchfunction. Some characteristics are likely to communities. Of course, the diversitymake more wide-ranging changes in body in such communities is affected by More to knowdesign than others. There is a role of time in particular characteristics of land,this as well. So, once a certain body design water, climate and so on. Roughcomes into existence, it will shape the effects estimates state that there are about tenof all other subsequent design changes, million species on the planet, althoughsimply because it already exists. In other we actually know only one or twowords, characteristics that came into millions of them. The warm and humidexistence earlier are likely to be more basic tropical regions of the earth, betweenthan characteristics that have come into the tropic of Cancer and the tropic ofexistence later. Capricorn, are rich in diversity of plant This means that the classification of life and animal life. This is called the regionforms will be closely related to their evolution. of megadiversity. Of the biodiversityWhat is evolution? Most life forms that we of the planet, more than half issee today have arisen by an accumulation of concentrated in a few countries –changes in body design that allow the Brazil, Colombia, Ecuador, Peru,organism possessing them to survive better. Mexico, Zaire, Madagascar,Charles Darwin first described this idea of Australia, China, India, Indonesia andevolution in 1859 in his book, The Origin of Malaysia.Species. 82 SCIENCE
    • Q uestions 7.3.1 MONERA 1. Which organisms are called These organisms do not have a defined primitive and how are they nucleus or organelles, nor do any of them different from the so-called show multi-cellular body designs. On the advanced organisms? other hand, they show diversity based on 2. Will advanced organisms be the many other characteristics. Some of them same as complex organisms? have cell walls while some do not. Of course, Why? having or not having a cell wall has very different effects on body design here from7.3 The Hierarchy of Classification- having or not having a cell wall in multi- cellular organisms. The mode of nutrition of Groups organisms in this group can be either by synthesising their own food (autotrophic) orBiologists, such as Ernst Haeckel (1894), getting it from the environmentRobert Whittaker (1959) and Carl Woese (heterotrophic). This group includes bacteria,(1977) have tried to classify all living blue-green algae or cyanobacteria, andorganisms into broad categories, called mycoplasma. Some examples are shownkingdoms. The classification Whittaker in Fig. 7.1.proposed 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 (or RestingArchaea) and Eubacteria (or Bacteria) is also sporein use. Further classification is done by naming Bacteriathe sub-groups at various levels as given inthe following scheme: Kingdom Phylum (for animals) / Division (for plants) Heterocyst Class Order Anabaena Family Genus Species Fig. 7.1: Monera Thus, by separating organisms on thebasis of a hierarchy of characteristics into 7.3.2 PROTISTAsmaller and smaller groups, we arrive at the This group includes many kinds of unicellularbasic unit of classification, which is a eukaryotic organisms. Some of these‘species’. So what organisms can be said to organisms use appendages, such as hair-likebelong to the same species? Broadly, a species cilia or whip-like flagella for moving around.includes all organisms that are similar Their mode of nutrition can be autotrophicenough to breed and perpetuate. or heterotrophic. Examples are unicellular The important characteristics of the five algae, diatoms and protozoans (see Fig. 7.2kingdoms of Whittaker are as follows: for examples).D IVERSITY IN L IVING O RGANISMS 83
    • to become multicellular organisms at certain Water vacuole stages in their lives. They have cell-walls made of a tough complex sugar called chitin. Cilia Examples are yeast and mushrooms (see Fig. 7.3 for examples). Macronucleus Micronucleus Oral groove Cytosome Food vacuole Cytopyge Waste Paramecium Ectoplasm Endoplasm Mitochondria Penicillium Agaricus Nucleus Aspergillus CrystalsFood vacuole Fig. 7.3: Fungi Advancing pseudopod Some fungal species live in permanent Contractile vacuole mutually dependent relationships with blue- green algae (or cyanobacteria). Such Amoeba relationships are called symbiotic. These symbiobic life forms are called lichens. We have all seen lichens as the slow-growing Flagellum (short) large coloured patches on the bark of trees. Eyespot Flagellum (long) 7.3.4 PLANTAE These are multicellular eukaryotes with cell Photoreceptor walls. They are autotrophs and use Contractile chlorophyll for photosynthesis. Thus, all Chloroplast vacuole Nucleus plants are included in this group. Since Nucleolus plants and animals are most visible forms of the diversity of life around us, we will look Euglena at the subgroups in this category later (section 7.4). Fig. 7.2: Protozoa 7.3.5 ANIMALIA7.3.3 FUNGI These include all organisms which areThese are heterotrophic eukaryotic multicellular eukaryotes without cell walls.organisms. They use decaying organic They are heterotrophs. Again, we will lookmaterial as food and are therefore called at their subgroups a little later insaprophytes. Many of them have the capacity section 7.5. 84 SCIENCE
    • Fig. 7.4: The Five Kingdom classificationQ uestions 7.4 Plantae 1. What is the criterion for The first level of classification among plants classification of organisms as depends on whether the plant body has well- belonging to kingdom Monera or differentiated, distinct components. The next Protista? level of classification is based on whether the 2. In which kingdom will you place differentiated plant body has special tissues an organism which is single- for the transport of water and other celled, eukaryotic and substances within it. Further classification photosynthetic? looks at the ability to bear seeds and whether 3. In the hierarchy of classification, the seeds are enclosed within fruits. which grouping will have the smallest number of organisms 7.4.1 THALLOPHYTA with a maximum of characteristics in common and Plants that do not have well-differentiated which will have the largest body design fall in this group. The plants in number of organisms? this group are commonly called algae. TheseD IVERSITY IN L IVING O RGANISMS 85
    • plants are predominantly aquatic. Examples 7.4.2 BRYOPHYTAare Spirogyra, Ulothrix, Cladophora and Chara(see Fig. 7.5). These are called the amphibians of the plant kingdom. The plant body is commonly differentiated to form stem and leaf-like structures. However, there is no specialised tissue for the conduction of water and other substances from one part of the plant body to another. Examples are moss (Funaria) and Marchantia (see Fig. 7.6). Cladophora Ulothrix Cell-wall Chloroplast Riccia Pyrenoids Nucleus Cytoplasm Ulva Marchantia Funaria Spirogyra Fig. 7.6: Some common bryophytes 7.4.3 PTERIDOPHYTA In this group, the plant body is differentiated into roots, stem and leaves and has specialised tissue for the conduction of water and other substances from one part of the plant body to another. Some examples are Marsilea, ferns and horse-tails (see Fig. 7.7). The thallophytes, the bryophytes and the pteridophytes have naked embryos that are called spores. The reproductive organs of plants in all these three groups are very Chara inconspicuous, and they are therefore called ‘cryptogamae’, or ‘those with hidden Fig. 7.5: Thallophyta – Algae reproductive organs’. 86 SCIENCE
    • 7.4.5 ANGIOSPERMS Leaf This word is made from two Greek words: angio means covered and sperma– means seed. The seeds develop inside an organ which is modified to become a fruit. These are also Sporocarp called flowering plants. Plant embryos in seeds have structures called cotyledons. Cotyledons are called ‘seed leaves’ because Stem in many instances they emerge and become Root green when the seed germinates. Thus, cotyledons represent a bit of pre-designed Marsilea Fern plant in the seed. The angiosperms are Fig. 7.7: Pteridophyta divided into two groups on the basis of the number of cotyledons present in the seed. On the other hand, plants with well- Plants with seeds having a single cotyledondifferentiated reproductive tissues that are called monocotyledonous or monocots.ultimately make seeds are called Plants with seeds having two cotyledons arephanerogams. Seeds are the result of the called dicots (see Figs. 7.9 and 7.10).reproductive 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 GYMNOSPERMSThis 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). Fig. 7.9: Monocots – Paphiopedilum Pinus Cycas Fig. 7.8: Gymnosperms Fig. 7.10: Dicots – IpomoeaD IVERSITY IN L IVING O RGANISMS 87
    • Fig. 7.11: Classification of plantsActivity ______________ 7.2 • How many petals are found in the flower of these plants?• Soak seeds of green gram, wheat, • Can you write down further maize, peas and tamarind. Once they characteristics of monocots and dicots Q become tender, try to split the seed. Do on the basis of these observations? all the seeds break into two nearly• equal halves? The seeds that do are the dicot seeds uestions and the seeds that don’t are the 1. Which division among plants has monocot seeds. the simplest organisms?• Now take a look at the roots, leaves and 2. How are pteridophytes different flowers of these plants. from the phanerogams?• Are the roots tap-roots or fibrous? 3. How do gymnosper ms and• Do the leaves have parallel or reticulate angiosperms differ from each venation? other? 88 SCIENCE
    • 7.5 Animalia layers of cells: one makes up cells on the outside of the body, and the other makes theThese are organisms which are eukaryotic, inner lining of the body. Some of these speciesmulticellular and heterotrophic. Their cells live in colonies (corals), while others have ado not have cell-walls. Most animals are solitary like–span (Hydra). Jellyfish and seamobile. anemones are common examples (see They are further classified based on the Fig. 7.13).extent and type of the body designdifferentiation found. Tentacles Tentacles Stinging cell7.5.1 PORIFERAThe word means organisms with holes. Theseare non-motile animals attached to some solid Mouthsupport. There are holes or ‘pores’, all overthe body. These lead to a canal system thathelps in circulating water throughout the Epidermisbody to bring in food and oxygen. These Mesogleaanimals are covered with a hard outside layer Gastrodermisor skeleton. The body design involves very Gastrovascular cavityminimal differentiation and division into Sea anemonetissues. They are commonly called sponges, Footand are mainly found in marine habitats. HydraSome examples are shown in Fig. 7.12. Fig. 7.13: Coelenterata 7.5.3 PLATYHELMINTHES The body of animals in this group is far more complexly designed than in the two other groups we have considered so far. The body is bilaterally symmetrical, meaning that the left and the right halves of the body have the Euplectelia Sycon same design. There are three layers of cells from which differentiated tissues can be made, which is why such animals are called triploblastic. This allows outside and inside body linings as well as some organs to be made. There is thus some degree of tissue formation. However, there is no true internal Spongilla body cavity or coelom, in which well- developed organs can be accommodated. The Fig. 7.12: Porifera body is flattened dorsiventrally, meaning from top to bottom, which is why these animals are called flatworms. They are either free-7.5.2 COELENTERATA living or parasitic. Some examples are free-These are animals living in water. They show living animals like planarians, or parasiticmore body design differentiation. There is a animals like liverflukes (see Fig. 7.14 forcavity in the body. The body is made of two examples).D IVERSITY IN L IVING O RGANISMS 89
    • Branched 7.5.5 ANNELIDA Eyes gastrovascular cavity Annelid animals are also bilaterally Scolex Sucker symmetrical and triploblastic, but in addition Acetabulum Neck they have a true body cavity. This allows true organs to be packaged in the body structure. There is, thus, extensive organ differentiation. Pharynx This differentiation occurs in a segmental Mouth and anus fashion, with the segments lined up one after the other from head to tail. These animals are found in a variety of habitats– fresh water, Liverfluke Tape worm Planareia marine water as well as land. Earthworms and leeches are familiar examples (see Fig. 7.16). Fig. 7.14: Platyhelminthes Tentacle7.5.4 NEMATODA PalpThe 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- Parapodia Genitalcoelom, is present. These are very familiar papillaeas parasitic worms causing diseases, such Anusas the worms causing elephantiasis (filarialworms) or the worms in the intestines(roundworm or pinworms). Some examples Parapodiaare shown in Fig. 7.15. Nereis Earthworm Leech Female Fig. 7.16: Annelida 7.5.6 ARTHROPODA Male This is probably the largest group of animals. These animals are bilaterally symmetrical and segmented. There is an open circulatory system, and so the blood does not flow in well- defined blood vessels. The coelomic cavity is blood-filled. They have jointed legs (the word ‘arthropod’ means ‘jointed legs’). Some Wuchereria familiar examples are prawns, butterflies, Ascaris houseflies, spiders, scorpions and crabs (see Fig. 7.15: Nematodes (Aschelminthes) Fig. 7.17). 90 SCIENCE
    • 7.5.8 ECHINODERMATA In Greek, echinos means hedgehog, and derma means skin. Thus, these are spiny Aranea(Spider) skinned organisms. These are exclusively Palaemon free-living marine animals. They are (Prawn) Palamnaeus triploblastic and have a coelomic cavity. They (Scorpion) also have a peculiar water-driven tube system that they use for moving around. They have hard calcium carbonate structures that they Butterfly use as a skeleton. Examples are starfish and sea urchins (see Fig. 7.19). Pariplaneta (Cockroach) Musca (House fly) Scolopendra (Centipede) Fig. 7.17: Arthropoda7.5.7 MOLLUSCA Antedon HolothuriaIn the animals of this group, there is bilateral (feather star) (sea cucumber)symmetry. 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). Echinus (sea urchin) Asterias (star fish) Fig. 7.19: Echinodermata 7.5.9 PROTOCHORDATA These animals are bilaterally symmetrical, Chiton triploblastic and have a coelom. In addition, Octopus they show a new feature of body design, namely a notochord, at least at some stages during their lives. The notochord is a long rod-like support structure (chord=string) that runs along the back of the animal separating Unio the nervous tissue from the gut. It provides a Pila place for muscles to attach for ease of movement. Protochordates may not have a Fig. 7.18: Mollusca proper notochord present at all stages in theirD IVERSITY IN L IVING O RGANISMS 91
    • lives or for the entire length of the animal. 7.5.10 (i) PISCESProtochordates are marine animals.Examples are Balanoglossus, Herdemania These are fish. They are exclusively water-and Amphioxus (see Fig. 7.20). living animals. Their skin is covered with scales/plates. They obtain oxygen dissolved in water by using gills. The body is streamlined, and a muscular tail is used for Proboscis movement. They are cold-blooded and their hearts have only two chambers, unlike the Collarette four that humans have. They lay eggs. We Collar can think of many kinds of fish, some with skeletons made entirely of cartilage, such as sharks, and some with a skeleton made of Anus Branchial region both bone and cartilage, such as tuna or rohu Gill pores [see examples in Figs. 7.21 (a) and 7.21 (b)]. Dorsally Posthepatic curved region genital wings Middosrsal ridge Synchiropus splendidus Caulophyryne jordani Hepatic caeca (Mandarin fish) (Angler fish) Hepatic region Pterois volitans Fig. 7.20: A Protochordata: Balanoglossus (Lion fish) Eye7.5.10 VERTEBRATA SpiracleThese animals have a true vertebral columnand internal skeleton, allowing a completelydifferent distribution of muscle attachmentpoints to be used for movement. Pelvic fin Vertebrates are bilaterally symmetrical, Dorsal fin Tailtriploblastic, coelomic and segmented, with Caudal fin Sting raycomplex differentiation of body tissues and Electric ray (Torpedo)organs. All chordates possess the following Dorsal fin Eye Tailfeatures: (i) have a notochord (ii) have a dorsal nerve cord Mouth Gills Pectoral Pelvic (iii) are triploblastic fin fin (iv) have paired gill pouches Scoliodon (Dog fish) (v) are coelomate.Vertebrates are grouped into five classes. Fig. 7.21 (a): Pisces 92 SCIENCE
    • Eye Head 7.5.10 (iii) REPTILIA Nostril Pectoral These animals are cold-blooded, have scales Mouth fin and breathe through lungs. While most of Caudal Pelvic Pectoral Mouth Dorsal them have a three-chambered heart, fin Brood fin fin crocodiles have four heart chambers. They fin pouch Tail lay eggs with tough coverings and do not need Labeo rohita (Rohu) Male Hippocampus to lay their eggs in water, unlike amphibians. (Sea horse) Snakes, turtles, lizards and crocodiles fall in Wing like pectoral this category (see Fig. 7.23). Scales Tail Pelvic fin Exocoetus (Flying fish) Turtle Chameleon Anabas (Climbing perch) Fig. 7.21 (b): Pisces7.5.10 (ii) AMPHIBIAThese animals differ from the fish in the lackof scales, in having mucus glands in the skin, King Cobraand 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). House wall lizard (Hemidactylus) Flying lizard (Draco) Salamander Toad Fig. 7.23: Reptilia 7.5.10 (iv) AVES These are warm-blooded animals and have a four-chambered heart. They lay eggs. There Rana tigrina is an outside covering of feathers, and two (Common frog) Hyla (Tree frog) forelimbs are modified for flight. They breathe through lungs. All birds fall in this category Fig. 7.22: Amphibia (see Fig. 7.24 for examples).D IVERSITY IN L IVING O RGANISMS 93
    • Whale White Stork (Ciconia ciconia) Rat Human Bat Cat Ostrich (Struthio camelus) Male Tufted Duck (Aythya fuligula) Fig. 7.25: Mammalia Q uestions 1. How do poriferan animals differ from coelenterate animals? 2. How do annelid animals differ from arthropods? 3. What are the differences between Sparrow amphibians and reptiles? Pigeon 4. What are the differences between animals belonging to the Aves group and those in the mammalia group? Carolus Linnaeus (Karl Crow von Linne) was born in Sweden and was a doctor by professsion. He was Fig. 7.24: Aves (birds) interested in the study of plants. At the age of 22,7.5.10 (V) MAMMALIA he published his first paper on plants. WhileMammals are warm-blooded animals with serving as a personal Carolus Linnaeusfour-chambered hearts. They have mammary physician of a wealthy (1707-1778)glands for the production of milk to nourish gover nment of ficial, he studied thetheir young. Their skin has hairs as well as diversity of plants in his employer’ssweat and oil glands. Most mammals familiar garden. Later, he published 14 papers andto us produce live young ones. However, a also brought out the famous bookfew of them, like the platypus and the echidna Systema Naturae from which alllay eggs, and some, like kangaroos give birth fundamental taxonomical researches haveto very poorly developed young ones. Some taken off. His system of classification wasexamples are shown in Fig. 7.25. a simple scheme for arranging plants so The scheme of classification of animals is as to be able to identify them again.shown in Fig. 7.26. 94 SCIENCE
    • Fig. 7.26: Classification of animalsD IVERSITY IN L IVING O RGANISMS 95
    • 7.6 Nomenclature which puts it along with the organisms it is most related to. But when we actually nameWhy is there a need for systematic naming of the species, we do not list out the wholeliving organisms? hierarchy of groups it belongs to. Instead, we limit ourselves to writing the name of the Activity ______________ 7.3 genus and species of that particular • Find out the names of the following organism. The world over, it has been agreed animals and plants in as many that both these names will be used in Latin languages as you can: forms. 1. Tiger 2. Peacock 3. Ant Certain conventions are followed while 4. Neem 5. Lotus 6. Potato writing the scientific names: As you might be able to appreciate, it 1. The name of the genus begins with awould be difficult for people speaking or capital letter.writing in different languages to know when 2. The name of the species begins with athey are talking about the same organism. small letter.This problem was resolved by agreeing upon 3. When printed, the scientific name isa ‘scientific’ name for organisms in the same given in italics.manner that chemical symbols and formulae 4. When written by hand, the genusfor various substances are used the world name and the species name have toover. The scientific name for an organism is be underlined separately.thus unique and can be used to identify itanywhere in the world. Activity ______________ 7.4 The system of scientific naming or • Find out the scientific names of anynomenclature we use today was introduced five common animals and plants. Doby Carolus Linnaeus in the eighteenth these names have anything in commoncentury. The scientific name of an organism with the names you normally use tois the result of the process of classification identify them? What you have learnt • Classification helps us in exploring the diversity of life forms. • The major characteristics considered for classifying all organisms 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 prepare their own food. • All living organisms are divided on the above bases into five kingdoms, namely Monera, Protista, Fungi, Plantae and Animalia. • The classification of life forms is related to their evolution. 96 SCIENCE
    • • Plantae and Animalia are further divided into subdivisions on the 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 of identification of the vast diversity of life around us. • The binomial nomenclature is made up of two words – a generic name and a specific name. Exercises 1. What are the advantages of classifying organisms? 2. How would you choose between two characteristics to be used for 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 basis for these divisions? 5. How are the criteria for deciding divisions in plants different from the criteria for deciding the subgroups among animals? 6. Explain how animals in Vertebrata are classified into further subgroups.D IVERSITY IN L IVING O RGANISMS 97